Biochemical and cellular evaluation of HUNK inhibition by an FDA approved drug as potential therapeutic strategy for HER2+ breast cancer

Kinase inhibitors have been on spotlight for cancer drug discovery ever since the approval of Imatinib and recently the 100 th small molecule kinase inhibitor was approved by the FDA showing the potential of kinase inhibitors for cancer therapeutics and beyond. HER2 kinase is an established drug target in breast cancer therapeutics with multiple inhibitors developed against this target over time. However, cancer developing drug resistance to these inhibitors over time remain as a prognostic challenge for aggressive breast cancer treatment. Recent studies investigating the HER2 resistance mechanism of breast cancers identify HUNK (hormonally upregulated neu-associated Kinase) playing a crucial role in promoting HER2+ breast cancer cell survival and inhibitors resistance via phosphorylation of Rubicon. Recently a first in class HUNK targeted inhibitor HSL119 has been identified and characterized to demonstrate potential of targeting HUNK as a treatment strategy for HER2 resistant breast cancers, but more potent inhibitors for this target are yet to be identified. To address this, we screened 145 FDA approved compounds in HUNK biochemical kinase assay in Reaction Biology's HotSpot assay platform and identified Momelotinib, an orally available JAK1/JAK2/ACVR1 inhibitor used to treat myelofibrosis, inhibiting HUNK with 7.9 nM IC 50 . NanoBRET target engagement assay confirmed Momelotinib binds cellular HUNK in live HEK293 cells. Furthermore, CellTiter-Glo assays demonstrated Momelotinib inhibits proliferation of HER2+ JIMT1 cells and triple-negative 4T1 breast cancer cells, while caspase-3/7 activation assays indicated Momelotinib induces apoptotic cell death in both lines. These findings highlight Momelotinib as a potential therapeutic candidate for overcoming HER2 inhibitor resistance in breast cancer.