Small-molecule CD73 inhibitors for the immunotherapy of cancer: a patent and literature review (2017-present).

INTRODUCTION: Hydrolysis of AMP to adenosine and inorganic phosphate is catalyzed by 5´-ectonucleotidase, e5NT, alias CD73, a metalloenzyme incorporating two zinc ions at its active site. e5NT is involved in crucial physiological and pathological processes, such as immune ho meostasis, inflammation, and tumor progression. CD73 inhibitors belonging to the monoclonal antibodies (MAbs) and small molecules started to be considered as candidates for the immunotherapy of tumors. AREAS COVERED: We review the drug design landscape in the scientific and patent literature on CD73 inhibitors from 2017 to the present. Small-molecule inhibitors were mostly discussed, although the MAbs are also considered. EXPERT OPINION: Considerable advances have been reported in the design of nucleotide/nucleoside-based CD73 inhibitors, after the X-ray crystal structure of the enzyme in complex with the non-hydrolyzable ADP analog, adenosine (α,β)-methylene diphosphate (AMPCP), was reported. A large number of highly effective such inhibitors are now available, through modifications of the nucleobase, sugar and zinc-binding groups of the lead. Few classes of non-nucleotide inhibitors were also reported, including flavones, anthraquinone ssulfonates, and primary sulfonamides. A highly potent ssmall-molecule CD73 inhibitor, AB680, is presently in the early phase of clinical trials as immunotherapeutic agents against various types of cancer.