l-Histidinol: Preclinical Therapeutic Studies in Combination with Antitumor Agents and Pharmacokinetic Studies in Mice¹

Therapeutic studies were conducted with l-histidinol, in combination with cyclophosphamide, bischloroethylnitrosourea, 5-fluorouracil, phenylalanine mustard, or cis-platinum(II)diammine dichloride, in several transplantable tumors in mice. These tumor types included murine L1210 P388 leukemias, M5076 sarcoma, mammary 16/C adenocarcinoma, human LOX melanoma, and colon HT-29 adenocarcinoma. Therapeutic benefits of adding l-histidinol to a regimen, compared to the regimen alone, were marginal. Pharmacokinetic studies indicated a rapid clearance of l-histidinol following a bolus dose (250 mg/kg i.p.), peak plasma concentration of 200 µg/ml (1.4 mm), and β phase t_½ of 12.6 min. Maximum tolerable plasma steady state concentrations with a 24-h infusion (2000 mg/kg/24 h) were no greater than 25 µg/ml (0.18 mm).