Synthesis of a cytotoxic insulin cross-linked to diphtheria toxin fragment a capable of recognizing insulin receptors

Abstract

Insulin has been cross-linked via a disulfide bond to the diphtheria toxin fragment A which is catalytically active in ADP-ribosylating elongation factor-2 but does not retain binding sites for toxin receptors. The purified conjugate proved to be cytotoxic to mouse Swiss/3T3 cells which are toxin resistant but express insulin receptors. This cytotoxicity coincided with a decrease in protein synthesis and with drastic morphology changes. In contrast, IN-2 cells, which are insulin-nonresponsive variants derived from mouse BALBc 3T3 cells, were resistant to the conjugate. Thus, the conjugate (a chimeric insulin) appears to mediate entry of the toxic fragment A into 3T3 cells through insulin receptors.