A Carrier-Mediated Prodrug Approach To Improve the Oral Absorption of Antileukemic Drug Decitabine

Decitabine (5-aza-2'-deoxycytidine, DAC) is a novel DNA rnethyltransferase (DNMT) inhibitor for the treatment of myelodysplastic syndrome, acute and chronic myeloid leukemia. However, it exhibits a low oral bioavailability (only 9% in mice), because of low permeability across the intestine membrane and rapid metabolism to inactive metabolite. To utilize the carrier-mediated prodrug approach for improved absorption of decitabine, a series of amino acid-decitabine conjugates were synthesized to target the intestinal membrane transporter, hPepT1. The Caco-2 permeability of the prodrugs was screened, and two L-val (aliphatic, compound 4a) and L-phe (aromatic, compound 4c) prodrugs with higher permeability were selected for further studies. The uptake of Gly-Sar by Caco-2 cells could be competitively inhibited by compounds 4a and 4c, with IC50 being 2.20 +/- 028 mM and 3.46 +/- 0.16 mM, respectively. The uptake of compounds 4a and 4c was markedly increased in the leptin-treated Caco-2 cells compared with the control Caco-2 cells, suggesting that hPepT1-mediated transport contributes to oral absorption of compounds 4a and 4c The prodrugs were evaluated for their stability in various phosphate buffers, rat plasma, tissue homogenates, and gastrointestinal fluids. Compounds 4a and 4c were stable in gastrointestinal tract at pH 6.0 but could be quickly converted into DAC in plasma and tissue homogenates after absorption. The oral absolute bioavailability of DAC was 46.7%, 50.9%, and 26.9% after compounds 4a, 4c, and DAC were orally administered to rats at a dose of 15 mg/kg, respectively. The bioavailability of compounds 4a and 4c in rats was both reduced to about 32% when orally coadministrated with typical hPepT1 substrate Gly-Sar (150 mg/kg). Overall, compounds 4a and 4c can significantly enhance the intestinal membrane permeability of DAC, followed by rapid and mostly bioactivation to parent drug in intestinal and hepatic tissues before entry into systemic circulation, and eventually improve oral bioavailability of DAC in rats. The hPepT1-targeted prodrug strategy is a promising strategy to improve the oral bioavailability of poorly absorbed decitabine.