Potent induction of apoptosis by beta-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 -lapa chone in human MM cells by colony formation assay. To determine whether the differential inhibition of colony formation occurs through antiproliferati ve activity, we performed MTT assays. The cytotoxicity of beta -lapachone o n human peripheral blood mononuclear cells was also measured by MTT assay. To determine whether the cell death induced by beta -lapachone occurs throu gh necrosis or apoptosis, we used the propidium iodide staining procedure t o 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 e xamined Bcl-2 expression, cytochrome C release, and poly(ADP ribose) polyme rase cleavage by Western blot assay. Results: We found that beta -lapachone (less than 4 muM) inhibits cell surv ival and proliferation by triggering cell death with characteristics of apo ptosis in ARH-77, HS Sultan, and MM.1S cell lines, in freshly derived patie nt MM cells (MM.As), MM cell lines resistant to dexamethasone (MM.1R), doxo rubicin (DOX.40), mitoxantrone (MR.20), and mephalan (LR5). Importantly, af ter treatment with beta -lapachone, we observed no apoptosis in peripheral blood mononuclear cells in either quiescent or proliferative states, freshl y isolated from healthy donors. In beta -lapachone treated ARH-77, cytochro me C was released from mitochondria to cytosol, and poly (ADP ribose) polym erase was cleaved, signature events of apoptosis. Finally, the apoptosis in duced 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.