TRPM2 (
transient receptor potential cation channel, subfamily M, member 2) is a nonselective
cation channel involved in the response to oxidative stress and in
inflammation. Its role in autoimmune and
neurodegenerative diseases makes it an attractive pharmacological target. Binding of the
nucleotide adenosine 5'-diphosphate
ribose (ADPR) to the cytosolic
NUDT9 homology (
NUDT9 H) domain activates the channel. A detailed understanding of how ADPR interacts with the TRPM2
ligand binding domain is lacking, hampering the rational design of modulators, but the terminal
ribose of ADPR is known to be essential for activation. To study its role in more detail, we designed synthetic routes to novel analogues of ADPR and 2'-deoxy-ADPR that were modified only by removal of a single
hydroxyl group from the terminal
ribose. The ADPR analogues were obtained by coupling
nucleoside phosphorimidazolides to deoxysugar
phosphates. The corresponding C2″-based analogues proved to be unstable. The C1″- and C3″-ADPR analogues were evaluated electrophysiologically by patch-clamp in TRPM2-expressing HEK293 cells. In addition, a compound with all
hydroxyl groups of the terminal
ribose blocked as its 1″-β- O-methyl-2″,3″- O-
isopropylidene derivative was evaluated. Removal of either C1″ or C3″
hydroxyl groups from ADPR resulted in loss of agonist activity. Both these modifications and blocking all three
hydroxyl groups resulted in TRPM2 antagonists. Our results demonstrate the critical role of these
hydroxyl groups in channel activation.