Growth inhibitory effects of Withaferin A on MDS-L cells – A human 5q Myelodysplastic Syndrome (MDS) cell line

Abstract

Abstract Myelodysplastic syndrome (MDS) affects bone marrow production of white blood cells and erythrocytes. At least 40% of MDS patients who go into remission after treatment eventually progress to acute myelogenous leukemia (AML) which is very difficult to treat. Hence, there is a compelling need for new and better therapies. Withaferin A (WFA), a withanolide isolated from Winter cherry (Withania somnifera), has been shown to have potent anti-cancer properties in several animal models of cancer. We found that WFA inhibited the growth of MDS-L cells, a human cell line derived from a 5q MDS patient. Treatment with WFA induced apoptosis of MDS-L cells, indicated by the cleavage of caspase-3 as early as 6hrs after treatment and a dose dependent increase of annexin positive cells. Cell cycle analysis revealed that WFA caused MDS-L cells to arrest at S and G2/M and accordingly there was a reduction in cyclin A/CDK2 and cyclin B/CDK1 respectively. WFA also inhibited the activity of the heat shock protein (Hsp 90) chaperone as shown by the degradation of its client proteins such as Akt, an important pro-survival kinase and increased expression of Hsp70 which partially compensates for decrease in Hsp90 function. Interestingly, the mechanism by which WFA acts on MDS-L cells is independent of its well-recognized action on Nf-κB. Microarray analysis of gene expression in MDS-L cells showed a dramatic increase in several genes that may have a role in Nf-κB independent growth inhibitory effects of WFA. Studies with a xenograft model of MDS-L cells in NSGS mice suggest WFA might also be effective in vivo. The potent anti-proliferative and anti-survival effects of WFA on MDS-L cells, suggest that it could be a novel therapeutic agent for the treatment of 5q MDS.