Cysteinyl Leukotrienes Signal Via Overexpressed CysLT1, but Not CysLT2 Receptor In Chronic Lymphocytic Leukemia

Abstract 3612

The G Protein-coupled receptors (GPCRs) CysLT1 and CysLT2 are both expressed in peripheral blood mononuclear cells (PBMNC). Their ligands are inflammatory mediators of the cysteinyl leukotriene (cysLT) family and contribute, together with ligands of other GPCRs such as chemokines, to migration and proliferation of a variety of cell types. In the present study, we demonstrate by real-time RT-PCR that CysLT1 mRNA is overexpressed in B-CLL cells compared to both normal PBMNC and normal CD19+ B cells, whereas only low levels of CysLT2 mRNA are present. GPCR-typical cellular responses such as intracellular calcium fluxes and actin polymerization, which were induced by the cysLT LTD4 in CLL cells in a dose-dependent manner, were suppressed by the CysLT1 antagonist MK571, the prototype of the lukast family of drugs used in asthma treatment (e.g., montelukast). However, MK571 and other lukasts also block the leukotriene transporter MRP. The fact that the CysLT1 antagonist LY171883, which has no effect on MRP, also abrogated the responses of CLL cells indicates that the effects of cysLTs are mediated solely by CysLT1. Moreover, also chemotaxis was induced by the cysLT LTD4 in B-CLL cells (optimum at low nanomolar concentrations) and could be blocked by MK571. We further observed inhibiting effects of MK571 on cysLT-induced Erk/MAP kinase phosphorylation in B-CLL cells, which suggests an involvement of CysLT1 in cell proliferation. Indeed, MK571 significantly induced apoptosis of CLL cells in vitro and reduced survival of cultured B-CLL cells. However, the concentrations for a significant reduction of cell viability were higher (1-10 μM) than the concentration required for efficient CysLT1 receptor inhibition (0.1 μM). Thus, the influence of MK571 on B-CLL cell survival may mainly be due to direct effects on apoptosis occuring at the higher dose level and/or blocking of the leukotriene transporter MRP. Accordingly, LY171883 and the combined CysLT1/2 antagonist Bay-u9773 did not induce CLL apoptosis. Our results suggest that CysLT1 is overexpressed in B-CLL cells and involved in cell trafficking, similar to the chemokine receptor CXCR4. Considering the redundancy among GPCRs and the limited effect of MK571 on cell survival, CysLT1 for its own represents a less attractive therapeutic target using the currently available CysLT1 antagonists of the lukast family. However, combined inhibition of several GPCRs highly expressed in CLL cells including cysLT1 and CXCR4 may constitute a promising therapeutic approach and should be further evaluated.