186P - Degradation of BRCA2 expression by hyperthermia sensitizes HRD-negative (BRCA2 wild-type) ovarian cancer cells to niraparib

Background

Poly (ADP-ribose) polymerase (PARP) inhibitors have significantly improved survival for advanced ovarian cancer patients as maintenance therapy and have become an important component of standard treatment for ovarian cancer. Ovarian cancer cells with BRCA mutations are particularly sensitive to PARP inhibitors, but how to improve the sensitivity of BRCA wild-type ovarian cancer to PARP inhibitors has become a focus of research. We identified if down-regulation of BRCA2 expression by hyperthermia (HT) sensitizes HRD-negative ovarian cancer to Niraparib.

Methods

BRCA2 mutations of human ovarian cancer OVCAR3, A2780 and mouse ID8 cells were identified by whole genome sequencing, and the expressions of BRCA2, PARP1, and γ-H2AX were detected by qPCR and Western Blot assays after HT treatment. The formation of RAD51 foci was observed by immunofluorescence microscopy and the apoptosis was measured with FCM, and colony formation was detected by crystal violet assay after combination treatment of HT and Niraparib. In vivo, female mice were implanted with BRCA2^wt and BRCA2^kd ID8 cells in the right hind leg; The mice bearing tumor received local HT treatment (for 1.5 h at 42°C) twice a week, with an interval of 48 h for 3 weeks and Niraparib p.o. at the dosage of 50 mg/kg 2 h prior to HT treatment. The tumor growth and survival were observed.

Results

Genome sequencing showed that A2780 and ID8 cells were BRCA2^wt and OVCAR3 cells were BRCA2^mt; Hyperthermia induced degradation of BRCA2 of A2780 and ID8 cells, leading to HRD status; RAD51 expression has no significant change but PARP1 expression was elevated. Hyperthermia inhibited the formation of RAD51 foci in these two cells, Niraparib, a PARP inhibitor, combined with HT treatment synergistically increased DSBs of DNA and the rate of apoptosis and inhibited the growth of A2780 and ID8 cells. The in vivo experiment showed that the treatment of Niraparib combined with HT slowed down the tumor growth rate and prolonged the survival of the mice bearing tumors.

Conclusions

Hyperthermia could enhance the sensitivity of BRCA2^wt ovarian cancer to PARP inhibitors.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Le Fund.

Disclosure

All authors have declared no conflicts of interest.