The researchers developed a degradable dendritic mesoporous organosilicone nanoparticle system and assembled it with ARV-771 and hyaluronic acid in a stepwise process. The resulting nanocomplex was designated DMONs-NH2@ARV-771@HA. Its organosilicone core served as the carrier for ARV-771, while the hyaluronic acid modification provided a means of directing the complex toward tumor cells.

According to the study abstract, the hyaluronic acid-modified nanoparticles transported cargo into tumor cells through CD44 receptor-mediated endocytosis. The authors described this as a specific and efficient route for cellular delivery. The result connected the carrier’s surface modification with targeted uptake, although the supplied evidence does not provide comparative uptake measurements or the performance of an uncoated formulation.

Payload release was designed around the cellular reducing environment. Glutathione reacted with the nanoparticle framework through a redox response, causing the DMONs-NH2 carrier to break up and release ARV-771 controllably. This response was intended to couple carrier disassembly with the cellular environment rather than relying on a mechanism that does not respond to glutathione.

Released ARV-771 was associated with degradation of BRD4 and selective action within tumor cells in the proof-of-concept experiments. The reported findings therefore link three stages of the platform: hyaluronic acid-mediated targeting, glutathione-responsive carrier disassembly and release of the PROTAC, and degradation of its target protein. The abstract does not quantify the extent of BRD4 degradation or establish whether the carrier improved efficacy relative to a standard delivery method.

The broader motivation for the work was the set of limitations associated with PROTAC delivery: unfavorable aqueous solubility, limited cell-membrane permeability, poor tissue selectivity and adverse side effects. The nanoparticle system was constructed to address these issues through targeted transport and responsive release. It did not independently demonstrate improved clinical safety or efficacy, and the reported results should not be interpreted as evidence of benefit in people.

Research on this platform remains at an early proof-of-concept stage. The supplied article summary reports delivery into tumor cells, carrier breakup following interaction with glutathione, ARV-771 release and BRD4 degradation, but it does not describe animal testing, human participants, dosing, toxicity measurements or long-term outcomes. The evidence consequently supports the behavior of the carrier in the reported experimental setting rather than its use as a clinical treatment.

By combining a hyaluronic acid targeting layer with a glutathione-responsive degradable organosilicone carrier, the researchers devised a two-function delivery system for ARV-771. The design uses cellular uptake to bring a PROTAC into tumor cells and intracellular redox conditions to trigger release. Whether this approach can improve PROTAC delivery in more complete biological models or overcome the broader limitations of PROTAC therapeutics remains unestablished in the supplied evidence.

Subject of Research: A responsive nanoparticle carrier for targeted delivery of the PROTAC ARV-771

Article Title: Hyaluronic acid-modified and glutathione-responsive degradable dendritic mesoporous organosilicone nanoparticles for augmenting targetability and degradation potency of PROTAC

Article References: Huang, L., Jiang, L., Li, W., Qin, G., Zhang, J., Wang, Y., Tang, Z., & Wang, Y. (2026). Hyaluronic acid-modified and glutathione-responsive degradable dendritic mesoporous organosilicone nanoparticles for augmenting targetability and degradation potency of PROTAC. Journal of Nanoparticle Research, 28(11), Article 275. https://doi.org/10.1007/s11051-026-06796-7

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06796-7

Keywords: PROTAC, ARV-771, nanoparticle delivery, hyaluronic acid, CD44, glutathione response, BRD4 degradation, organosilicone, tumor targeting, Hyaluronic, acid-modified, glutathione-responsive

Osteosarcoma is a pediatric bone cancer with lower survival than many other cancers. Relapsed and metastatic disease have especially poor outcomes, and the study report notes that no new treatment for osteosarcoma has been approved in the last 40 years. The experimental strategy uses a PROTAC, a type of compound that marks a protein for destruction, to remove EP300 while an AKT inhibitor blocks the AKT signaling pathway. Food and Drug Administration-approved AKT inhibitors already exist, but the reported experiments did not test an approved AKT inhibitor as a clinical treatment for children with osteosarcoma. The work instead examined the combination as a preclinical therapeutic strategy.

The investigation built on previous work showing that EP300 could be targeted with a PROTAC. That approach had shown benefit in models of neuroblastoma, leading the researchers to explore whether EP300 degradation might also work in osteosarcoma. When they tested osteosarcoma samples, they found that a small but meaningful subset was disproportionately sensitive to EP300 degradation. The result did not indicate that all osteosarcomas depend strongly on EP300. Instead, it suggested that particular molecular features can make some tumors vulnerable to selectively reducing the protein, providing the starting point for identifying a rational combination treatment.

To determine what distinguished the responsive tumors, the scientists examined their genetics. Most osteosarcoma samples that were sensitive to EP300 degradation carried mutations that hyperactivated the AKT pathway. AKT is a central regulator of many cellular processes and is commonly dysregulated in cancer. The presence of AKT-hyperactivating mutations provided a mechanistic rationale for testing AKT inhibition alongside EP300 degradation: combining the two approaches could exploit the connection between an active AKT program and dependence on EP300. In mouse xenografts established from patient tumors, the paired drugs had a synergistic effect. The combination slowed tumor growth and increased survival in those models compared with the individual approaches or control conditions, supporting the idea that AKT hyperactivation may mark tumors sensitive to the combination.

“We found a compound combination that looks promising for a disease that is exceptionally challenging to treat and has not had a major therapeutic improvement for a long time,” said Adam Durbin, MD, PhD, of the St. Jude Department of Oncology and a co-corresponding author of the study. Durbin said the approach may have potential in patients with metastatic disease, who are among the least responsive to current therapies. That statement identifies a possible area of interest rather than a demonstrated clinical result. The reported experiments did not treat people with metastatic osteosarcoma, and the evidence for the combination came from laboratory models rather than a patient cohort. The study therefore shows preclinical activity while leaving its effectiveness in human disease unestablished.

The central biological finding was that dysregulated AKT signaling can reprogram osteosarcoma cells into a state of selective reliance on EP300. In the sensitive models, reducing the available EP300 protein impaired tumor-cell fitness more strongly than it did in resistant models. The effect was concentrated in a defined molecular subset rather than occurring uniformly across osteosarcoma samples. The researchers proposed that mutations associated with AKT hyperactivation may serve as a biomarker for sensitivity to the combination. The finding gives the experimental treatment a molecular rationale and suggests a way to define which tumors may be most responsive, but the potential of tumor genetics to guide treatment selection has not been validated in people.

Brian Abraham, PhD, of the St. Jude Department of Computational Biology and the other co-corresponding author, said the results connect an osteosarcoma’s genotype to a rationally selected therapy. He compared this strategy with precision interventions used in other diseases, including leukemias, where treatments can be selected according to a tumor’s genetic characteristics. The osteosarcoma study provides a strategic framework for making a similar genotype-to-therapy connection: AKT-pathway mutations may help identify tumors that are unusually dependent on EP300 and therefore vulnerable to combined degradation and inhibition. The current evidence does not yet show that genome sequencing can reliably predict an individual patient’s response, and it does not identify a clinical selection rule based on the mouse-model findings.

The researchers performed biochemical comparisons between sensitive and resistant tumors to investigate why AKT hyperactivation and EP300 degradation acted synergistically in the selected models. They found that sensitive cancers had a slower rate of global protein production than resistant counterparts. This distinction appeared to make EP300 degradation more consequential in sensitive cells. In resistant tumors, a higher overall level of protein production appeared to compensate for the loss of EP300, allowing malignant cells to “outrun” the degrader. The result indicates that the effectiveness of protein degradation can depend not only on the selected target but also on the cellular machinery that produces proteins. It does not imply that every resistant tumor follows the same biochemical mechanism, because the reported comparison was made within the study’s experimental models.

The protein-production finding has implications beyond osteosarcoma because pharmaceutical companies are developing PROTACs for many diseases. If diseased cells increase protein production sufficiently, they may overcome degradation of a selected target and contribute to treatment failure. Conversely, protein-production capacity may help identify circumstances in which a degrader is more likely to work. The study provides an early mechanistic example of this principle in osteosarcoma, linking the slower global protein production found in sensitive cancers with the effectiveness of EP300 degradation. It does not establish a universal biomarker for PROTAC sensitivity. The researchers’ suggestion that genome sequencing may eventually help identify a patient whose osteosarcoma is likely to respond remains a future prospect rather than a validated clinical test.

