Therapeutic resistance remains one of oncology’s most difficult challenges. Cancer cells are genetically and biologically adaptable, and treatment can select for populations that activate alternative pathways to repair damage, continue dividing or evade cell death. As a result, a therapy that produces a strong response at first may eventually lose its effect, allowing the disease to return. “Therapeutic resistance is a main obstacle to achieve effective and durable cancer treatments,” said Dr. Weei-Chin Lin, professor of medicine—hematology and oncology and of molecular and cellular biology at Baylor, who led the study.

The Baylor team focused on TopBP1 because the protein functions as a kind of molecular switchboard. Rather than controlling only one process, TopBP1 coordinates multiple pathways involved in DNA replication, DNA damage responses and cancer-cell survival. The researchers concentrated on a region known as the BRCT7/8 domain, which acts as a docking interface for other regulatory proteins. Interrupting this interface could therefore affect several cancer-promoting systems at once, potentially reducing the ability of malignant cells to compensate when one pathway is blocked.

Among the proteins that interact with TopBP1-BRCT7/8 are MIZ1, a regulator that can suppress the cancer-driving protein MYC; mutant forms of p53, which may acquire functions that actively promote tumor growth; and PLK1 and CIP2A, proteins that support cell division and help cancer cells withstand stress. These interactions give TopBP1-BRCT7/8 an unusually broad influence over tumor biology. The researchers reasoned that a compound capable of selectively disrupting the domain might weaken several lines of defense at the same time.

To find such a compound, the team combined computer-based structural modeling with laboratory screening. Thousands of chemical molecules were evaluated for their ability to fit into the BRCT7/8 binding region and interfere with its interactions. An initial hit, called 3B6, provided a chemical starting point, but it was not sufficiently effective to serve as a promising drug candidate. Researchers chemically modified the compound through multiple rounds of optimization, ultimately producing CS18, which displayed stronger activity in cellular experiments.

The experiments indicated that CS18 affects cancer cells through several connected mechanisms. When the compound binds to TopBP1-BRCT7/8, the activity of MYC and mutant p53 declines, while proteins involved in DNA repair become less effective. At the same time, genes that restrict uncontrolled cell growth become more active. This combination may leave cancer cells unable to repair treatment-induced damage or maintain the signaling programs required for survival, increasing the likelihood that they will undergo programmed cell death.

CS18 produced these effects across a range of malignant cell types, including triple-negative breast cancer, ovarian cancer, lung adenocarcinoma, lung squamous cell carcinoma and acute myeloid leukemia. In the researchers’ tests, the compound was less damaging to noncancerous cells than to cancer cells, although such findings do not establish safety in humans. The broad activity was particularly important because it suggested that TopBP1 inhibition could be relevant across tumors driven by different genetic abnormalities rather than being limited to a single cancer subtype.

The most notable results emerged when CS18 was combined with existing treatments. In cancer models, the compound enhanced the activity of PARP inhibitors, drugs that prevent cells from repairing certain forms of DNA damage. Tumor cells already operating under heavy replication and repair stress may be especially dependent on the remaining repair pathways, making them vulnerable when TopBP1 signaling is also disrupted. CS18 likewise strengthened the effect of osimertinib, a targeted therapy used against certain lung cancers driven by mutant epidermal growth factor receptor, or EGFR.

The combination was particularly effective in cells that had already developed resistance to osimertinib. Adding CS18 restored their sensitivity to the EGFR inhibitor and increased cancer-cell death, indicating that TopBP1 blockade may help dismantle resistance mechanisms rather than simply adding another independent source of toxicity. In animal models, treatment combinations significantly reduced tumor growth without major weight loss or other obvious signs of toxicity during the experiments. However, the results remain preclinical, and further studies will be needed to determine how the compound is absorbed, distributed and metabolized, as well as whether its benefits outweigh potential risks in people.

