Transition-state analogs of human purine nucleoside phosphorylase (PNP) bind with picomolar (pM) dissociation constants. The PNP-inhibitor re-equilibration rates (t1/2 for activity regain) vary from 5 to 24 min for seven Immucillins with dissociation constants of 161 to 2 pM. In vitro t1/2 off-rates for DADMe-Immucillin-H by competitive exchange are ~80 min. Treatment of human erythrocytes with DADMe-Immucillin-H, a 19 pM inhibitor, causes rapid inhibition of cellular PNP. Loss of [14C]DADMe-Immucillin-H from erythrocytes during multiple washes is slow, to give a t1/2 of ~100 hr. When the loss of [14C]DADMe-Immucillin-H from erythrocytes is measured in the presence of excess unlabeled DADMe-Immucillin-H, the loss rate increased to a t1/2 of ~80 min, the intrinsic rate. Human volunteers treated with a single oral dose of DADMe-Immucillin-H exhibit complete PNP inhibition and require 59 days to regain 50% of blood PNP activity, corresponding to the erythropoiesis rate. Picomolar transition-state analogues exhibit long lifetimes on their targets in cells because of a high probability of target-recapture relative to loss to the extracellular space.

In vitro and in vivo target life for immucillin transition-state analogs

2019 Spring National Meeting

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