Screening of Microbial Extracts for Tyrosine Kinase Inhibitors.

Protein tyrosine kinase activity (PTK) is associated with the activity of many cellular and viral oncogene products1'2) as well as signal transduction events for several growth factor receptors such as epidermal growth factor (EGF), platelet derived growth factor (PDGF) and insulin3'4). Activation of specific PTK mediated processes have been associated with proliferative diseases such as cancer5), artherosclerosis6) and probably pso-riasis6'7). This has led to the general concept that PTK inhibition may combat hyperproliferative conditions which result from enhanced activity of PTKs8'9). Several synthetic inhibitors of PTKshave been characterized along with a number of natural products of microbial, plant and marine origin. Amongthese are tyrphostins9),