Polymeric prodrugs, 4. IN vitro study of the drug release on a model p‐nitroanilide bound onto polyanionic carrier

The process of chymotrypsin catalysed hydrolysis of L‐phenylalanyl‐4‐nitroanilide (Phe‐NNp) residues bound via 6‐aminohexanoic acid (ϵ‐Ahx) spacer to the polyanionic carrier, poly( N ‐vinylpyrrolidone‐ co ‐maleic acid), was studied. The initial rate of hydrolysis was measured at pH 8 as a function of mole ratio of side chains (‐ϵ‐Ahx‐Phe‐NNp) randomly distributed along the backbone. The polyanionic carrier studied shows a pronounced effect on the process, as overall kinetic parameters ( k cat and K m ) of ‐ϵ‐Ahx‐Phe‐NNp, attached to the polymer, differsignificantly from the respective values of the low‐molecular‐weight substrate analogue, succinyl‐ϵ‐Ahx‐Phe‐NNp. Relationship between the side chain content and the k cat / K m values, examined in the range of 1 to 20 mol‐%, exhibits a saturation‐profile. The limiting value of k cat / K m (5 · 10 3 1 · mol −1 · s −1 ) appeared to be as much as 8‐times higher than that of succinyl‐ϵ‐Ahx‐Phe‐NNp. The course of chymotrypsin catalysed hydrolysis of the polymer‐substrate bearing 20 mol‐% of side chains shows first order kinetics, with the conversion approaching asymptotically 100%. pH dependence of the maximum velocity of hydrolysis ( V m ), determined in the range 5–10, shows a maximum at about pH 8. The enzyme activity profile is broadened toward acidic region.