Some
gliomas,
melanomas and
squamous carcinomas have large numbers of
EGF receptors which could, in these cases, be used for targeting with toxic agents. We investigated whether
EGF could be conjugated to
dextran, which is a suitable carrier for toxic agents, without losing its ability to bind to the receptor.
Dextran of 20 kDa molecular weight was activated with I-cyano-4-dimethylamino pyridinium tetrafluoroborate (CDAP) yielding highly active pyridinium-isourea derivatives.
EGF was coupled to the activated
dextran through the amino terminus and
glycine was added to
block residual activity. The
EGF-dextran conjugate was, after purification on
Sephadex G25 and Sephacryl 200 columns, tested for its receptor binding properties on human
malignant glioma, U343MGaC12:6, cells. The conjugate inhibited binding of 125I-EGF in a competitive assay, showing that the binding was receptor-specific.
Dextran conjugated with
glycine, without
EGF, had no inhibitory effect. The conjugate was radio-labelled either on the
EGF part with 125I or on the
dextran part with 3H-glycine, and the internalization patterns were compared to the internalization of 125I-EGF. The radioactivity of the conjugates remained cell-associated for more than 20 hr, regardless of whether the radioactivity was on the
EGF or on the
dextran part, while the radioactivity of unconjugated
EGF rapidly disappeared from the cells. Most of the cell-associated radioactivity was, at all analysed time intervals, located intracellularly. Thus, it seems promising to use
dextran, conjugated with
EGF, as a carrier of, for example, toxic radioactive nuclides.