L-Canavanine modulates cellular growth, chemosensitivity and P-glycoprotein substrate accumulation in cultured human tumor cell lines.
L-Canavanine (L-CAV) is a naturally occurring L-arginine analog that induces the formation of non-functional proteins in a variety of organisms. Previous studies have shown that L-CAV is cytotoxic for several human tumor cell lines. In this study, we have evaluated the cytotoxicity of L-CAV for both parental and multi-drug resistant (MDR) human tumor cells. We have also determined the effect of L-CAV exposure on cellular expression and activity of the MDR P-glycoprotein (P-gp) membrane efflux pump, and the effect of L-CAV on cellular accumulation of P-gp substrates. The effect of pre-treatment with non-cytotoxic doses of L-CAV on cellular sensitivity to ten standard antineoplastic agents was also evaluated, in order to assess the chemosensitization potential of L-CAV. 3-(4,5-Dimethylthiazol-)2,5-diphenyl tetrazolium bromide (MTT) cytotoxicity assays revealed that the MDR variants of human uterine sarcoma and leukemic cells were equally sensitive to L-CAV as compared with their respective parental controls. Although the presence of free L-CAV in the uptake media did not influence cellular accumulation of P-gp substrates, cells cultured for 72 h in 250 microM L-CAV accumulated from 16 to 23% less P-gp substrate than untreated controls. Although L-CAV-cultured sarcoma cells accumulated 17% less doxorubicin (DOX) than untreated controls, they were three times more sensitive to its cytotoxic effects. L-CAV-treated cells were also significantly more sensitive to cisplatin, 5-fluorouracil, mitoxantrone and bleomycin than were untreated controls. Indirect immunofluorescence revealed that 72-h exposure to as much as 1000 microM L-CAV did not alter cellular expression of P-gp. These studies suggest that L-CAV may be equally cytotoxic for both parental and MDR tumor cells, and that L-CAV neither induces the expression of, nor is a substrate for, P-gp. The observation that L-CAV pre-treatment reduces cellular accumulation of DOX, yet sensitizes tumor cells to DOX and other DNA-targeting antineoplastic drugs, suggests a role for L-CAV as a chemosensitizer for the chemotherapy of cancer.
Worthen
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Division of Medicinal Chemistry and Pharmaceutics, College of Pharmacy, University of Kentucky, Lexington 40536, USA.
Chien
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Tsuboi
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Bartik
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Crooks
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D018435:ATP Binding Cassette Transporter, Subfamily B / Q000187:drug effects* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D002172:Canavanine / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004317:Doxorubicin / Q000493:pharmacokinetics / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D006801:Humans; D020128:Inhibitory Concentration 50; D020014:K562 Cells; D011803:Quinine / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014747:Vinblastine / Q000493:pharmacokinetics / Q000494:pharmacology
D018435:ATP Binding Cassette Transporter, Subfamily B; D000970:Antineoplastic Agents; D002172:Canavanine; D014747:Vinblastine; D004317:Doxorubicin; D011803:Quinine