miR-182-mediated downregulation of BRCA1 impacts DNA repair and sensitivity to PARP inhibitors

Poly(ADP-ribose) polymerase-1 inhibition: preclinical and clinical development of synthetic lethality

The hereditary forms of breast cancer identified by BRCA1 and BRCA2 genes have a defect in homologous DNA repair and demonstrate a dependence on alternate DNA repair processes by base excision repair, which requires poly(ADP-ribose) polymerase 1 (PARP-1). siRNA and deletion mutations demonstrate that interference with PARP-1 function results in enhanced cell death when the malignancy has a defect in homologous recombination. These findings resulted in a plethora of agents in clinical trials that interfere with DNA repair, and these agents offer the potential of being more selective in their effects than classic chemotherapeutic drugs. An electronic search of the National Library of Medicine for published articles written in English used the terms "PARP inhibitors" and "breast cancer" to find prospective, retrospective and review articles. Additional searches were done for articles dealing with mechanism of action. A total of 152 articles dealing with breast cancer and PARP inhibition were identified. PARP inhibition not only affects nonhomologous repair, but also has several other nongenomic functions. Mutational resistance to these agents was seen in preclinical studies. To date, PARP-1 inhibitors were shown to enhance cytotoxic effects of some chemotherapy agents. This new class of agents may offer more therapeutic specificity by exploiting a DNA repair defect seen in some human tumors with initial clinical trials demonstrating antitumor activity. Although PARP inhibitors may offer a therapeutic option for selected malignancies, the long-term effects of these agents have not yet been defined.

A new role for miR-182 in DNA repair

A role for miRNAs in modulating cellular responses to DNA damage and chemotherapy is emerging. In this issue of Molecular Cell, Moskwa and colleagues propose a novel function for miR-182 in the posttranscriptional regulation of BRCA1 expression and in DNA repair (Moskwa et al., 2011).

PARP inhibitors in cancer therapy: promise, progress, and puzzles

A recent article in the New England Journal of Medicine by O'Shaughnessy et al. provides evidence that a treatment strategy aimed at inducing DNA damage with chemotherapy while simultaneously disabling repair using a PARP inhibitor might offer hope for patients with a treatment-refractory form of breast cancer.