The central player in the study is SOX9, short for SRY-box transcription factor 9. Transcription factors are proteins that bind to specific DNA sequences and control whether nearby genes are read into messenger RNA, and SOX9 is well known for its roles in embryonic development and tissue stem cell maintenance. In cancer, SOX9 has previously been implicated in tumor growth and progression, but its involvement in the metabolic transformation of metastatic colorectal cancer cells had remained largely unexplored. The new work positions SOX9 as a direct regulator of de novo lipogenesis, the process by which cells manufacture fatty acids from scratch rather than importing them from the bloodstream.

To dissect this relationship, the researchers combined several complementary approaches. They performed integrated transcriptomic and targeted lipidomic analyses, comparing the gene expression profiles and lipid compositions of cells with and without elevated SOX9. The transcriptomic data revealed changes in the expression of genes involved in fatty acid synthesis, while the lipidomic measurements showed that SOX9 overexpression increased the abundance of fatty acids and other lipid species within the cells. This convergence of genomic and metabolomic evidence provided the first indication that SOX9 overexpression drives fatty acid synthesis and lipid accumulation in colorectal cancer cells.

The team then verified these findings using an arsenal of imaging and analytical techniques. Nile Red staining, a fluorescent dye that preferentially labels neutral lipids, revealed increased lipid content in SOX9-overexpressing cells. Flow cytometry allowed the researchers to quantify lipid accumulation across large cell populations, confirming that the effect was consistent rather than confined to a few cells. Transmission electron microscopy provided ultrastructural evidence, visualizing the intracellular lipid deposits at nanometer resolution. Finally, Nanolive label-free lipid droplet imaging captured the dynamics of lipid storage structures inside living cells. Together, these methods demonstrated that SOX9 overexpression dramatically enhances intracellular lipid deposition, effectively transforming colorectal cancer cells into lipid-storing factories.

The clinical relevance of these observations became apparent when the researchers examined human tissue samples. SOX9 was found to be upregulated in colorectal cancer tissues compared with healthy tissue, and its expression was further enriched in metastatic lesions, the colonies of cancer cells that have established themselves in distant organs. Importantly, patients whose tumors showed high SOX9 levels had poorer outcomes, suggesting that the transcription factor is not merely a bystander in disease progression but a marker, and likely a driver, of aggressive disease.

Functional experiments cemented the link between SOX9-driven lipid production and metastatic behavior. In laboratory assays, cells with elevated SOX9 showed markedly increased migration and invasion, the two cellular behaviors that precede and enable metastatic spread. The team also performed lung metastatic colonization assays in animal models, which measure the ability of circulating cancer cells to seed and grow tumors in the lung. SOX9 overexpression promoted lung metastatic colonization, demonstrating that the lipid-reprogramming effect translates into real metastatic capacity in vivo.

Perhaps the most therapeutically significant result came from the rescue experiments. When the researchers inhibited fatty acid synthase, commonly abbreviated FASN, the enzyme that catalyzes the final steps of fatty acid synthesis, the pro-metastatic effects of SOX9 were significantly attenuated. Migration, invasion and lung colonization all declined when the fat-production line was shut down, even in cells still overexpressing SOX9. This result indicates that FASN sits downstream of SOX9 in the pathway and that the lipid synthesis it drives is not incidental but functionally required for SOX9 to promote metastasis. In principle, this makes the SOX9-FASN axis a metabolic vulnerability that could be targeted with drugs designed to starve metastatic cells of their lipid supply.

Mechanistically, the study went beyond correlation to show how SOX9 controls FASN in the first place. Using CUT&Tag sequencing, a technique that maps where a protein of interest binds across the genome, the researchers identified SOX9 occupancy at sites near the FASN promoter, the regulatory DNA region that controls how strongly the FASN gene is transcribed. This genomic binding evidence was complemented by luciferase reporter assays, in which the FASN promoter was fused to a light-producing reporter gene. When SOX9 was present, reporter activity increased, demonstrating that SOX9 can directly stimulate FASN promoter activity. Further reporter analyses using mutated promoter sequences supported a sequence-dependent mode of regulation, meaning SOX9 requires specific DNA motifs in the proximal FASN promoter to exert its effect, a hallmark of genuine direct transcriptional control rather than an indirect effect mediated through other genes.

