CHEK2 SIGNALING IS THE KEY REGULATOR OF OOCYTE SURVIVAL AFTER CHEMOTHERAPY

ABSTRACT Radiation and chemotherapy can damage the primordial follicle reserve in female cancer patients leading to ovarian failure and infertility. Preservation of ovarian function requires treatment strategies that prevent loss of immature oocytes in primordial follicles during cancer therapy. Checkpoint kinase 2 (CHEK2) inhibition prevents loss of primordial oocytes caused by DNA damage and thus is a promising target for ovoprotective treatment against genotoxic agents. To determine which cancer treatments could benefit from ovoprotective activity of CHEK2 inhibition we investigated oocyte survival in Chek2 -/- mice exposed to different chemotherapy drugs. Here, we show that loss of CHEK2 function prevents elimination of primordial oocytes damaged by cisplatin, cyclophosphamide, mafosfamide, doxorubicin, and etoposide, suggesting it could be used to reduce ovarian damage caused by wide range of drugs. Using genetic knockouts we reveal a critical role for TRP53 in oocyte response to chemotherapy drugs and show that both targets of CHEK2—TAp63 and TRP53— are activated by cisplatin and cyclophosphamide. Furthermore, we show that checkpoint kinase inhibitor and radiation- and chemotherapy sensitizer AZD7762 reduces oocyte elimination after radiation and chemotherapy treatments, despite its cytotoxic effect on ovarian somatic cells. Altogether, these findings demonstrate the role for CHEK2 as the master regulator of primordial oocyte survival or death and credential its targeting for ovoprotective treatments. SIGNIFICANCE Chemotherapy and radiation are ovotoxic and increase the risk of premature ovarian insufficiency and infertility in women cancer survivors. Development of treatment strategies preserving ovarian function and ensuring future reproductive health of female cancer patients depends on better understanding of the mechanisms underlying ovarian toxicity caused by different chemotherapy treatments. Preservation of long-term ovarian function can only be achieved by preventing the loss of immature oocytes in primordial follicles during toxic cancer therapies. Checkpoint kinase 2 (CHEK2) inhibition is an attractive strategy for protecting ovarian reserve with a potential additional benefit of sensitizing cancer cells to radiation and chemotherapy. Using a genetic approach, we show that blocking CHEK2 function is sufficient to prevent elimination of primordial oocytes damaged by chemotherapy drugs such as cisplatin, cyclophosphamide, mafosfamide, doxorubicin and etoposide. Many chemotherapy drugs are used in combination (e.g. cyclophosphamide with doxorubicin), thus the protective effect of CHEK2 inhibition is likely to be beneficial for a broad spectrum of patient treatments.