Synergistic effect of Chloroquine and Panobinostat in ovarian cancer through induction of DNA damage and inhibition of DNA repair

Abstract

Ovarian cancer (OC) is the deadliest gynecologic malignancy, which is mainly due to late-stage diagnosis and chemotherapy resistance. Therefore, new and more effective treatments are urgently needed. The in vitro effects of Panobinostat (LBH), a histone deacetylase inhibitor that exerts pleiotropic antitumor effects but induces autophagy, in combination with Chloroquine (CQ), an autophagy inhibitor that avoid this cell survival mechanism, were evaluated in 4 OC cell lines. LBH and CQ inhibited ovarian cancer cell proliferation and induced apoptosis, and a strong synergistic effect was observed when combined. Deeping into their mechanisms of action we show that, in addition to autophagy modulation, treatment with CQ increased reactive oxygen species (ROS) causing DNA double strand breaks (DSBs), whereas LBH inhibited their repair by avoiding the correct recruitment of the recombinase Rad51 to DSBs. Interestingly, CQ-induced DSBs and cell death caused by CQ/LBH combination were largely abolished by the ROS scavenger N-Acetylcysteine, revealing the critical role of DSB generation in CQ/LBH-induced lethality. This role was also manifested by the synergy found when we combined CQ with Mirin, a well-known homologous recombination repair inhibitor. Altogether, our results provide a rationale for the clinical investigation of CQ/LBH combination in ovarian cancer.

Hydralazine and Panobinostat Attenuate Malignant Properties of Prostate Cancer Cell Lines

“…Previous reports from our group [ 3 ] and others [ 59 , 60 , 61 ] had already demonstrated that hydralazine and panobinostat were DNA damage-inducing agents. The mechanisms underlying the effect of panobinostat can be traced to its capacity to modulate DNA damage response (DDR) proteins [ 62 , 63 ] and to the induction of reactive oxygen species (ROS) [ 64 , 65 ], a characteristic that is shared with other HDACis [ 66 , 67 ].…”

Chloroquine-Induced DNA Damage Synergizes with Nonhomologous End Joining Inhibition to Cause Ovarian Cancer Cell Cytotoxicity

“…It has been described that some HDAC inhibitors, including Panobinostat, affect DNA DSB repair by inhibiting homologous recombination (HR) [ 32 , 40 , 41 , 42 ]. Indeed, we have recently reported that LBH inhibits the correct recruitment of Rad51 to DSB sites in OCCLs, which explains the HR defect [ 32 ]. However, the effect of HDAC inhibitors on DSB repair by NHEJ seems to be controversial [ 34 , 35 ].…”

“…CQ has been demonstrated to exert pleiotropic cellular effects, including the generation of reactive oxygen species (ROS) [ 32 , 49 , 50 , 51 , 52 ]. We have recently shown that CQ-induced ROS production in OCCLs leads to the generation of DNA-DSBs [ 32 ].…”

“…CQ has been demonstrated to exert pleiotropic cellular effects, including the generation of reactive oxygen species (ROS) [ 32 , 49 , 50 , 51 , 52 ]. We have recently shown that CQ-induced ROS production in OCCLs leads to the generation of DNA-DSBs [ 32 ]. These types of lesions are usually repaired by two main pathways, HR and NHEJ; the latter has been described to occur with a higher frequency and to be faster than HR [ 48 ].…”

“…However, it has also been reported that the ability of CQ to inhibit autophagy is not the only mechanism by which it exerts its antitumor effect [ 10 , 15 , 28 , 29 , 30 , 31 ]. In this regard, we have recently published that CQ increases reactive oxygen species (ROS) in OC cell lines, causing DNA double-strand breaks (DSBs) [ 32 ], the most lethal form of DNA damage [ 33 ]. In that work, we also described that the combination of CQ with Panobinostat (LBH) exerted a strong synergistic effect, which was explained by the ability of this histone deacetylase inhibitor (HDACi) to reduce the efficiency of homologous recombination (HR), one of the pathways involved in DSB repair.…”