A Multicenter Phase I Trial of PX-866, an Oral Irreversible Phosphatidylinositol 3-kinase Inhibitor, in Patients with Advanced Solid Tumors

Purpose: The objectives of the study were to evaluate the maximum tolerated dose (MTD), safety, pharmacodynamics, pharmacokinetics, and antitumor activity of PX-866 in patients with incurable cancers.

Experimental Design: This was a phase I, open-label, dose-escalation study. Drug was administered orally once per day either on an intermittent (arm 1; days 1-5 and 8-12 of a 28-day cycle) or continuous (arm 2; days 1-28 of a 28-day cycle) schedule. Additional patients were treated at the arm 2 MTD in a food effects substudy.

Results: Eighty-four patients were treated in the arm 1 (n = 51), arm 2 (n = 20), and food effects (n = 13) cohorts. The most frequent study drug-related adverse events were gastrointestinal disorders (69.0%), with diarrhea being the most common (48.8%). The MTD was 12 and 8 mg for arm 1 and 2, respectively. The dose-limiting toxicities (DLT) consisted of grade III diarrhea (n = 3) and grade III elevated aspartate aminotransferase (AST; n = 1). The pharmacokinetics profile was dose proportional, with no evidence of drug accumulation. PX-866-associated inhibition of platelet pAKTSER473 was observed at the arm 2 MTD. The best response per Response Evaluation Criteria in Solid Tumors (RECIST) was stable disease in 22% of evaluable patients in arm 1, 53% in arm 2, and 11% in the food effects cohort. Eight patients were on study for 4 or more months.

Conclusions: This first-in-human study shows that PX-866, an irreversible small-molecule inhibitor of phosphatidylinositol 3-kinase (PI3K), was well tolerated and was associated with prolonged stable disease, particularly when using a continuous dosing schedule.