INHIBITION OF DNA TOPOISOMERASE-I AND TOPOISOMERASE-II AND INDUCTION OF APOPTOSIS BY ERBSTATIN AND TYRPHOSTIN DERIVATIVES

Inhibitors of protein tyrosine kinases (PTK) and DNA topoisomerases ar e potential antitumour agents. Drugs which bind to the ATP site of PTK , such as genistein, are common inhibitors to both types of enzymes. E leven erbstatin and tyrphostin derivatives, which inhibit epidermal gr owth factor receptor PTK activity by competing with both the peptide s ubstrate and ATP were tested for their capacity to inhibit DNA topoiso merases I and II. Erbstatin, two synthetic derivatives with a modified side chain and the tyrphostin AG 786 inhibited both topoisomerases in the same range of concentrations (20-50 mu M). The tyrphostin AG 213 inhibited only topoisomerase II. In this series, absence of PTK inhibi tory effect was correlated with the absence of DNA topoisomerase inhib ition, while the detection of PTK inhibition may or may not be associa ted with DNA topoisomerase inhibition. In contrast to genistein, none of these molecules induced the stabilization of the topoisomerase-DNA cleavable complex, either in vitro or in vivo. Alcaline elution analys is revealed that erbstatin did not induce the formation of protein ass ociated DNA strand breaks. However, an extensive degradation of the ce llular DNA was observed which was shown to result from an internucleos omal fragmentation. Furthermore, typical morphological modifications a ssociated with apoptosis ware observed in the erbstatin treated cells by electron microscopy. These data indicate that erbstatin induces an apoptotic cell death.