Vol. 59, Issue 4, 784-794, April 2001

Induction of CDK Inhibitors (p21^WAF1 and p27^Kip1) and Bak in the -Lapachone-Induced Apoptosis of Human Prostate Cancer Cells

Ming-Jaw Don, Yen-Hwa Chang, Kuang-Kuo Chen, Li-Kang Ho, and Yat-Pang Chau

National Research Institute of Chinese Medicine (M.-J.D.); Division of Urology, Department of Surgery, Taipei-Veterans General Hospital (Y.-H.C., K.-K.C.); Departments of Urology (Y.-H.C., K.-K.C.) and Pharmacology (L.-K.H.), School of Medicine, National Yang-Ming University; and Institute of Anatomy and Cell Biology, School of Life Science, National Yang-Ming University (Y.-P.C.)

-Lapachone, a novel anti-neoplastic drug, induces various cancer cells to undergo apoptosis. In a previous report, we showed that -lapachone-induced apoptosis of HL-60 cells is mediated by oxidative stress. However, in the present study, we found that -lapachone-induced apoptosis of human prostate cancer (HPC) cells may be independent of oxidative stress. In contrast to the 10-fold -lapachone-induced increase in H₂O₂ production seen in HL-60 cells, only a 2- to 4-fold increase was observed in HPC cells. N-acetyl-L-cysteine (NAC), a thiol antioxidant, inhibited the apoptosis in DU145 cells after 12 h exposure to -lapachone. Nonetheless, NAC, along with other antioxidants, failed to exert similar effect in HPC cells subjected to -lapachone treatment for 24 h. Under this premise, we suggest that the oxidative stress may not play a crucial role in -lapachone-mediated HPC cell apoptosis. Here we demonstrate that damage to genomic DNA is the trigger for the apoptosis of HPC cells induced by -lapachone. According to our results, -lapachone stimulates DNA dependent kinase expression and poly(ADP-ribose) polymerase cleavage in advance of significant morphological changes. -Lapachone promotes the expression of cyclin-dependent kinase (cdk) inhibitors (p21^WAF1 and p27^Kip1), induces bak expression, and subsequently stimulates the activation of caspase-7 but not of caspase-3 or caspase-8 during the apoptosis of HPC cells. Taken together, these results suggest that the signaling pathway involving the -lapachone-induced apoptosis of HPC cell may be by DNA damage, induction of cdk inhibitors (p21 and p27), and then subsequent stimulation of caspase-7 activation.