Differentiation therapy could be one strategy for stopping cancer cell proliferation. A plant steroid, diosgenin, is known to induce megakaryocytic differentiation in human erythroleukemia (HEL) cells. In recent studies, the use of sedimentation field-flow fractionation (SdFFF) allowed the preparation of subpopulations that may differ in regard to sensitivity to differentiation induction. The specific goal of this study was to determine the relationship between cell cycle stage and sensitivity to megakaryocytic differentiation induction of HEL cells. After first confirming the capacity of diosgenin to specifically select targets, hyperlayer SdFFF cell sorting was used to prepare fractions according to cell cycle position from crude HEL cells. The sensitivities of these fractions to diosgenin-induced differentiation were then tested. The coupling of SdFFF cell separation to imaging flow cytometry showed that G1-phase cells were more sensitive to differentiation induction than S/G2M-phase cells, confirming the relationship between cell status at the start of induction, the extent of the biological event, and the potential of SdFFF in cancer research.

We studied the relationship between diosgenin-induced apoptosis and arachidonic acid metabolism in two cancer cell lines, the HT-29 and HCT-116. Diosgenin is a steroidal saponin known for its antiproliferative and pro-apoptotic effects on cancer cells. We focused our attention on two enzymes intervening in two different pathways of arachidonic metabolism: cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX). HT-29 and HCT-116 cells express 5-LOX but only HT-29 cells express COX-2 since HCT-116 are deficient. After 40 microM diosgenin treatment, we observed apoptosis hallmarks in both cell lines but HT-29 cells were more resistant with delayed apoptosis. In these cells, COX-2 expression and activity were increased and for the first time we showed that diosgenin also increased 5-LOX expression and enhanced leukotriene B4 production. Inhibition of 5-LOX by AA-861 significantly reduced apoptosis in both cell lines but COX-2 inhibition by NS-398 strongly sensitized HT-29 cells to diosgenin-induced apoptosis compared to HCT-116 cells. In this study, we showed the implication of COX-2 and 5-LOX in diosgenin-induced apoptosis but these results demonstrate how difficult it is to assess the correlation between the apoptotic signalling pathway of diosgenin and arachidonic acid metabolism with certitude.