537MO First-in-human study of JNJ-64619178, a protein arginine methyltransferase 5 (PRMT5) inhibitor, in patients with advanced cancers

PRMT5 regulates proteins important for tumorigenesis via symmetric arginine dimethylation (SDMA). JNJ64619178 is an oral, potent and selective PRMT5 inhibitor that demonstrates efficacy in multiple tumor models. Here, we present a phase I study of JNJ64619178 in adults with advanced solid tumors and non-Hodgkin lymphoma (Part 1). Dose escalation was supported by a modified continual reassessment method. Patients (pts) received JNJ64619178 either intermittently (14 days on/7 days off) or once daily (QD) on a 21-day cycle. Safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy were evaluated to identify the recommended phase II doses (RP2D). Fifty-four pts were enrolled as of 17 Mar 2020. The most common tumor types were adenoid cystic carcinoma (ACC; 20%), prostate cancer (15%), and uveal melanoma (13%). Median age was 59 (range 28-82), and median number of prior systemic therapies was 3 (range 0-11). Dosing ranged from 0.5 mg to 4 mg intermittently, and from 1 mg to 2 mg QD. Median treatment duration was 1.5 mo (range 0.4-22.4). The only dose-limiting toxicity observed was thrombocytopenia, at 3 and 4 mg intermittently and 2 mg QD. Fifty-one pts (91%) experienced treatment-related adverse events (TRAE), the most common being thrombocytopenia (52%), anemia (41%), nausea (39%), fatigue (32%), dysgeusia (30%), asthenia (24%), and diarrhea (20%). Grade 3/4 TRAEs in >1 pt were thrombocytopenia (20%), anemia (17%), and neutropenia (6%). Thirty pts (56%) had dose interruptions or reductions due to AE. JNJ64619178 plasma Cmax and AUC were linearly dose-proportional. Robust target engagement, as measured by plasma SDMA, was achieved even with intermittent dosing. A confirmed partial response (RECIST) was observed in ACC, and 7 pts (13%) with ACC, prostate cancer, salivary gland carcinomas, and other tumor types had stable disease >6 mo. Two provisional RP2Ds were selected: 1.5 mg intermittently and 1 mg QD. JNJ64619178 demonstrated manageable toxicity and preliminary evidence of antitumor activity at selected dose levels. Intermittent dosing maintains target inhibition. Assessment of two provisional RP2Ds is ongoing.