Effects of sequential treatments with chemotherapeutic drugs followed by TRAIL on prostate cancer in vitro and in vivo

BACKGROUND Tumor necrosis factor related apoptosis‐inducing ligand/Apo2 ligand (TRAIL/Apo‐2L) is a novel anticancer agent, capable of inducing apoptosis preferentially in tumor and transformed cells. TRAIL‐R1/death receptor (DR)4 and TRAIL‐R2/DR5 are members of the tumor necrosis factor (TNF) receptor family, and can be activated by the TRAIL. We examined the clinical potential of chemotherapeutic drugs and TRAIL for the treatment of prostate cancer. METHODS Prostate and bladder cancer cells were exposed to chemotherapeutic drugs (paclitaxel, vincristine, vinblastine, etoposide, doxorubicin, and camptothecin) and TRAIL. Cell viability was measured by sodium 3′[1‐(phenylaminocarbonyl)‐3,4‐tetrazolium]‐bis (4‐methoxy‐6‐nitro) assay; expressions of death receptors and Bcl‐2 family members were measured by Western blotting, ELISA and ribonuclease protection assay. PC‐3 tumor cells xenografted athymic nude mice were exposed to chemotherapeutic drugs and TRAIL, either alone or in combination, to measure tumor growth and survival of mice. Apoptosis was measured by annexin V–FITC/propidium iodide staining, and terminal deoxynucleotidyltransferase‐mediated nick end labeling assay. Caspase‐3 activity was measured by the Western blotting and immunohistochemistry. RESULTS TRAIL induced apoptosis with varying sensitivity. Chemotherapeutic drugs (paclitaxel, vincristine, vinblastine, etoposide, doxorubicin, and camptothecin) significantly augmented TRAIL‐induced apoptosis in cancer cells through up‐regulation of DR4, DR5, Bax, and Bak, and induction of caspase activation. Mitochondrial pathway enhanced the synergistic interactions between drugs and TRAIL. The sequential treatment of mice with chemotherapeutic drugs followed by TRAIL induced caspase‐3 activity, and apoptosis, inhibited angiogenesis, completely eradicated the established tumors, and enhanced survival of mice. CONCLUSIONS Chemotherapeutic drugs can be used to enhance the therapeutic potential of TRAIL in prostate cancer. © 2004 Wiley‐Liss, Inc.