HeLa cells were treated for 24 hours with panel a: cisplatin (cddp), panel b: adriamycin (adr) or panel c: gemcitabine (gem) at or close to IC50 plus hydralazine (h) and valproic acid (v). Afterwards medium was removed and fresh medium containing only hydralazine and valproic acid was added for additional 48 hours after which viability was measured. There was a significant higher cytotoxicity of the chemotherapeutic agent when used in combination with hydralazine plus valproic acid. Cisplatin alone at 12 μM caused a reduction in viability to 37% in HeLa cells which was essentially zero viability when cells were co-treated with hydralazine plus valproic acid (h-v-c). The increasing toxicity of the combination was also seen with adriamycin and gemcitabine. Viability was 42% and 45% in the chemotherapy drugs alone versus 27% and 37% respectively when hydralazine plus valproic acid were added to chemotherapy drugs (h-v-c). (Reproduced from ref. 89. Cancer Cell Int 2006,6:2).