An open label, multicenter, phase II study of KRT-232, an oral small molecule inhibitor of MDM2, for the treatment of patients with Merkel cell carcinoma (MCC) who have failed treatment with anti-PD-1/L1 immunotherapy.

Abstract

TPS9602 Background: Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer with a poor prognosis in patients with advanced disease, with mortality as high as 46%. An oncogenic Merkel cell polyomavirus (MCPyV) is present in about 80% of MCC tumors, which inactivates tumor suppressors p53 and RB. Virus-positive MCC has proven to be an immunologically responsive disease and the recently approved PD-L1 inhibitor avelumab (March 2017) has improved the prognosis of patients with advanced MCC. However, despite the addition of immune checkpoint inhibitors to the treatment paradigm, a lack of response or disease progression occurs in up to two-thirds of avelumab patients previously treated with chemotherapy, and 32-44% of first-line patients treated with the PD-1 inhibitors nivolumab or pembrolizumab. KRT-232 is a potent and selective small molecule targeted drug that binds to murine double minute chromosome 2 (MDM2) and inhibits the MDM2/tumor protein 53 (p53) protein-protein interaction. Inactivating mutations in p53 have rarely been found in MCC, and the majority of MCCs with the presence of MCPyV express p53WT. The purpose of this study is to evaluate the tolerability and efficacy of KRT-232 in p53WT MCC patients who have been treated with anti-PD-1/L1 immunotherapy. Methods: The primary objective is ORR by RECIST v1.1 after 2 cycles (42 days) as determined by independent review. A Simon two-stage design is employed. In Stage 1, up to 13 eligible patients will be enrolled and treated with 240 mg KRT-232 once daily (QD) on Days 1-7 of a 21-day cycle. If the predesignated efficacy threshold is reached in Stage 1, enrollment for Stage 2 will include an additional 14 patients (for a total of 27 patients). The study is enrolling in the U.S. Clinical trial information: NCT03787602.