Withaferin A (WA) is present abundantly in Withania somnifera, a well-known Indian medicinal plant. Here we demonstrate how WA exhibits a strong growth-inhibitory effect on several human leukemic cell lines and on primary cells from patients with lymphoblastic and myeloid leukemia in a dose-dependent manner, showing no toxicity on normal human lymphocytes and primitive hematopoietic progenitor cells. WA-mediated decrease in cell viability was observed through apoptosis as demonstrated by externalization of phosphatidylserine, a time-dependent increase in Bax/Bcl-2 ratio; loss of mitochondrial transmembrane potential, cytochrome c release, caspases 9 and 3 activation; and accumulation of cells in sub-G0 region based on DNA fragmentation. A search for the downstream pathway further reveals that WA-induced apoptosis was mediated by an increase in phosphorylated p38MAPK expression, which further activated downstream signaling by phosphorylating ATF-2 and HSP27 in leukemic cells. The RNA interference of p38MAPK protected these cells from WA-induced apoptosis. The RNAi knockdown of p38MAPK inhibited active phosphorylation of p38MAPK, Bax expression, activation of caspase 3 and increase in Annexin V positivity. Altogether, these findings suggest that p38MAPK in leukemic cells promotes WA-induced apoptosis. WA caused increased levels of Bax in response to MAPK signaling, which resulted in the initiation of mitochondrial death cascade, and therefore it holds promise as a new, alternative, inexpensive chemotherapeutic agent for the treatment of patients with leukemia of both lymphoid and myeloid origin.

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A reversed-phase HPLC method for the simultaneous analysis of nine structurally similar withanolides, namely, 27-hydroxy withanone, 17-hydroxy withaferin A, 17-hydroxy-27-deoxy withaferin A, withaferin A, withanolide D, 27-hydroxy withanolide B, withanolide A, withanone and 27-deoxywithaferin A, has been developed using a linear binary gradient solvent system comprising methanol and water containing 0.1% acetic acid. Both photodiode array and evaporative light scattering detection were used to profile the extract compositions and to quantify the withanolides therein. Homogeneity and purity of each peak was ascertained by comparative evaluation of the on-line UV spectra of the eluted compounds with those of the reference compounds. The method has been validated with respect to various parameters of performance quality including computation regression analysis based on calibration curves, peak resolution factor, asymmetry factor, tailing factor, RSD (%) of retention time and peak area response, limit of quantivation, limit of detection, precision and recovery. The developed method has been applied to the analysis of leaf and root tissues of Withania somnifera for withanolide content.

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