Targeting cell metabolism in chronic lymphocytic leukaemia (CLL) through the inhibition of monocarboxylate transporters (MCT) -1 and -4.

Chronic lymphocytic leukaemia (CLL) is a lymphoid malignancy which despite advances in the treatment options available is still incurable. Characterised by the gradual accumulation of CD5+ B cells, the paradigm that this is due to failed apoptosis has been challenged and a significant proliferative component has been identified. However, despite the crosstalk between pathways which regulate metabolism and proliferation the metabolic characteristics of these cells are not fully understood. Furthermore, there is a renewed interest in the field of cancer cell metabolism because of the Warburg effect, a hallmark of malignancy whereby cells preferentially switch to aerobic glycolysis and rapidly consume glucose. This has led to the development of new drugs such as AZD3965 an inhibitor of monocarboxylate transporter 1 (MCT1), which along with MCT4 mediates the export of lactate, a toxic bi-product of glycolysis, out of the cell. The aim of this project was to assess whether therapeutically targeting MCT -1 and -4 would be a viable approach for CLL. Chapter 2 of this thesis examines expression of MCT -1 and -4 as well as a specific chaperone protein needed for the surface expression of these proteins, CD147. This chapter confirms the presence of both MCT -1 and -4 and CD147 in normal B cells as well as demonstrating for the first time that these transporters are expressed in CLL cells using Western blotting and qRT-PCR to assess the MCTs and flow cytometry to measure CD147. The levels of both MCTs and CD147 are demonstrated to be significantly reduced in CLL cells in comparison normal B cells likely due to the adoption of a quiescent phenotype to aid cell survival. The following chapter investigates this further by assessing whether there are any changes in expression under the influence of microenvironmental stimuli, specifically CD40 ligand (CD40L). In this chapter it is demonstrated for the first time that MCT4 is upregulated in CLL cells in response to CD40L. Analysis of gene expression using a Fluidigm Biomark™ array suggests this is due to the induction of glycolysis and that CLL cells may promote fatty acid synthesis as well as instigating changes in the metabolism of the tumour stroma possibly to provide substrates. Finally, chapter 4 evaluates the sensitivity of CLL cell lines to AZD3965 using cell death and cell viability assays. Both MEC-1 and HG3 CLL cell lines are shown to be resistant to MCT1 inhibition using AZD3965 and silencing of MCT4 using siRNA cells also has no effect on the viability of MEC-1 cells. That MCT4 can compensate for MCT1 inhibition is shown by the transient expression of MCT4 in a Raji cell line where only MCT1 is expressed. Taken together, the data presented in this study indicates that while the inhibition of MCT1 is likely to be ineffective dual inhibition of both MCT -1 and -4 may be a viable strategy for the localised inhibition of CLL in the secondary tissues. Furthermore, MCT inhibition in this disease may have the potential to negate mechanisms of resistance and protection from oxidative stress mediated by CD40L