Immunosensitization of prostate carcinoma cell lines for lymphocytes (CTL, TIL, LAK)-mediated apoptosis via the Fas-Fas-ligand pathway of cytotoxicity.
Several reports suggest that immunotherapy mediated by cytotoxic lymphocytes is beneficial in the destruction of drug-resistant tumor cells. Cytotoxic T lymphocytes kill target cells by two main mechanisms, namely by the perforin pathway and by the Fas-ligand (Fas-L) pathway. The role of the Fas-L pathway in tumor cell killing is not clear because many Fas(+)-expressing tumor cells are resistant to the Fas-L agonist cytotoxic anti-Fas antibody. The human prostate tumor cell lines (PC-3, DU145, and LnCAP) express Fas on the cell surface but are resistant to killing by anti-Fas antibody. This study examined the sensitivity of prostate tumor cells to Fas-L-mediated cytotoxicity and sensitization of the tumor cells by drugs to Fas-L-mediated killing. All three prostate tumor cell lines are resistant to Fas-L killing as determined by the use of the murine CTL hybridoma PMMI that kills only through the Fas-L pathway. However, the addition of subtoxic concentrations of CDDP or VP-16 significantly sensitized the PC-3 and DU145, but not LnCAP, tumor cells to Fas-L killing and apoptosis by PMMI. The sensitization of tumor cells by drugs was inhibited by neutralizing anti-Fas antibody. These findings demonstrate that immunoresistant Fas(+)-expressing DU145 and PC-3 prostate tumor cells can be sensitized by drugs to Fas-L killing. We then examined the role of Fas-L killing by TIL and LAK cells. All three prostate tumor cell lines were sensitive to killing by TIL and LAK and cell killing was primarily mediated through the Ca(2+)-dependent perforin pathway because it was blocked by the addition of EGTA/MgCl2. Sensitization by CDDP or VP-16 did not significantly augment killing of untreated tumor cells by TIL or LAK cells. However, in the presence of EGTA/MgCl2, the addition of CDDP or VP-16 significantly augmented killing of PC-3 and DU145, but not LnCAP, by TIL and LAK, and killing was blocked by neutralizing anti-Fas antibody. These findings demonstrate that both TIL and LAK exhibit a Fas-L-mediated killing pathway that is revealed once the perforin pathway is blocked by the Ca2+ chelator EGTA/MgCl2. Altogether, these findings show that drug-resistant, Fas(+)-expressing PC-3 and DU145 prostate tumor cells can be sensitized by CDDP and VP-16 to killing by Fas-L-bearing CTL, TIL, and LAK cells. Sensitization of tumor cells by drugs may augment the efficacy of immunotherapy in the eradication of tumor cells that are resistant to Fas-L-mediated killing.
Frost
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P
Department of Microbiology and Immunology, UCLA School of Medicine, USA.
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Belldegrun
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A
Bonavida
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B
D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002277:Carcinoma / Q000276:immunology*; D002945:Cisplatin / Q000494:pharmacology; D003601:Cytotoxicity Tests, Immunologic; D003602:Cytotoxicity, Immunologic; D053222:Fas Ligand Protein; D006801:Humans; D015979:Killer Cells, Lymphokine-Activated / Q000276:immunology; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D011471:Prostatic Neoplasms / Q000276:immunology*; D015398:Signal Transduction; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014407:Tumor Cells, Cultured
C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D002945:Cisplatin