Evaluation of a targeted prodrug strategy of enhance oral absorption of poorly water-soluble compounds.

PURPOSE: The purpose of this research was to examine a targeted prodrug strategy to increase the absorption of a poorly water-soluble lipophilic compound.
METHODS: Three water-soluble prodrugs of Cam-4451 were synthesized. The amino acid (Cam-4562, Cam-4580) or phosphate (Cam-5223) ester prodrugs introduced moieties ionized at physiological pH and targeted intestinal brush-border membrane enzymes for reconversion to the parent. Selectivity for reconversion of the three prodrugs was examined in rat intestinal perfusate and brush-border membrane suspensions. Bioavailability of Cam-4451 in rats was evaluated after administering orally as the parent or as prodrugs in a cosolvent vehicle or in methylcellulose.
RESULTS: Cam-5223 was highly selective for reconversion at the brush-border, but was rapidly reconverted in intestinal perfusate. Cam-4562 was not as selective but was more stable in the perfusate, whereas Cam-4580 was neither selective nor stable. Oral bioavailability of Cam-4451 was 14% after dosing as the parent in the cosolvent vehicle, 39% and 46%, respectively, as Cam-4562 and Cam-5223. Oral bioavailability was only 3.6% when the parent was dosed in methylcellulose, whereas the bioavailability was 7-fold higher when dosed as the phosphate prodrug.
CONCLUSIONS: Water-soluble prodrugs that target brush-border membrane enzymes for reconversion can be useful in improving drug oral bioavailability.