Overall, the experiments point to a genotype-guided strategy for a subset of osteosarcoma: recognize tumors with hyperactivated AKT signaling, then exploit their reliance on EP300 by combining protein degradation with AKT inhibition. The paired treatment reduced tumor growth and extended survival in patient-tumor mouse xenografts, while the biochemical analysis offered a possible explanation for the selective response. The scope of the evidence is important. The research was an experimental study based on cells, biochemical comparisons and mouse models, not a clinical trial, and the frequency of the sensitive molecular pattern in a broader human metastatic population was not established by the report. The results also do not define a clinical regimen or show how the combination would perform in people. Even with those limitations, the study identifies a testable therapeutic avenue for a pediatric cancer in which meaningful treatment improvements have been difficult to achieve.

Subject of Research: Preclinical testing of EP300 degradation and AKT inhibition in osteosarcoma models

Article Title: Combination therapy reveals potential vulnerability in aggressive osteosarcoma

Article References: Combination therapy reveals potential vulnerability in aggressive osteosarcoma. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: osteosarcoma, EP300, AKT signaling, PROTAC, protein degradation, pediatric cancer, targeted therapy, tumor genetics, drug synergy, xenograft models, Combination, therapy

The review emphasizes that resistance is not a single event but a heterogeneous, evolving process. Clinically, it is classified as primary—relapse within the first two years of adjuvant endocrine therapy or progression within six months of first-line treatment for advanced disease—or secondary, which encompasses later relapses and progression on subsequent lines. According to the updated ABC6/7 consensus definitions, the presence of a known ESR1 mutation also falls under secondary resistance. In practice, the authors argue, endocrine sensitivity and resistance are better understood as a continuum, interpreted alongside prior treatment exposure, disease tempo, and molecular biomarkers rather than rigid categories.

At the molecular level, the most direct route to resistance runs through the estrogen receptor gene itself, ESR1. Mutations in this gene are exceedingly rare in untreated primary tumors but climb to approximately 20 to 40 percent in metastatic disease after aromatase inhibitor therapy. The most common alterations, Y537S and D538G, cluster in the ligand-binding domain of the receptor. These missense mutations change the receptor’s three-dimensional conformation so that it recruits coactivators and drives transcription continuously, even without estrogen. This ligand-independent activation renders aromatase inhibitors—which work by depleting estrogen—ineffective, and it also weakens the binding of fulvestrant, the first-generation selective estrogen receptor degrader, producing partial cross-resistance.

Whole-transcriptome sequencing has uncovered a second structural mechanism: ESR1 gene fusions. In endocrine-resistant metastatic lesions, researchers have identified fusions such as ESR1–YAP1 and ESR1–CCDC170. When ESR1–YAP1 forms, the potent transcriptional activation domain of YAP1 replaces the receptor’s ligand-binding domain, allowing estrogen-independent growth. ESR1–CCDC170 takes a different route, forming a complex with HER2, HER3, and SRC that activates the SRC–PI3K–AKT pathway; knocking down this fusion reduces HER2/HER3 expression and restores endocrine sensitivity. Beyond these structural changes, resistant cells undergo broader transcriptional reprogramming, in which epigenetic modifications enhance ER binding at specific chromatin sites and sustain the transcriptional programs tumors need to survive—a phenomenon the authors call transcriptional dependency, which complicates any single-target strategy.

When the ER pathway is pharmacologically blocked, tumor cells frequently reroute their signaling through growth factor pathways, a process known as crosstalk. The PI3K/AKT/mTOR pathway has attracted the most attention: roughly 40 percent of HR+/HER2− patients harbor activating PIK3CA mutations, which drive proliferation and can induce ligand-independent phosphorylation of ER through downstream kinases such as S6K1. Conversely, when endocrine therapy suppresses ER signaling, the negative feedback ER normally exerts is released, AKT phosphorylation rises, and receptor tyrosine kinase signaling through HER3 and IGF1R intensifies. Even without HER2 amplification, ligand-driven HER2/HER3 heterodimerization can activate SRC/PI3K/AKT signaling and, through the HER2/HER3–HDAC2–FOXA1 axis, reshape ER transcription by redirecting the receptor toward resistance, invasion, and metastasis loci. The authors caution that HER2-low or HER2-ultralow classifications are treatment-selection descriptors for antibody–drug conjugates, not mechanisms of resistance in themselves.

Resistance to CDK4/6 inhibitors follows its own logic. These drugs work by arresting the cell cycle at the G1-to-S transition, an effect that depends on an intact retinoblastoma (Rb) protein. When the RB1 gene is lost or mutated, E2F transcription factors escape suppression, the cell cycle proceeds, and cells become less dependent on the CDK4/6–Cyclin D1 complex. Although RB1 inactivation is not highly frequent in metastatic HR+/HER2− disease, its impact is well defined: among patients treated with palbociclib plus fulvestrant, those with RB1 loss show markedly shorter progression-free survival. Additional escape routes include amplification of Cyclin E1 or overexpression of CDK2, which allow cells to rely on the Cyclin E–CDK2 complex, and loss of FAT1, which inactivates the Hippo pathway. Single-cell studies also implicate the tumor microenvironment, where immunosuppressive cell populations expand under the selective pressure of CDK4/6 inhibition.

These mechanistic insights are now being translated into drugs. Next-generation oral selective estrogen receptor degraders, or SERDs, offer better bioavailability than injectable fulvestrant. Elacestrant, the first approved oral SERD, significantly prolonged progression-free survival versus standard endocrine therapy in ESR1-mutated patients previously treated with a CDK4/6 inhibitor in the phase III EMERALD trial. Camizestrant outperformed fulvestrant regardless of ESR1 status in SERENA-2, and imlunestrant, another oral SERD, extended median progression-free survival to 5.5 versus 3.8 months in ESR1-mutated patients in EMBER-3; when combined with abemaciclib, imlunestrant achieved 10.9 versus 5.5 months, and the FDA approved imlunestrant on September 25, 2025 for ESR1-mutated advanced disease after at least one prior endocrine line. A parallel approach uses PROTACs—proteolysis-targeting chimeras such as vepdegestrant (ARV-471)—which hijack the cell’s ubiquitin–proteasome machinery to degrade ER directly, with preclinical degradation exceeding 90 percent. In the phase III VERITAC-2 trial, vepdegestrant doubled median progression-free survival to 5.0 versus 2.1 months in the ESR1-mutated cohort, though the overall population showed no significant benefit, underscoring the importance of biomarker selection. Complete estrogen receptor antagonists, or CERANs such as OP-1250, block both ER transcriptional activation domains while promoting receptor degradation, and preclinical data suggest possible blood–brain barrier penetration.

Bypass signaling has yielded its own arsenal. Inavolisib, a selective PI3Kα inhibitor that also promotes degradation of the mutant p110α protein, extended median progression-free survival to 15.0 versus 7.3 months and median overall survival to 34 versus 27 months in the phase III INAVO120 trial when added to palbociclib and fulvestrant in first-line PIK3CA-mutated disease. The pan-AKT inhibitor capivasertib, tested with fulvestrant in CAPItello-291, improved median progression-free survival to 7.2 versus 3.6 months overall and 7.3 versus 3.1 months in tumors with PIK3CA, AKT1, or PTEN alterations, with some benefit even in pathway-wild-type tumors. On the mTOR front, everolimus plus exemestane raised median progression-free survival from 4.1 to 10.6 months by central assessment in BOLERO-2, though at the cost of grade 3–4 stomatitis, infections, rash, and hyperglycemia. The multitargeted inhibitor gedatolisib, which blocks multiple PI3K isoforms and mTORC1/2 simultaneously, achieved 9.3 versus 2.0 months in PIK3CA wild-type disease after CDK4/6 progression in VIKTORIA-1, with relatively low rates of hyperglycemia and stomatitis, and received FDA approval in combination with fulvestrant, with or without palbociclib, on July 14, 2026.

