The topoisomerase I inhibitor topotecan increases the sensitivity of prostate tumor cells to TRAIL/Apo-2L-induced apoptosis.
PURPOSE.:TRAIL/Apo-2L is cytotoxic against numerous prostate tumor cell lines; however, some lines are more resistant than others. Identification of an agent that increases prostate tumor cell sensitivity to TRAIL/Apo-2L would prove valuable for TRAIL/Apo-2L-mediated tumor therapy. Thus, we examined the effect of combining five clinically approved chemotherapeutic agents with TRAIL/Apo-2L for treating prostate tumor cells.


METHODS
Four human prostate tumor cell lines were initially tested for TRAIL/Apo-2L sensitivity. Subsequent studies examined whether the TRAIL/Apo-2L-induced killing of DU-145 cells was augmented in the presence of the chemotherapeutic molecules, as measured by annexin V-FITC/propidium iodide staining. Furthermore, caspase 8 activation and BID cleavage were examined by immunoblotting. RT-PCR and flow cytometry were performed to monitor TRAIL-R1 and TRAIL-R2 levels after chemotherapeutic treatment.


RESULTS
DU-145 cells were the least responsive of the prostate tumor cell lines tested to TRAIL/Apo-2L-induced death. Surprisingly, only topotecan, a topoisomerase I inhibitor, when used in combination with rTRAIL/Apo-2L led to significant apoptosis of DU-145 cells, as measured by caspase 8 activation, BID cleavage, and annexin V-FITC/PI staining. Topotecan alone had little to no toxicity on the DU-145 cells. Furthermore, the increase in TRAIL/Apo-2L sensitivity following topotecan treatment correlated with increased expression of TRAIL-R1 and TRAIL-R2 and decreased intracellular levels of the antiapoptotic protein survivin.


CONCLUSIONS
Our results define a promising direction for alternative therapies against androgen-independent prostate cancers. The sensitivity of DU-145 cells to TRAIL/Apo-2L was dramatically increased when combined with topotecan, suggesting that low-dose topotecan treatment to upregulate TRAIL-R1 and TRAIL-R2 and downregulate survivin, followed by TRAIL/Apo-2L administration, may be a viable therapy for treating cancer of the prostate.
Griffith
Thomas S
TS
Department of Urology, University of Iowa, 200 Hawkins Drive, Iowa City, IA 52242-1089, USA. thomas-griffith@uiowa.edu
Kemp
Troy J
TJ
D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000627:therapeutic use*; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008297:Male; D008562:Membrane Glycoproteins / Q000627:therapeutic use*; D008869:Microtubule-Associated Proteins / Q000494:pharmacology*; D009363:Neoplasm Proteins; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D000077022:Survivin; D053221:TNF-Related Apoptosis-Inducing Ligand; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000627:therapeutic use*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000627:therapeutic use*
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C107489:BIRC5 protein, human; D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D051034:Inhibitor of Apoptosis Proteins; D008562:Membrane Glycoproteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D000077022:Survivin; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D059004:Topoisomerase I Inhibitors; D014409:Tumor Necrosis Factor-alpha; D019772:Topotecan