The significance of this work lies in how it connects two major themes in modern cancer biology: transcriptional dysregulation and metabolic reprogramming. Cancer cells are known to rewire their metabolism to support rapid growth, survival under stress and dissemination, and increased lipid synthesis has emerged as a recurring feature of aggressive tumors. Lipids are not merely building blocks for new membranes in dividing cells; they also serve as signaling molecules, energy reserves and components of the machinery cells use to change shape and move through tissue. By showing that a developmental transcription factor can impose a lipogenic program on colorectal cancer cells and that this program is required for metastatic colonization, the study offers a coherent explanation for how metabolic flexibility and metastatic competence are coupled at the level of gene regulation.

The findings also suggest practical directions for future research and treatment development. Because FASN inhibition can rescue the metastatic phenotypes induced by SOX9, drugs targeting fatty acid synthase, some of which have already entered clinical evaluation for other cancers, could potentially benefit colorectal cancer patients whose tumors show high SOX9 expression. SOX9 itself, as a transcription factor, has historically been considered a difficult drug target, but its downstream metabolic dependencies offer an alternative point of attack. The study also raises the possibility that SOX9 expression levels could serve as a biomarker to identify patients at high risk of metastasis who might be candidates for metabolic therapies. As with all preclinical research, the results will need to be validated in larger clinical cohorts and tested in appropriately designed trials before they change patient care, but the identification of a defined SOX9-FASN lipid metabolic axis gives researchers a concrete molecular handle on one of the deadliest phases of colorectal cancer.

Subject of Research: SOX9-mediated regulation of lipid metabolism and metastasis in colorectal cancer

Article Title: SOX9 reprograms lipid metabolism via FASN to promote metastasis in colorectal cancer

Article References: Wang, H., Wei, L., Xiang, X., Li, J., Wang, Y., Jiang, Z., Li, X., Li, Y., Pan, Y., & Liang, X. (2026). SOX9 reprograms lipid metabolism via FASN to promote metastasis in colorectal cancer. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09055-4

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09055-4

Keywords: colorectal cancer, SOX9, FASN, lipid metabolism, metastasis, fatty acid synthesis, de novo lipogenesis, transcription factors, cancer metabolism, CUT&Tag, lung metastasis, Journal of Translational Medicine

The central obstacle the researchers set out to overcome is a vicious cycle linking low oxygen to drug resistance. Solid tumors, especially aggressive ones like triple-negative breast cancer, are chronically starved of oxygen because their hastily built blood vessels are irregular and dysfunctional. Oxygen can only diffuse about 100 to 200 micrometers from a functioning vessel, leaving tumor cores severely hypoxic. In this oxygen-poor environment, a transcription factor called hypoxia-inducible factor-1 alpha, or HIF-1α, becomes stabilized and switches on genes for ATP-binding cassette transporters—most notably P-glycoprotein, the efflux pump encoded by ABCB1. P-glycoprotein literally pumps chemotherapeutics like paclitaxel back out of the cell, rendering them useless. Blood transfusions and hyperbaric oxygen therapy can ease systemic hypoxia, but neither reliably relieves hypoxia inside the tumor itself.

Previous attempts to solve this problem have used hemoglobin-based oxygen carriers, since hemoglobin is the body’s natural oxygen transporter and can also catalyze the generation of reactive oxygen species. But free hemoglobin degrades rapidly, is dose-dependently toxic, and provokes systemic inflammation. Liposome-encapsulated hemoglobin improves stability, yet conventional formulations lack spatial precision, often pooling in the liver and spleen. The new study, led by Xunyi You and colleagues with senior author Ye Cao, took a different route: rather than relying on passive accumulation, the team attached their drug-loaded liposomes loosely to the surfaces of intact red blood cells—a strategy known as RBC hitchhiking.

The concept is elegantly physical. The liposomes bind to red blood cells through weak, reversible interactions such as van der Waals forces and electrostatic attraction, without being internalized. When the cell-liposome complexes are injected intravenously, they travel through the bloodstream until they squeeze through narrow capillaries. The shear forces in these tight passages mechanically scrape the nanoparticles off the red cell surfaces and transfer them to the capillary endothelium, dramatically increasing accumulation in the first capillary-rich organ downstream of the injection site. For drugs injected into a tail vein, that organ is the lung—precisely where triple-negative breast cancer metastasizes. The team’s earlier work had already shown that combining liposomes with RBC hitchhiking extends blood half-life and boosts pulmonary accumulation.

