Cisplatin is frequently used to treat solid tumors; however, nephrotoxicity due to its reactive oxygen species-mediated effect limits its use. We tested the ability of cationized catalase, a catalase derivative, to inhibit nephrotoxicity in cisplatin-treated mice. Immunohistochemical analysis showed that the catalase derivative concentrated in the kidney more efficiently than native catalase. Repeated intravenous doses of cationized catalase significantly decreased cisplatin-induced changes in serum creatinine, blood urea nitrogen, nitrite/nitrate levels, lactic dehydrogenase activity, and renal total glutathione and malondialdehyde contents. In addition, cationized catalase effectively blunted cisplatin-induced proximal tubule necrosis but had no significant effect on the cisplatin-induced inhibition of subcutaneous tumor growth. Repeated doses of catalase, especially cationized catalase, significantly increased the survival of cisplatin-treated tumor-bearing mice preventing cisplatin-induced acute death. Our studies suggest that catalase and its derivatives inhibit cisplatin-induced nephrotoxicity, thus improving the efficiency of cisplatin to treat solid tumors.

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In spite of the successful application of cisplatin (CDDP) as a chemotherapy agent, alone or in combination against several solid tumors, 1,2) it would be desirable to modify it by synthetic chemical or pharmaceutical formulation methods, in order to overcome some of its side effects, especially its nephrotoxicity.3) In order to reduce the nephrotoxicity, which is associated with CDDP treatment, we developed a CDDP complex using chondroitin sulfate A (CSA), a polycarboxyl polysaccharide. The CDDP-CSA complex had the same activity as the parent drug but showed reduced nephrotoxicity at high doses of CDDP. 4) Thus, the results suggest that CDDP-CSA might reversibly release the active parent drug, due to reversible binding with the carboxyl group of the CSA, as observed with other carbohydrate compounds. 5)Therefore, it is important to examine the stability of the CDDP-CSA complex in the circulation, since plasma proteins may potentially compete for CDDP to form irreversibly bound species. Approximately 90% of the platinum in the blood exists in a protein-bound form following intravenous administration of CDDP. 6,7)Based on the above objective, we compared the plasma levels of total and protein-free platinum for both CDDP and the CDDP-CSA complex following intravenous administration. The availability of protein-free platinum in the circulation was used to evaluate the stability toward the protein binding. Moreover, the stability of the complex in the kidney was examined by incubation with a kidney homogenate. MATERIALS AND METHODSChemicals and Animals CDDP was purchased from Sigma Chemical Company (St. Louis, MO, U.S.A.). Chondroitin sulfate A (CSA) with a mean molecular weight of 23 KDa was obtained from Seikagaku Corporation (Kanagawa, Japan). A CDDP-CSA complex was prepared by dissolving CDDP (1 mg/ml) and CSA (8.4 mg/ml) in deionized water, followed by shaking for 2 d until a reaction equilibrium of 80-85% of the CDDP forming a complex with the CSA had been reached. All other chemicals were of analytical grade. 7-week-old male Wistar rats (230-250 g) were used in the experiments.Measurement of Total and Unbound Platinum Plasma Disposition Cannulations were performed on rats via the femoral vein and artery using polyethylene tubing (PE50) as described previously.4) CDDP was dissolved in saline at a concentration of 1 mg/ml; the prepared complex (containing 1 mg/ml of CDDP) was made iso-osmotic by the addition of glucose. The freshly prepared solution, CDDP or CDDP-CSA was then administered at a dose of 2 mg/kg via the formal vein. Blood samples (0.3-0.4 ml) were collected from the femoral artery at 2, 5, 10, 30, 60, 90, 120, and 180 min into heparinized microtubes, followed by rapid centrifugation, in order to isolate the plasma immediately. Following this procedure, 0.2 ml of plasma was added to an equal volume of a cold mixture of 10% TCA and 5% HCl, and the supernatant was analyzed for TCA-soluble platinum which represents the sum of the free and reversibly bound species. 8)The remaining plasma samples were u...