Definition

An orally bioavailable inhibitor of the ectoenzyme CD73 (cluster of differentiation 73; 5′-ecto-nucleotidase; 5′-NT; ecto-5′-nucleotidase), with potential immunomodulating and antineoplastic activities. Upon oral administration, CD73 inhibitor ORIC-533 targets and binds to CD73, leading to clustering of and internalization of CD73. This prevents CD73-mediated conversion of adenosine monophosphate (AMP) to adenosine and decreases the amount of free adenosine in the tumor microenvironment (TME). This prevents adenosine-mediated lymphocyte suppression and increases the activity of CD8-positive effector cells and natural killer (NK) cells. This also activates macrophages and reduces the activity of myeloid-derived suppressor cells (MDSCs) and regulatory T lymphocytes (Tregs). By abrogating the inhibitory effect on the immune system and enhancing the cytotoxic T-cell-mediated immune response against tumor cells, tumor cell growth decreases. In addition, clustering and internalization of CD73 decreases the migration of cancer cells and prevents metastasis. CD73, a plasma membrane protein belonging to the 5′-nucleotidase (NTase) family, catalyzes the conversion of extracellular nucleotides, such as AMP, to membrane-permeable nucleosides, such as adenosine. It is upregulated in a variety of cancer cell types and plays a key role in adenosine-mediated immunosuppression within the TME.