Zongertinib, a Novel HER2 Tyrosine Kinase Inhibitor, Maintains an Anticancer Activity for Trastuzumab Deruxtecan-Resistant Cancers Harboring HER2-Overexpression

Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate comprising trastuzumab linked to a payload DXd, has been extensively used to treat various cancers harboring HER2 overexpression. However, resistance development has been a major challenge to T-DXd treatment. To explore treatment strategies for T-DXd-resistant cancers, we examined two T-DXd-resistant cells named DSR32 and DSR4, which were obtained from HER2 gene-amplified H2170 lung cancer and N87 gastric cancer cells, respectively. The uptake of T-DXd and its transport to lysosomes in DSR32 cells were reduced. Subsequently, <i>HER2</i> gene copy number (from 54 to 12) was reduced, which decreased HER2 expression on the cell surface. Thus, T-DXd-resistance might be observed due to the reduced T-DXd uptake caused by decreased HER2 expression in DSR32 cells. In DSR4 cells, no change was observed in HER2 expression and in the uptake and transport of T-DXd. The reduced linker cleavage activity may be associated with T-DXd resistance in DSR4 cells. Meanwhile, both DSR32 and DSR4 cells maintained HER2 activation; thus, zongertinib, a HER2-selective tyrosine kinase inhibitor, blocked the HER2 pathway, induced apoptosis, and inhibited colony formation. Overall, zongertinib can provide therapeutic relief to patients with HER2-overexpressing cancer who have developed resistance to T-DXd.