Carrier-bound Methotrexate. IV. Antiproliferative Activity of Polyaspartamide-MTX Conjugates against Leukemic Lymphoblast Cell Lines

Polymeric conjugates of methotrexate (MTX) with macromolecular carriers, obtained from amine-functionalized polyaspartamides by coupling with one of the drug’s carboxyl groups, are used in this preliminary screening project for in vitro cytotoxicity assessment. The water-soluble conjugates, crudely fractionated by aqueous dialysis, possess mass-average molecular masses in the range of 20000–30000. Screens are performed by standard procedures against cultured CEM/S human leukemic lymphoblast cells, a drug-sensitive line, and against CEM/E, its drug-resistant subline, for comparison also against unconjugated MTX. All compounds tested, including the unconjugated drug, display decreasing activity on going from CEM/S to CEM/E, resistance factors (IC50 [CEM/E]/IC50[CEM/S]) being in the vicinity of 15–20 for MTX as well as for the majority of conjugates. On the other hand, comparisons of IC50 values for conjugates versus free drug, both against CEM/S and CEM/E, show vastly superior antiproliferative performance of the drug in the carrier-anchored state over the free form, with activity factors (IC50[free MTX]/IC50 [conjugate]) typically in the 10–50 range and higher. On the basis of these promising in vitro findings, the polyaspartamide-MTX conjugates are considered to be excellent candidates for further cell culture and extended in vivo tests.KEYWORDS: Methotrexate conjugates, polyaspartamide, CEM leukemic lymphoblasts.