A phase I delayed-start, randomized and pharmacodynamic study of metformin and chemotherapy in patients with solid tumors

Purpose Metformin activates AMP-related pathways leading to inactivation of mammalian target of rapamycin (mTOR) and suppression of its downstream effectors, crucial for cancer growth. Epidemiologic studies showed a reduced incidence and improved survival in cancer patients. We conducted a prospective phase I study to assess the safety of metformin in combination with chemotherapy in patients with solid tumors. Methods We conducted a delayed-start randomized trial of non-diabetic patients in two stages. In Stage 1, we randomized patients to two arms: concurrent arm (metformin with chemo) vs. delayed arm (chemo alone). In Stage 2, patients in delayed arm were crossed over to receive metformin. Patients received metformin 500 mg twice daily with chemotherapy to define dose-limiting toxicities (DLTs) in both stages. Secondary endpoints assessed adverse events (AEs) and response rates. Translational correlates included effects of metformin on expression and phosphorylation of 5' adenosine monophosphate-activated protein kinase (AMPK) by western blot in PBMCs. Results A total of 100 patients were enrolled (51 in delayed arm vs. 49 concurrent arm). Rate of DLTs in patients receiving metformin with chemotherapy was 6.1% vs. 7.8% in patients receiving chemotherapy alone. DLTs seen with addition of metformin included those associated with established chemo adverse events. No lactic acidosis or hypoglycemia occurred. Restaging showed stable disease in 46% at cessation of metformin. 28% of patients with measurable tumor markers showed improvement. AMPK phosphorylation showed a four- to sixfold increase in AMPK phosphorylation after metformin. Conclusions This is the largest phase I study of metformin combined with chemotherapy, which suggests that metformin can be given safely with chemotherapy, and offers a platform for future studies. Post-metformin increase in AMPK phosphorylation may potentially explain lack of disease progression in nearly half of our patients.