Carboxypeptidase-G2, thymidine, and leucovorin rescue in cancer patients with methotrexate-induced renal dysfunction.

PURPOSE: Methotrexate nephrotoxicity can lead to delayed methotrexate elimination and the development of life-threatening toxicity, which may not be preventable with the standard rescue agent leucovorin. In preclinical studies, we previously demonstrated that carboxypetidase-G2 (CPDG2) rapidly hydrolyzes methotrexate to nontoxic metabolites. A protocol for the compassionate use of CPDG2 in patients who develop nephrotoxicity while receiving high-dose methotrexate was therefore developed. The pharmacologic and clinical outcome of CPDG2 rescue administered with thymidine and leucovorin in 20 patients is presented here. METHODS: Patients with high-dose methotrexate-induced renal dysfunction received one to three doses of CPDG2, 50 U/kg body weight intravenously (i.v.), thymidine 8 g/m2/d by continuous i.v. infusion, and standard pharmacokinetically guided leucovorin rescue. Plasma concentrations of methotrexate and its inactive metabolite 4-deoxy-4-amino-N10-methylpteroic acid (DAMPA) were measured before and after CPDG2 using high-pressure liquid chromatography (HPLC). Tolerance of CPDG2 and thymidine, development of methotrexate toxicities, and recovery of renal function were monitored. RESULTS: Twenty patients who received high-dose methotrexate for osteosarcoma (n = 11), lymphoid cancers (n = 8), and gastric cancer (n = 1) developed nephrotoxicity (median serum creatinine, 3.2 mg/dL) and elevated plasma methotrexate concentrations (median, 201 mumol/L at hour 46). CPDG2 and thymidine rescue was well tolerated and resulted in a rapid 95.6% to 99.6% reduction in the plasma methotrexate concentration. Methotrexate-related toxicity was mild to moderate. Serum creatinine returned to normal values at a median of 22 days. CONCLUSION: CPDG2, thymidine, and leucovorin rescue was highly effective in 20 patients at high risk for developing life-threatening methotrexate toxicity after the onset of methotrexate-induced nephrotoxicity and delayed methotrexate excretion.