2‑Substituted α,β-Methylene-ADP Derivatives: Potent Competitive Ecto-5′-nucleotidase (CD73) Inhibitors with Variable Binding Modes

CD73 inhibitors are promising drugs
for the (immuno)­therapy of
cancer. Here, we present the synthesis, structure–activity
relationships, and cocrystal structures of novel derivatives of the
competitive CD73 inhibitor α,β-methylene-ADP (AOPCP) substituted
in the 2-position. Small polar or lipophilic residues increased potency,
2-iodo- and 2-chloro-adenosine-5′-O-[(phosphonomethyl)­phosphonic
acid] (15, 16) being the most potent inhibitors
with Ki values toward human CD73 of 3–6
nM. Subject to the size and nature of the 2-substituent, variable
binding modes were observed by X-ray crystallography. Depending on
the binding mode, large species differences were found, e.g., 2-piperazinyl-AOPCP
(21) was >12-fold less potent against rat CD73 compared
to human CD73. This study shows that high CD73 inhibitory potency
can be achieved by simply introducing a small substituent into the
2-position of AOPCP without the necessity of additional bulky N6-substituents. Moreover, it provides valuable
insights into the binding modes of competitive CD73 inhibitors, representing
an excellent basis for drug development.