Pharmacokinetics and Macrophage Inhibitory Cytokine-1 Pharmacodynamics of the Murine Double Minute 2 Inhibitor, Navtemadlin (KRT-232) in Fed and Fasted Healthy Subjects

A Population Pharmacokinetic-Pharmacodynamic Model of Navtemadlin, its Major Active Metabolite (M1) and Serum Macrophage Inhibitory Cykokine-1 (MIC-1)

Navtemadlin is a potent, selective, orally available inhibitor of murine double minute 2 that restores p53 activity to induce apoptosis in TP53 wild-type malignancies. Using richly sampled pharmacokinetic (PK) and pharmacodynamic (PD) data from healthy volunteers, a population PK/PD model was developed. A population PK (PPK) model described the PK characteristics of navtemadlin and its major metabolite acyl glucuronide (M1) and quantified enterohepatic recirculation (EHR). Post hoc individual PK parameters from this model were coupled with PD data for serum macrophage inhibitory cytokine-1 (MIC-1, GDF15), a cytokine biomarker of p53 activation, to construct a population PK/PD model that described plasma concentration-driven MIC-1 excursions and enabled simulation of the extent and duration of navtemadlin PD effects. The median apparent clearance (CL/F) and apparent central volume (V2/F) of navtemadlin were 36.4 L/hr and 159 L. The typical maximum stimulatory effect (S_max) was close to the median maximum MIC-1 ratio to baseline of 7.29 in observed data. Simulation revealed a dose-dependent increase of MIC-1 with steady state attained in approximately 7 days, in a 7-day-on/21-day-off dose regimen. Elevated MIC-1 concentrations persist through 17-19 days, leaving about 9-11 PD-free days in a 28-day cycle.

Milademetan is a highly potent MDM2 inhibitor in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine carcinoma of the skin with 2 etiologies. Merkel cell polyomavirus (MCPyV) integration is present in about 80% of all MCC. Virus-positive MCC (MCCP) tumors have few somatic mutations and usually express WT p53 (TP53). By contrast, virus-negative MCC (MCCN) tumors present with a high tumor mutational burden and predominantly UV mutational signature. MCCN tumors typically contain mutated TP53. MCCP tumors express 2 viral proteins: MCPyV small T antigen and a truncated form of large T antigen. MCPyV ST specifically activates expression of MDM2, an E3 ubiquitin ligase of p53, to inhibit p53-mediated tumor suppression. In this study, we assessed the efficacy of milademetan, a potent, selective, and orally available MDM2 inhibitor in several MCC models. Milademetan reduced cell viability of WT p53 MCC cell lines and triggered a rapid and sustained p53 response. Milademetan showed a dose-dependent inhibition of tumor growth in MKL-1 xenograft and patient-derived xenograft models. Here, along with preclinical data for the efficacy of milademetan in WT p53 MCC tumors, we report several in vitro and in vivo models useful for future MCC studies.