• PARP inhibitors are among the most widely used therapies for ovarian cancer, but their long-term effectiveness is limited by acquired resistance 

• Researchers found a signaling pathway activated by the tumor microenvironment was a major driver of resistance, and blocking the pathway was able to resensitize tumors 

• The pathway was activated because the tumor microenvironment is acidic, which is common in several tumor types, demonstrating broad potential for this approach  

• Several drugs targeting this pathway already are in development, supporting potential future clinical investigation 

HOUSTON, JULY 29, 2026 ― Researchers at The University of Texas MD Anderson Cancer Center have discovered a promising strategy to overcome PARP inhibitor resistance in ovarian cancer, one of the most common barriers to the long-term effectiveness of this widely used treatment.  

Targeting a signaling pathway activated by the acidic tumor microenvironment restored sensitivity to PARP inhibitors in preclinical models, suggesting a potential new therapeutic strategy for overcoming acquired resistance. The study, published in Cancer Research, was led by Rugang Zhang, Ph.D., professor and chair of Experimental Therapeutics, and Kaixin Cheng, Ph.D., postdoctoral fellow in the Rugang Zhang Laboratory. 

“PARP inhibitors have transformed treatment for many patients with ovarian cancer, but resistance often limits their long-term effectiveness,” Zhang said. “This study revealed that the tumor microenvironment plays a critical role in driving treatment resistance and suggests a potential strategy for restoring sensitivity to PARP inhibitors and extending their benefit for patients.” 

How does an acidic microenvironment help tumors evade treatment? 

Acidity is a hallmark of many tumors, which often accumulate acid due to abnormal metabolism and poor blood flow. While tumor acidity has long been associated with resistance to cancer therapies, its effects on PARP inhibitor response remained unclear. 

PARP inhibitors block a key DNA repair pathway that cancer cells rely on for survival. These therapies are particularly effective in ovarian cancers that already have defects in DNA repair, such as tumors with BRCA mutations. However, many tumors eventually develop resistance to PARP inhibitors, leaving patients with fewer effective treatment options. 

In this study, researchers found that ovarian cancer cells exposed to acidic conditions became significantly less sensitive to PARP inhibitors. Acidic environments activated a signaling network involving ERK, p300 and PARP1 – proteins that collectively regulate cellular signaling, gene activity and DNA repair. Activation of this pathway reduced PARP trapping, a process in which PARP inhibitors lock PARP enzymes at sites of DNA damage to prevent repair. By reducing PARP trapping, this pathway decreases the effectiveness of these drugs. 

How does targeting this signaling pathway reverse treatment resistance? 

A large-scale CRISPR genetic screen identified p300 as a critical driver of the resistance pathway activated by tumor acidity. Researchers discovered that p300 adds a small chemical tag to PARP1 through a process called acetylation. This modification helped cancer cells avoid the DNA damage caused by PARP inhibitors.  

Disrupting this process with p300 inhibitors restored sensitivity to PARP inhibitors in ovarian cancer cells, leading to stronger antitumor responses across multiple preclinical models, including those with acquired PARP inhibitor resistance. 

The findings also suggest PARP1 acetylation and ERK activation may have potential as biomarkers of treatment resistance. Analysis of tumor samples from ovarian cancer patients treated with PARP inhibitors found that tumors with higher levels of activated ERK and acetylated PARP1 were more likely to be resistant to treatment and were associated with poorer outcomes.  

What’s next for this research? 

This study provides a strong rationale for further research on p300 inhibitors in ovarian cancer treatment. Future clinical trials could evaluate whether combining p300 inhibitors with PARP inhibitors could overcome treatment resistance or perhaps improve outcomes for patients who typically do not benefit from PARP inhibitors. 

Several p300 inhibitors, including IACS-16559, an agent developed by UT MD Anderson’s Therapeutics Discovery division, are being evaluated preclinically or are in early-stage clinical development, supporting the potential for further investigation of this therapeutic strategy. 

Additional research is needed to determine whether PARP1 acetylation and ERK activation could serve as biomarkers for predicting treatment response. Future studies also may identify additional mechanisms within the tumor microenvironment that drive treatment resistance, further expanding opportunities for therapeutic intervention. 

“One of the most striking findings was that the same amount of treatment was still reaching cancer cells, meaning the problem was not drug delivery,” Cheng said. “These findings suggest that the acidic tumor microenvironment may be an important therapeutic target alongside the cancer cell.” 

*** 

This research was supported by the National Institutes of Health, the U.S. Department of Defense, the Cancer Prevention and Research Institute of Texas (CPRIT), the Ovarian Cancer Research Alliance, and institutional support from UT MD Anderson and The Wistar Institute. For a full list of collaborating authors, disclosures and funding sources, see the full paper in Cancer Research.

Journal

Cancer Research

DOI

10.1158/0008-5472.CAN-26-0834

Ovarian cancer, particularly in its platinum-resistant form, represents one of the most formidable challenges in oncology. Resistance to platinum-based chemotherapy, the longstanding frontline standard, heralds a grim prognosis for many patients. In this context, the new clinical guidelines are not merely incremental adjustments but radical reassessments that integrate molecular profiling and precision medicine to redefine therapeutic decision-making. The core of this redefinition pivots on understanding the tumor’s evolving genomic landscape and circumventing intrinsic or acquired drug resistance.