Perhaps the most striking shift is toward acting before tumors visibly progress. Liquid biopsy studies show that circulating tumor DNA can detect ESR1 mutations in 20 to 50 percent of previously treated metastatic cases, often predicting poorer aromatase inhibitor responses. In the randomized PADA-1 trial, switching from an aromatase inhibitor to fulvestrant—both with palbociclib—as soon as rising ESR1 mutation levels were detected in ctDNA significantly prolonged median progression-free survival. The phase III SERENA-6 trial went further: patients on first-line aromatase inhibitor plus CDK4/6 therapy whose ctDNA revealed emergent ESR1 mutations, but who had no radiographic progression, were switched to camizestrant while continuing the same CDK4/6 inhibitor. The extended analysis showed median progression-free survival of 16.8 versus 9.2 months and second progression-free survival of 25.7 versus 19.1 months—compelling evidence that molecular progression can be intercepted before clinical relapse. The authors note that assay performance is platform-specific: droplet digital PCR excels at tracking predefined ESR1 hotspots with detection limits of 0.07 to 0.19 percent mutant allele fraction, while targeted next-generation sequencing offers broader coverage but platform-dependent sensitivity, and negative plasma results should prompt repeat or tissue-based testing when suspicion is high.

The review also maps the frontier beyond established targets. Epigenetic therapies, including EZH2 inhibitors such as tazemetostat and HDAC inhibitors, aim to reverse the chromatin states that sustain resistant transcriptional programs. Metabolic reprogramming offers another angle: resistant cells increasingly depend on fatty acid oxidation and oxidative phosphorylation, with CPT1A-mediated transport of long-chain fatty acids into mitochondria sustaining ATP production in slow-cycling persister cells; the CPT1 inhibitor etomoxir showed greater activity in resistant than sensitive cells in preclinical models, though such approaches remain investigational. After endocrine resistance is established, antibody–drug conjugates provide antigen-directed options: sacituzumab govitecan improved survival in heavily pretreated patients in TROPiCS-02, and datopotamab deruxtecan was FDA-approved in January 2025 for previously treated metastatic HR+/HER2− disease. The authors conclude that no single biomarker captures the full resistance landscape, and that integrating multi-omics analysis, single-cell sequencing, and dynamic ctDNA monitoring will be essential to move clinical management from empiric treatment switching toward truly individualized, mechanism-guided, whole-course care.

Subject of Research: Molecular mechanisms of endocrine resistance and emerging targeted therapies in HR-positive/HER2-negative breast cancer

Article Title: Endocrine resistance in HR+/HER2− breast cancer: molecular mechanisms and emerging therapeutic strategies

Article References: Shen, T., Li, H., Zhang, X., & Zhou, Q. (2026). Endocrine resistance in HR+/HER2− breast cancer: molecular mechanisms and emerging therapeutic strategies. Frontiers in Oncology, 16, Article 1983430. https://doi.org/10.3389/fonc.2026.1983430

Image Credits: AI Generated

DOI: 10.3389/fonc.2026.1983430

Keywords: endocrine resistance, HR-positive HER2-negative breast cancer, ESR1 mutations, oral SERDs, PROTAC, PI3K/AKT/mTOR pathway, CDK4/6 inhibitors, circulating tumor DNA, liquid biopsy, antibody-drug conjugates, epigenetic therapy, precision oncology

The research, led by Yinghuan Liu, Xianying Li, Tong Zhou, Jianhua Xie and colleagues under the supervision of Yongjun Wang, Dong Han and Lifu Li, focuses on N-acetyltransferase 10, or NAT10, the only known mammalian enzyme that installs N4-acetylcytidine, abbreviated ac4C, onto cytidine residues within mRNA. This chemical acetylation is a member of the expanding family of epitranscriptomic marks, modifications that do not change the genetic sequence itself but alter how RNA molecules behave, influencing their stability, localization, translation efficiency and fidelity. By stabilizing particular transcripts, ac4C can effectively turn up the volume of specific genes without the cell ever touching its DNA.

The team began by asking whether NAT10 is present in diseased valves. Analyzing tissue from 50 patients with calcific aortic valves and 50 non-calcified controls, they found that NAT10 mRNA and protein were both significantly elevated in the diseased tissue. A parallel increase appeared in a mouse model, in which apolipoprotein E-deficient mice fed a high-cholesterol diet for 24 weeks develop aortic valve calcification that mirrors the human condition. Dot blot assays measuring total RNA acetylation revealed that global ac4C levels rose alongside NAT10 in both human and mouse calcified valves, suggesting that the enzyme’s catalytic output, not merely its abundance, tracks with disease.

Cellular studies sharpened the picture. The chief cellular culprit in valve calcification is the human valvular interstitial cell, or hVIC, which under pathological stress abandons its usual quiescent state and transforms into an osteoblast-like cell that lays down mineral. When the researchers isolated hVICs and valve endothelial cells from patients, NAT10 was substantially higher in the interstitial cells, identifying them as the primary source of the enzyme in diseased valves. When hVICs were bathed in osteogenic medium, NAT10 expression climbed in a time-dependent manner together with the osteogenic marker osterix. Silencing NAT10 blunted the appearance of osteogenic markers, calcified nodule formation and calcium deposition, while forcing NAT10 overexpression intensified all of these features, effects that held true in cells from both diseased and healthy donors.

Correlation analyses in a second, independent validation cohort of 50 patients linked NAT10 to disease severity in a clinically meaningful way. NAT10 expression rose in step with the osteogenic markers osterix and osteopontin, and higher NAT10 levels were associated with a smaller aortic valve area and greater mean and peak transvalvular pressure gradients on echocardiography. In other words, the more NAT10 a patient’s valve expressed, the worse the valve functioned, positioning the enzyme as both a potential biomarker and a therapeutic target.

To find what NAT10 was actually doing downstream, the investigators performed a rigorous three-way screen. They intersected genes downregulated when NAT10 was knocked down in hVICs, established NAT10 perturbation targets from the RM2Target database, and aortic valve calcification genes curated in the Open Targets Platform. The overlap narrowed to just seven candidates: COL1A1, PCSK9, SCG2, UBE2C, FN1, THBS2 and SERPINE1. Rescue experiments then delivered a decisive verdict. Knocking down PCSK9, but none of the other six genes, almost completely abolished the pro-calcific phenotype driven by NAT10 overexpression, establishing PCSK9 as the dominant functional effector of the pathway.

PCSK9 is best known as a cholesterol regulator, famous for degrading low-density lipoprotein receptors in the liver and for the blockbuster antibody drugs that block it. But recent genetic and experimental work has implicated PCSK9 directly in valve calcification as well. The new study shows that NAT10 regulates PCSK9 post-transcriptionally. RNA decay assays using actinomycin D to halt transcription demonstrated that NAT10 knockdown shortened the half-life of PCSK9 mRNA, while NAT10 overexpression prolonged it, with corresponding changes in PCSK9 protein production and secretion. In human calcific valves, NAT10 and PCSK9 expression correlated positively, tying the molecular mechanism to clinical tissue.

The mechanistic proof that ac4C is the responsible mark came from a series of elegant experiments. RNA immunoprecipitation showed that PCSK9 mRNA is bound by both NAT10 and anti-ac4C antibodies, and that NAT10 depletion reduces the ac4C signal on the transcript. A predicted acetylation motif within positions 1886 to 1900 of the PCSK9 coding sequence was tested with luciferase reporters: mutating the cytosines in that motif to thymines made the reporter insensitive to NAT10 knockdown, whereas the wild-type reporter responded strongly. The researchers also deployed a catalytically dead NAT10 mutant, G641E, which retains expression but cannot acetylate RNA. Only the wild-type enzyme, not the mutant, boosted PCSK9 stability and production, proving that the acetyltransferase activity itself is essential. Control experiments confirmed that knockdown of NAT10 did not perturb other components of the ac4C machinery, including the cofactor THUMPD1, the reader NOP58 and the putative eraser SIRT7, underscoring the specificity of the effect.

The most clinically compelling results came from the mouse experiments. Apolipoprotein E-deficient mice on a high-cholesterol diet were treated either with remodelin, a small-molecule NAT10 inhibitor, or with NP1192, a first-in-class PROTAC degrader that selectively drags NAT10 into the cellular destruction machinery. Because remodelin is known to interact with multiple cellular targets, the PROTAC served as an orthogonal check on specificity. Both compounds partially reversed the echocardiographic hallmarks of aortic stenosis, reduced valve leaflet thickness and calcium deposition on histology, suppressed the osteogenic markers osterix and osteopontin, and lowered NAT10 protein and global ac4C levels in valve tissue. Crucially, blood glucose, total cholesterol, LDL, triglycerides and circulating PCSK9 were unchanged by treatment, indicating that the benefit arose from local action within the valve rather than from systemic lipid lowering, and that the anti-calcific effect was on-target rather than a metabolic side effect.

