e15106 Background: Extracellular adenosine suppresses immune cells’ function through binding to its receptor A2aR. In the tumor microenvironment, adenosine concentration could be several hundred-fold higher than in blood. DZD2269 was designed to fully block A2aR in a wide range of adenosine concentrations. In preclinical studies, DZD2269 could most effectively restore immune cell function inhibited by high levels of adenosine among A2aR antagonists currently in clinical studies. In mouse syngeneic prostate cancer model, DZD2269 could significantly enhance the antitumor activity of anti-PD1 antibody as well as radiotherapy. Two ongoing clinical studies of DZD2269 in healthy volunteers (PAN-GU 2, NCT04932005) and patients with metastatic castration resistant prostate cancer (PAN-GU 1, NCT04634344) are being conducted to characterize its safety, PK, PD and to assess its preliminary anti-tumor efficacy. Here, we report clinical data from the PAN-GU 2 study. Methods: The phase 1 healthy volunteer study is a double-blind, placebo-controlled study to evaluate safety, PK, and effect on biomarkers. It consists of three parts: single ascending dose (SAD): 5, 10, 20, 40, 80 and 160 mg; multiple ascending dose (MAD): from 10 mg BID for 7 consecutive days; and food effect (FE): fasted, low-fat or high-fat meal condition. A2aR pathway blockade by DZD2269 is evaluated by analyzing pCREB inhibition on whole blood T cells following ex vivo stimulation with 10 µM NECA. Results: In SAD part of the healthy volunteer study, a total of 48 subjects received a single oral dose of DZD2269 (n = 36) from 5 mg to 160 mg or placebo (n = 12). There were 7 TEAEs reported by 4 subjects and no ≥ grade 3 TEAE or SAE. After a single oral dose, the rate of absorption of DZD2269 was moderate (median tmax: 1.0 to 2.75 hr). DZD2269 exhibited low to moderate clearance (averaged value: 16.1 to 45.3 L/h) and extensive volume of distribution (averaged value: 209 to 738 L), resulting in a mean t1/2 of 7 ̃ 10 hr; a trend of increased t1/2 was observed at higher dose levels. Systemic exposure of DZD2269 (AUC and Cmax) increased in an approximately dose-dependent manner. Based on PK/PD analysis, approximately 90% pCREB inhibition could be achieved by a single dose of 80mg for 24 hours. Conclusions: Single oral dose of DZD2269 ranging from 5 mg to 160 mg was safe and well tolerated. Good PK/PD correlation was demonstrated in the study. DZD2269 could effectively reverse high adenosine induced immunosuppression. A phase1/2 study evaluating safety and efficacy of DZD2269 in patients is ongoing. Clinical trial information: NCT04932005.