Clinicopathological features of homologous recombination-deficient epithelial ovarian cancers: sensitivity to PARP inhibitors, platinum, and survival.

Up to 50% of epithelial ovarian cancers (EOC) display defects in the homologous recombination (HR) pathway. We sought to determine the ramifications of the homologous recombination-deficient (HRD) status on the clinicopathologic features, chemotherapy response, and survival outcomes of patients with EOCs. HR status was determined in primary cultures from ascitic fluid in 50 chemotherapy-naïve patients by a functional RAD51 immunofluorescence assay and correlated with in vitro sensitivity to the PARP inhibitor (PARPi), rucaparib. All patients went on to receive platinum-based chemotherapy; platinum sensitivity, tumor progression, and overall survival were compared prospectively in HR-competent versus HRD patients. Compared with HR-competent patients, the HRD group was predominantly serous with a higher median CA125 at presentation. HRD was associated with higher ex vivo PARPi sensitivity and clinical platinum sensitivity. Median follow-up duration was 14 months; patients in the HRD group had lower tumor progression rates at 6 months, lower overall/disease-specific death rates at 12 months, and higher median survival. We therefore suggest that HRD as predicted by a functional RAD51 assay correlates with in vitro PARPi sensitivity, clinical platinum sensitivity, and improved survival outcome.

Poly(ADP-ribose) polymerase-1 (PARP-1) pharmacogenetics, activity and expression analysis in cancer patients and healthy volunteers.

There is a wide inter-individual variation in PARP-1 {PAR [poly(ADP-ribose)] polymerase 1} activity, which may have implications for health. We investigated if the variation: (i) is due to polymorphisms in the PARP-1 gene or PARP-1 protein expression; and (ii) affects patients' response to anticancer treatment. We studied 56 HV (healthy volunteers) and 118 CP (cancer patients) with supporting in vivo experiments. PARP activity ranged between 10 and 2600 pmol of PAR/106 cells and expression between 0.02-1.55 ng of PARP-1/µg of protein. PARP-1 expression correlated with activity in HV (R2=0.19, P=0.003) and CP (R2=0.06, P=0.01). A short CA repeat in the promoter was significantly associated with increased cancer risk [OR (odds ratio), 5.22; 95% CI (confidence interval), 1.79-15.24]. PARP activity was higher in men than women (P=0.04) in the HV. Male mice also had higher PARP activity than females or castrated males. Oestrogen supplementation activated PARP in PBMCs (peripheral blood mononuclear cells) from female mice (P=0.003), but inhibited PARP-1 in their livers by 80%. PARP activity and expression were not dependent on the investigated polymorphisms, but there was a modest correlation of PARP activity with expression. Studies in the HV revealed sex differences in PARP activity, which was confirmed in mice and shown to be associated with sex hormones. Toxic response to treatment was not associated with PARP activity and/or expression.

Therapeutic potential of poly(ADP-ribose) polymerase inhibitor AG014699 in human cancers with mutated or methylated BRCA1 or BRCA2.

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.

Doxorubicin-induced suppression of poly(ADP-ribose) polymerase-1 (PARP-1) activity and expression and its implication for PARP inhibitors in clinical trials.

PURPOSE: Monozygotic twins provide an excellent tool to study environmental effects on human health. Poly(ADP-ribose) polymerase-1 (PARP-1) is an important enzyme primarily involved in DNA repair and genomic stability and is under clinical investigation as a target for anticancer therapy. As a part of a PARP pharmacogenetics study, elderly male monozygotic twins, one healthy and the other with a Trojani grade 3 sarcoma treated with doxorubicin (DOX: 142.5 mg/m(2)), were recruited for the study. METHODS: PARP activity and expression were measured in peripheral blood mononuclear cells (PBMCs) by methods validated to GCLP standard and used as a pharmacodynamic endpoint for clinical trials. RESULTS: The mean PARP activity for the patient before treatment was 160 pmol PAR/10(6) cells and was similar to that of his brother (130 pmol PAR/10(6) cells). There was approximately ninefold decrease (P = 0.001) in PARP activity in a second sample from the patient taken 21 days after the first DOX administration (17 pmol PAR/10(6) cells) and a decrease in PARP-1 expression. Investigations into BALB/C mice revealed that DOX treatment (5 mg/kg) resulted in a significant transient decrease in PARP activity after 1 h (63% control, P << 0.05) and 24 h (53% control, P << 0.05) but that PARP activity was restored 1 week after DOX treatment (86% control, P = 0.24). CONCLUSIONS: We showed here that administration of DOX can have a profound effect on the measured level of PARP activity and expression in PBMCs from patients and animals. Results obtained in clinical trials where PARP activity is used as a pharmacodynamic marker of PARP inhibition could reflect the effect of a chemotherapeutic on PBMCs rather than the effectiveness of a tested PARP inhibitor.