RESUMEN
PURPOSE: A previous study reported radiation protection from mucosal injury with D-methionine (D-met) in preclinical evaluation; therefore, the pharmacokinetics, safety, and utility of D-met were evaluated clinically. EXPERIMENTAL DESIGN: The pharmacokinetics of D-met following oral administration of a bioavailable formulation (MRX-1024) was evaluated in normal volunteers. Subsequently, 25 patients were enrolled on a phase 1 study of MRX-1024 concurrent with radiation therapy (RT) with or without weekly cisplatinum. Toxicity and mucosal events were evaluated weekly. RESULTS: Oral MRX-1024 resulted in rapid and dose-dependent increases in plasma D-met concentrations with a half-life of 3 hours. When administered concurrent with RT without chemotherapy, it was associated with a modest increase in grade 2 (two of six patients) and grade 3 (one of six patients) emesis. In those treated with MRX-1024 along with RT and weekly cisplatinum, there was no appreciable increase in emesis. Overall, five patients withdrew from the study due to emesis (four grade 2 and one grade 3). Only one incidence of dose-limiting toxicity (grade 3 emesis) was identified in 25 patients (4%). Finally, in 18 evaluable patients treated with MRX-1024 at 100 mg/kg twice daily (BID), the incidence of severe (grade 3) oral mucositis was 6% (1 of 18) with no grade 4 mucositis. CONCLUSIONS: There is a dose-dependent increase in D-met exposure following MRX-1024 administration at 50 and 100 mg/kg, and MRX-1024 is safe for use concurrent with combined radiation and chemotherapy. The observed rate of mucositis seems less than that for similar treatment regimens within the published literature.
