The subject invention provides a pharmaceutical composition comprising an inhibitory RNA (iRNA) that mediates sequence-specific degradation of the mRNA encoding Poly (ADP-ribose) polymerase 1 (PARP1) and methods of treating cancers by administering the pharmaceutical composition to a subject in need thereof. In one embodiment, the iRNA is miR-223, particularly, miR-223-3p or a modified miR-223-3p having substitutions and/or deletions in the sequence of miR-223-3p. In another embodiment, the cancer cells comprise one or more mutations in the genes that mediate homologous recombination DNA repair, for example, BRCA1 and/or BRCA2 genes. The cancer can be breast cancer, ovarian cancer, prostate cancer, pancreatic cancer or mesothelioma. Methods of treating cancer, for example, a cancer comprising BRCA1 and/or 2 mutations, using a combination of iRNA and a second cancer therapeutic are also provided.
