Lysosomal degradability of poly(alpha-amino acids)

The lysosomal degradability of poly(alpha-amino acids) based on poly(L-glutamic acid) and its derivatives/copolymers was evaluated to gain insight into the subcellular fate of the macromolecules as water soluble polymeric drug carriers. The results indicate that both the incorporation of hydrophobic comonomers and modification of the carboxylic groups of glutamic acid side chains with hydroxyalkylamine increase the lysosomal degradability of the copolymers. Decreased lysosomal degradability of L-glutamic acid copolymers containing tripeptides terminated in p-nitroanilide (drug model) in the side chains confirmed that drug conjugation alters the degradation pattern of the polymeric carriers. The percentages of the enzymatic release of p-nitroaniline from its polymeric complex with time is relatively independent of the contents of the tripeptidyl p-nitroanilides attached to the polymeric conjugates. Determination of the degradation products by electrospray mass spectroscopy showed that no fragments less than 10(3) D were generated by lysosomal enzymes, whereas the main degradation products by papain and chymotrypsin were tripeptides and tetrapeptides. The conclusions derived from these data strongly suggest that these macromolecules, if used as lysosomotropic drug carriers, may accumulate in the lysosomes and limit their usefulness in some applications.