Abstract:
Histone deacetylase inhibitors (HDACi) have been found to cause growth arrest and apoptosis of many malignant cells and its antitumor activity has been linked to their ability to induce gene expression through the increased acetylation of histones. In present-day medicine the HDACi are widely used as an anticancer drugs alone or in combination with chemotherapy agents. One of the most studied HDACi is sodium butyrate (NaB). NaB is short-chain fatty acid formed naturally in the colon by fermentation of dietary fibers. NaB exhibits several effects on cells such as inhibition of proliferation and apoptosis. Although NaB has been studied in several human cancer cells, its effect in human ovarian cancer cells and in normal human fibroblasts has yet to be characterized. Haemanthamine (HA) belongs to the crinine type of alkaloids and represents promising therapeutic agent because of its anticancer activities. The anticancer effect of HA has been proved in a number of different types of cancer cells. In our previous study we have elucidated the anticancer effect of HA in leukemic cell lines. Our results have shown that HA treatment cause the inhibition of proliferation, accumulation of cells preferentially at G1 and G2 phases as well as induction of apoptosis in leukemia cells. However the mechanisms of action of HA are not completely clear and there are no information about its effect in human ovarian cancer cells. It was reported that HDACi may enhance sensitivity of other anticancer agents, but there are no studies combining naturally occurring compound such as HA with the HDACi. This unknown problem was the main object for the present study, in which we assessed the effect of HA and NaB alone as well as in combination in human ovarian carcinoma cells A2780 and in non-cancerous normal human fibroblasts MRC-5. Sensitization of cells to both compounds was accompanied by activation of proteins regulating cell cycle. HA in combination with NaB increased acetylation of histones and decreased activation of check-point kinases and p21WAF1/Cip1 in comparison to treatment with NaB alone. Further the combination of agents caused suppression of cells in the G1 phase and an increase in the population of cells in the G2 phase. Importantly, HA enhanced the effect of NaB in both cell types, but the effect was more pronounced and significant in A2780 cancer cells. A possible anticancer effect of HDACi sodium butyrate alone or in combination with haemanthamine remained unknown in these cell types and the present study contributes to its enlightment. Our observations reported here point to the need for continued development of strategies for sensitizing cancer cells to therapies that kill cells by inducing DNA damage
