Background: Mutations in BRCA1 and BRCA2 (BRCA1/2), components of the homologous recombination DNA repair (HRR) pathway, are associated with hereditary breast and ovarian cancers. Poly(ADP-ribose) polymerase (PARP) inhibitors are selectively cytotoxic to animal cells with defective HRR, but results in human cancer cells have been contradictory. We undertook, to our knowledge, the first comprehensive in vitro and in vivo investigations of the antitumor activity of the PARP inhibitor AG014699 in human cancer cells carrying mutated or epigenetically silenced BRCA1/2.
Methods: We used nine human cell lines, four with nonmutated BRCA1/2 (MCF7, MDA-MB-231, and HCC1937-BRCA1 [breast cancer] and OSEC-2 [ovarian surface epithelial]), two with mutated BRCA1 (MDA-MB-436 and HCC1937 [breast cancer]), one with mutated BRCA2 (CAPAN-1 [pancreatic cancer]), one that was heterozygous for BRCA2 (OSEC-1 [ovarian surface epithelial]), and one with epigenetically silenced BRCA1 (UACC3199 [breast cancer]), and two Chinese hamster ovary cell lines, parental AA8 and XRCC3 mutated IRS 1SF. We assessed cytotoxicity, DNA damage, and HRR function. Antitumor activity of AG014699 was determined by growth of xenograft tumors (five mice per treatment group). Long-term safety of AG014699 was assessed.
Results: AG014699 (≤10 μM) was cytotoxic to cells with mutated BRCA1/2 or XRCC3 and to UACC3199 cells with epigenetically silenced BRCA1 but not to cells without BRCA1/2 or XRCC3 mutations or that were heterozygous for BRCA2 mutation. AG014699 induced DNA double-strand breaks in all nine cell lines studied. HRR was observed only in cells with functional BRCA1/2 proteins. Growth of xenograft tumors with BRCA1/2 mutations or with epigenetically silenced BRCA1 was reduced by AG014699 treatment, and combination treatment with AG014699 plus carboplatin was more effective than either drug alone. AG014699 was not toxic in mice with nonmutated or heterozygous BRCA2.
Conclusion: Human cancer cells or xenograft tumors with mutated or epigenetically silenced BRCA1/2 were sensitive to AG014699 monotherapy, indicating a potential role for PARP inhibitors in sporadic human cancers.