Discovery of PARP1-PROTAC as novel strategy against PARP inhibitor resistance via promoting ferroptosis in mutant-p53 triple-negative breast cancer

Background and Purpose: The acquired resistance to PARP inhibitors (PARPi) caused by point mutations in PARP1 protein is hard to overcome through current strategies. In order to explore modalities to conquer resistance and identify patients who are most likely to benefit from PARP1-targeted therapy, we developed a proteolysis-targeted-chimaera (PROTAC) to degrade mutant PARP1 in p53-mutant TNBC. Experimental Approach: Based on analysis of the resistant mutations, we attempted to use PROTAC strategy to increase the sensitivity of cells expressing PARPi-resistant proteins that identified from patients. The antineoplastic activity of our synthetic degrader was evaluated in multiple human cell lines, as well as the xenograft model with p53 mutation. The proteomics subsequently was used to reveal the potential mechanism of the degrader. Ferroptosis, as main mechanism, was assayed via detecting SLC7A11 signaling, glutathione and lipid peroxidation. Besides, according to genetic alteration analysis from patients, three common p53 mutations were selected to assess PARP1-related cell death. Key Results: We developed a PROTAC termed “NN3”, and this compound could trigger ubiquitination and proteasome-mediated PARP1 degradation. Interestingly, compared with other reported PARP1 degraders, NN3 has a unique antitumor mechanism and it promote ferroptosis effectively via decreasing the SLC7A11/GPX4 pathway in HR-proficient TNBC cells, whether or not these cells express drug resistance-related PARP1 mutations. More importantly, NN3 showed potent activity and low toxicity in vivo studies on mutant-p53 TNBC. Conclusion and Implications: We identify PROTAC-mediated degradation of PARP1 as a novel strategy against PARPi resistance and a paradigm for targeting mutant-p53 cancers by inducing ferroptosis.