Potent Competitive Inhibitors of Ecto-5′-nucleotidase (CD73) based on 6-(Het)aryl-7-deazapurine Ribonucleoside 5′- <i>O</i> -Bisphosphonates

CD73 generates immunosuppressive adenosine in the tumor microenvironment and is a promising target for cancer immunotherapy. We have designed and systematically studied diverse 2-substituted 7-deazapurine ribonucleoside 5'-<i>O</i>-bisphosphonates bearing a variety of (het)-aryl groups at position 6 and discovered their highly potent and selective CD73 inhibition activity. The most active compounds (with single-digit picomolar <i>K</i> _i) contained bicyclic (het)-aryl groups at position 6 in combination with chlorine at position 2. Further optimization of pharmacokinetic properties identified inhibitors with low clearance, long half-life, high solubility, and excellent selectivity over CD39 and NTPDase3. They effectively suppressed adenosine formation in MDA-MB-231 cells, rescued CD8⁺ T cell activation, and were nontoxic to human fibroblasts. Overall, their profile compares favorably with <b>AB680</b>, a CD73 inhibitor currently in phase I/II clinical trials.