The study is not without caveats, which the authors acknowledge candidly. Calcific valve disease involves endothelial cells and macrophages in addition to interstitial cells, and NAT10’s role in those compartments was not explored; cell-type-specific knockout models will be needed to disentangle the contributions. Transcriptome-wide mapping of ac4C targets was not performed, so other NAT10-regulated transcripts may contribute to the phenotype. The upstream signals that raise NAT10 expression in the diseased valve, whether mechanical stress, lipid retention, oxidative stress or inflammatory cytokines, remain unidentified. Even so, the work delivers something the field has lacked: a concrete, druggable epitranscriptomic axis, NAT10-ac4C-PCSK9, that connects RNA chemistry to the bone-like transformation of the aortic valve. If future clinical studies confirm that NAT10 degraders such as NP1192 can slow or stop valve calcification in patients, the humble acetyl group on a single cytidine may turn out to be the handle medicine has been searching for on one of cardiology’s hardest diseases.

Subject of Research: The role of NAT10-mediated mRNA N4-acetylcytidine modification of PCSK9 in calcific aortic valve disease

Article Title: NAT10 exacerbates aortic valve calcification via PCSK9 mRNA ac4C acetylation

Article References: Liu, Y., Li, X., Zhou, T., Xie, J., Jiang, H., Zheng, B., Peng, J., Li, L., Han, D., & Wang, Y. (2026). NAT10 exacerbates aortic valve calcification via PCSK9 mRNA ac4C acetylation. iScience, 29(11), Article 117812. https://doi.org/10.1016/j.isci.2026.117812

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117812

Keywords: NAT10, ac4C, PCSK9, aortic valve calcification, calcific aortic valve disease, epitranscriptomics, valvular interstitial cells, RNA modification, PROTAC, NP1192, osteogenic differentiation, mRNA stability

Ependymoma is the second most common malignant brain tumour in children, and PFA is its most frequent subgroup. Roughly half of patients relapse despite maximal tumour resection followed by focal radiotherapy, and only about a quarter of relapsed children survive beyond five years. Within PFA, tumours carrying chromosomal instability, in the form of gain of chromosome 1q or loss of chromosome 6q, form an ultra-high-risk subset for whom standard treatment is rarely curative. Previous work explained part of the 1q story, showing that extra copies of MDM4 suppress p53 signalling and that the enzyme UCK2 may render 1q-gain tumours sensitive to 5-fluorouracil, a hypothesis now being tested in North American and European trials. The 6q story, however, remained a black box.

The new study, led by Andrew Donson and Andrea Griesinger at Children’s Hospital Colorado together with Timothy Ritzmann at the University of Nottingham and collaborators in Manchester, Toronto and Heidelberg, reanalysed a large international cohort of 101 children with recurrent, methylation-classified PFA ependymomas. The numbers are stark. At first diagnosis, 6q loss appears in only a small minority of tumours, around four percent in isolation and eight percent when combined with 1q gain. But at first recurrence, 34 percent of tumours carry 6q loss, rising to 47 percent by second recurrence and 69 percent by third and later recurrences. Tumours harbouring 6q loss accounted for 45 percent of all deaths in the cohort, and by late recurrence essentially all 1q-gain tumours had also acquired 6q loss, explaining the catastrophic outcomes of tumours carrying both lesions.

To find the gene driving this behaviour, the team homed in on an autopsy sample with a focal deletion on 6q spanning 13.6 megabases, a region containing 60 genes of which eight are documented tumour suppressors. The decisive clue came from partial deletions: among 60 cases of 6q loss, ten had only partial deletions, and every one of those partial deletions encompassed the LATS1 locus. LATS1, or Large Tumour Suppressor Kinase 1, is a well-established brake on cell proliferation in lung, breast, gastric, liver, kidney, colorectal and blood cancers. Patients with partial versus whole 6q loss fared equally badly, with median overall survival near 50 months in both groups, arguing that LATS1 loss, not deletion size, defines the aggressive phenotype.

Bulk RNA sequencing confirmed that LATS1 transcript levels are markedly reduced in 6q-loss tumours, which showed the lowest LATS1 expression of any paediatric brain tumour type examined, and that expression falls further with each successive recurrence. The 6q-loss tumours also had significantly higher Ki-67 proliferation indices, pointing to an intrinsically more proliferative state. To test causality, the researchers used lentiviral vectors to force LATS1 expression back into two 6q-loss PFA cell lines, MAF-811 and MAF-928. Restoring the protein reliably suppressed proliferation in both lines, while 6q wild-type ependymoma and paediatric glioblastoma comparator lines kept growing normally, evidence that these tumour cells have become dependent on LATS1’s absence.

The mechanistic thread runs through the Hippo pathway, an ancient signalling cascade that controls organ size and cell fate. In healthy cells, LATS1 phosphorylates the co-transcriptional activator YAP at a specific site, serine 127, trapping it in the cytoplasm and marking it for degradation. When LATS1 is lost, YAP escapes into the nucleus and teams up with TEAD family transcription factors to drive pro-growth gene programs. Immunohistochemistry on 75 PFA tumours showed significantly elevated nuclear and cytoplasmic YAP in 6q-loss cases, and reintroducing LATS1 into MAF-811 cells raised phospho-YAP levels, confirming the pathway’s functional restoration. The researchers note that this mechanism mirrors findings in other ependymoma variants, including rare YAP1-fusion supratentorial tumours and NF2-mutant spinal ependymomas, suggesting Hippo dysregulation is a recurring theme across the disease.

Among the TEAD factors, TEAD2 emerged as the standout. Its RNA was significantly elevated in 6q-loss tumours and rose across successive recurrences, and it ranked 45th out of 28,595 transcripts for correlation with shortened time to progression. High TEAD2 target-gene activity predicted poor progression-free survival with a hazard ratio of 3.2. A prominent TEAD2 target, DNMT1, a DNA methyltransferase that silences tumour suppressors and locks cells into a stem-like state, dropped sharply after LATS1 knock-in, tying the genetic lesion to a concrete epigenetic output.

The therapeutic payoff came from two classes of experimental compounds. The TEAD palmitoylation inhibitor VT107, an analogue of the clinical-stage agent VT3989, showed high nanomolar potency against both 6q-loss cell lines while sparing most comparator paediatric brain tumour lines. Even more striking was the TEAD-targeted PROTAC degrader H122, a proteolysis-targeting chimera that recruits cellular disposal machinery to destroy TEAD proteins. The 6q-loss lines were killed at low single-digit to double-digit nanomolar concentrations, roughly one hundred times more sensitive than to VT107, and Western blots confirmed complete TEAD degradation within four hours. With the first-ever PROTAC, vepdegestrant, recently FDA-approved for breast cancer, this drug class offers a credible route to the clinic for ependymoma patients.

Spatial transcriptomics added a final, telling layer. Using Xenium single-molecule imaging on more than one million cells from 14 tumour sections, the team mapped TEAD2 expression across distinct neoplastic cell populations. TEAD2 was highly enriched in undifferentiated, stem-like ependymoma cells known as UEC-A, including their proliferative subpopulation, in both 6q-loss and wild-type tumours. The finding suggests these progenitor-like cells, previously linked to oncofetal reprogramming and relapse, may be the engine of PFA aggression, driven by TEAD2 much as gain-of-function TEAD signalling expands the neural progenitor pool during development.

The authors argue that 6q status should be incorporated into risk stratification and future trials of recurrent PFA ependymoma, and that Hippo-targeted therapy has near-term translational potential for these children, for whom relapse is currently a terminal event. A phase 1/2 trial of VT3989 in mesothelioma has already shown partial responses and stable disease, and a phase 3 study is planned, offering a shortcut to paediatric testing. Much work remains, including preclinical 6q-loss models to evaluate candidate inhibitors, but the study delivers what the field has lacked: a defined molecular driver of ultra-high-risk PFA ependymoma and, for the first time, a druggable path against it.

