Doxorubicin increases the effectiveness of Apo2L/TRAIL for tumor growth inhibition of prostate cancer xenografts.
BACKGROUND
Prostate cancer is a significant health problem among American men. Treatment strategies for androgen-independent cancer are currently not available. Tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) is a death receptor ligand that can induce apoptosis in a variety of cancer cell lines, including androgen-independent PC3 prostate carcinoma cells. In vitro, TRAIL-mediated apoptosis of prostate cancer cell lines can be enhanced by doxorubicin and correlates with the downregulation of the anti-apoptotic protein c-FLIP. This study evaluated the effects of doxorubicin on c-FLIP expression and tumor growth in combination with Apo2L/TRAIL in a xenograft model.


METHODS
In vitro cytotoxic effects of TRAIL were measured using a MTS-based viability assay. For in vivo studies, PC3 prostate carcinoma cells were grown subcutaneously in athymic nude mice and tumor growth was measured following treatment with doxorubicin and/or Apo2L/TRAIL. c-FLIP expression was determined by western blot analysis. Apoptosis in xenografts was detected using TUNEL. Statistical analysis was performed using the student t-test.


RESULTS
In vitro experiments show that PC3 cells are partially susceptible to Apo2L/TRAIL and that susceptibility is enhanced by doxorubicin. In mice, doxorubicin did not significantly affect the growth of PC3 xenografts but reduced c-FLIP expression in tumors. Expression of c-FLIP in mouse heart was decreased only at the high doxorubicin concentration (8 mg/kg). Combination of doxorubicin with Apo2L/TRAIL resulted in more apoptotic cell death and tumor growth inhibition than Apo2L/TRAIL alone.


CONCLUSIONS
Combination of doxorubicin and Apo2L/TRAIL is more effective in growth inhibition of PC3 xenografts in vivo than either agent alone and could present a novel treatment strategy against hormone-refractory prostate cancer. The intracellular mechanism by which doxorubicin enhances the effect of Apo2L/TRAIL on PC3 xenografts may be by reducing expression of c-FLIP.
El-Zawahry
Ahmed
A
Department of Microbiology & Immunology, Medical University of South Carolina, Charleston, SC, USA. elzawaha@musc.edu <elzawaha@musc.edu>
McKillop
John
J
Voelkel-Johnson
Christina
C
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004317:Doxorubicin / Q000008:administration & dosage / Q000627:therapeutic use*; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000627:therapeutic use*; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000517:prevention & control*; D053221:TNF-Related Apoptosis-Inducing Ligand; D014183:Transplantation, Heterologous; D014409:Tumor Necrosis Factor-alpha / Q000627:therapeutic use*
D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; C506387:Cflar protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C505654:Tnfsf10 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D004317:Doxorubicin