The researchers describe CS18 as a candidate for further drug development, not as an available cancer treatment. Additional work will need to establish the compound’s precise pharmacology, optimal dosing, long-term safety and effectiveness in more representative tumor models. Clinical trials would ultimately be required to determine whether the strategy can help patients whose cancers resist PARP inhibitors, osimertinib or other therapies. If those studies are successful, targeting TopBP1-BRCT7/8 could lead to combination treatments designed not only to shrink tumors, but also to prevent cancer cells from activating escape routes that enable relapse.

Subject of Research: Cells

Article Title: Development of a structurally distinct TopBP1 inhibitor that enhances PARP blockade and reverses osimertinib resistance

Web References: https://doi.org/10.1126/sciadv.aeg1996; https://www.bcm.edu/people-search/weei-chin-lin-25464

References: Science Advances, DOI: 10.1126/sciadv.aeg1996

Keywords

CS18, TopBP1, cancer drug resistance, cancer therapy, PARP inhibitors, osimertinib, lung cancer, triple-negative breast cancer, ovarian cancer, acute myeloid leukemia, molecular oncology, drug development

TNBC represents a formidable subset of breast cancers characterized by the absence of estrogen receptor, progesterone receptor, and HER2 expression, which deprives clinicians of the traditional hormonal and targeted therapies that benefit other breast cancer types. The standard chemotherapeutic agent gemcitabine often encounters resistance, severely compromising treatment efficacy. Against this backdrop, the newly reported dual-targeting strategy aims to dismantle TNBC’s multifaceted defense mechanisms at the molecular level.

The study intricately explores the apoptotic pathways modulated by BH3 mimetics. These small molecules mimic the activity of pro-apoptotic BH3-only proteins, which are pivotal in tipping the balance towards programmed cell death. Cancer cells frequently subvert this apoptotic machinery through overexpression of anti-apoptotic BCL-2 family proteins, promoting survival despite cytotoxic insults. The introduction of BH3 mimetics serves to neutralize these anti-apoptotic shields, reinstating apoptosis and sensitizing cancer cells to therapy.

Beyond apoptosis, the PI3K/mTOR signaling cascade is a central regulator of cell growth, proliferation, and survival pathways, frequently hyperactivated in TNBC. Targeting this axis with dual inhibitors disrupts cancer cell metabolism and growth signals, rendering cells more vulnerable. The combination therapy examined capitalizes on this dual assault by simultaneously curbing aberrant survival signals while reigniting intrinsic death pathways.

Through meticulous cellular and molecular assays, this research elucidates the synergistic effects achieved by merging BH3 mimetic-induced apoptosis with PI3K/mTOR pathway suppression. Importantly, the combined treatment re-sensitized gemcitabine-resistant TNBC cell lines, triggering marked reductions in proliferation and survival. The findings convey a nuanced understanding of resistance mechanisms and present a viable therapeutic strategy to circumvent them.

Significantly, the study documents the downregulation of key anti-apoptotic proteins as a consequence of BH3 mimetic action, which diminishes the cancer cells’ ability to evade gemcitabine’s cytotoxicity. Concurrently, dual PI3K/mTOR inhibition inhibits downstream effectors such as AKT, 4EBP1, and S6 kinase, which are instrumental in preserving malignant phenotypes. The cooperative inhibition of these pathways culminates in heightened apoptotic rates, underscoring the potency of addressing multiple nodes within oncogenic signaling.

Moreover, the research extends beyond in vitro evaluations by incorporating in vivo tumor models that corroborate the enhanced efficacy of the combination therapy. Tumors previously exhibiting resistance to gemcitabine demonstrated significant regression when subjected to concurrent BH3 mimetic and dual PI3K/mTOR inhibitor treatment. These data reinforce the translational potential of this combinatorial approach.

Crucially, the authors emphasize the therapy’s specificity, noting that non-malignant cells showed limited sensitivity to the drug combination, suggesting a favorable therapeutic window. This specificity heralds a promising safety profile that could mitigate the severe side effects commonly associated with conventional chemotherapies.

The intricate mechanism of overcoming gemcitabine resistance lies not only in inducing apoptosis but also in modulating autophagy and metabolic adaptations that cancer cells employ to survive chemotherapy. The dual inhibition appears to disrupt these compensatory survival strategies, exposing the vulnerability of TNBC’s resilience under combined therapeutic pressure.

