Background: Curaxin CBL0137 is a novel compound with broad anticancer activity in animal models. The drug is a non-genotoxic DNA intercalator that interferes with histone/DNA binding causing decondensation of chromatin in tumor cells, functional inactivation of histone chaperone FACT, activation of p53 and IFN responses, and inhibition of pro-cancer transcriptional factors, MYC, NF-kB, HSF1, and HIF1a. Methods: The study enrolled adults with advanced chemorefractory solid tumors, ECOG PS ≤2, and adequate organ function. The primary objective was to find the maximum tolerated dose (MTD) and recommended dosing regimen (RDR). Secondary objectives were to evaluate CBL0137 safety, pharmacokinetics, and efficacy. CBL1037 was given orally once daily (QD) for the first 14 days of repeated 28-day cycles. A 3+3 dose escalation determined the MTD, defined as the highest dose at which ≤1 of 6 pts had Cycle 1 dose-limiting toxicity (DLT). Pharmacokinetics were assessed on Days 1 and 13. Efficacy was evaluated every 8 weeks. Results: 60 pts were enrolled (females/males [n]: 42/18; median [range] age 56 [25-76] years; ECOG PS [n] 0/1/2: 8/49/3); cancer types [n]: ovarian cancer [15], colorectal cancer [14], breast cancer [11], others [20]) over 16 dose levels ranging from 4 mg to 200 mg QD. Durations of therapy ranged from 6 to 342 days. Three DLTs were observed: prolongation of QTc Gr 3 (88 mg QD), neutropenia/thrombocytopenia Gr 4 (200 mg QD), and LV dysfunction Gr 3 (200 mg QD). Dose-dependent nausea/vomiting was observed and was Gr 2-4 at 200 mg QD. Gr 1/2 photosensitization occurred in 11 subjects across doses from 48 to 200 mg QD but was successfully managed with sun protection and resulted in no dose modifications or discontinuations. On Day 1, mean (range) plasma CBL0137 T_max values were 5.1 (1-10) hrs. Generally linear increases in AUC occurred with increasing CBL0137 dose. Mean (range) t_1/2 values were 25.6 (0.3-166) hrs, with minor dose dependency. Mean (range) Day 13/Day 1 C_trough ratios showed 3.6 (1.7-7.2)-fold accumulations. Disease control was registered in 11 pts who had stable disease (SD). Target lesion regressions up to 21% were documented in 4 patients with breast cancer (2), sarcoma (1), and ovarian cancer (1). Pts with breast cancer (1) and sarcoma (1) had SD for > 36 weeks. Conclusions: The Phase 2 RDR for oral CBL0137 was established as 180 mg QD x 14 days in 28-day cycles based on bone marrow and gastrointestinal DLTs at 200 mg QD. CBL0137 showed a manageable safety profile with efficacy signals. Further study as a component of combinations is planned. Clinical trial information: 847.