Potent induction of apoptosis by β-lapachone in human multiple myeloma cell lines and patient cells

Background: Human multiple myeloma (MM) remains an incurable hematological malignancy. We have reported that beta -lapachone, a pure compound derived from a plant, can induce cell death in a variety of human carcinoma cells, including ovary, colon, lung, prostate, pancreas, and breast, suggesting a wide spectrum of anticancer activity. Materials and Methods: We first studied anti-survival effects of beta -lapachone in human MM cells by colony formation assay. To determine whether the differential inhibition of colony formation occurs through antiproliferative activity, we performed MTT assays. The cytotoxicity of beta -lapachone on human peripheral blood mononuclear cells was also measured by MTT assay. To determine whether the cell death induced by beta -lapachone occurs through necrosis or apoptosis, we used the propidium iodide staining procedure to determine the sub-G1 fraction, Annexin-V staining for externalization of phosphatidylserine, and fragmentation of cellular genomic DNA subjected to gel electrophoresis. To investigate the mechanism of anti-MM activity, we examined Bcl-2 expression, cytochrome C release, and poly(ADP ribose) polymerase cleavage by Western blot assay. Results: We found that beta -lapachone (less than 4 muM) inhibits cell survival and proliferation by triggering cell death with characteristics of apoptosis in ARH-77, HS Sultan, and MM.1S cell lines, in freshly derived patient MM cells (MM.As), MM cell lines resistant to dexamethasone (MM.1R), doxorubicin (DOX.40), mitoxantrone (MR.20), and mephalan (LR5). Importantly, after treatment with beta -lapachone, we observed no apoptosis in peripheral blood mononuclear cells in either quiescent or proliferative states, freshly isolated from healthy donors. In beta -lapachone treated ARH-77, cytochrome C was released from mitochondria to cytosol, and poly (ADP ribose) polymerase was cleaved, signature events of apoptosis. Finally, the apoptosis induced by beta -lapachone in MM cells was not blocked by either interleukin-6 or Bcl-2, which confer multidrug resistance in MM. Conclusions: Our results suggest potential therapeutic application of beta -lapachone against MM, particularly to overcome drug resistance in relapsed patients.