Mutant p53 Directs PARP to Regulate Replication Stress and Drive Breast Cancer Metastasis

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• TP53 mutations are prevalent in triple-negative breast cancer (TNBC), driving genomic instability and metastasis.
• Poly (ADP-ribose) polymerase (PARP) is crucial for DNA repair and replication fork stability.
• The role of oncogenic signaling in influencing PARP function during replication stress is not fully understood.

Purpose of the Study:

• To elucidate the mechanism by which mutant p53 (mtp53) influences PARP function to sustain proliferation under replication stress.
• To evaluate the efficacy of combining a PARP inhibitor (talazoparib) with an alkylating agent (temozolomide) in preclinical models of TNBC.
• To determine if mtp53 status can serve as a predictive biomarker for this combination therapy.

Main Methods:

• Treatment of mtp53 and wild-type p53 (wtp53) TNBC cells and organoids with talazoparib and temozolomide.
• Assessment of cell death, DNA damage markers (cleaved PARP, γH2AX), and oncoprotein levels (MDMX).
• Evaluation in orthotopic xenografts and patient-derived xenografts (PDXs), including transcriptomic profiling and DNA fiber combing after CRISPR-mediated deletion of mtp53 C-terminal domain.

Main Results:

• The combination of temozolomide and talazoparib induced synergistic cytotoxicity selectively in mtp53-expressing TNBC cells and organoids.
• Combination therapy significantly reduced circulating tumor cells and lung metastases in mtp53 R273H xenografts.
• Transcriptomic analysis revealed downregulation of MDMX, VEGF, and NF-κB, and increased γH2AX in tumors from combination-treated animals.
• CRISPR-mediated deletion of the mtp53 C-terminal domain impaired tumor growth and metastasis.
• mtp53 utilizes its C-terminal domain to exploit PARP for replication stress adaptation.

Conclusions:

• Mutant p53 reprograms PARP activity via its C-terminal amino acids to maintain tumor cell survival under replication stress.
• p53 status is a key determinant of response to combined PARP inhibitor and DNA-damaging chemotherapy in TNBC.
• The mutant p53-PARP axis represents a novel therapeutic target and mtp53 is a predictive biomarker for PARPi therapy in TNBC.