Validation And Implementation Of Screens For Partial Agonists And Antagonists Of The Erbb4/Her4 Receptor Tyrosine Kinase: Targeted Melanona Drug Discovery

Introduction: Gain-of-function mutations in the gene encoding the ErbB4 (HER4) receptor tyrosine kinase have been detected in melanoma cell lines and these cell lines are dependent on ErbB4 expression for proliferation. Consequently, ErbB4 antagonists hold promise as targeted melanoma therapeutics and we have sought to identify small molecule ErbB4 antagonists. Our approach is based on the observation that the Q43L mutant of the ErbB4 peptide growth factor agonist Neuregulin 2beta (NRG2b) functions as a partial agonist at ErbB4; NRG2b/Q43L stimulates ErbB4 tyrosine phosphorylation, fails to stimulate ErbB4 coupling to cell proliferation, antagonizes stimulation of cell proliferation by ErbB4 full agonists, and causes ErbB4 down-regulation. Experimental procedures: We have developed a high-throughput screening (HTS) strategy that can be used to identify ErbB4 antagonists. The primary screen identifies molecules that stimulate ErbB4 tyrosine phosphorylation. The secondary screen distinguishes between molecules that stimulate and fail to stimulate ErbB4-dependent proliferation. The tertiary screen identifies molecules that antagonize agonist stimulation of ErbB4-dependent proliferation. Results: An phospho-ErbB4 sandwich ELISA assay identifies molecules that stimulate ErbB4 tyrosine phosphorylation with high sensitivity and fidelity (Z’ u003e0.5). MTT assays using a cell line that displays ErbB4-dependent proliferation distinguish between molecules that stimulate and fail to stimulate ErbB4-dependent proliferation (Z’u003e0.5) and identify molecules that antagonize agonist stimulation of ErbB4 dependent proliferation (Z’u003e0.5). These assays have been used to identify small molecules that stimulate ErbB4 tyrosine phosphorylation. Efforts to determine whether these hits function as ErbB4 full agonists or partial agonists (antagonists) are underway and will be reported. Structures of these small molecule ErbB4 full and partial agonists may be reported, pending submission of a provisional patent application. Conclusions: We have validated an HTS strategy for identifying ErbB4 partial agonists that function as ErbB4 antagonists and deployment of that strategy has led to the identification of several hits. Such molecules may hold promise as targeted therapeutics for melanoma and other ErbB4-dependent tumors. Citation Format: Richard Cullum, Allan David, David J. Riese. Validation and implementation of screens for partial agonists and antagonists of the ErbB4/HER4 receptor tyrosine kinase: Targeted melanona drug discovery. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1353.