Modulating ovarian stress signaling pathways by allosteric BCR-Abl inhibitors/activators

Premature ovarian failure and infertility are adverse effects of cancer therapies. The mechanism that causes the chemotherapy-induced depletion of the ovarian reserve is still unclear. In this thesis, we aim to identify the signaling pathways underlying the ovarian reserve loss, in order to prevent the damaging effects of chemotherapy. We evaluated the effects against follicle reserve of cyclophosphamide, one of the most damaging chemotherapeutic drugs, used in the treatment of several cancer types such as breast cancer and non-Hodgkin lymphoma. In vivo studies showed that the cyclophosphamideinduced loss of ovarian reserve occurred through a sequential mechanism. Cyclophosphamide exposure induced the activation of both DNAPK-γH2AXcheckpoint kinase 2 (CHK2)-p53/TAp63 and protein kinase B (AKT)- forkhead box O3 (FOXO3a) signaling axes in the nucleus of oocytes. Concomitant administration of an allosteric ABL inhibitor and cyclophosphamide modulated both pathways while protecting the ovarian reserve from chemotherapy assaults. Consequently, the fertility of the treated mice was prolonged. On the contrary, the administration of an allosteric ABL activator enhanced the lethal effects of cyclophosphamide while shortening mouse fertility. Therefore, kinase-independent inhibition, through small allosteric compounds, may serve as an effective ovarian-protective strategy in women under chemotherapy. Furthermore, we observed that the concomitant activation of DNAPK-H2AX-checkpoint kinase 2 (CHK2)-p53/TAp63 and AKT/FOXO3a pathways occurs with other chemotherapeutic drugs. Reserve oocytes, both damaged and recruited into growth, were also found after treatment with bleomycin. Of note, bleomycin is a chemotherapeutic drug with a mechanism of action completely different from cyclophosphamide. Thus, following genotoxic stress, we proposed a general model in which the DNA damage response and the quiescence loss are not separated events, but they are strictly correlated and led reserve oocyte to death after chemotherapy resulting in premature ovarian failure and infertility.