Abstract P4-16-06: Histone deacetylases inhibitor SAHA enhances anti-tumor effects of poly (ADP-ribose) polymerase (PARP) inhibitor olaparib in breast cancer cells

Abstract

Abstract Background: The poly (ADP-ribose) polymerase (PARP) inhibitor, olaparib, has been found to have a therapeutic potential for treating cancers that have an impaired DNA repair ability. However, some cancer presents acquired resistance to PARP inhibitor or platinum. Histone deacetylases (HDACs) are important to enable functional homologous recombination (HR) by regulating the expression of HR-related genes and promoting the accurate assembly of HR-directed subnuclear foci. Thus, HDAC inhibitors have emerged recently as a class of therapeutic agents for the treatment of cancer by inhibiting DNA repair. For this mechanism, HDAC inhibition would enhance the anti-tumor effect of PARP inhibitor in cancer cells by blocking DNA repair pathway. Materials and Methods: We determined whether SAHA, a HDAC inhibitor could enhance the growth inhibition of olaparib on breast cancer cell lines using MTT assay. We examined whether exposure to SAHA affects the expression level of genes involved in HR. The accumulation of DNA double strand breaks (DSBs) induced by combination treatment was accessed by the comet assay. Cell cycle analysis and molecular changes induced by combination of olaparib plus SAHA were also performed. These in vitro data were validated in the in vivo xenograft model as well. Results: Triple-negative breast cancer cell lines showed heterogeneous response to dual inhibition of PARP and HDACs. SAHA enhanced olaparib-induced cell death of MDA-MB-157 and HCC1143 but not of HCC70 and MDA-MB-468. Combination of olaparib plus SAHA caused a greater decrease of pAKT, pERK, and pSTAT3 in MDA-MB-157 and HCC1143 cells compared with monotherapy either olaparib or SAHA. Furthermore, inhibition of PARP increased the accumulation of DNA DSBs induced by SAHA in these two cell lines, MDA-MB-157 and HCC1143. There was no change in proliferative pathway activation in HCC70 and MDA-MB-468 cells with combination of olaparib plus SAHA. Our findings showed that triple-negative breast cancer cells are differentially effective to combination of SAHA plus olaparib which increased levels of unrepaired DNA DSBs. Conclusion: HDAC inhibitor SAHA enhances growth inhibitory activity of PARP inhibitor olaparib in several triple-negative breast cancer cells with increased accumulation of DNA DSBs. Our results provide a rationale for the future clinical trials of olaparib combined with SAHA in the treatment of cancers that have an impaired DNA repair ability. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-16-06.