Abstract 492: Pharmacological inhibition of CXCR4 increases the anti-tumor activity of conventional and targeted therapies in B cell lymphoma models
Authors: Barnabei Laura , Arribas Alberto J. , Cascione Luciano , Guidetti Francesca , Spriano Filippo , Tarantelli Chiara , Rinaldi Andrea , Stathis Anastasios , Rossi Davide , Zucca Emanuele , Zimmermann Johann , Bertoni Francesco 
Published: April 2023

Abstract
Introduction: CXCR4 is expressed in different B cell lymphoid neoplasms, and its levels are upregulated by BCR/PI3K blockade. High expression has been associated with resistance to BCR/PI3K inhibitors and gene mutations with reduced sensitivity to BTK inhibitors. We assessed whether its pharmacological inhibition with the potent CXCR4 inhibitor SPX5551 (POL5551) increases the antitumor activity of anti-lymphoma agents in lymphoma models, including some with secondary resistance to PI3K/BTK inhibitors.
Methods: Antiproliferative activity was measured in mantle cell lymphoma (MCL, n=10), chronic lymphocytic leukemia (CLL,2), and marginal zone lymphoma (MZL, 2 + 4 derivatives with secondary resistance to PI3K and BTK inhibitors) cell lines exposed (72h) to increasing doses of compounds as single and in combination. Drugs included ibrutinib, copanlisib, idelalisib. The beneficial effect of the combinations versus the single agents was considered both as synergism (Chou-Talalay combination index), and as potency and efficacy (MuSyC algorithm). Mechanisms of action were studied by RNA-Seq, cell cycle and apoptosis assays, and immunofluorescence.
Results: Combination of SPX5551 with conventional or targeted therapies was beneficial, either additive or synergistic, across all tested lymphomas. The combination of SPX5551 and ibrutinib was superior to single treatments in MCL, MZL or CLL, with stronger benefit in MZL and MCL than CLL. SPX5551/copanlisib showed synergism in both MCL and MZL, and SPX5551 addition overcame resistance in MZL with secondary resistance to idelalisib, copanlisib or ibrutinib. These results were confirmed using the clinically available drug candidate balixafortide (SPX6326, POL6326).RNA-Seq in the MCL REC1 model showed a much bigger impact of the SPX5551+ibrutinib on transcriptome than single agents: 2100 transcripts differentially expressed in the combination group vs DMSO (P&lt;0.01), 662 (ibrutinib), 260 (SPX5551). Downmodulated transcripts by the combination belonged to cytokine-mediated, TNF, NFkB, TLR, JAK-STAT pathways, MYC targets. Compared to single agents, the combo had a stronger downregulation of, among others, TNF, EGR2/3, CCL3/4, CXCL10, CXCR3, CD83, DUSP2, BIRC3, MIR17HG, MYC. Upregulated genes by SPX5551+ibrutinib involved apoptosis and p53. SPX5551 addition to ibrutinib further increased cells in subG0 phase and induced apoptosis compared to single agents. Consistent with changes observed by transcriptomic profiling, combination downmodulated pAKT, RELA and RELB protein levels compared to single treatments.
Conclusions: Results suggest that a combination with the CXCR4 inhibitor SPX5551 adds beneficial effect to BCR inhibitors and might overcome resistance to PI3K/BTK inhibitors. Adding SPX551 to the treatment of patients with B cell lymphoma warrants further exploration.
Citation Format: Laura Barnabei, Alberto J. Arribas, Luciano Cascione, Francesca Guidetti, Filippo Spriano, Chiara Tarantelli, Andrea Rinaldi, Anastasios Stathis, Davide Rossi, Emanuele Zucca, Johann Zimmermann, Francesco Bertoni. Pharmacological inhibition of CXCR4 increases the anti-tumor activity of conventional and targeted therapies in B cell lymphoma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 492.