Subject of Research: LATS1 deletion on chromosome 6q and Hippo pathway activation in ultra-high-risk posterior fossa A ependymoma

Article Title: Chromosome 6q mediated loss of LATS1 tumour suppression as a targetable mechanism of ultra-high-risk posterior fossa A ependymoma

Article References: Donson, A. M., Griesinger, A. M., Chapman, R. J., Grundy, R. G., Kilday, J.-P., Ramaswamy, V., Levy, J. M. M., Kaufman, M. L., Amani, V., Sundheimer, J. K., Pajtler, K. W., Foreman, N. K., & Ritzmann, T. A. (2026). Chromosome 6q mediated loss of LATS1 tumour suppression as a targetable mechanism of ultra-high-risk posterior fossa A ependymoma. Acta Neuropathologica, 152(1), Article 52. https://doi.org/10.1007/s00401-026-03098-z

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03098-z

Keywords: ependymoma, PFA ependymoma, LATS1, chromosome 6q loss, Hippo pathway, YAP, TEAD2, tumour suppressor, PROTAC, VT107, pediatric brain tumour, spatial transcriptomics

The research, led by Shaon Basu and Markus Ralser at Charité Universitätsmedizin Berlin and the Francis Crick Institute, together with a team at AstraZeneca, focused on degraders of the androgen receptor, a transcription factor that drives treatment-resistant prostate cancer. First-line therapies for prostate cancer typically block androgen receptor signaling with antagonist drugs, but tumors inevitably acquire mutations at the androgen receptor locus, rendering the drugs ineffective and the disease lethal. Degraders promise a way around this resistance by directly destroying the receptor inside tumor cells. Despite this promise, no androgen receptor degrader has yet demonstrated improved efficacy over standard treatment with an acceptable safety profile, echoing the fate of first-generation bromodomain degraders that failed in cancer patients because of dose-limiting toxicity.

The team’s strategy began with a technological foundation: a fast, scalable proteomic workflow capable of monitoring how thousands of proteins respond to drug treatment in a 96-well plate format. HepG2 cells, a well-established model for screening liver toxicity, were cultivated and treated with liquid-handling robots, and their proteins were digested into peptides and analyzed by data-independent acquisition mass spectrometry on two platforms, using scanning SWATH acquisition on a Sciex TripleTOF 6600 and dia-PASEF acquisition on a Bruker timsTOF HT. Neural network-based processing with the DIA-NN software, benchmarked against a hepatocarcinoma-specific spectral library, quantified thousands of proteins per sample with minimal batch effects and low technical variance, making the approach suitable for industrial-scale screening.

To validate the platform, the researchers exposed HepG2 cells to 78 FDA-approved drugs whose targets span human, bacterial and fungal proteins. Forty-seven of these compounds, particularly those with favorable safety profiles, triggered no significant proteomic response. The remaining 31 induced measurable changes, and the proteomes faithfully reflected each drug’s mechanism of action: methotrexate altered less than one percent of the proteome while its primary target, dihydrofolate reductase, ranked among the most upregulated proteins, whereas the chemotherapy doxorubicin reshaped seven percent of the proteome in a pattern consistent with DNA damage. Intriguingly, the dominant proteomic signatures often corresponded to off-target rather than on-target interactions, including disruption of ribosomal translation, endoplasmic reticulum stress and mitochondrial dysfunction. The antifungal clotrimazole, for example, induced broad rearrangements driven by xenobiotic response proteins and mitochondrial impairment despite the absence of its fungal target in human cells. A principal component analysis cleanly separated compounds with narrow therapeutic windows, such as chemotherapeutics and immunosuppressants, from safer drugs.

With the platform validated, the team turned to the central question: what off-target effects do experimental androgen receptor degraders produce? Because HepG2 cells do not express the androgen receptor, any proteomic response to these compounds must reflect off-target engagement. The researchers profiled a library of 204 structurally unique androgen receptor degraders, including clinically advanced candidates such as bavdegalutamide (ARV-110) and an AstraZeneca compound referred to as compound 1, alongside control degraders targeting BRD4, CDK4 and CDK9. The screening campaign generated 2,113 proteomic samples reaching depths of roughly 4,000 proteins each. The results were striking: despite the absence of their intended target, several androgen receptor degraders perturbed up to 57 percent of the proteome, with an average of 19 percent of proteins differentially expressed, a far stronger response than that elicited by the FDA-approved drug library. Notably, degraders targeting proteins actually expressed in HepG2 cells, such as BRD4, produced responses that partly reflected the biology of their targets, confirming that the platform can distinguish on-target from off-target signatures.

The off-target responses clustered according to chemical structure. Degraders recruiting the cereblon E3 ligase, particularly those using phthalimide derivatives and achiral DHU warheads, produced the broadest perturbations, while those recruiting the von Hippel-Lindau ligase produced the weakest. Crucially, the toxicity was not inherent to the recruiter alone: lenalidomide by itself elicited no proteomic response, while other cereblon ligands induced moderate or strong changes. Functional enrichment analysis pointed decisively at the mitochondrial compartment, with pathways involving mitochondrial protein-containing complexes responding in a dose-dependent manner. When the researchers tested whether the compounds impaired respiration by culturing cells in galactose medium, which forces cells to rely on mitochondrial ATP production, several cereblon-recruiting degraders reduced viability in a dose-dependent fashion. Compound 1 showed a half-maximal inhibitory concentration of 0.73 micromolar in galactose medium, while its constituent building blocks, lenalidomide and an androgen receptor-binding analog of enzalutamide, were inactive above 20 micromolar, indicating a gain-of-function toxicity arising from the assembled degrader molecule.

To pinpoint the molecular mechanism, the team applied machine learning to the proteomic data. Univariate linear regression linking protein expression changes to galactose toxicity revealed that nine of the ten best-fitting proteins localized to mitochondria, and four of these were subunits of electron transport chain complex I, the NADH dehydrogenase that initiates the proton gradient driving ATP synthesis. The complex I protein NDUFA5 showed the strongest relationship, with a coefficient of determination of 0.57. A second-pass gradient-boosted decision tree model, refined through Shapley additive explanations analysis and retrained on top features, achieved a cross-validation area under the precision-recall curve of 80 percent, with complex I proteins dominating the feature importance rankings. Biochemical validation followed: compound 1 reduced oxygen consumption in HepG2 cells, and in assays using bovine heart mitochondrial membranes it potently inhibited NADH oxidation through the complex I-III-IV axis with an IC50 of 0.2 micromolar, roughly 100-fold more potent than lenalidomide and 45-fold more potent than enzalutamide, while leaving complex II activity untouched. The degrader, in other words, was a selective complex I inhibitor.

The most consequential step came next. Because the toxicity was not inherent to the recruiter chemistry, the researchers reasoned that proteomics could identify degraders lacking complex I engagement. Their trained models assigned compound 1 a predicted toxicity score of 91 out of 100, comparable to known hepatotoxins such as troglitazone, but attributed far lower scores of 47 and 35 to two close structural analogs, compounds 2 and 3, which differed only in the linker region and carried a 7-methoxy modification on the lenalidomide moiety. Experimentally, the analogs induced no complex I proteomic signature, did not impair mitochondrial respiration, and showed a complex I IC50 of 6.5 micromolar versus 0.2 micromolar for compound 1. In primary human hepatocytes, compound 1 caused acute cell death at 2.7 micromolar, whereas compounds 2 and 3 were tolerated above 20 micromolar. The analogs also lost the unwanted degradation of the cereblon neosubstrates IKZF3 and SALL4, proteins linked to bone marrow and developmental toxicity, likely owing to the methoxy modification.

Safety gains did not come at the expense of efficacy. All three compounds inhibited proliferation of androgen receptor-positive prostate cancer cell lines, but only compound 1 suppressed androgen receptor-negative lines, suggesting improved selectivity for the refined analogs. Compound 3 degraded the androgen receptor as effectively as compound 1 in LNCaP cells and dose-dependently suppressed prostate-specific antigen expression. It also displayed favorable pharmacokinetics, with low clearance in human liver microsomes and rat hepatocytes and 50 percent oral bioavailability in mouse. RNA sequencing confirmed that compound 3 modulated androgen response signaling similarly to enzalutamide while reducing MYC oncogenic signaling and G2/M checkpoint pathways, consistent with cell-cycle arrest, and without perturbing oxidative phosphorylation at any time point.

The decisive test came in vivo. In a C4-2 xenograft model of castration-resistant prostate cancer in immunocompromised mice, three days of oral dosing with compound 3 at 30 milligrams per kilogram reduced androgen receptor protein levels in tumors by more than 70 percent. Over 28 days of treatment, compound 3 achieved 56 percent tumor growth inhibition, compared with just 15 percent for enzalutamide at 50 milligrams per kilogram, and both treatments were well tolerated with no significant body weight loss. The study establishes that systematic, high-throughput proteomics paired with interpretable machine learning can trace unwanted proteomic signatures back to specific chemical features, here a linker region, and guide the rational design of safer, more selective degraders. As polypharmacological modalities such as degraders and antibody-drug conjugates continue to enter the clinic, the authors argue that this proteome-guided framework offers a versatile route to de-risk drug development before candidates ever reach patients.

