Synthesis, Characterization, Interactions, and Immunomodulatory Function of Ectonucleotidase CD39/CD73 Inhibitor 8-Butylthioadenosine 5'-Monophosphate

Ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1, CD39) catalyzes the extracellular hydrolysis of ATP generating AMP, while ecto-5'-nucleotidase (CD73) further hydrolyzes AMP yielding immunosuppressive adenosine. 8-Butylthioadenosine 5'-monophosphate (8-BuS-AMP) was described as a CD39 inhibitor but has been poorly characterized. The standard CD39 antagonist ARL 67156 is not suitable for in vivo studies due to metabolic instability. In the present study, we optimized and upscaled the synthesis of 8-BuS-AMP and performed a comprehensive investigation of its properties. It behaves as a competitive inhibitor at human and mouse CD39, and additionally inhibits CD73. Docking studies using a homology model of human CD39 and determination of an atomic-resolution (1.06 Å) cocrystal structure with human CD73 indicated the inhibitor's interactions within the substrate binding pockets and explained the compound's stability toward hydrolysis. 8-BuS-AMP is metabolically highly stable in human and mouse liver microsomes. It inhibited ε-adenosine formation from ε-ATP and ε-AMP in human synovial fluid and enhanced activation and proliferation of peripheral human T lymphocytes. Thus, 8-BuS-AMP is a recommended tool compound for studying purinergic signaling in vitro and in vivo, being superior to the standard CD39 inhibitor ARL 67156. Moreover, it may serve as a lead structure to develop drugs for the immunotherapy of cancer.

Glycerol-Based Polymer to Improve the Cellular Uptake of Liposomes

Nanomedicines modify the pharmacology of pharmaceutical ingredients, but most require cell internalization to deliver their payloads. Hence, modifying the surface properties of nanomedicines can improve their interactions with cells and modulate their pharmacology. Herein, we devised a polymer that increases how nanomedicines are internalized by cells. The alkylated poly(monoglycerol acrylate) (PMGA) polymer was synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization with a terminal double 18-carbon moiety that allows its anchoring on the surface of liposomes. PMGA-decorated liposomes are internalized more efficiently in immune cells, compared to formulations without the polymer. Using inhibitors of internalization pathways, we established that PMGA promotes cell entry by the fast endophilin-mediated endocytosis (FEME). In comparison, noncoated control liposomes were mostly internalized by clathrin-mediated endocytosis. This work highlights the potential of PMGA to increase the internalization of nanomedicines by immune cells, and target a novel internalization pathway.