Building on that foundation, the researchers formulated liposomes from the phospholipid DPPC, the pH-sensitive lipid DOPE, and cholesterol, encapsulating both paclitaxel and purified hemoglobin in a single nanoparticle. The resulting LEHP particles measured between 100 and 200 nanometers in diameter with a polydispersity index below 0.2, indicating a highly uniform population, and transmission electron microscopy confirmed smooth, spherical structures. Paclitaxel encapsulation efficiency was 83.32 percent for hemoglobin-free liposomes and 58.27 percent for the hemoglobin-loaded version, the reduction likely reflecting the protein occupying space in the aqueous core. Critically, the hemoglobin inside LEHP showed a P50 of about 10.20 mmHg—substantially lower than the roughly 26.5 mmHg of normal adult hemoglobin—meaning a left-shifted oxygen dissociation curve and enhanced oxygen loading in the pulmonary circulation, with favorable release under the low-oxygen conditions of the tumor.

The hitchhiking step itself proved remarkably gentle on the carrier cells. After optimizing the ratio of liposomes to red blood cells, confocal microscopy showed liposomes uniformly coating the erythrocyte membranes while preserving their native biconcave disc shape. The engineered cells maintained their CD47 expression—the “don’t eat me” signal that prevents clearance by the immune system—showed no significant increase in phosphatidylserine exposure, retained normal osmotic fragility profiles, and kept their deformability index unchanged, preserving the mechanical flexibility needed to squeeze through splenic sinuses and lung capillaries.

Inside tumor cells, the payload executes a coordinated attack on two fronts. First, delivered hemoglobin alleviates hypoxia, which destabilizes HIF-1α and removes the transcriptional activation of ABCB1, sharply downregulating P-glycoprotein and restoring the cell’s vulnerability to paclitaxel. Second, the iron released from hemoglobin fuels the Fenton reaction, converting hydrogen peroxide into highly reactive hydroxyl radicals. The team documented the three hallmarks of ferroptosis—an iron-dependent form of cell death driven by lipid peroxidation: elevated labile ferrous iron, surging lipid peroxides, and a collapse of mitochondrial membrane potential. Molecular analysis showed LEHP suppressing the antioxidant guardian GPX4 and its regulator Nrf2 along with the cystine transporter SLC7A11, while upregulating the transferrin receptor, driving NCOA4-mediated ferritinophagy to liberate stored iron, and boosting ACSL4 to supply polyunsaturated fatty acid substrates for membrane oxidation. When cells were pretreated with ferrostatin-1, a specific ferroptosis inhibitor, LEHP-induced cell death was profoundly reversed—confirming ferroptosis as the dominant killing mechanism, with a minor complementary contribution from apoptosis at high drug concentrations.

The DOPE lipid added a self-amplifying delivery trick. In the acidic lysosome, DOPE destabilizes membranes and releases hemoglobin; the liberated ferrous iron then generates radicals that attack the polyunsaturated fatty acids concentrated in the lysosomal membrane itself. That peroxidation increases membrane permeability, accelerating the escape of both hemoglobin and paclitaxel into the cytosol—a ROS-dependent positive feedback loop that the team observed as early as two hours after treatment. The researchers describe the net effect as “re-oxygenation injury”: chronically hypoxic cells, adapted to survive without oxygen, are suddenly overwhelmed by an oxygen influx that their antioxidant defenses cannot absorb, triggering a catastrophic oxidative collapse.

In vivo, the advantages compounded. In mice bearing 4T1 breast cancer lung metastases, RBC-hitchhiked liposomes produced a 2.7-fold increase in pulmonary fluorescence intensity and a 4.6-fold improvement in the lung-to-liver ratio compared with liposomes alone, with lung signals persisting up to 48 hours. In the therapeutic experiment, paclitaxel monotherapy failed to arrest tumor progression, and each partial strategy—hemoglobin without hitchhiking, or hitchhiking without hemoglobin—fell short on its own. Only the fully integrated RBC-LEHP platform achieved sustained regression: at the day 13 endpoint, pulmonary bioluminescence in the RBC-LEHP group was (7.70 ± 2.86) × 10⁴, roughly three orders of magnitude below the LEP group’s (2.19 ± 0.37) × 10⁷. Histology showed intact bronchial architecture and no edema or fibrosis in treated lungs, with no systemic toxicity in the heart, liver, spleen, or kidneys, and reduced Ki67 proliferation, CD31-marked microvessel density, and MMP2 and MMP9 metastasis markers.

