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

Abstract

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.