Subject of Research: Proteome-guided discovery and mitigation of toxicity mechanisms in androgen receptor-targeted protein degraders

Article Title: Proteome-guided drug discovery maps and mitigates therapeutic degrader toxicity

Article References: Basu, S., Yu, J. S. L., Bosak, J., Bagal, S. K., Crafter, C., Fallan, C., Lemke, O., Freiwald, A., White, M. E. H., Vernardis, S. I., Messner, C. B., Michaloglou, C., Pryde, K., Ramos-Montoya, A., Regan, S., Rodrigo-Brenni, M., Roth, S., Ruffilli, C., Mülleder, M., … Ralser, M. (2026). Proteome-guided drug discovery maps and mitigates therapeutic degrader toxicity. Nature Chemical Biology. https://doi.org/10.1038/s41589-026-02347-2

Image Credits: AI Generated

DOI: 10.1038/s41589-026-02347-2

Keywords: proteomics, targeted protein degradation, PROTAC, androgen receptor, prostate cancer, mitochondrial toxicity, complex I, machine learning, drug discovery, hepatotoxicity, cereblon, mass spectrometry

The SMAD pathway is one of the central information conduits in animal cells. It is switched on by more than thirty ligands of the TGF-β superfamily, which bind to serine/threonine kinase receptors at the cell surface. When a ligand latches on, type II receptors phosphorylate and activate type I receptors, which in turn phosphorylate receptor-associated SMAD proteins. These activated R-SMADs partner with the common mediator SMAD4, travel into the nucleus and steer the transcription of target genes. The pathway splits into two major branches: the TGF-β branch, carried by ligands such as TGF-β, Activins and GDFs through the type I receptors ALK4 and ALK5 into SMAD2 and SMAD3, and the BMP branch, carried by BMP ligands through ALK1, ALK2 and ALK3 into SMAD1, SMAD5 and SMAD9. In endothelial cells this division of labor is beautifully choreographed during angiogenesis. Tip cells at the leading edge of a sprouting vessel rely on SMAD1/5/9 activation by BMP2, BMP6 and BMP7 to navigate, while stalk cells behind them depend on SMAD2/3 signaling through TGF-β to proliferate and form a proper lumen. In mature vessels, BMP9 and BMP10 keep the endothelium quiescent through SMAD1/5/9.

When this balance breaks, human disease follows. Mutations in ALK1, the BMP9 receptor, or its co-receptor endoglin weaken SMAD1/5/9 signaling and cause hereditary hemorrhagic telangiectasia, a disorder marked by fragile arteriovenous malformations and recurrent bleeding. Conversely, mutations in BMPR2 that heighten SMAD2/3 activity contribute to pulmonary arterial hypertension, in which vessels narrow and remodel abnormally. Understanding how individual cells weigh pro- and antiangiogenic inputs is therefore not just a question of basic biology but a prerequisite for new therapies. Yet most of what we know about SMAD signaling comes from population averages, which can mask the striking variability that individual cells display.

To see signaling cell by cell, the team built stable reporter lines in EA.hy926 cells, a widely used model of human vascular endothelium derived from fusing primary umbilical vein cells with a lung carcinoma line. They fused the cDNA of SMAD1 to the yellow fluorescent protein mVenus under a constitutive ubiquitin C promoter, and co-expressed a histone H2B-CFP nuclear marker so that automated image analysis could segment and track every nucleus over time. Parallel reporters were generated for SMAD5 and SMAD9. Western blotting confirmed that the tagged proteins were phosphorylated with the same kinetics as their endogenous counterparts after BMP9 stimulation, peaking around 1.5 hours, and RT-qPCR showed that key target genes such as Endothelin 1 and ID2 were induced normally, indicating that the reporters did not distort the pathway they were meant to observe.

Time-lapse microscopy at ten-minute intervals over sixteen hours then delivered the first surprise: enormous cell-to-cell heterogeneity. After BMP9 addition, essentially all cells pushed SMAD1 into the nucleus within about an hour, but what happened next differed dramatically. Some cells settled into stable signaling, while others repeatedly shuttled SMAD1 back and forth in pulsatile waves. The population median showed a sharp peak at roughly 1.5 hours followed by a gradual return to baseline, and even a medium-only control, containing no added ligand, elicited a small translocation peak, revealing exquisite sensitivity to trace amounts of BMP-family ligands left in the serum. Dose-response experiments showed that peak SMAD1 translocation saturated at about 0.375 nanograms per milliliter of BMP9, with a half-maximal effective concentration of just 0.06 nanograms per milliliter. Higher doses produced sustained nuclear occupancy and delayed adaptation, consistent with the idea that signaling duration is governed largely by ligand depletion as receptors internalize and degrade their cargo.

The three R-SMADs of the BMP branch, often assumed to be interchangeable, turned out to differ quantitatively in revealing ways. SMAD5 required the highest ligand concentrations to respond, showing the largest EC50 of the three, and failed to react even to the residual ligand in the medium-only control, suggesting it cannot compensate at low signal doses. SMAD9, by contrast, returned to the cytoplasm more slowly than SMAD1 or SMAD5 once the ALK1 inhibitor K02288 was applied, hinting that its prolonged nuclear retention may serve processes requiring sustained gene expression, such as pulmonary vascular remodeling. Pharmacological validation confirmed that BMP9 signaling runs through ALK1, with an IC50 of 192 nanomolar for SMAD1, and lower values of 47 and 107 nanomolar for SMAD5 and SMAD9 respectively.

The pivotal discovery came when the team screened a panel of TGF-β superfamily ligands. Despite the presence of receptors for BMP2, BMP6 and BMP7, only BMP9 and BMP10 drove robust nuclear translocation of SMAD1, SMAD5 and SMAD9 in these endothelial cells, even at very high ligand concentrations. Suspecting an intracellular brake rather than an extracellular one, the researchers focused on FKBP12, the FK506-binding protein known to dock onto the glycine-serine-rich region of type I receptors and physically block their phosphorylation by type II receptors. FKBP12 was highly expressed in the cells. To remove it cleanly, the team used a proteolysis-targeting chimera, a bifunctional molecule that recruits the von Hippel-Lindau ubiquitin ligase to FKBP12 and triggers its degradation. Western blots confirmed dose- and time-dependent FKBP12 loss, and the consequences were striking: with FKBP12 gone, BMP7 and Activin A, ligands that had previously been mute, suddenly provoked strong SMAD1 activation through ALK2, while the response to BMP9 and BMP10 remained almost unchanged.

FKBP12 did more than simply unlock a second receptor. Using a dual reporter line expressing YFP-SMAD1 and mCherry-SMAD2 simultaneously, the researchers showed that BMP7 normally produces a weak SMAD1 response and a robust SMAD2 response. Degrading FKBP12 shifted the balance: SMAD1 translocation rose, particularly at high BMP7 concentrations, while the SMAD2 response fell. Co-stimulation experiments with BMP9 and TGF-β, which engage distinct receptor complexes, produced no mutual attenuation, ruling out feedback loops or pathway competition as the explanation. Instead, the data point to limited shared receptor availability and differential receptor complex composition. The authors propose that BMP7-induced SMAD2 activation depends on heterodimeric ALK2/ALK4 complexes, whereas SMAD1 activation after FKBP12 removal relies on ALK2 homodimers, and that Activin A can additionally engage ALK4 homodimers. In this model, FKBP12 does not merely silence receptors; it actively determines which receptor assemblies form and therefore which branch of the pathway a given ligand will engage.

