Abstract 5559: Receptor tyrosine kinase-like orphan receptor 1 (ROR1) in BTKi-treated mantle cell lymphoma

Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma with a poor patient overall survival rate. While Bruton tyrosine kinase inhibitors (BTKis) have shown benefit in relapsed/refractory MCL (Wang M, et al., 2018; Song Y, et al.,2020; Wang ML et al., 2013) a portion of patients eventually progress. Here, we explored which biomarkers might be associated with resistance to acalabrutinib, a second generation BTKi, by analyzing samples from MCL patients who were on treatment or progressed on acalabrutinib from the ACE-LY-004 study (NCT02213926), as well as using a pre-clinical MCL cell line model. Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is an important oncofetal protein and a target of clinical relevance in MCL. It was previously attributed to a bypass resistance mechanism to first generation BTKi ibrutinib (Zhang et al., 2019). We hence analyzed ROR1 expression levels using available exploratory biomarker flow cytometry data from ACE-LY-004, which revealed that MCL patients who progressed or pre-progressed on acalabrutinib showed a higher percentage of circulating CD5+ROR1+ tumor cells (78.3%; n=7 and 63.6%; n=4 respectively) than patients who continued responding to treatment (23.8%; n=6). Interestingly, although progression was associated with higher frequency of CD5+ROR1+ tumor cells, the per-cell surface ROR1 expression on these cells from patients who pre-progressed/ progressed on acalabrutinib treatment (longitudinal analysis; n=6) was lower. While acute 5-day BTKi treatment in the Jeko-1 MCL cell line led to transiently higher surface expression of ROR1, chronic 4-month exposure of sensitive cells led to ROR1 surface downregulation in acalabrutinib or reversible BTKi acquired resistant (R) Jeko-1 MCL cells. Total ROR1 expression (western blot), was increased in Jeko-1R versus sensitive, suggesting that BTKi chronically treated MCL cells may upregulate intracellular ROR1 and/or partially internalize surface ROR1. To assess potential therapeutic implications of decreased surface expression of ROR1 in MCL post BTKi treatment, we assessed activity of a ROR1-targeted ADC (Zilovertamab vedotin; Wang et al., 2021) in BTKi-R cells. In line with downregulated surface ROR1 levels, the response to ZV was lower in BTKi-R compared to sensitive cells. However, Wnt5a (ROR1 ligand) expression was increased in these Jeko-1R cells, indicating a potential increase in ligand-dependent ROR1 activity. These preliminary results highlight the possible association between ROR1 expression on MCL tumor cells and BTKi response. To further dissect the interplay between ROR1 and second generation/reversible BTKi treatment in MCL, studies utilizing a multi-omics integration approach, BTKi-R MCL cell lines, and ex vivo propagated MCL patient cell models are ongoing. Citation Format: Anuvrat Sircar, Sara Parsa, Laura B. Prickett, Veerendra Munugalavadla, Catherine Rhee, Richard Tourdot, Anders Nelson, Michael Ophir, Wenyan Zhong, Matthew Sung, Daniel Auclair, Christine D. Palmer. Receptor tyrosine kinase-like orphan receptor 1 (ROR1) in BTKi-treated mantle cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5559.