The goal of this study was to determine safety, tolerability and pharmacokinetics of 2ME2 in patients with solid tumors and determine maximum tolerated dose (MTD). The following hypotheses were tested: 1) 2ME2 will be well tolerated in clinic when given orally and will have quantifiable effects on the ex vivo markers of angiogenesis and apoptosis; 2) 2ME2 will exhibit linear pharmacokinetics; 3) Plasma protein binding will be extensive and linear; 4) Sulfation will be the major metabolic pathway for 2ME2.This was a phase I dose escalation study. Twenty patients with refractory solid tumors were enrolled. 2ME2 was administered orally starting at 400 mg bid with dose escalation upto 3000 mg bid. Pharmacokinetic sampling was done up to 50 hours after single oral dose for characterization of pharmacokinetics and plasma drug concentrations which were determined by liquid chromatography tandem mass-spectrometry [LC/MS/MS, LOQ: 1ng/mL]. Circulating plasma concentrations were very low at all dose levels with high interindividual pharmacokinetic variability. Median plasma half-life was about 1-2 days. The unphysiologically high oral CL/F and Vd/F reflect low oral bioavailability of 2ME2. There was no dose proportional increase in Cmax or AUClast. There were no dose limiting toxicities at highest dose level, therefore MTD was not defined. The trial was closed due to extremely low plasma concentrations of 2ME2 achieved. Hepatic in vitro metabolism studies showed that 2ME2 was metabolized by CYP 450 enzymes (CYP 1A1, 1A2, 3A4, 3A5 and 2E1) to four major metabolites. Hepatic phase II metabolism studies revealed two major glucuronide metabolites of 2ME2. Sulfation did not play a major role in metabolism of 2ME2. Total in-vivo hepatic clearance was estimated as 862 mL/min, primarily due to glucuronidation. Less than 0.01 % of total administered dose of 2ME2 was excreted unchanged in urine, and about 1% was excreted as glucuronides. Plasma protein binding of 2ME2 was studied using equilibrium dialysis. Mean unbound fraction of 2ME2 (fu) in plasma of patients and healthy human volunteers was 0.019 ± 0.0043 and 0.027 ± 0.0019 respectively. Binding was concentration-independent and unaffected by presence of 2-methoxyestrone. 2ME2 binds to albumin, a1-acid glycoprotein (AAG) and sex-hormone binding globulin (SHBG).