2-(Phosphonomethyl)-pentanedioic
acid (2-PMPA) is a potent (IC50 = 300 pM) and selective
inhibitor of glutamate carboxypeptidase
II (GCPII) with efficacy in multiple neurological and psychiatric
disease preclinical models and more recently in models of inflammatory
bowel disease (IBD) and cancer. 2-PMPA (1), however,
has not been clinically developed due to its poor oral bioavailability
(<1%) imparted by its four acidic functionalities (c Log P = −1.14). In an attempt
to improve the oral bioavailability of 2-PMPA, we explored a prodrug
approach using (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (ODOL), an FDA-approved
promoiety, and systematically masked two (2), three (3), or all four (4) of its acidic groups. The
prodrugs were evaluated for in vitro stability and in vivo pharmacokinetics
in mice and dog. Prodrugs 2, 3, and 4 were found to be moderately stable at pH 7.4 in phosphate-buffered
saline (57, 63, and 54% remaining at 1 h, respectively), but rapidly
hydrolyzed in plasma and liver microsomes, across species. In vivo,
in a single time-point screening study in mice, 10 mg/kg 2-PMPA equivalent
doses of 2, 3, and 4 delivered
significantly higher 2-PMPA plasma concentrations (3.65 ± 0.37,
3.56 ± 0.46, and 17.3 ± 5.03 nmol/mL, respectively) versus
2-PMPA (0.25 ± 0.02 nmol/mL). Given that prodrug 4 delivered the highest 2-PMPA levels, we next evaluated it in an
extended time-course pharmacokinetic study in mice. 4 demonstrated an 80-fold enhancement in exposure versus oral 2-PMPA
(AUC0–t
: 52.1 ± 5.9 versus
0.65 ± 0.13 h*nmol/mL) with a calculated absolute oral bioavailability
of 50%. In mouse brain, 4 showed similar exposures to
that achieved with the IV route (1.2 ± 0.2 versus 1.6 ±
0.2 h*nmol/g). Further, in dogs, relative to orally administered 2-PMPA, 4 delivered a 44-fold enhanced 2-PMPA plasma exposure (AUC0–t
for 4: 62.6 h*nmol/mL
versus AUC0–t
for 2-PMPA: 1.44
h*nmol/mL). These results suggest that ODOL promoieties can serve
as a promising strategy for enhancing the oral bioavailability of
multiply charged compounds, such as 2-PMPA, and enable its clinical
translation.