Purpose: Originally isolated on the basis of its ability to induce p53, serdemetan showed potent activity in various preclinical models, inducing S-phase arrest and apoptosis in TP53 wild-type and mutant tumors. This study evaluated the safety and tolerability of serdemetan, determined the pharmacokinetic and pharmacodynamic profiles, and identified a recommended phase II dose. Patients and Methods: Patients (71) with refractory solid tumors were allocated to dose-escalating cohorts (3+3 patients each) and received oral serdemetan once daily in 21-day cycles to determine the maximum tolerated dose (MTD) and dose-limiting toxicities (DLT). Plasma was collected for pharmacokinetic analyses. Paired baseline and on-treatment skin and tumor biopsies were done; blood samples were collected for pharmacodynamic analyses, including p53 and macrophage inhibitory cytokine-1 induction. Results: The MTD of serdemetan was determined to be 350 mg once daily. During this study, grade 3 QTc prolongation was the most common DLT and nausea (66.2%) was the most frequent treatment-emergent adverse event. Serdemetan was rapidly absorbed after oral administration and exhibited dose-proportional pharmacokinetics. At steady state, mean maximum plasma concentration (Cmax) was 2,330 ng/mL and mean area under plasma concentration curve (AUC 0-24h) was 43.0 μg.h/mL, with serdemetan 300 mg/d. There was a dose- and exposure-dependent p53 induction. One patient with breast cancer showed a partial response; 22 (38.6%) patients had stable disease. Conclusions: Serdemetan treatment was associated with p53 induction in both tumor and surrogate tissue pharmacodynamic studies and modest clinical activity. Although serdemetan was well tolerated with dose-proportional pharmacokinetics, exposure-related QTc liability was observed. ©2011 AACR.