Integrating high-throughput genomic and proteomic analyses, the study delineates alterations in gene expression profiles linked to cell cycle arrest, apoptosis induction, and metabolic stress signaling. These comprehensive molecular landscapes offer insight into how the synergistic treatment remodels the cancer cell environment, tipping the scales decisively against tumor survival.

Of particular note is the potential of this therapeutic regimen to serve as a blueprint for tackling resistance in other difficult-to-treat cancers exhibiting similar molecular aberrations. The concept of combining apoptosis induction with growth pathway inhibition could revolutionize the approach to multidrug-resistant malignancies.

The implications for clinical application are profound. This research paves the way for tailored clinical trials aimed at validating efficacy and safety in patients, especially those with advanced or refractory TNBC. If successful, this could inaugurate a new chapter in breast cancer therapeutics defined by precision and adaptive combination strategies.

Furthermore, this investigative endeavor underscores the critical importance of understanding tumor biology at a granular level to design interventions that are not only innovative but also mechanistically informed. The marriage of targeted therapies with established chemotherapeutics exemplifies the evolving paradigm in oncology toward combination regimens that exploit tumor vulnerabilities comprehensively.

In an age where cancer drug resistance remains a formidable barrier, this study’s breakthrough offers a beacon, leveraging molecular synergy to re-sensitize tumors previously impervious to frontline treatments. The scientific community eagerly anticipates subsequent clinical validations and the prospect of integrating this approach into standard care regimes.

This research enriches the existing compendium of cancer biology by providing clarity on the interplay between apoptosis and growth signaling in TNBC and invites further exploration into combinatorial regimens optimizing patient outcomes.

As the fight against breast cancer advances, such innovative, carefully studied strategies are essential to surmounting the formidable challenges imposed by inherently resistant cancer types, holding promise to reshape survival trajectories for countless patients.

Subject of Research: Triple-negative breast cancer (TNBC) and overcoming gemcitabine resistance via combination therapy targeting apoptotic and PI3K/mTOR pathways.

Article Title: BH3 mimetic and dual PI3K/mTOR inhibitor attenuates gemcitabine resistance in triple-negative breast cancer.

Article References:
Selimoglu, G., Ayvaz, S. & Bolat, Z.B. BH3 mimetic and dual PI3K/mTOR inhibitor attenuates gemcitabine resistance in triple-negative breast cancer. Med Oncol 43, 10 (2026). https://doi.org/10.1007/s12032-025-03143-z

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s12032-025-03143-z

Pancreatic cancer remains among the deadliest malignancies, with a dismal five-year survival rate hovering around 13%. One reason for this poor prognosis is the cancer’s ability to survive in hostile environments and evade the cytotoxic effects of traditional chemotherapy and radiation. To combat this resilience, Indiana University researchers examined the molecular underpinnings that enable tumor cells to flourish despite aggressive treatments. They zeroed in on Ref-1, a multifunctional protein involved in DNA repair, redox signaling, and cellular response to oxidative stress, hypothesizing that its inhibition could sensitize tumors to therapy.

Intriguingly, the study revealed that another protein, peroxiredoxin-1, operates in tandem with Ref-1 to bolster pancreatic cancer cells’ survival. PRDX1 is an antioxidant enzyme that reduces peroxides, thus protecting cells from oxidative damage. This partnership appears to be a key driver of the cancer’s robust defense system. When researchers selectively knocked down PRDX1 alongside pharmacologically inhibiting Ref-1 with a novel agent called APX2014, the dual attack provoked substantial tumor shrinkage and increased cancer cell death in preclinical models.

The specificity of PRDX1’s role was a surprising finding. Of all the related peroxiredoxins tested, only loss of this protein sensitized tumors significantly to Ref-1 blockade. This suggests a unique and exploitable vulnerability within the pancreatic tumor microenvironment. Mark Kelley, PhD, the lead author of the study and a distinguished pediatric oncology researcher at Indiana University, noted that the combined inhibition of both Ref-1 and PRDX1 outperformed treatments targeting either protein alone. Animal experiments supported this conclusion, showing smaller tumors and enhanced survival outcomes.