These signaling shifts translated into real cellular behavior. The SMAD1/5/9 target gene DLL4 dropped sharply after BMP9 treatment and stayed flat when only SMAD2/3 was engaged, but FKBP12 degradation made BMP7 a potent DLL4 repressor as well. The gene ID2, regulated by both branches, showed additive induction when both pathways fired. Over 48 hours of single-cell tracking, BMP9 significantly boosted endothelial motility, an effect abolished by ALK1 inhibition, while BMP7 increased motility more modestly, and combining BMP7 with FKBP12 degradation produced an additive enhancement that ALK4/5 inhibition could curtail. The findings suggest that SMAD1/5/9 and SMAD2/3 cooperate rather than compete in shaping endothelial phenotypes, with FKBP12 acting as a fine-tuning dial. Therapeutically, the implications are tantalizing. The immunosuppressant FK506, known clinically as tacrolimus, displaces FKBP12 from receptor complexes and is already being piloted to reduce bleeding in hereditary hemorrhagic telangiectasia, while FKBP12-specific PROTACs could offer a more selective route that spares the immune system. The authors caution that EA.hy926 cells are a hybrid model and that the receptor-complex model rests on pharmacological inference, so validation in primary endothelial cells and in vivo disease models remains the essential next step. Even so, the study reframes FKBP12 from a passive receptor cap into an active architect of ligand-specific signaling, one that cells may exploit, and clinicians may one day target, to restore the delicate balance their vessels depend on.

Subject of Research: FKBP12-dependent regulation of ligand-specific SMAD signaling in living endothelial cells

Article Title: FKBP12 determines ligand-specific SMAD signaling in individual living endothelial cells

Article References: Huang, Z., Lenhardt, S., Snyder, P., Bulldan, A., Hausch, F., & Loewer, A. (2026). FKBP12 determines ligand-specific SMAD signaling in individual living endothelial cells. iScience, 29(10), Article 117728. https://doi.org/10.1016/j.isci.2026.117728

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117728

Keywords: SMAD signaling, FKBP12, endothelial cells, BMP9, TGF-β, ALK1, ALK2, PROTAC, live-cell microscopy, angiogenesis, hereditary hemorrhagic telangiectasia, pulmonary arterial hypertension

The original call for papers read like a catalogue of the field’s hottest frontiers: targeted protein degradation, molecular glues, covalent inhibitors, antibody-drug conjugates, macrocycles, nucleoside therapeutics, immuno-oncology agents, natural-product discovery, multicomponent reactions, advanced imaging and screening technologies, and artificial intelligence. That breadth is significant in itself. A decade ago, many of these approaches were considered speculative or confined to a handful of specialist laboratories. Today they constitute a mainstream toolkit, and the 58 accepted articles show researchers across medicinal chemistry, chemical biology, and pharmacology routinely combining them rather than working in silos. The result, according to the editorial framing the collection, is a discovery enterprise that is faster, more efficient, and increasingly sophisticated in how it approaches molecular design.

A central theme running through the issue is the development of efficient and diversity-oriented synthetic strategies for bioactive molecules. The published articles describe asymmetric and visible-light-promoted reactions, multicomponent and one-pot syntheses, iron-catalyzed functionalization, nanocatalytic and sonochemical methods, skeletal editing, total synthesis, and optimized synthetic routes. Each of these techniques addresses a persistent bottleneck in drug discovery: the speed and reliability with which chemists can actually make the molecules that computational and biological studies suggest might work. Visible-light photocatalysis, for example, allows bond formations under mild conditions that were previously difficult or impossible, while skeletal editing permits late-stage modifications of molecular frameworks that would once have required rebuilding a candidate from scratch. Multicomponent reactions compress multi-step sequences into single operations, dramatically shortening the path from idea to testable compound.

Crucially, the synthetic advances described in the collection are not presented as ends in themselves. The resulting compounds, which include diverse indoles, indolizines, heterocycles, molecular hybrids, peptides, and natural-product analogues with enhanced structural and stereochemical complexity, were investigated as anticancer, antimicrobial, antitubercular, antiviral, anti-inflammatory, antidiabetic, antiseizure, and neuroprotective agents. This direct linkage between methodology and biological application is what distinguishes the current wave of synthetic innovation from earlier eras in which method development and drug hunting often proceeded on separate tracks. When a new catalytic reaction can be evaluated within weeks against disease-relevant cell models, the feedback loop between chemistry and pharmacology tightens, and the odds that an interesting molecule becomes a therapeutic candidate improve accordingly.

Another striking pattern in the collection is the continuing shift beyond the traditional one drug-one target paradigm that dominated pharmaceutical research for much of the past half-century. Among the highlighted examples are dual inhibitors targeting BTK/FLT3, COX-2/5-LOX, and FAAH/sEH, enzyme pairs relevant to cancer and inflammation, alongside multifunctional agents designed for Alzheimer’s disease and reviews of xanthone hybrids and pyrazolopyrimidine-based dual inhibitors. Multi-target design acknowledges that complex diseases rarely hinge on a single protein, and that modulating several nodes of a pathological network simultaneously can be more effective than maximal blockade of one. The approach demands a different kind of medicinal chemistry, one in which selectivity is engineered across multiple binding sites rather than maximized against a single target, and the articles in the issue show that scaffold design and mechanistic understanding are being integrated to meet exactly that challenge.

The issue also surveys work on established and emerging molecular targets, including FAK, HDAC, ERα, PI3Kδ, p38 MAPK, EZH2, DprE1, histamine H1 and H2 receptors, SFRP1, PDE4B, and nitric oxide synthase. This list spans kinases, epigenetic enzymes, nuclear receptors, phosphodiesterases, and bacterial cell-wall biosynthesis machinery, reflecting the wide biological terrain on which modern medicinal chemistry now operates. A dedicated review on PROTAC technology underscores the prominence of targeted protein degradation, one of the most promising new therapeutic modalities of the past decade. Rather than inhibiting a protein’s activity, degraders recruit cellular disposal machinery to eliminate the disease-causing protein altogether, an approach that can succeed against targets long considered undruggable by conventional small molecules. Its inclusion alongside classical target families illustrates how new modalities are being folded into, rather than replacing, the existing discovery apparatus.

Natural products and biomolecule-inspired scaffolds remain a major focus of the collection, and the evidence assembled suggests that nature is far from exhausted as a source of molecular diversity. Studies on phorbazole D, menominin A, polyprenylated acylphloroglucinols, oleanolic and alepterolic acids, Eucommiae folium, µ-conotoxins, honey-bee antimicrobial peptides, and marine cyclopeptides demonstrate the remarkable chemical inventiveness of the natural world, from terrestrial plants to venomous cone snails and social insects. What has changed is the technology brought to bear on these molecules. Total synthesis, analogue generation, chemical ligation, mass spectrometry, network pharmacology, and cell-based screening are overcoming longstanding challenges in natural-product discovery and optimization, problems of supply, structural complexity, and limited optimization potential that historically kept many natural products out of the clinic despite compelling biological activity.

The synergy between computation and experimentation emerges as perhaps the defining feature of the modern discovery pipeline. Molecular docking, molecular dynamics simulations, pharmacophore modeling, network pharmacology, and integrated in silico-in vitro workflows now support compound prioritization and mechanistic studies across the collection. These are not decorative additions; they determine which of millions of conceivable molecules get synthesized and tested, effectively allocating scarce laboratory resources. AI-assisted analysis, label-free cell-based screening, high-resolution LC-Orbitrap mass spectrometry, and zebrafish disease models further illustrate advances in compound characterization, phenotypic screening, and translational validation. Phenotypic screening in whole organisms such as zebrafish is particularly notable, because it allows compounds to be evaluated for efficacy and toxicity in a living system before the costly transition to mammalian models, catching failures earlier and more cheaply than traditional pipelines allow.

The collective message of the 58 articles is that new technologies in drug discovery are not defined by any single platform or methodology, but by the integration of innovative chemistry, emerging therapeutic modalities, computational prediction, advanced screening technologies, and rigorous biological validation. This multidisciplinary convergence is expanding druggable chemical space, the universe of molecules that can realistically be made, characterized, and developed into medicines, while accelerating therapeutic discovery and enabling increasingly sophisticated approaches to drug design. For decades, the pharmaceutical industry has grappled with declining productivity per research dollar, and collections like this one suggest a credible path forward: rather than betting on any single breakthrough, the field is stacking multiple incremental advantages in synthesis, target biology, computation, and screening into compounding gains across the entire pipeline.

In closing the special issue, Shi thanks the authors, reviewers, and the editorial team of Molecular Diversity, and expresses the hope that the collection will stimulate new collaborations, inspire continued technological innovation, and contribute to making drug discovery faster, more efficient, and more successful while preserving the molecular and mechanistic diversity that underpins transformative medicines. That emphasis on diversity is more than rhetorical. History shows that transformative drugs often emerge from unexpected chemical territory, and the deliberate cultivation of varied scaffolds, modalities, and screening strategies is the best insurance against the field narrowing prematurely around fashionable targets. If the technologies surveyed here continue to mature and interconnect, the coming decade of drug discovery may look markedly different from the last, with molecules designed, synthesized, and validated at a pace and precision that earlier generations of researchers could scarcely have imagined.

