Phase 1 study of MK-4166, an anti-human glucocorticoid-induced tumor necrosis factor receptor (GITR) antibody, as monotherapy or with pembrolizumab (pembro) in patients (pts) with advanced solid tumors.

Abstract

9509 Background: Ligation of GITR on immune cells decreases Treg-mediated suppression and enhances T cell proliferation. MK-4166 is a humanized IgG1 agonist monoclonal antibody targeting GITR. Data from the first-in-human phase 1 study (NCT02132754) of MK-4166 as monotherapy (mono) or in combination with pembro (combo) are presented. Methods: MK-4166 was tested alone (0.0015 mg IV-900 mg Q3W ×4 doses) or with pembro (fixed dose 200 mg IV Q3W up to 35 doses) in the absence of toxicity or progression. Study included a dose escalation/confirmation cohort (metastatic solid tumors) and an expansion cohort (treatment-naive and pretreated melanoma). A T cell–inflamed gene expression profile (GEP) was assessed using RNA from baseline tumor samples. End points – primary: safety/tolerability, maximum tolerated dose (MTD) of MK-4166; secondary: pharmacokinetics (PK), pharmacodynamics (PD); exploratory: objective response rate (ORR) per irRECIST1.1. Results: Of 113 pts, 48 received mono and 65 combo; 20 were in the melanoma expansion. Common AEs ( > 20%) were fatigue, infusion-related reaction, nausea, abdominal pain, and pruritus; 43 pts had grade ≥3 AEs (38.1%); 6 (5.3%) were treatment-related. One dose-limiting toxicity (bladder perforation in a urothelial pt with a neobladder) possibly related to study drug was observed with mono. MTD was not reached. No treatment-related deaths were observed. MK-4166 PK/PD showed target-mediated drug disposition concomitant with decreased GITR availability on T cells in blood with increasing doses. Four objective responses (4/45; ORR, 9%) were seen with combo in dose escalation. For ICI-naive melanoma pts (n = 13) in expansion, ORR was 69% (95% CI, 38-91), including 4 CRs and 5 PRs. No response was observed in 7 pts previously treated with ICI. High ORRs were observed in noninflamed and inflamed ICI-naive melanoma pts. Conclusions: MK-4166 at a dose up to 900 mg as monotherapy and in combination with pembro was well tolerated, with dose-related evidence of target engagement. Responses were observed with MK-4166 900 mg plus pembro, particularly in pts with melanoma naive to ICIs. Clinical trial information: NCT02132754.