The ramifications extend beyond pancreatic cancer. The dual protein inhibition strategy also impacts the tumor microenvironment — the surrounding tissue, immune cells, and extracellular matrix that collectively support tumor growth and spread. By disrupting these interactions, the therapy undermines the cancer’s capacity to adapt and resist treatment, potentially translating into improved clinical responses. This broad efficacy suggests applicability to other aggressive cancers with similar survival pathways.

The innovative drug APX2014, developed by the team, is a potent inhibitor of Ref-1’s redox functions. Ref-1 regulates transcription factors such as NF-κB and HIF-1α, which are essential to cancer cell proliferation and survival under oxidative stress. By blocking Ref-1, APX2014 impairs the tumor’s ability to respond to DNA damage and oxidative insults. Coupling this with PRDX1 suppression amplifies oxidative stress within the cancer cells, pushing them toward apoptosis.

Future work will build on these promising results by identifying additional agents capable of targeting PRDX1 effectively. Researchers are also planning to test the combined therapeutic approach in other cancer types to assess its wider impact. Beyond laboratory models, there is an active interest in designing clinical trials that can evaluate the safety and efficacy of these drug combinations in patients, seeking to translate the molecular insights into tangible medical benefits.

This discovery underscores the evolving understanding of redox biology in cancer pathophysiology. Tumor cells exploit redox-modulating proteins to survive the hostile conditions generated by both their own metabolism and therapeutic interventions. Targeting these proteins simultaneously disrupts essential survival pathways. Such insights could revolutionize how researchers approach drug resistance, enabling development of more durable and precise anticancer regimens.

Furthermore, the study highlights the importance of tumor microenvironmental factors in dictating therapy outcomes. By not only attacking the cancer cells but also their ecological niche, researchers hope to prevent relapse and metastasis, which remain major challenges in pancreatic cancer management. This comprehensive strategy may be the key to finally improving prognoses for patients afflicted by this formidable disease.

Funding for this research was provided by the National Institutes of Health and the Riley Children’s Foundation, reflecting the collaborative effort required to tackle complex cancers. Collaboration among the Indiana University School of Medicine’s Herman B Wells Center for Pediatric Research and the IU Melvin and Bren Simon Comprehensive Cancer Center was instrumental in achieving these breakthroughs.

The research team encourages continued exploration of combination therapies that dismantle multiple layers of tumor defense, aiming to outsmart pancreatic cancer’s notorious resistance mechanisms. By thoroughly understanding and targeting cancer’s cellular and microenvironmental survival strategies, the scientific community moves closer to devising treatments that could transform outcomes for one of the most challenging cancers to manage.

In summary, Indiana University researchers have identified a novel double-target strategy against pancreatic cancer by inhibiting Ref-1 and PRDX1 concurrently. This approach causes significant tumor regression and prolongs survival in preclinical models, heralding a new frontier in cancer therapeutics. The balance of redox signaling within tumors is crucial, and its disruption offers a promising weapon in the fight against cancer’s deadliest forms.

Subject of Research: Pancreatic cancer; redox biology; tumor microenvironment; combination cancer therapy targeting Ref-1 and PRDX1 proteins.

Article Title: Combination Inhibition of Ref-1 and PRDX1 Reveals Novel Vulnerabilities in Pancreatic Cancer

News Publication Date: Not explicitly stated in content

Web References:

• Redox Biology journal article: https://www.sciencedirect.com/science/article/pii/S2213231725003611?via%3Dihub
• IU School of Medicine: https://medicine.iu.edu/
• Herman B Wells Center for Pediatric Research: https://medicine.iu.edu/research-centers/pediatrics
• IU Melvin and Bren Simon Comprehensive Cancer Center: https://cancer.iu.edu/index.html

Image Credits: Tim Yates, IU School of Medicine

Keywords: Pancreatic cancer, Ref-1, PRDX1, redox biology, cancer therapy, drug resistance, tumor microenvironment, APX2014, combination therapy, oxidative stress, cancer research, Indiana University