Worthen D R, Chien L, Tsuboi C P, Mu X Y, Bartik M M, Crooks P A
Division of Medicinal Chemistry and Pharmaceutics, College of Pharmacy, University of Kentucky, Lexington 40536, USA.
Cancer Lett. 1998 Oct 23;132(1-2):229-39. doi: 10.1016/s0304-3835(98)00233-x.
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.
L-刀豆氨酸（L-CAV）是一种天然存在的L-精氨酸类似物，可在多种生物体中诱导无功能蛋白质的形成。先前的研究表明，L-CAV对几种人类肿瘤细胞系具有细胞毒性。在本研究中，我们评估了L-CAV对亲本和多药耐药（MDR）人类肿瘤细胞的细胞毒性。我们还确定了L-CAV暴露对MDR P-糖蛋白（P-gp）膜外排泵的细胞表达和活性的影响，以及L-CAV对P-gp底物细胞内积累的影响。还评估了用无细胞毒性剂量的L-CAV预处理对细胞对十种标准抗肿瘤药物敏感性的影响，以评估L-CAV的化学增敏潜力。3-（4,5-二甲基噻唑-2）-2,5-二苯基四氮唑溴盐（MTT）细胞毒性试验表明，人子宫肉瘤和白血病细胞的MDR变体与其各自的亲本对照相比，对L-CAV同样敏感。尽管摄取培养基中游离L-CAV的存在不影响P-gp底物的细胞内积累，但在250μM L-CAV中培养72小时的细胞积累的P-gp底物比未处理的对照少16%至23%。尽管L-CAV培养的肉瘤细胞积累的阿霉素（DOX）比未处理的对照少17%，但它们对其细胞毒性作用的敏感性高三倍。L-CAV处理的细胞对顺铂、5-氟尿嘧啶、米托蒽醌和博来霉素的敏感性也明显高于未处理的对照。间接免疫荧光显示，暴露于高达1000μM L-CAV 72小时不会改变P-gp的细胞表达。这些研究表明，L-CAV对亲本和MDR肿瘤细胞可能具有同等的细胞毒性，并且L-CAV既不诱导P-gp的表达，也不是P-gp的底物。L-CAV预处理可减少DOX的细胞内积累，但使肿瘤细胞对DOX和其他靶向DNA的抗肿瘤药物敏感，这一观察结果表明L-CAV作为癌症化疗的化学增敏剂具有一定作用。
