Randomized Phase II Trial of the Cyclin-Dependent Kinase Inhibitor Dinaciclib (MK-7965) Versus Capecitabine in Patients With Advanced Breast Cancer

Introduction Effective therapies after failure of treatment with anthracyclines and taxanes are needed for patients with metastatic breast cancer. Dinaciclib (MK-7965, formerly SCH727965), a small-molecule cyclin-dependent kinase inhibitor, has demonstrated antitumor activity in phase I studies with solid-tumor patients. This phase II trial was designed to assess the efficacy and safety of dinaciclib compared with that of capecitabine in women with previously treated advanced breast cancer. Patients and Methods Patients were randomized to receive either dinaciclib at 50 mg/m 2 , administered as a 2-hour infusion every 21 days, or 1250 mg/m 2 capecitabine, administered orally twice daily in 21-day cycles. Results An unplanned interim analysis showed that the time to disease progression was inferior with dinaciclib treatment compared with capecitabine treatment; therefore, the trial was stopped after 30 patients were randomized. Dinaciclib treatment demonstrated antitumor activity in 2 of 7 patients with estrogen receptor–positive and human epidermal growth factor receptor 2–negative metastatic breast cancer (1 confirmed and 1 unconfirmed partial response), as well as acceptable safety and tolerability. Grade 3 or 4 treatment-related adverse events were common and included neutropenia, leukopenia, increase in aspartate aminotransferase, and febrile neutropenia. Population pharmacokinetic model–predicted mean dinaciclib exposure (area under the concentration-time curve extrapolated to infinity [AUC [I] ]) at 50 mg/m 2 was similar to that observed in a previous phase I trial, and no drug accumulation was observed after multiple-dose administration. Conclusion Although dinaciclib monotherapy demonstrated some antitumor activity and was generally tolerated, efficacy was not superior to capecitabine. Future studies may be considered to evaluate dinaciclib in select patient populations with metastatic breast cancer and in combination with other agents.