Survival of primary, but not of cancer cells after combined Plk1-HDAC inhibition

In the current study we examined the combination of SAHA and SBE13 in cancer and non-cancer cells. HeLa cells displayed a synergistically reduced cell proliferation, which was much weaker in hTERT-RPE1 or NIH-3T3 cells. Cell cycle distribution differed in HeLa, hTERT-RPE1 and NIH-3T3 cells. SAHA-treated HeLa cells showed slightly increasing cell numbers in G2/M phase, but after combination with SBE13 strongly elevated cell numbers in G2/M and S phase, accompanied by decreasing G0/G1 percentages. hTERT-RPE1 and NIH-3T3 cells showed strongly enriched cell numbers in G0/G1 phase. Western blot and quantitative real time analyses revealed reduced Plk1 mRNA and protein in all cells. p21 protein was strongly induced in cancer, but not in non-cancer cells, corresponding to a different localization in immunofluorescence studies. Additionally, these revealed an abundantly present pRb protein in HeLa cells after any treatment but almost completely vanished pRb staining in treated hTERT-RPE1 cells. These differences could be approved in Western blots against Parp and Caspase 3, which were activated in HeLa, but not in hTERT-RPE1 cells. Thus, we observed for the first time a differential effect of cancer versus non-cancer cells after treatment with SAHA and SBE13, which might be due to the dual role of p21.