Project Funding Details

PARP inhibitors (PARPi) have emerged as targeted therapies for breast and ovarian cancers and, more in general, cancers exhibiting homologous recombination deficiency (HRD) and BRCAness phenotype. Besides HRD, compromised fork protection and accumulation of ssDNA gaps greatly contribute to PARPi efficacy in BRCA-deficient cancers. In the absence of BRCA1/2, crucial factors for stalled replication fork protection, failure to recruit RAD51 results in extensive MRE11-dependent pathological fork degradation, leading to fork collapse and DNA damage accumulation. Similarly, the replication fork caretaker factor Werner helicase interacting protein 1 (WRNIP1) is implicated in RAD51 stabilisation at perturbed forks, one of the mechanisms contributing to PARPi resistance. Since WRNIP1 binds RAD51 at perturbed forks, we hypothesise that loss of WRNIP1 underlies PARPi sensitivity by impairing RAD51 stabilisation and gap suppression. Considering the frequent overexpression of WRNIP1 in breast and ovarian cancers, we assume that the elevated WRNIP1 levels may induce PARPi resistance in cancer cells, bypassing the need for BRCA2 in RAD51 stabilisation at perturbed forks. The primary objective of the proposal is to elucidate the role of WRNIP1 overexpression in the molecular mechanisms of chemoresistance in tumours, especially those with BRCAness phenotype. Investigating the pathway involving WRNIP1 could identify factors relevant for developing, as long-term objective, a drug-combined strategy against PARPi-resistant tumours. The proposal also aims to evaluate whether WRNIP1 overexpression can serve as a predictor for the efficacy of PARPi treatment. Combining cancer cell models engineered for inducible gene silencing of BRCA2 and WRNIP1 overexpression, stably cell lines expressing mutant forms of WRNIP1 with cell biology and biochemistry, the research will delineate how WRNIP1 modulates chemosensitivity in BRCAness cancers. Fork protection and RAD51 function will be evaluated to determine if WRNIP1 overexpression stabilizes RAD51 at stalled forks. Furthermore, a panel of cancer cell lines and RNAi will be used to assess if WRNIP1 levels influence chemosensitivity to PARPi or reveal novel vulnerabilities. Preliminary findings show that WRNIP1 overexpression counters PARPi/CIS sensitivity in BRCA2-deficient cancer cell lines. This proposal is expected to elucidate the mechanism underpinning this resistant phenotype. Furthermore, we expect to pave the way for a future rational evaluation of WRNIP1 status as a predictive marker for PARPi treatment efficacy. Additional mechanistic studies will identify factors within the WRNIP1-associated pathway that can be utilised to enhance the sensitive of cancer cells to PARPi. This research holds promise in providing mechanistic insights into the development of resistance to PARPi in cancer cells and predicting treatment efficacy. Understanding the sensitization mechanisms could extend the therapeutic benefits of PARPi to various cancers with HRD backgrounds, broadening the scope beyond BRCAness cancers.