Receptor Tryosine Kinase Inhibitors as Potent Weapons in War Against Cancers

Receptor Tyrosine Kinases class I (RTK class I, EGF receptor family) constitute a family of transmembrane proteins involved in various aspects of cell growth and survival and have been implicated in the initiation and progression of several types of human malignancies. Activation of EGFR may be because of overexpression, mutations resulting in constitutive activation, or autocrine expression of ligand. In contrast, activation of HER2 occurs mainly by overexpression, which leads to spontaneous homodimerization and activation of downstream signaling events in a ligandindependent manner. EGFR and HER2 have now been validated as a clinically relevant target, and several different types of agents inhibiting these receptors are currently in development. The EGFR inhibitors Erlotinib, Gefitinib, and Cetuximab have undergone extensive clinical testing and have established clinical activity in non small cell lung cancer (NSCLS) and other types of solid tumors. Several of the other erbB inhibitors are also undergoing advanced clinical testing, either alone or in combination with other agents. This review reports various inhibitors, natural, small molecules and monoclonal antibodies, along with their reported activities for various members of erbB family. It will highlight the potential for the development of novel anti-cancer molecules.