Background: Protein kinase C iota (PKCi) is overexpressed in non-small cell lung (NSCLC), ovarian and pancreatic cancers and promotes tumorigenesis. The gold compound aurothiomalate (ATM) inhibits downstream activation of Rac1 by PKCi. We sought to determine the maximum tolerated dose (MTD) of ATM. Methods: We conducted a phase I dose escalation trial of ATM in patients with NSCLC, ovarian or pancreatic cancer. In the dose escalation cohort patients received ATM IM weekly for three cycles (cycle duration 4 weeks) at 25 mg, 50 mg or 75 mg in a 3+3 design. The dose was not escalated for individual patients. Up to 9 subjects were allowed to enroll in the expansion cohort at the MTD. Blood samples were analyzed for elemental gold levels. Patients were evaluated for response every eight weeks with computed tomography using modified response evaluation criteria in solid tumors. Results: Fifteen patients, all pretreated, enrolled in this study. There were ten patients with NSCLC, four with ovarian cancer and one with pancreatic cancer. Six patients were treated at the 25 mg dose, 6 patients at 50 mg, and 2 at 75 mg. There was 1 dose limiting toxicity (DLT) at 25 mg (hypokalemia), 1 DLT at 50 mg (urinary tract infection), and none at 75 mg. There were 3 grade 3 hematologic toxicities in the dose escalation cohort. The recommended MTD of ATM is 50 mg, and 1 subject was treated in the expansion cohort at 50 mg. Patients received treatment for a median of 2 cycles (range 1-3). The best response observed was stable disease in 2 subjects. There appeared to be a dose-related accumulation of steady-state plasma concentrations of gold with concentrations exceeding 20 µM after one month of therapy with 75 mg of ATM and after 2 months of therapy with 50 mg of ATM, consistent with linear pharmacokinetics. Conclusions: In summary, this phase I study was successful in identifying ATM 50 mg IM weekly as the MTD. In this heavily pre-treated group of patients in who we observed at best stable disease, it remains unclear whether future investigations that target PKCi should focus on single agent ATM, combination therapy with ATM, or other PKCi inhibitors that are currently in development. Clinical trial information: NCT00575393.