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Ellington – FANCA-deficient cancer cells are sensitized to PARPi and ATRi by homologous recombination-independent mechanisms

 

FANCA-deficient cancer cells are sensitized to PARPi and ATRi by homologous recombination-independent mechanisms (2024)

Undergraduate: Simon Ellington


Faculty Advisor: Gaorav Gupta
Department: Biochemistry & Biophysics, Radiation Oncology

PARP inhibitors (PARPi) are a class of DNA damage-inducing drugs currently used in the clinic to treat cancers with mutations in BRCA1/2, which show elevated sensitivity to PARPi. This PARPi sensitivity is traditionally thought to be mediated by deficiency in homologous recombination (HR) — an important DNA repair process — conferred by loss of BRCA1/2. As such, HR-deficiency is currently the sole criterion for selecting patients for PARPi treatment. However, the complete set of mechanisms underlying sensitivity to PARPi, as well as the types of genetic alterations which may confer PARPi sensitivity, remain poorly understood. Through an in vivo CRISPR screen, we identified loss of FANCA as synthetic lethal with PARPi, indicating that tumors deficient in the DNA damage response (DDR) gene FANCA are more sensitive to PARPi than control tumors. Using viability assays, we demonstrated that loss of FANCA confers sensitivity to PARPi in breast and lung cancer cell lines and further showed that PARPi and ATR inhibitors (ATRi) act synergistically to kill FANCA knockout (KO) cancer cells. By detecting nuclear markers of DDR signaling pathways, we showed that following treatment with PARPi, FANCA KO cancer cells display no impairment of HR repair compared to FANCA WT cells. Furthermore, we demonstrated that under DNA replication stress, FANCA KO breast cancer cells display increased PARP1 signaling compared to FANCA WT cells, suggesting a potential moonlighting function of FANCA as a backup to PARP1 in the cellular response to replication stress. These findings demonstrate alternative mechanisms of PARPi sensitivity outside of HR deficiency and provide a rationale for clinical investigation of PARPi activity in patients with FANCA-mutant cancers, which make up 4% of metastatic breast cancer cases.