A phase I study of pivaloyloxymethyl butyrate, a prodrug of the differentiating agent butyric acid, in patients with advanced solid malignancies.

Pivaloyloxymethyl butyrate (AN-9), an acyloxyalkyl ester prodrug of butyric acid (BA), has demonstrated greater potency than BA at inducing malignant cell differentiation and tumor growth inhibition and has demonstrated more favorable toxicological, pharmacological, and pharmaceutical properties than BA in preclinical studies. The principal objective of this study was to determine the feasibility of administering AN-9 as a 6-h i.v. infusion daily for 5 days every 3 weeks in patients with advanced solid malignancies. The study also sought to determine the principal toxicities and maximum tolerated dose of AN-9 on this intermittent schedule, as well as the effects of AN-9 on fetal hemoglobin production, a parameter indicative of RBC differentiation. None of the 28 patients treated with 85 total courses of AN-9 at dosages ranging from 0.047 to 3.3 g/m 2 /day every 3 weeks experienced dose limiting toxicity. Mild to moderate nausea, vomiting, hepatic transaminase elevation, hyperglycemia, fever, fatigue, anorexia, injection site reaction, diarrhea, and visual complaints were observed. Dose escalation of AN-9 was limited by the maximum feasible volume of its intralipid formulation vehicle that could be administered safely on this schedule, resulting in a maximum deliverable dose of 3.3 g/m 2 /day. There was no consistent increase in fetal hemoglobin with AN-9 treatment. A partial response was observed in a previously untreated patient with metastatic non-small cell lung cancer. Additional disease-directed clinical evaluations of AN-9 are necessary to establish the breadth of its antitumor activity and to assess its role as an effective differentiating agent.