Comparative Pharmacology of a Bis-Pivaloyloxymethyl Phosphonate Prodrug Inhibitor of Enolase after Oral and Parenteral Administration

Metabolically labile prodrugs can experience stark differences
in catabolism incurred by the chosen route of administration. This
is especially true for phosph­(on)­ate prodrugs, in which successive
promoiety removal transforms a lipophilic molecule into increasingly
polar compounds. We previously described a phosphonate inhibitor of
enolase (HEX) and its bis-pivaloyloxymethyl ester prodrug (POMHEX)
capable of eliciting strong tumor regression in a murine model of
enolase 1 (ENO1)-deleted glioblastoma following parenteral
administration. Here, we characterize the pharmacokinetics and pharmacodynamics
of these enolase inhibitors in vitro and in vivo after oral and parenteral administration. In support
of the historical function of lipophilic prodrugs, the bis-POM prodrug
significantly improves cell permeability of and rapid hydrolysis to
the parent phosphonate, resulting in rapid intracellular loading of
peripheral blood mononuclear cells in vitro and in vivo. We observe the influence of intracellular trapping in vivo on divergent pharmacokinetic profiles of POMHEX
and its metabolites after oral and parenteral administration. This
is a clear demonstration of the tissue reservoir effect hypothesized
to explain phosph­(on)­ate prodrug pharmacokinetics but has heretofore
not been explicitly demonstrated.