Antifolate activity of pyrimethamine enhances temozolomide-induced cytotoxicity in melanoma cells.
Most metastatic melanoma patients fail to respond to available therapy, underscoring the need to develop more effective treatments. We screened 2,000 compounds from the Spectrum Library in human melanoma cell lines to identify compounds that enhanced the cytotoxic effect of temozolomide, a drug used to treat metastatic melanoma. Screening was done with the temozolomide-resistant melanoma cell line SK-MEL-19, and six compounds were identified that had little or no inherent cytotoxicity but significantly enhanced growth-inhibition by temozolomide. These compounds were tested in five additional melanoma cell lines. Cell proliferation and death assays were used to compare the efficacy of single agent temozolomide versus combination treatments. Effects of combination treatment on levels of DNA double-strand breaks, the DNA repair protein O(6)-methylguanine-DNA-methyltransferase, apoptosis [measured by cleaved caspase-3 and poly(ADP-ribose) polymerase], and cell cycle were examined. Pyrimethamine, an antiparasitic, sensitized melanoma cells to temozolomide. Temozolomide combined with Pyrimethamine synergistically inhibited cell proliferation in melanoma cells with combination index values of 0.7 or less. In addition, combination treatment induced cell cycle arrest and increased both DNA damage and apoptosis. The increase in cell death due to combination treatment was rescued by leucovorin. Other folate antagonists were also effective enhancers of temozolomide-induced cytotoxicity, and the effects of antifolates were also evident in gliomas. Our screening approach led to the identification of Pyrimethamine, an orally available drug that efficiently crosses the blood-brain barrier, as a potent enhancer of the efficacy of temozolomide as an antineoplastic agent via inhibition of folate metabolism.
Chen
Ming
M
The Ronald O. Perelman Department of Dermatology, and the New York University Cancer Institute Clinical Cancer Center, New York, New York, USA.
Osman
Iman
I
Orlow
Seth J
SJ
D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D005493:Folic Acid Antagonists / Q000737:chemistry / Q000494:pharmacology*; D005910:Glioma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D015394:Molecular Structure; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011739:Pyrimethamine / Q000737:chemistry / Q000494:pharmacology*; D000077204:Temozolomide
D018906:Antineoplastic Agents, Alkylating; D005493:Folic Acid Antagonists; D003606:Dacarbazine; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3; D000077204:Temozolomide; D011739:Pyrimethamine