title: HIV-1 protease inhibitor, ritonavir: a potent inhibitor of CYP3A4, enhanced the anticancer effects of docetaxel in androgen-independent prostate cancer cells in vitro and in vivo.
abstract: We previously showed that HIV-1 protease inhibitors (PIs) slowed the proliferation of human myeloid leukemia cells and enhanced their differentiation in the presence of all-trans-retinoic acid. In this study, we found that PIs, including ritonavir, saquinavir, and indinavir, inhibited the growth of DU145 and PC-3 androgen-independent prostate cancer cells as measured by a clonal proliferation assay. Recent studies showed that ritonavir inhibited cytochrome P450 3A4 enzyme (CYP3A4) in liver microsomes. The CYP3A4 is involved in drug metabolism and acquisition of drug resistance. To clarify the drug interaction between ritonavir and other anticancer drugs, we cultured DU145 cells with docetaxel either alone or in combination with ritonavir. Ritonavir enhanced the antiproliferative and proapoptotic effects of docetaxel in the hormonally independent DU145 prostate cancer cells in vitro as measured by the clonogenic soft agar assay and detection of the activated form of caspase-3 and cleavage of poly(ADP-ribose) polymerase using Western blot analysis. Real-time PCR showed that docetaxel induced the expression of CYP3A4 at the transcriptional level, and ritonavir (10(-5) mol/L) completely blocked this induction. An ELISA-based assay also showed that ritonavir inhibited DNA binding activity of nuclear factor kappaB (NFkappaB) in DU145 cells, which is a contributor to drug resistance in cancer cells. Furthermore, combination treatment of docetaxel and ritonavir dramatically inhibited the growth of DU145 cells present as tumor xenografts in BNX nude mice compared with either drug alone. Importantly, docetaxel induced expression of CYP3A4 in DU145 xenografts, and ritonavir completely blocked this induction. Ritonavir also inhibited NFkappaB DNA binding activity in DU145 xenografts. Extensive histologic analyses of the liver, spleen, kidneys, bone marrow, skin, and subcutaneous fat pads from these mice showed no abnormalities. In summary, combination therapy of ritonavir and anticancer drugs holds promise for the treatment of individuals with advanced, drug resistant cancers.
authors.affiliation: Division of Hematology/Oncology, Cedars-Sinai Medical Center and UCLA School of Medicine, Los Angeles, California, USA. ikezoet@ed.kochi-ms.ac.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ikezoe
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Hisatake
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Takeuchi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ohtsuki
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Said
authors.forename: Hirokuni
authors.initials: H
authors.lastname: Taguchi
authors.forename: H Phillip
authors.initials: HP
authors.lastname: Koeffler
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics; D004273:DNA, Neoplasm / Q000378:metabolism; D000077143:Docetaxel; D004357:Drug Synergism; D017320:HIV Protease Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D015497:HIV-1 / Q000201:enzymology; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D019438:Ritonavir / Q000008:administration & dosage / Q000494:pharmacology*; D043823:Taxoids / Q000008:administration & dosage / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004273:DNA, Neoplasm; D017320:HIV Protease Inhibitors; D016328:NF-kappa B; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D043823:Taxoids; D000077143:Docetaxel; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D019438:Ritonavir