Cannabinoid Receptors and CXCR4 Cross-Talk in Lymphoma Cells

Background: Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma with a high rate of relapses after therapy. Chronic lymphocytic leukemia (CLL) is a heterogeneous disease with varied outcome. For both diseases there is a need for new therapies. Cannabinoid receptors (CBs), which are overexpressed in most cases of MCL and CLL compared to normal B cells (Islam et al., 2003; Gustafsson et al., 2008; Freund et al., 2016) are promising novel therapeutic targets. CBs are membrane-bound receptors that convey signals from the microenvironment to the cells. There are two types of CBs: CB1 and CB2. CB1 is suggested to be involved in retention and/or egress of MCL cells from the tissue to the blood circulation (Wasik et al., 2014). CB2 is expressed by normal B-cells where it regulates positioning and retention of cells in tissue (Pereira et al., 2009; Basu et al., 2011; Muppidi et al., 2011) and in pre-B-cell acute lymphoblastic leukemia, involved in the energy metabolism (Chan et al., 2017). The retention/egress of the B-cell lymphoma cells is mainly regulated by chemokine receptors and adhesion molecules. The chemokine receptor CXCR4 is one of the most highly expressed chemokine receptors in MCL and CLL. 2-arachidonoylglycerol (2-AG, CB1/CB2 endogenous ligand) and CXCL12 (CXCR4 ligand) are synthetized and secreted by stromal cells in the bone marrow (Kose et al., 2018; Burger and Gribben, 2014). The endocannabinoids levels in cancer are suggested to have a role in cancer progression (Sailler et al., 2014) while CXCL12 is already a candidate target for therapy using a CXCR4 inhibitor AMD3100.

Aim: To investigate a possible crosstalk between CBs and CXCR4 in MCL and CLL cells.

Methods: Patients with newly diagnosed MCL (n=8) or CLL (n=25) gave informed consent to participate in the study. Lymphoma cells were enriched by negative selection. Fifteen primary lymphoma samples and the JeKo MCL cell line were subjected to chemotaxis towards CXCL12 and/or 2-AG. CXCR4 membrane expression was assessed by flow cytometry. Selective CB1 and CB2 antagonists were used to investigate the underlying mechanisms. CB1, CB2 and CXCR4 encoding genes levels were measured by qPCR and normalized to B cells from tonsil.

Results and Conclusion: 2-AG induced chemotaxis in 11/15 MCL and CLL samples. In JeKo, 2-AG-induced migration was blocked by a CB2 antagonist, suggesting that signaling via CB2 is involved. When the primary cells were subjected to migration towards CXCL12, two patterns of chemotaxis were observed. The first pattern was seen in 7/15 samples that migrated towards CXCL12. In these samples, the migration was inhibited when 2-AG was combined with CXCL12. The second type of response was observed in 8/15 samples, those samples did not migrate towards CXCL12 but chemotaxis was enhanced by combining 2-AG and CXCL12. MCL and CLL samples expressed variable mRNA levels of CB1 (RFI range: 0.0-204) and CB2 (RFI range: 0.8-14.3) and all expressed CXCR4 at mRNA (RFI range: 0.1-215.8) and protein (MFI range: 1278-19301) levels that did not differ neither between the two diseases nor between the two migratory groups. When all 15 samples were combined, CB1 mRNA levels, but not CB2 mRNA, correlated to the chemotaxis towards CXCL12 (Spearman correlation coefficient = 0.626; p=0.01). In contrast, CB2 mRNA levels, but not CB1, correlated to chemotaxis towards 2-AG (Spearman correlation coefficient = 0.532; p=0.04), which is in agreement with the effects observed in JeKo. Furthermore, CB1 and CB2 mRNA levels correlated to chemotaxis towards the combination of CXCL12 and 2-AG both (for CB1 mRNA: Spearman correlation coefficient= 0.588; p=0.02 and for CB2 mRNA: 0.589; p=0.02). Neither CXCL12-induced CXCR4 receptor internalization, nor recycling was influenced by 2-AG incubation. Our findings indicate a novel pathway regulating chemotaxis of MCL and CLL implicating a cross-talk between CBs and CXCR4. The fact that the capacity to internalize CXCR4 remained intact after incubation with 2-AG suggests that the reduced CXCL12-mediated migration when 2-AG was combined could be due to an impaired downstream signaling in lymphoma cells.

Importance: Lymphoma cells residing in the tissue receive pro-survival stimuli and are protected from chemotherapy by signals from the microenvironment. A better understanding of how lymphoma cell migration and tissue retention are regulated can be a step towards more efficient therapies.