Topical delivery of 5-fluorouracil (5-Fu) by 3-alkylcarbonyl-5-Fu prodrugs

Abstract

The solubilities in isopropyl myristate ( S IPM) and pH 4.0 buffer ( S AQ) and the partition coefficients between IPM and pH 4.0 buffer ( K IPM:AQ) have been measured for a series of 3-alkylcarbonyl-5-fluorouracil prodrugs (3-AC-5-FU). The 3-AC-5-FU prodrugs were all 100 times more soluble in IPM and the first two members of the series were also more soluble in pH 4.0 buffer than 5-FU. The abilities of the 3-AC-5-FU prodrugs to deliver total 5-FU species through hairless mouse skin from IPM suspensions ( J i) were also measured. The 3-propionyl derivative 3, which exhibited the highest S AQ in the series, gave the highest J i value. The S IPM, S AQ and molecular weights (mw) of the 3-AC-5-FU series correctly predicted the rank order and very closely (0.10 log units) predicted the absolute values for log J i using the transformed Potts–Guy equation. Although the series of 3-AC-5-FU prodrugs was generally quite effective at increasing J i (2–20 times), the best 3-AC-5-FU prodrug was not as effective as the best 1-alkylcarbonyl-5-FU prodrug (1-AC-5-FU) at increasing J i and the ability of the 3-AC-5-FU prodrugs to increase the concentration of total 5-FU species in the skin was 2–5 times less than the 1-AC-5-FU prodrugs. Thus, the 1-AC-5-FU prodrugs remain as the best prodrugs with which to enhance the topical delivery of 5-FU.