Perhaps most strikingly, the treatment remodeled the tumor immune microenvironment, markedly increasing infiltration of CD4-positive and CD8-positive T cells and shifting the lung tumors from an immunologically cold state toward an inflamed, hot one. High-throughput proteomics of lung tissue confirmed the mechanism at the systems level: NCOA4 upregulation and GPX4 downregulation enforcing ferroptotic commitment, HIF-1α and P-gp suppression restoring chemosensitivity, and suppression of the epigenetic driver EZH2 and the pro-survival factor CEBPB dismantling the tumor’s transcriptional survival programs. The authors caution that some hepatic accumulation was observed at 24 hours, though without histological signs of liver damage, and that systemic immune responses in peripheral lymphoid organs remain to be profiled. Still, the study establishes a compelling template—targeted delivery, hypoxia alleviation, ferroptosis plus chemotherapy, tumor suppression—that could extend beyond breast cancer to any malignancy whose resistance is rooted in the oxygen-starved depths of the tumor.

Subject of Research: A biomimetic erythrocyte-hitchhiking liposome system delivering hemoglobin and paclitaxel to overcome hypoxia-driven chemoresistance in triple-negative breast cancer lung metastasis via ferroptosis

Article Title: Oxygen-augmented erythrocyte-liposome hybrids to overcome paclitaxel resistance in triple-negative breast cancer metastasis via enhanced ferroptosis

Article References: You, X., Zhu, K., Li, W., Wang, H., Zhong, R., Li, S., Liu, J., Wong, Y. S., Venkatraman, S. S., & Cao, Y. (2026). Oxygen-augmented erythrocyte-liposome hybrids to overcome paclitaxel resistance in triple-negative breast cancer metastasis via enhanced ferroptosis. Materials Today Bio, 41, Article 103705. https://doi.org/10.1016/j.mtbio.2026.103705

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103705

Keywords: triple-negative breast cancer, ferroptosis, red blood cell hitchhiking, liposomes, tumor hypoxia, HIF-1alpha, P-glycoprotein, paclitaxel, drug resistance, lung metastasis, hemoglobin, nanomedicine

The rationale behind the trial was grounded in a genuine biological puzzle. In an earlier phase 1 study, inhaled recombinant human interleukin-15, or rhIL-15, proved safe in dogs with metastatic osteosarcoma and melanoma and produced durable responses in a subset of animals. Intriguingly, dogs that entered the trial with lower absolute lymphocyte counts were statistically more likely to benefit. The Davis team hypothesized that reducing lymphocytes before treatment might remove so-called cytokine sinks, circulating immune cells that soak up interleukin-15 before it can reach the natural killer cells and CD8-positive memory T cells the drug is meant to energize.

Lymphodepletion is a well-established strategy in human adoptive cell therapy, where chemotherapy is routinely used before infusing engineered T cells to improve their expansion and persistence. Doxorubicin, a mainstay chemotherapy agent in veterinary medicine, had previously been shown to reduce circulating T lymphocytes in tumor-bearing dogs. The researchers therefore designed a trial in which dogs received a standard dose of doxorubicin, 30 milligrams per square meter for larger animals or 1 milligram per kilogram for smaller ones, followed one week later by two weeks of inhaled rhIL-15 at 50 micrograms twice daily, delivered by nebulizer at home by trained owners.

The study population consisted of ten client-owned dogs with histologically or cytologically confirmed melanoma or bone tumors, all carrying at least one lung lesion of a centimeter or larger on thoracic radiographs. Five dogs had osteosarcoma, four had melanoma, and one had a multilobular tumor of bone. Eligibility criteria were strict: dogs needed adequate organ function, no prior rhIL-15 exposure, no recent chemotherapy or immunotherapy, and screening echocardiograms to rule out cardiac disease that could be worsened by doxorubicin. The trial was approved by the UC Davis institutional review boards, and all owners provided informed consent.

When the results came in, the numbers told a sobering story. Two dogs progressed before the Day 35 response assessment, leaving eight evaluable patients. One dog achieved a complete response that has now lasted more than two years, two had stable disease, and five progressed. That translates to an overall response rate of 10 percent and a clinical benefit rate of 30 percent, figures essentially indistinguishable from the phase 1 trial of inhaled rhIL-15 alone, which reported a response rate of 11 percent and a clinical benefit rate of 39 percent. The trial had been powered to detect a jump in response rate from 11 to 50 percent, so the null result is unlikely to be a statistical fluke of modest effect size.

