The intracellular release of methotrexate from a synthetic drug carrier system targeted to fc receptor-bearing cells

Abstract

Methotrexate was conjugated to trinitrophenyl (TNP)-labeled poly ( d -lysine) either directly, or through a disulfide or a triglycine spacer. Conjugates were complexed with heparin and anti-TNP antiserum and tested for their growth inhibitory effects in cultured cells. When tested in Fc receptor-positive WEHI-3 cells, the anti-TNP immune complex of the conjugate with the disulfide spacer was more effective than that with the triglycine spacer. It had no effect on the growth of Fc receptor-negative L-929 cells. Without spacer, the direct conjugate was ineffective in both cell lines. The growth inhibitory effect of the drug-containing immune complexes was partially abolished in presence of an irrelevant, drug-free immune complex. NH 4Cl at 3 m M did not increase the cytotoxicity of the disulfide conjugate complexes, and decreased the effect of the triglycine conjugate complexes. These findings suggest that: (1) hapten-polymer conjugates can be used as drug carriers for targeting Fc receptor-bearing cells when given with an anti-hapten antibody, (2) disulfide spacers are effectively cleaved following Fc receptor-mediated endocytosis of a drug-carrying immune complex, (3) disulfide spacers are most likely to be cleaved in compartments other than endosomes or lysosomes.