Carrier‐bound methotrexate. II. Water‐soluble polyaspartamide methotrexate conjugates with amide links in polymer–drug spacer

Abstract

AbstractIn Part I of this series, conjugation of methotrexate (MTX) to water‐soluble polyaspartamide carriers was accomplished through ester link formation between an MTX carboxyl group and a carrier‐attached hydroxyl function. Contrasting with that type of anchoring link, this project utilizes amide formation as the means of drug conjugation. This is achieved through condensation of one of the drug's carboxyl groups with a carrier‐attached primary amine function. Derived from polysuccinimide by a time‐proven nucleophilic ring‐opening process in the presence of aliphatic diamines, polyaspartamide‐type carriers 1–12 comprise subunits equipped with tert‐amine or hydroxyl side group terminals for hydrosolubilization and other subunits equipped with primary amine terminals as drug‐binding sites. MTX conjugation with these carriers is effected in aprotic solvent, the reaction being mediated by 2‐(1H‐benzotriazol‐1‐yl)‐1,1,3,3‐tetramethyluronium hexafluorophosphate. The water‐soluble conjugates are fractionated and purified by size exclusion chromatography and dialysis; they are isolated by freeze‐drying in typical yields of 40–65%. In the molar MTX/NH2 feed ratios that are chosen (generally 1.2–1.3) and with the mole fractions of drug‐binding subunits restricted to 10 and 20%, drug loading in the resultant conjugates approximates 20–30% by mass. In follow‐on study, conjugates 1‐MTX–12‐MTX thus obtained will be screened in cell culture tests for antiproliferative activity against a number of human cancer lines. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3415–3424, 2006