Central to these developments is the appreciation that platinum resistance is not a monolithic state but rather a spectrum of biological behaviors underpinned by distinct molecular alterations. Tumors may employ diverse mechanisms incorporating enhanced DNA repair capacity, alterations in drug transport and metabolism, and evasion of apoptosis pathways. Appreciating this heterogeneity has catalyzed the exploration of combinatorial strategies including PARP inhibitors, immune checkpoint blockade, and novel agents targeting specific vulnerabilities in resistant cancer cells.

Notably, PARP inhibitors have emerged as frontrunners in the management of platinum-sensitive and, increasingly, select platinum-resistant ovarian cancers harboring homologous recombination deficiencies. Ray-Coquard and Moore emphasize that expanded molecular diagnostic testing is critical to identify candidates who may benefit from such targeted therapies. Nevertheless, the clinical efficacy of PARP inhibitors in resistant settings is nuanced, necessitating careful sequencing with other modalities to mitigate cross-resistance and cumulative toxicities.

In parallel, immunotherapy represents a promising frontier, albeit with mixed results in ovarian cancer to date. The authors underscore the importance of dissecting tumor microenvironment characteristics to stratify patients likely to respond to immune checkpoint inhibitors. Combinational approaches that sensitize tumors to immune attack, such as pairing with anti-angiogenic agents or epigenetic modulators, are under rigorous investigation and may soon enter routine clinical practice.

The article also details the growing importance of antibody-drug conjugates (ADCs) in circumventing drug resistance by harnessing targeted delivery of cytotoxic agents. Recent approvals and clinical trial successes of ADCs in ovarian cancer validate this strategy as a potent alternative or adjunct, particularly for heavily pretreated patients. The ability to deliver payloads directly to cancer cells mitigates systemic toxicity and opens avenues for overcoming traditional resistance mechanisms.

Critical to the effective deployment of these therapies is the sequencing and timing of interventions—a complex challenge highlighted prominently by Ray-Coquard and Moore. The authors contend that previous linear treatment paradigms are giving way to flexible, patient-tailored sequences guided by dynamic biomarkers and real-time assessment of tumor evolution. This approach not only aims to maximize efficacy but also preserve quality of life by judiciously balancing therapeutic intensity and tolerability.

Another facet reshaping treatment algorithms is the role of re-challenge with platinum-based agents in select cases. While counterintuitive at first glance, the authors present evidence supporting the notion that re-sensitization to platinum can sometimes be achieved through prior use of non-cross-resistant agents or targeted therapies that modulate resistance pathways. This underscores the need for sophisticated clinical judgment and molecular guidance in treatment planning.

Furthermore, the incorporation of next-generation sequencing and liquid biopsies is revolutionizing the ability to monitor tumor dynamics noninvasively. Such technologies facilitate early detection of emerging resistance mutations and inform timely alterations in therapy, maximizing the window for effective intervention. This precision oncology framework, though still in nascent stages for ovarian cancer, holds tremendous promise for personalizing care.

The psychosocial implications of these evolving treatment sequences are also significant. Patients with platinum-resistant ovarian cancer often confront dwindling options and substantial treatment-related burdens. The new standards emphasize supportive care integration and shared decision-making to align therapeutic goals with patient preferences and quality of life considerations. This holistic approach is indispensable in ensuring that advancements translate into meaningful clinical benefits.

Economically, the expanding armamentarium and complexity of treatment sequencing present logistical and reimbursement challenges. Ray-Coquard and Moore discuss the imperative for cost-effectiveness analyses and healthcare system adaptability to accommodate cutting-edge therapies without exacerbating disparities. Sustainable implementation will require collaboration between clinicians, policymakers, and patient advocacy groups.

Looking forward, ongoing and upcoming clinical trials are poised to further refine sequencing strategies and identify biomarkers predictive of response for novel agents. The authors highlight innovative study designs incorporating adaptive protocols and biomarker-driven cohorts that may accelerate the path to practice-changing evidence. These endeavors reflect a broader commitment to dismantling the therapeutic impasse posed by platinum resistance.

In conclusion, the article by Ray-Coquard and Moore offers a comprehensive and forward-looking synthesis of the current state and future directions in managing platinum-resistant ovarian cancer. Their work elucidates how evolving scientific understanding, technological innovations, and clinical acumen coalesce to redefine treatment sequencing. This transformation holds the promise of improved survival and quality of life for patients confronting this aggressive and recalcitrant disease, making it a watershed moment in the oncology landscape.

The challenges remain formidable, yet the convergence of new standards and emerging constraints provides a roadmap for tailored, dynamic, and effective therapeutic strategies. As the oncology community embraces this new era, continued multidisciplinary collaboration and patient-centered innovation will be vital to translating these scientific advances into clinical realities.

Article References:

Ray-Coquard, I., Moore, K.N. New standards and new constraints redefine treatment sequencing in platinum-resistant ovarian cancer.
Nat Rev Clin Oncol (2026). https://doi.org/10.1038/s41571-026-01168-5

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