Enhanced Therapeutic Effects of Carboplatin by Buthionine Sulfoximine in MBT-2 Bladder Tumor

Min, Kyung Joon; Ahn, Hanjong; Kim, Hyeon Hoe; Lee, Eun Sik; Lee, Chong wook

Abstract

Glutathione based detoxification system in tumor cells was proposed as one of the drug resistance mechanisms and appeared to play as an obstacle in anticancer chemotherapy. It was evaluated that depletion of glutathione content in MBT-2, murine bladder tumor cells by buthionine sulfoximine could enhance the chemotherapeutic effect of carboplatin. Glutathione contents were measured by an enzymatic assay and chemosensitivity was assessed by MTT colorimetric test. Twenty-four hours exposure to 1, 2.5, 5 and 10uM buthionine sulfoximine reduced intracellular glutathione levels to 84.9, 24.8, 18.3 and 11.0% of the control level, respectively, in MBT-2 tumor cell line. Pretreatment with 2.5, 5 and 10uM buthionine sulfoximine for 24 hours and continuous exposure to buthionine sulfoximine and carboplatin for 72 hours potentiated the carboplatin cytotoxicity by 1.26, 1.56 and 1.90 folds, respectively. The potentiation of antitumor effect of carboplatin in C3H/He mice MBT-2 tumor by buthionine sulfoximine was evaluated with the use of tumor growth and tumor volume-doubling time. Glutathione contents in the tumor and liver were reduced to 12.8 and 21.8% of the control level by oral administration of 30mM buthionine sulfoximine for 5 days. No significant change in serum creatinine levels and renal histology was found in the mice treated with buthionine sulfoximine. Combination of carboplatin and buthionine sulfoximine significantly reduced tumor growth rate and delayed tumor volume-doubling time compared to carboplatin alone(p <0.05), while buthionine sulfoximine alone did not influence the tumor growth(p >0.05). Weight loss or mortality due to carboplatin and buthionine sulfoximine administration was not noted. Since buthionine sulfoximine significantly enhanced the effect of carboplatin on murine bladder tumor without apparent toxicity, combination of buthionine sulfoximine and carboplatin could be a new strategy in chemotherapy against advanced bladder cancer.