Subject of Research: Emerging technologies and multidisciplinary approaches in drug discovery

Article Title: New technologies in drug discovery

Article References: Shi, T. (2026). New technologies in drug discovery. Molecular Diversity. https://doi.org/10.1007/s11030-026-11711-2

Image Credits: AI Generated

DOI: 10.1007/s11030-026-11711-2

Keywords: drug discovery, medicinal chemistry, targeted protein degradation, PROTAC, molecular glues, natural products, artificial intelligence, multicomponent reactions, phenotypic screening, dual inhibitors, chemical biology, Molecular Diversity

The protein at the center of the new work is the retinoic acid receptor alpha, or RARα, which is highly active in colorectal tumors and drives both proliferation and metastatic invasion. Traditional RARα modulators, built on retinoic acid scaffolds, suffer from chemical instability, excessive lipophilicity, and poor oral bioavailability, and they can provoke toxicity in the liver, skin, and bones. To escape these limitations, the researchers turned to proteolysis-targeting chimera, or PROTAC, technology. PROTACs are bifunctional molecules that simultaneously grip a target protein and an E3 ubiquitin ligase, forming a ternary complex that tags the target for destruction by the cell’s own ubiquitin–proteasome system. Because each PROTAC molecule dissociates after every degradation event and can engage targets repeatedly, this catalytic mechanism holds the promise of overcoming the drug resistance that plagues conventional inhibitors.

The team began with AR7, an atypical RARα antagonist, and selected its optimized derivative CA77.1 as the target-binding ligand. Molecular docking against the RARα structure (PDB:5K13) revealed that CA77.1 binds with a calculated energy of −7.379 kcal/mol, anchored by a key hydrogen bond to Arg276 and an extensive hydrophobic network. Crucially, a terminal methyl group on CA77.1 protrudes into the solvent-exposed region outside the ligand-binding pocket, providing an ideal attachment point for a linker without disturbing the core binding interactions. By covalently joining CA77.1 to thalidomide, a ligand for the E3 ubiquitin ligase CRBN, the researchers created a degrader that remains active in both oxygen-rich and hypoxic tumor regions, overcoming the hypoxia-dependent activation that limited the parent compounds.

Through systematic synthesis of six candidate molecules with varying carbon-chain and piperazine linkers, the team identified Z1 as the standout. Z1 degraded RARα with a DC50 of 6.02 ± 1.05 μM and a maximum degradation of 85.4 percent, an activity roughly 43.6 times greater than that of CA77.1 itself. Western blotting confirmed that Z1 left the related receptors RARβ and RARγ untouched, demonstrating high subtype selectivity. Mechanistic experiments sealed the case: cycloheximide chase assays showed accelerated decay of pre-existing RARα protein, while pre-treatment with the competitive ligand ATRA, the E1 enzyme inhibitor MLN4924, the proteasome inhibitor MG132, or excess thalidomide all blocked degradation, confirming the classical PROTAC pathway of direct binding and ubiquitin-proteasome-mediated clearance.

Molecular dynamics simulations running 100 nanoseconds provided atomistic support for the design. Z1 formed stable hydrogen bonds with both RARα and CRBN, with calculated binding free energies of −139.394 kJ/mol and −111.138 kJ/mol respectively, and per-residue energy decomposition pinpointed Pro407, Val395, and Ser225 as the thermodynamic core of RARα recognition. Functionally, Z1-induced degradation suppressed phosphorylation of AKT at Ser473 in a concentration-dependent manner while leaving total AKT unchanged, and it markedly reduced expression of MMP2, an enzyme that tumors use to invade surrounding tissue. This AKT–MMP2 axis, the authors note, had not been systematically characterized in earlier RARα degradation studies and offers a fresh mechanistic window into how acute protein elimination restrains cancer progression.

In vitro assays in HCT116 colorectal cancer cells painted a striking picture of Z1’s antitumor potency. Flow cytometry showed concentration-dependent arrest of cells at the G2/M phase, with the arrested population rising 3.7-fold at 100 μM. At 50 μM, Z1 completely abolished colony formation, whereas the same concentration of CA77.1 allowed more than 300 colonies to grow. Annexin V staining revealed that Z1 drove 34.6 to 55.2 percent of cells into late apoptosis, well above the 24.6 percent seen with CA77.1. Scratch assays demonstrated up to 90.4 percent inhibition of cell migration, and Transwell experiments showed that 50 μM Z1 cut the invasion rate to 10.8 percent, an 81.2 percent reduction relative to the parent compound.

Yet like all PROTACs, Z1 carries the field’s chronic handicaps: high molecular weight, poor water solubility, and weak membrane permeability. The team’s solution came from an unexpected source, the roots of Polygonatum sibiricum, a plant long valued in traditional medicine. Using a juicing, filtration, and ultracentrifugation workflow, the researchers isolated exosome-like nanoparticles, or PsELNs, that measure roughly 116 nanometers across, carry a mildly negative zeta potential of −5.8 mV, and display the characteristic disk-like morphology of plant vesicles. Their cargo of triglycerides forms a hydrophobic core that stabilizes hydrophobic drugs, while their natural tropism for colonic tissue and their ability to accumulate in tumors through the enhanced permeability and retention effect make them unusually well suited to colorectal cancer applications.

Encapsulation of Z1 within PsELNs achieved a drug-loading efficiency of 43.1 percent, exceeding values reported for goji berry and ginger vesicles, and the loaded particles grew only modestly to 143 nm while retaining an intact bilayer. Stability testing was impressive: at acidic pH 5.5 mimicking the tumor microenvironment, 77.38 percent of Z1 remained intact after 24 hours versus just 40.65 percent for the free drug, and the formulation resisted thermal stress at 44 °C, stayed stable in serum for 72 hours, and showed minimal leakage over 60 days of storage. Confocal microscopy and flow cytometry confirmed that Z1/PsELNs entered HCT116 cells far more efficiently than free Z1, and the encapsulated drug degraded RARα with a DC50 of 2.95 μM, a 2.2-fold improvement that translated into stronger apoptosis induction and greater cytotoxicity in vitro.

The decisive test came in living animals. Near-infrared imaging of tumor-bearing nude mice showed that DiR-labeled PsELNs accumulated in tumors at 2.13 times the level of the free dye, peaking at 24 hours after injection, while hemolysis rates below 5 percent confirmed blood compatibility. Over 16 days of tail-vein treatment, the Z1/PsELNs group showed significantly stronger tumor growth inhibition than mice receiving free Z1, with in vivo antitumor efficacy increasing 1.8-fold. Histopathology revealed extensive tumor cell damage, Ki67 staining showed the fewest proliferating cells, and both immunohistochemistry and Western blotting confirmed the lowest RARα levels in the nanoparticle-treated tumors, all without body-weight loss or organ damage. The authors propose that the intestinal stability and colon-targeting behavior of PsELNs could eventually support an oral PROTAC formulation, a goal that would address both gastrointestinal degradation and site-specific accumulation. By fusing event-driven protein degradation chemistry with a biocompatible, naturally derived delivery vehicle, the study charts a credible translational path for PROTAC therapeutics in colorectal cancer and illustrates how plant nanotechnology may help the next generation of degrader drugs reach their targets intact.

Subject of Research: A RARα-targeting PROTAC delivered by Polygonatum sibiricum exosome-like nanoparticles for colorectal cancer therapy

Article Title: Synthesis of RARα–PROTAC and its delivery via Polygonatum sibiricum exosome-like nanoparticles for the treatment of colorectal cancer

Article References: Zhu, G., Zhao, Y., Chen, M., Lu, S., Xu, L., Chen, G., Zeng, L., & Chen, J. (2026). Synthesis of RARα–PROTAC and its delivery via Polygonatum sibiricum exosome-like nanoparticles for the treatment of colorectal cancer. Materials Today Bio, 40, Article 103651. https://doi.org/10.1016/j.mtbio.2026.103651

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103651

Keywords: colorectal cancer, PROTAC, RARα, protein degradation, Polygonatum sibiricum, exosome-like nanoparticles, drug delivery, nanomedicine, ubiquitin-proteasome system, AKT signaling, MMP2, targeted therapy