In vitro activity: ONT-380 has nanomolar activity against purified HER2 enzyme and is approximately 500-fold selective for HER2 versus EGFR in cell-based assays. ONT-380 (ARRY-380) selectively inhibits the receptor tyrosine kinase HER2 relative to EGFR. In HER2 overexpressing cell lines, ONT-380 blocks proliferation and the phosphorylation of HER2 and its downstream effector, Akt. By contrast, in the EGFR overexpressing cell lines, it weakly inhibits phosphorylation and proliferation, demonstrating that ONT-380 may have potential to block HER2 signaling without causing the toxicities of EGFR inhibition

Kinase Assay: Irbinitinib, formerly known as ARRY-380 and ONT-380 or Tucatinib, is a potent and selective small molecule inhibitor of HER2 with IC50 value of 8 nM, it is equally potent against truncated p95-HER2, and is 500-fold more selective for HER2 versus EGFR. Irbinitinib acts by blocking the proliferation and phosphorylation of HER2 and its downstream effector, Akt. By contrast, in the EGFR overexpressing cell lines, it weakly inhibits phosphorylation and proliferation, demonstrating that Irbinitinib may have potential to block HER2 signaling without causing the toxicities of EGFR inhibition. Therefore, it has the potential to be used as an anticancer agent.

Cell Assay: ONT-380 has nanomolar activity against purified HER2 enzyme and is approximately 500-fold selective for HER2 versus EGFR in cell-based assays. In the EGFR overexpressing cell lines, it weakly inhibits phosphorylation and proliferation, demonstrating that Irbinitinib may have potential to block HER2 signaling without causing the toxicities of EGFR inhibition.