Synergistic anticancer effect of panobinostat and topoisomerase inhibitors through ROS generation and intrinsic apoptotic pathway induction in cervical cancer cells

Various combinations of drugs may be effective in the treatment of different types of cancer. Previously, we have shown that combinations of the histone deacetylase inhibitor panobinostat and the topoisomerase inhibitors topotecan or etoposide act synergistically, but the underlying mode of action has remained unknown. Here, we aimed at uncovering the mechanisms underlying this synergism. The effects of (combinations of) panobinostat and topotecan or etoposide on cervical cancer-derived HeLa and SiHa cells were assessed using morphological evaluations, scratch wound healing assays, cell cycle analyses, AO/EB staining assays, Annexin V/PI staining assays, reactive oxygen species (ROS) and mitochondrial membrane potential measurements and Western blotting. We found that combinations of panobinostat and the topoisomerase inhibitors topotecan or etoposide synergistically enhanced the induction of apoptosis in both HeLa and SiHa cells. This enhanced apoptosis induction was found to be mediated through increased ROS production and induction of the mitochondrial apoptotic pathway. We also found that the combination treatment resulted in inhibition of the PI3K/AKT and NF-kappa B pro-survival pathways and in activation of the ERK pathway, which is associated with intrinsic apoptosis. From our data we conclude that combinations of panobinostat and the topoisomerase inhibitors topotecan or etoposide provoke strong cell death responses in cervical cancer-derived cells via induction of the intrinsic apoptotic pathway. Since this drug combination may potentially be effective in the treatment of cervical cancer, further preclinical investigations are warranted.