Enhanced Oral Bioavailability of 2-(Phosphonomethyl)-pentanedioic Acid (2-PMPA) from its (5-Methyl-2-oxo-1,3-dioxol-4-yl)methyl (ODOL)-Based Prodrugs

Abstract

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 (AUC_0-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 (AUC_0-t for 4: 62.6 h*nmol/mL versus AUC_0-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.

Keywords: 2-PMPA; glutamate carboxypeptidase II; oral bioavailability; pharmacokinetics; prodrugs.

Scheme 1.

Reagents and Conditions: (i) DCC, DMAP, TMSE-OH, CH₂Cl₂, room temperature (rt); (ii) H₂, Pd/C, tetrahydrofuran (THF), rt; (iii) ODOL-OH, EDC·HCl, HOBt, dimethylformamide (DMF), rt; (iv) TMSBr, MeCN, 0 °C, Then H₂O; (v) ODOL-OH, PPh₃, DIAD, THF, rt; and (vi) TFA, CH₂Cl₂, 0 °C^{a a}Total efficiency of the synthetic pathway for 2, 5.6% over six steps.

Scheme 2.

Reagents and Conditions: (vii) H₂, Pd/C, THF, rt; (viii) ODOL-OH, EDC·HCl, HOBt, DMF, rt; (ix) TMSBr, MeCN, 0 °C, Then H₂O; (x) ODOL-OH, PPh₃, DIAD, THF, rt; (xi) LiN₃, DMF, rt^{a a}Total effciency of the synthetic pathway for 4, 40% over four steps and for 3, 26% over five steps.

Figure 1.

2-PMPA plasma concentration at 30 min post oral administration of ODOL prodrugs of 2-PMPA (2–4) to male CD-1 mice as a single dose at 10 mg/kg 2-PMPA equivalent dose. Data expressed as a mean ± standard error of mean (SEM) (n = 3), with statistics quantified using one-way ANOVA with Dunnett’s multiple comparison test: (**) p < 0.01 and (*) p < 0.05. Based on these results, 4 was prioritized for full pharmacokinetic evaluation in mice.

Figure 2.

Pharmacokinetic studies of 2-PMPA (IV) and 4 (PO) in mice at a dose of 10 mg/kg 2-PMPA equivalent showing the (A) plasma and (B) brain concentration versus time profile of 2-PMPA. Data expressed as mean ± SEM, n = 3, per time point. Oral bioavailability of 2-PMPA from 4 was found to be 50%. (C) Mean ± SEM pharmacokinetic parameters of 2-PMPA in plasma and brain following 10 mg/kg equivalent oral administration of 4 and intravenous administration of 2-PMPA in mice. Brain to plasma ratios are calculated from mean total AUC_brain versus AUC_plasma for each route. *Pharmacokinetic data of 2-PMPA in mice following oral administration is adopted from our previously published manuscript for the comparison of oral exposure with 4.

Figure 3.

(A) Pharmacokinetic profile of 2-PMPA (n=2) and 4 (n =3) in male beagle dogs at a dose of 1 mg/kg 2-PMPA equivalent. Data expressed as mean for 2-PMPA and mean ± SEM for 4. (B) Mean ± SEM pharmacokinetic parameters of 2-PMPA in plasma following a 1 mg/kg equivalent oral administration of 2-PMPA and 4 in beagle dogs.