ARC-8: Phase I/Ib study to evaluate safety and tolerability of AB680 + chemotherapy + zimberelimab (AB122) in patients with treatment-naive metastatic pancreatic adenocarcinoma (mPDAC).
Authors: Manji Gulam Abbas , Wainberg Zev A. , Krishnan Kartik , Giafis Nick , Udyavar Akshata , Quah Cheng Seok , Scott Jennifer , Berry Wade , DiRenzo Daniel , Gerrick Kimberline , Jin Lixia , Bendell Johanna C. 
Published: January 2021

404 Background: AB680, a potent, selective small-molecule inhibitor of soluble and membrane-bound CD73, targets a major pathway of extracellular adenosine production with the aim of eliminating adenosine-mediated immunosuppression within the tumor microenvironment. In mPDAC, programmed cell death protein-1 (PD-1) axis inhibitors have limited clinical activity as monotherapies or combined with standard-of-care (SOC) chemotherapy. KRAS mutations, present in >90% of invasive PDACs, are associated with significantly elevated CD73 expression and poor clinical outcomes. Thus, mPDAC may be particularly sensitive to CD73 inhibition combined with SOC chemotherapy + anti–PD-1 antibody (zimberelimab [Zim]) treatment. Methods: ARC-8 (NCT04104672) is an ongoing phase 1b, dose escalation and expansion study in patients (pts) with treatment-naive mPDAC. In the dose escalation, AB680 (25, 50, 75, or 100 mg) is administered intravenously once every 2 weeks (Q2W) with standard doses of nab-paclitaxel/gemcitabine (NP/Gem) + Zim (240 mg) in a 3+3 design to determine the recommended dose for expansion (RDE). In the dose expansion, AB680 will be administered at the RDE with NP/Gem + Zim. Adverse events (AEs) and dose-limiting toxicities (DLTs) are recorded and graded per NCI CTCAE 5.0. AB680 pharmacokinetics, pharmacodynamics, and biomarker evaluations are also being performed throughout the study. Clinical activity is assessed every 8 weeks per RECIST v1.1. Results: As of 04SEPT2020, enrolled patients include 4 in Cohort 1 (25 mg AB680), 6 in Cohort 2 (50 mg AB680), and 3 in Cohort 3 (75 mg AB680). Initial AE profiles were similar to those observed for NP/Gem. The most common treatment-related AEs were fatigue (n=6, 43%), anemia (n=4, 29%), and neutrophil count decrease (n=4, 29%); anemia (n=2, 14%) was the most common treatment-related grade 3/4 AE. Initial pharmacodynamic data (50 mg dose) indicated excellent peripheral target coverage at AB680 trough concentrations. Best overall responses for 9 evaluable pts were 3 with partial response (1 in Cohort 1; 2 in Cohort 2), including a complete response of a target lesion, and 5 with stable disease (1 in Cohort 1; 4 in Cohort 2). One pt in Cohort 1 discontinued the study due to progressive disease. As of the cutoff date, 1 DLT (Grade 2 autoimmune hepatitis) occurred in Cohort 2; the event completely resolved with steroids and the pt was able to resume study treatment. No DLTs were reported in Cohort 3. Conclusions: Preliminary results from ARC-8 indicate that AB680, the first clinical-stage small-molecule CD73 inhibitor, in combination with SOC chemotherapy + Zim has a manageable safety profile consistent with that expected for each agent alone and demonstrates early signals of clinical activity. Dose escalation to 100 mg AB680 (Cohort 4) is ongoing to inform RDE selection. Clinical trial information: NCT04104672.