Targeting ROR1 with KAN571C disrupts resistance networks in mantle cell lymphoma

Resistance to Bruton tyrosine kinase (TK) and BCL2 inhibitors, such as ibrutinib (Ibru) and venetoclax (Ven), remains a major therapeutic challenge in mantle cell lymphoma (MCL), which limits treatment options. Receptor TK-like orphan receptor 1 (ROR1), aberrantly expressed in MCL and other malignancies but largely absent in normal adult tissues, has been implicated in tumor cell proliferation, survival, and migration. This study aimed to elucidate the mechanisms underlying Ibru and Ven resistance in MCL and to investigate the therapeutic potential of targeting ROR1 using the small-molecule inhibitor KAN571C in Ibru- and/or Ven-resistant MCL cell lines. Ibru-, Ven-, and Ibru + Ven (Double)-resistant models were generated from the JEKO-1, Granta-519, and Z138 MCL cell lines. The cytotoxic effects of Ibru, Ven, and KAN571C were assessed in both naive and drug-resistant models using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays. Western blotting was used to analyze downstream signaling alterations after exposure to KAN571C. KAN571C induced potent cytotoxicity in both naive and drug-resistant models, preferentially in Ven- and Ibru/Ven-resistant cells. Mechanistically, KAN571C dephosphorylated ROR1 at TK and proline-rich domains, suppressed downstream phosphatidylinositol 3-kinase/AKT and β-catenin signaling, and activated caspase-dependent apoptosis. Notably, long-term exposure (2 weeks) failed to establish KAN571C-resistant cell lines. Our findings identify ROR1 as a convergent mediator of resistance in MCL and highlight KAN571C as a potential therapeutic strategy to overcome treatment refractoriness.