Poly (ADP-ribose) polymerase (PARP): Rationale, preclinical and clinical evidences of its inhibition as breast cancer treatment

Introduction: The chance to take advantage of genetic defects of cancer cells is a promising clinical tool in breast cancer therapy. Among the genetic aberrations, dysfunctions in DNA repair mechanisms are quite common and suitable for an attractive antitumor effect. Poly (ADP-ribose) polymerase I (PARP-1) is an enzyme with many functions in transcriptions and cell cycle regulation and in coordination of cellular response to DNA damage. Its involvement in tumorigenesis is witnessed by the overexpression found in different primary human tumors, where the increased enzymatic activity leads to cancer cell protection against DNA damage and instability. Therefore, activity of PARP and the opportunity to block it, mainly in cancer cells also deficient in other mechanisms of repair, are promising.Areas covered: In this review, areas covered include the main DNA repair mechanisms, the role of PARP enzymatic activity in diverse cell pathways as well as the preclinical and clinical data with PARP inhibitors.Expert opinion: Despite the theoretical role of PARP inhibitors as therapeutic strategy in specific subtypes of breast cancer (hereditary BRCA1/BRCA2 mutation-related cancers and sporadic triple-negative breast cancer), questions are still open. More exhaustive knowledge is needed about other important functions of PARPs in cellular homeostasis and about escape mechanisms of cancer cells to inhibitory effect of PARP inhibitors.