PARP inhibitor

Overview

Poly(ADP-ribose) polymerase (PARP) inhibitors are a class of targeted anticancer agents that exploit defects in DNA damage repair pathways, particularly homologous recombination (HR). PARP enzymes play a central role in detecting and repairing single-strand DNA breaks; when inhibited, unresolved breaks collapse replication forks into double-strand breaks. In tumor cells already harboring deficiencies in HR — such as those with loss-of-function mutations in BRCA1 or BRCA2 DNA repair associated genes — this dual impairment of repair pathways leads to synthetic lethality, resulting in selective cancer cell death while largely sparing normal cells. olaparib, one of the earliest and most clinically validated agents in this class, exemplifies the mechanism and has been approved across multiple HR-deficient tumor types including ovarian, breast, and prostate cancers.

The therapeutic utility of PARP inhibitors is closely tied to the concept of BRCAness — a broader genomic phenotype characterized by deficient homologous recombination repair (HRD), even in the absence of germline BRCA mutations. The presence of PTEN loss and other HR pathway alterations has been associated with sensitivity to this drug class. Understanding and expanding the HRD-positive patient population, overcoming intrinsic and acquired resistance, and identifying synergistic combination strategies represent the principal frontiers of contemporary PARP inhibitor research.

Focus of Latest Publications

Recent literature reflects a rapidly evolving landscape for PARP inhibitors, with investigations spanning prostate, ovarian, and hereditary breast cancers and addressing both mechanisms of efficacy and resistance.

Prostate Cancer

Several studies have examined the role of PARP inhibitors in metastatic castration-resistant prostate cancer (mCRPC). A 2026 review in the International Journal of Oncology positioned PARP inhibitors as a central component of novel therapeutic strategies beyond androgen receptor pathway inhibition, specifically highlighting their utility in tumors bearing homologous recombination repair deficiencies. This contextualizes PARP inhibitors alongside other emerging modalities such as antibody-drug conjugates, bispecific T cell engagers, checkpoint inhibitors, and agents targeting glutamate carboxypeptidase II (PSMA). Notably, a meta-analysis reported in the International Journal of Cancer found that androgen receptor signaling inhibitors conferred longer overall survival than PARP inhibitor-based regimens in prostate cancer, underscoring ongoing debate about optimal treatment sequencing.

A mechanistically significant study published in JCI Insight demonstrated that VIC-1911, an Aurora kinase A inhibitor, induces mitotic defects and functional BRCAness in prostate cancer cells — thereby sensitizing HR-proficient tumors to PARP inhibition. This work illustrates a strategy for expanding PARP inhibitor eligibility beyond genetically HRD-positive disease by pharmacologically inducing an HRD phenotype. In parallel, research published in Cancer Letters identified a role for M1C in mediating LINE-1 transposon transcription in PARP inhibitor-treated castration-resistant prostate cancer cells, providing molecular insight into adaptive responses that may underlie resistance in HR-deficient settings.

ovarian cancer

In ovarian cancer, two studies addressed the critical question of how prior PARP inhibitor exposure shapes subsequent treatment outcomes. A propensity score-matched analysis published in the International Journal of Clinical Oncology evaluated platinum-based chemotherapy efficacy in patients with platinum-sensitive recurrent ovarian cancer (PSROC), stratifying patients by prior PARP inhibitor exposure. The study design reflected the clinical reality that olaparib and related agents are now frequently used as frontline maintenance therapy, making it essential to characterize how prior PARPi affects later platinum sensitivity.

A mechanistically important study in Science Translational Medicine identified a novel resistance pathway in ovarian cancer involving POSTN+ myofibroblasts — a cancer-associated fibroblast subtype — that are activated by genomic instability through the STING–WNT axis. This stromal reprogramming converts the immune-activating signals generated by genomic instability into an immunosuppressive microenvironment, directly limiting PARP inhibitor efficacy. Specifically, WNT3a/7a-mediated Wnt/β-catenin signaling was implicated in suppressing CD8+ S100B+ T cell activity, providing a mechanistic bridge between STING signaling, stromal biology, and PARPi resistance. These findings suggest that co-targeting the tumor microenvironment — for instance, by combining PARP inhibitors with checkpoint inhibitor — may be necessary to overcome stromal immunosuppression.

Hereditary breast cancer

A study in Experimental & Molecular Medicine delineated four molecular subtypes of hereditary breast cancers based on the nature of their genomic instability. Functional analyses in cell line models suggested that PARP inhibitors and cytotoxic chemotherapy are preferentially active in HRD and copy-number (CN) unstable subtypes, while tumors with high mutational burden (MUT subtype) may instead be candidates for immunotherapy. This subtype-stratified framework reinforces the importance of genomic profiling in matching patients to PARP inhibitor therapy and situating it within a broader precision oncology context that includes BRCA1 and BRCA2 mutation status.

Key Publications

Jun Impact of prior PARP inhibitor exposure on the efficacy of platinum-based chemotherapy in platinum-sensitive recurrent ovarian cancer: a propensity score-matched analysis. (International journal of clinical oncology, 2026, PMID 41882282): "To evaluate the efficacy of platinum-based chemotherapy in platinum-sensitive recurrent ovarian cancer (PSROC) between patients with and without prior exposure to poly(ADP-ribose) polymerase inhibitor (PARPi)."
May Genomic instability drives POSTN+ myofibroblasts via STING-WNT axis to promote immunosuppression and PARPi resistance in ovarian cancer. (Science translational medicine, 2026, PMID 42202048): "...thereby converting genomic instability-driven immune activation into suppression and limiting poly(ADP-ribose) polymerase inhibitor (PARPi) efficacy."
May AURKA inhibitor VIC-1911 induces mitotic defects and functional BRCAness, sensitizing prostate cancer to PARP inhibition. (JCI insight, 2026, PMID 41915443): "Notably, VIC-1911 showed synergistic effects in inhibiting PCa cell growth in vitro and xenograft tumor growth in vivo with poly (ADP-ribose) polymerase inhibitors, which have proven effective in PCa with a deficiency in homologous recombination (HR) repair."
Apr M1C mediates LINE-1 transcription in PARP inhibitor-treated prostate cancer cells. (Cancer letters, 2026, PMID 41690451): "Advanced castration-resistant prostate cancer (CRPC) is responsive to PARP inhibitors, but only in settings of defects in homologous recombination (HR)."
Apr Clinical Benefit and Safety of Combined Immunotherapy and Targeted Therapy in Prostate Cancer. (International journal of cancer, 2026, PMID 42017392): "The androgen receptor signaling inhibitor subgroup exhibited longer survival than the PARP inhibitor subgroup."
Apr Novel therapeutic strategies for metastatic castration‑resistant prostate cancer: Beyond androgen receptor pathway inhibition (Review). (International journal of oncology, 2026, PMID 41992975): "These include PARP inhibitors for tumors with homologous recombination repair deficiencies."
Apr Delineation of the heterogeneity underlying genomic instability in hereditary breast cancers reveals four disease subtypes. (Experimental & molecular medicine, 2026, PMID 41991965): "Functional analysis in cell lines suggests poly (ADP-ribose) polymerase inhibitors and cytotoxic chemotherapy sensitivity in HRD and CN tumors, whereas immune features in MUT tumors support vulnerability to immunotherapy."