Neoadjuvant therapy of BRCA1-driven ovarian cancer by combination of cisplatin, mitomycin C and doxorubicin

BRCA Mutations-The Achilles Heel of Breast, Ovarian and Other Epithelial Cancers

Two related tumor suppressor genes, BRCA1 and BRCA2, attract a lot of attention from both fundamental and clinical points of view. Oncogenic hereditary mutations in these genes are firmly linked to the early onset of breast and ovarian cancers. However, the molecular mechanisms that drive extensive mutagenesis in these genes are not known. In this review, we hypothesize that one of the potential mechanisms behind this phenomenon can be mediated by Alu mobile genomic elements. Linking mutations in the BRCA1 and BRCA2 genes to the general mechanisms of genome stability and DNA repair is critical to ensure the rationalized choice of anti-cancer therapy. Accordingly, we review the literature available on the mechanisms of DNA damage repair where these proteins are involved, and how the inactivating mutations in these genes (BRCAness) can be exploited in anti-cancer therapy. We also discuss a hypothesis explaining why breast and ovarian epithelial tissues are preferentially susceptible to mutations in BRCA genes. Finally, we discuss prospective novel therapeutic approaches for treating BRCAness cancers.

Molecular tests for prediction of tumor sensitivity to cytotoxic drugs

Chemotherapy constitutes the backbone of cancer treatment. Several predictive assays assist personalized administration of cytotoxic drugs and are recommended for use in a clinical setting. The deficiency of DNA repair by homologous recombination (HRD), which is caused by inactivation of BRCA1/2 genes or other genetic events, is associated with high tumor responsiveness to platinum compounds, bifunctional alkylating agents and topoisomerase II poisons. Low activity of MGMT predicts the efficacy of nitrosoureas and tetrazines. Some clinically established pharmacogenetic tests allow for the adjustment of drug dosage, for example, the analysis of DPYD allelic variants for administration of fluoropyrimidines and UGT1A1 genotyping for the use of irinotecan. While there are promising molecular predictors of tumor sensitivity to pemetrexed, gemcitabine and taxanes, they remain in the investigational stage and require additional validation. Comprehensive molecular analysis of tumors obtained from drug responders and non-responders is likely to reveal new clinically useful predictive markers for cytotoxic therapy.

Cytotoxic and targeted therapy for BRCA1/2-driven cancers

Tumors arising in BRCA1/2 germline mutation carriers usually demonstrate somatic loss of the remaining BRCA1/2 allele and increased sensitivity to platinum compounds, anthracyclines, mitomycin C and poly (ADP-ribose) polymerase inhibitors (PARPi). Exposure to conventional platinum-based therapy or PARPi results in the restoration of BRCA1/2 function and development of resistance to systemic therapy, therefore, there is a need for other treatment options. Some studies suggested that the use of specific drug combinations or administration of high-dose chemotherapy may result in pronounced tumor responses. BRCA1/2-driven tumors are characterized by increased immunogenicity; promising efficacy of immune therapy has been demonstrated in a number of preclinical and clinical investigations. There are outstanding issues, which require further consideration. Platinum compounds and PARPi have very similar mode of antitumor action and are likely to render cross-resistance to each other, so their optimal position in cancer treatment schemes may be a subject of additional studies. Sporadic tumors with somatically acquired inactivation of BRCA1/2 or related genes resemble hereditary neoplasms with regard to the spectrum of drug sensitivity; the development of user-friendly BRCAness tests presents a challenge. Many therapeutic decisions are now based on the BRCA1/2 status, so the significant reduction of the turn-around time for predictive laboratory assays is of particular importance.