P1.14-20 Tarloxotinib as a Novel Therapeutic Strategy for Oncogenic Alterations Across the ErbB Family of Receptors

Abstract

The ErbB family of receptors tyrosine kinases (EGFR, HER2, HER3, and HER4) have been implicated in multiple different tumor types. The implementation of comprehensive next generation sequencing has allowed the identification of diverse gene alterations that function as oncogene drivers in these receptors. Some of the non-common gene alterations identified are resistant to marketed EGFR/HER2 inhibitors. Tarloxotinib is a prodrug that generates a potent and irreversible pan-HER inhibitor (tarloxotinib-E) under hypoxic conditions associated with tumors. In this study we evaluated the effect of tarloxotinib on several types of oncogenic mutations and fusions that involve the ErbB family of receptors. cDNAs encoding EGFR kinase domain duplications (EGFR-EGFR), EGFR-RAD51 gene fusion, EGFR-ERBB4, ERBB2-GRB7 and EZR-ERBB4 gene fusion were expressed in Ba/F3 cells. Using spheroid assays we evaluated the proliferation of A172 glioblastoma cell line treated with tarloxotinib, tarloxotinib-E or 1st, 2ndor 3rdgeneration EGFR/HER2 TKIs. We analyze the on target and signaling effects elicited by tarloxotinib-E via immunoblots. Using a nude mice xenograft model of the human derived cell line CUTO17 wi the EGFR exon 20 insertion p.N771_H773dupNPH, we evaluated tumor, tissue and blood drug levels by mass spectrometry and the effect of tarloxotinib on tumor growth. Our results demonstrate that tarloxotinib-E inhibits phosphorylation of EGFR with a kinase duplication and inhibits proliferation in a spheroid invasion assay in A172 cells. In the CUTO17 EGFR exon 20 model, treatment with tarloxotinib inhibited tumor growth. Intratumor levels of tarloxotinib-E were ∼20 times higher than skin and ∼50 times higher than plasma demonstrating selective tumor conversion of tarloxotinib. Cell growth inhibition (EC50) of novel HER family fusions (EGFR-EGFR, EGFR-RAD51, EGFR-ERBB4, ERRB2-GRB7 and EZR-ERBB4) will be presented. Tarloxotinib is a potent irreversible inhibitor in vitro for cells that harbor oncogenic alterations across the ERBB gene family, including EGFR kinase domain duplications, ErbB fusions and exon-20 insertions. Tarloxotinib is selectively activated in hypoxic tumor regions demonstrating a novel mechanism to generate a therapeutic window and avoid on-target EGFR-related toxicities.