The hematological data confirmed the team did achieve the biological precondition they set out to create. Seven days after doxorubicin, mean absolute lymphocyte counts fell from 1,452 to 1,023 cells per microliter, a statistically significant drop that brought the dogs to lymphocyte levels comparable to those seen in responding patients from the earlier trial. White blood cells, monocytes, and neutrophils also declined significantly, and one dog developed grade 4 neutropenia with fever that resolved within two days of hospitalization and supportive care. Crucially, adding doxorubicin did not increase the toxicity of the inhaled cytokine therapy itself, and no allergic reactions or pulmonary adverse events were attributed to rhIL-15.

Transcriptomic analysis added an unexpected layer of insight. Using the NanoString nCounter canine immuno-oncology panel covering 780 genes, the researchers profiled peripheral blood mononuclear cells collected before doxorubicin, after doxorubicin, and after two weeks of inhaled rhIL-15. While overall lymphocyte counts fell, the relative proportions of T cells, CD8-positive T cells, exhausted CD8-positive T cells, natural killer cells, and Th1 cells did not change significantly, indicating that doxorubicin depleted lymphocytes indiscriminately rather than selectively removing suppressive populations. The one clear casualty was the B cell compartment: B cell scores and B cell function genes, including CD19, CD79B, MS4A1, and immunoglobulin genes, dropped significantly and had not recovered by Day 21, consistent with the rapid proliferation rate of B cells making them especially vulnerable to chemotherapy.

Perhaps the most tantalizing clue came from the single dog that achieved a complete response. That patient initially appeared to progress at Day 35, with new lung lesions appearing on radiographs, but after receiving palliative radiation to its primary mandibular melanoma, every lung lesion resolved by week 15. The researchers suggest this may represent pseudoprogression, a well-recognized phenomenon in human immunotherapy where apparent tumor growth reflects immune cell infiltration rather than true malignancy, though an abscopal effect triggered by the radiation cannot be excluded. Transcriptomically, this dog trended toward higher T cell, CD8-positive T cell, and cytotoxic cell scores, and started with a lower exhausted CD8 T cell score than non-responders, hinting that baseline immune fitness may predict who benefits from inhaled rhIL-15.

The study carries important limitations that the authors acknowledge candidly. Ten patients is a small cohort, and two dogs did not survive to formal response assessment. The therapy used human rather than canine interleukin-15, which likely provoked neutralizing antibodies, although the two-week treatment window was chosen to minimize that risk. Target lesions smaller than the standard 2-centimeter RECIST threshold were permitted, matching the phase 1 design but introducing radiographic measurement imprecision. Tumor type may also have influenced outcomes, since one of the stable disease patients had a multilobular tumor of bone, an inherently slower-growing cancer.

Even so, the trial delivers a valuable double message. First, it definitively rules out standard-dose doxorubicin preconditioning as a way to enhance inhaled rhIL-15 efficacy, redirecting the field toward other combination strategies such as radiation, which has already shown promise with cytokine therapy in canine sarcoma and melanoma. Second, it confirms that durable, multi-year complete responses are achievable even in dogs with diffuse pulmonary metastatic disease, a population whose prognosis otherwise hovers below 80 days. For the dogs that respond, and for the human osteosarcoma and melanoma patients their disease so closely mirrors, that signal is worth chasing with better-designed combinations.

Subject of Research: Doxorubicin preconditioning and inhaled recombinant human IL-15 immunotherapy in dogs with pulmonary metastasis

Article Title: Evaluating the impact of doxorubicin preconditioning on the efficacy of inhaled recombinant human IL-15 immunotherapy in dogs with pulmonary metastasis

Article References: Luker, M. E., York, D., Al-Nadaf, S., Johnson, E. G., Withers, S. S., Cruz, S. M., Lejeune, A., Skorupski, K. A., Young, J., Cohen-Davidyan, T., Sparger, E. E., Culp, W. T., Murphy, W. J., Kent, M. S., Canter, R. J., & Rebhun, R. B. (2025). Evaluating the impact of doxorubicin preconditioning on the efficacy of inhaled recombinant human IL-15 immunotherapy in dogs with pulmonary metastasis. Veterinary Oncology, 2(1), Article 23. https://doi.org/10.1186/s44356-025-00040-5

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00040-5

Keywords: immunotherapy, interleukin-15, doxorubicin, canine osteosarcoma, melanoma, lung metastasis, lymphodepletion, veterinary oncology, natural killer cells, CD8 T cells, pseudoprogression, transcriptomics