Histone deacetylase inhibitor trichostatin A sensitises cisplatin-resistant ovarian cancer cells to oncolytic adenovirus.

Ovarian cancer is often termed a silent killer due to the late onset of symptoms. Whilst patients initially respond to chemotherapy, they rapidly develop chemo-resistance. Oncolytic adenoviruses (OAds) are promising anti-cancer agents engineered to "hijack" the unique molecular machinery of cancer cells enabling tumour-selective viral replication. This allows spread to adjacent cells and amplification of oncolysis within the tumour. OAds represent an excellent opportunity for ovarian cancer therapy via intra-peritoneal delivery, however the efficacy of OAds thus far is limited. Here, we evaluate chromatin (histone) modification in chemo-resistant cells and its relationship to Ad efficacy (wild-type or oncolytic Ad). In contrast to cisplatin-sensitive A2780 cells that show an efficient reduction of cell viability by Ad in the presence of cisplatin, cisplatin-resistant A2780/cp70 cells show diminishing Ad-mediated reduction of cell viability with escalating doses of cisplatin. Histone deacetylase (HDAC)-2 and to a lesser extent HDAC1 were up-regulated in cisplatin-resistant but not cisplatin-sensitive cells. Cisplatin-resistant cells treated with a pan-HDAC inhibitor trichostatin A (TsA) significantly enhanced Ad-mediated reduction of cell viability in the presence of cisplatin. Cells treated with TsA alone did not reduce cell viability suggesting these findings are Ad-dependent. Thus, we identify HDAC inhibition as a potential means to sensitise cisplatin-resistant ovarian cancer cells to virotherapies, an observation that may offer improved outcomes for patients with late stage, chemotherapy-resistant ovarian cancer.