Co-targeting poly(ADP-ribose) polymerase (PARP) and histone deacetylase (HDAC) in triple-negative breast cancer: Higher synergism in BRCA mutated cells.

Despite similarities with BRCA-mutated breast cancers, triple-negative breast cancers (TNBC) remain resistant to poly(ADP-ribose) polymerase (PARP) inhibitors as single agents. Histone deacetylase inhibitors (HDACi) can decrease expression of proteins involved in DNA repair. We thus hypothesized that a HDACi (suberoylanilide hydroxamic acid (SAHA) or belinostat) could sensitize TNBC to the PARP inhibitor olaparib. Human TNBC cells were co-treated with olaparib and either SAHA or belinostat, and their effects on survival, proliferation, cell cycle, apoptosis and DNA repair pathways were evaluated. Subcutaneous xenografts were used to determine the effect of the combination treatment in vivo. HDACi and olaparib synergistically inhibited proliferation of a panel of 8 TNBC cell lines in vitro and in nude mice harboring TNBC xenografts in vivo. We noted a weaker synergism in PTEN-deficient TNBC cells and a stronger synergism in BRCA1-mutated TNBC cells. In the BRCA1-mutated cell line HCC-1937, we observed a drastic decrease in the expression of proteins involved in homologous recombination (HR), leading to a large imbalance of the ratio P-H2AX/RAD51. In BRCA1 wild type (wt) cell lines, effect of the combination treatment relied on DNA damage-induced cell cycle arrest followed by induction of apoptosis. In summary, these results provide a preclinical rationale to combine a HDACi with a PARP inhibitor to reduce HR efficiency in TNBC and sensitize these aggressive tumors to PARP inhibition.

Marijon H ，Lee DH ，Ding L ，Sun H ，Gery S ，de Gramont A ，Koeffler HP ... -  《-》

Histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), enhances anti-tumor effects of the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib in triple-negative breast cancer cells.

Min A ，Im SA ，Kim DK ，Song SH ，Kim HJ ，Lee KH ，Kim TY ，Han SW ，Oh DY ，Kim TY ，O'Connor MJ ，Bang YJ ... -  《-》

Suberoylanilide hydroxamic acid (SAHA) enhances olaparib activity by targeting homologous recombination DNA repair in ovarian cancer.

Approximately 50% of serous epithelial ovarian cancers (EOC) contain molecular defects in homologous recombination (HR) DNA repair pathways. Poly(ADP-ribose) polymerase inhibitors (PARPi) have efficacy in HR-deficient, but not in HR-proficient, EOC tumors as a single agent. Our goal was to determine whether the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), can sensitize HR-proficient ovarian cancer cells to the PARPi AZD-2281 (olaparib). Ovarian cancer cell lines (SKOV-3, OVCAR-8, NCI/ADR-Res, UWB1.289 BRCA1null and UWB1.289+BRCA1 wild-type) were treated with saline vehicle, olaparib, SAHA or olaparib/SAHA. Sulforhodamine B (SRB) assessed cytotoxicity and immunofluorescence and Western blot assays assessed markers of apoptosis (cleaved PARP) and DNA damage (pH2AX and RAD51). Drug effects were also tested in SKOV-3 xenografts in Nude mice. Affymetrix microarray experiments were performed in vehicle and SAHA-treated SKOV-3 cells. In a microarray analysis, SAHA induced coordinated down-regulation of HR pathway genes, including RAD51 and BRCA1. Nuclear co-expression of RAD51 and pH2AX, a marker of efficient HR repair, was reduced approximately 40% by SAHA treatment alone and combined with olaparib. SAHA combined with olaparib induced apoptosis and pH2AX expression to a greater extent than either drug alone. Olaparib reduced cell viability at increasing concentrations and SAHA enhanced these effects in 4 of 5 cell lines, including BRCA1 null and wild-type cells, in vitro and in SKOV-3 xenografts in vivo. These results provide preclinical rationale for targeting DNA damage response pathways by combining small molecule PARPi with HDACi as a mechanism for reducing HR efficiency in ovarian cancer.

Konstantinopoulos PA ，Wilson AJ ，Saskowski J ，Wass E ，Khabele D ... -  《-》

Synergistic loss of prostate cancer cell viability by coinhibition of HDAC and PARP.

Tumors with BRCA germline mutations are defective in repairing DNA double-strand breaks (DSB) through homologous recombination (HR) pathways, making them sensitive to PARP inhibitors (PARPi). However, BRCA germline mutations are rare in prostate cancer limiting the ability to therapeutically target these pathways. This study investigates whether histone deacetylase (HDAC) inhibitors (HDACi), reported to modulate DSB repair pathways in sporadic cancers, can downregulate DSB repair pathways and sensitize prostate cancer cells to PARPi. Prostate cancer cells cotreated with the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA) and the PARPi, olaparib, demonstrated a synergistic decrease in cell viability compared with single-agent treatment (combination index < 0.9), whereas normal prostatic cells did not. Similarly, clonogenicity was significantly decreased after cotreatment. Flow cytometric cell-cycle analysis and Annexin-V staining revealed significant apoptosis upon treatment with SAHA+olaparib. This coincided with increased DNA damage observed by immunofluorescence microscopy analysis of γH2AX foci, a marker of DSBs. In addition, immunoblot analysis showed a significant and persistent increase in nuclear γH2AX levels. Both SAHA and olaparib downregulated the expression of HR-related proteins, BRCA1 and RAD51, whereas SAHA + olaparib had an additive effect on RAD51. Silencing RAD51 sensitized prostate cancer cells to SAHA and olaparib alone. Collectively, cotreatment with HDACi and PARPi downregulated HR-related protein expression and concomitantly increased DNA damage, resulting in prostate cancer cell death. These findings provide a strong rationale for supporting the use of combined HDAC and PARP inhibition in treating advanced prostate cancer.

Chao OS ，Goodman OB Jr 《-》

Prexasertib treatment induces homologous recombination deficiency and synergizes with olaparib in triple-negative breast cancer cells.

Mani C ，Jonnalagadda S ，Lingareddy J ，Awasthi S ，Gmeiner WH ，Palle K ... -  《-》