Prolonged cell cycle arrest by the CDK4/6 antagonist narazaciclib restores ibrutinib response in preclinical models of BTKi‐resistant mantle cell lymphoma

Introduction: Bruton tyrosine kinase inhibitors (BTKi) have transformed the therapeutic landscape of mantle cell lymphoma (MCL); however, primary and acquired resistance to these agents remains a challenge. Previous studies suggested that narazaciclib (ON123300), second-generation, orally bioavailable clinical-stage CDK4/6 inhibitor (CDKi), may trigger cycle arrest significant tumor growth inhibition (TGI) in BTKi-resistant MCL models. Methods: We compared efficacy safety with health authority approved CDKi association different BTKi, panel 10 lines distinct sensitivity first-in-class ibrutinib. used CellTiter-Glo proliferation assay, FACS-mediated quantification apoptosis, RNA sequencing followed by gene set enrichment analysis (GSEA), RT-PCR western blot validations. In addition, we evaluated narazaciclib/ibrutinib combo vivo an immune-competent chicken embryo chorioallantoic membrane (CAM) xenograft. Results: Narazaciclib exhibited highest antitumor activity among (mean IC50: 3.61 ± 2.1 µM), regardless their Although there was no correlation between activation CDK4/CDK6-pRb pathway MCL, transcriptomic phenotypic analyses revealed predominant downregulation E2F target genes G2/M checkpoint response (NES > 2.5) upon treatment. This feature associated intracellular accumulation p21, p16, phospho-p27, decreased mitotic index, G1 blockade, apoptosis onset. When combined ibrutinib, but not second generation acalabrutinib, achieved synergistic both BTK-sensitive BTK-resistant cells. The combination improved rather slight constant (+10%–15%) augmentation phase blockade down-modulation cycle-associated transcriptome. Both phospho-histone H3 upregulation p-p27/p27 also underwent 10%–15% improvement combination-treated vivo, while single agent 28% TGI CAM model, narazaciclib-ibrutinib reduced spreading 65% allowed 50% reduction malignant B infiltration into bone marrow, detectable toxicity. Conclusions: Narazaciclib, due its completely MoA from BTKi involving direct modulation cycle, can achieve ibrutinib vitro especially models MCL. Ongoing phospho-proteomics genetic edition assays will help deciphering molecular bases this unique drug cooperation at level. Encore Abstract - previously submitted AACR 2023 research funded by: study financially supported Onconova Therapeutics, Spanish Ministry Science Innovation (grant PID2021-123039OB-C21) (to GR). MFS holds predoctoral fellowship (FI19/00338) Instituto de Salud Carlos III. work carried out under CERCA Program (Generalitat Catalunya). Keywords: Aggressive B-cell non-Hodgkin lymphoma, Combination Therapies, Molecular Targeted Therapies Conflicts interests pertinent abstract. A. Makovski-Silverstein Employment or leadership position: Therapeutics S. Cosenza G. Roué Research funding: