Poly[N-(2-hydroxypropyl)methacrylamide] conjugates of methotrexate - Synthesis and in vitro drug release

Two hexamethylenediamine (HMDA) derivatives of the anti-cancer drug methotrexate (MTX) were synthesized in which either the alpha-carboxylic [HMDA-MTX(I)] or gamma-carboxylic [HMDA-MTX(II)] group of glutamic acid in the methotrexate structure were modified by reaction with HMDA. Both HMDA-MTX(I) and HMDA-MTX(II) were coupled with poly[N-(2-hydroxypropyl)methacrylamide] via oligopeptide -GlyGly-, -GlyLeuGly- and -Gly-DL-PheLeuGly- spacers and physico-chemical characterization of the polymer-drug conjugates was performed. The in vitro release of HMDA-MTX(I) and HMDA-MTX(II) or their respective amino acid derivatives from polymeric conjugates during their incubation with the thiol protease cathepsin B solution or with a mixture of lysosomal enzymes isolated from rat liver (tritosomes) was studied in detail. The results show that the rate of release of HMDA-MTX(I) and HMDA-MTX(II) from the polymer carrier depends on the detailed structure of the drug and can be controlled by modification of the structure of the oligopeptide spacer. The course of the reaction and the structure of the products of the enzyme-catalysed hydrolysis (free drug or its amino acid derivative) were studied using HPLC and amino acid analysis. (C) 1997 Elsevier Science BN.