First-in-human study of HMPL-295, an ERK1/2 inhibitor, in patients with advanced solid tumors: Dose-escalation results of monotherapy.

e15112 Background: HMPL-295 (’295) is an extracellular signal-regulated kinase 1 and 2 (ERK1/2) inhibitor with potent activity in non-clinical studies. This is a first-in-human, dose escalation study of ’295 in patients (pts) with advanced solid tumors. Here, we report the results of the mono dose escalation stage. Methods: Pts with advanced solid tumors who have failed standard therapy were enrolled to receive ’295 once daily (QD) in 28-day cycles or ’295 QD 2 weeks on/1 week off (2w on/1w off) in 21-day cycles. The mTPI-2 design was used for dose escalation, having explored from 5 to 75 mg QD in 6 cohorts, as well as 75 mg and 100 mg QD 2w on/1w off. The study aims to determine the maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D), safety, tolerability, pharmacokinetics/pharmacodynamics (PK/PD), and preliminary efficacy (best of response, BOR). Results: As of Dec 11, 2023, 47 pts with advanced solid tumors were enrolled (n=1, 1, 3, 6, 12, 5, 13, 6 in 5, 10, 20, 40, 50, 75 mg QD cohorts, 75, 100 mg QD 2w on/1w off cohorts, respectively), with a median age of 58 years, 23 (48.9%) male pts. During the dose escalation from 5 to 75 mg QD cohort, 1 pt given 40 mg QD experienced a dose-limiting toxicity (DLT) of grade 3 dermatitis acneiform and 2 pts given 75 mg QD experienced DLTs of grade 3 rash and acute kidney injury (AKI). As for intermittent-administration cohorts, 2 pts given 100 mg QD 2w on/1w off experienced DLTs of grade 3 AKI and rash maculo-papular. After multiple-dose oral administration, ’295 plasma concentrations reach peak at 1.0-2.0 hours post dose and the exposure (C max and AUC) displayed dose dependent increase. The accumulation ratio (AUC) was 2.1–3.4 after repeat dosing, reaching steady-state around day 15. ’295 inhibited ribosomal S6 kinase (RSK) phosphorylation which is a downstream signaling molecule regulated by ERK1/2 and stimulated by phorbol 12-myristate 13-acetate (PMA). The BOR was partial response each in 1 pt with duodenal adenocarcinoma in 40 mg QD cohort,1 pt with endometrial cancer in 50 mg QD cohort and 1 pt with non-small cell lung cancer (NSCLC) in 75 mg QD 2w on/1w off cohort. Stable disease with tumor shrinkage was also observed in 2 pts with NSCLC on 50 mg QD and 75 mg QD 2w on/1w off cohort respectively, and 1 pt with pancreatic ductal adenocarcinoma in 100 mg QD 2w on/1w off cohort. 25 (53.2%) pts reported grade ≥3 TEAEs. The most common (≥10.0%) ≥ grade 3 TEAEs were rash (10.6%) and anemia (10.6%). Conclusions: Considering safety, tolerability, PK/PD and preliminary efficacy results, RP2D was determined to be 50 mg QD. Clinical trial information: NCT04908046 .