Development of Novel Therapeutic Approaches for Chronic Lymphocytic Leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common blood cancer in the U.K., and is currently not curable with chemotherapy. CLL is a disease of mid to late life, and although some patients never require treatment, many currently die within years despite chemotherapy. New treatments are needed to improve the outcome of this disease. New insights into the basic biology of CLL have identified new therapeutic targets. CLL cells evade the normal processes of programmed cell death (apoptosis) by producing high levels of an anti-apoptotic protein Bcl-2. New drugs that counteract the protective effect of Bcl-2 have been developed. Moreover, it is also known that CLL cases requiring treatment depend largely on signals transmitted through their B-cell antigen receptor (BCR) for survival and proliferation. A class of drugs currently in use in the myeloid form of chronic leukaemia, tyrosine-kinase inhibitors (e.g. imatinib), inhibit key molecules involved in BCR signalling. Using primary human CLL samples and comparing with normal healthy controls this project aims to assess these two therapeutic approaches, focussing on their combination. This work will be performed by a haematology clinician and the results of the study have the potential to inform future clinical trials in CLL.

Chronic lymphocytic leukaemia (CLL) is the most common leukaemia in the western world. CLL is a disease with a variable clinical course, with many patients living with stable disease requiring no intervention, while others die within a few years despite treatment. Recent progress has been made in identifying prognostic factors, such as ZAP-70 expression, immunoglobulin heavy chain variable region mutation status, and cytogenetic abnormalities, which may predict those who are likely to require early therapy. As current chemotherapy cannot offer cure in CLL, novel therapeutic are being sought to eliminate minimal residual disease, and offer hope to those refractory to current treatments.
Recent advances in the understanding of CLL cell biology have opened up new therapeutic avenues. The Bcl-2 family of proteins regulate the intrinsic pathway of apoptosis, and are key mediators of CLL cell survival. Circulating CLL cells over-express Bcl-2 and related anti-apoptotic proteins, with resultant protection from apoptosis. Small-molecule Bcl-2 inhibitors have the ability to restore the normal balance of apoptotic proteins, and have shown promise in in vitro studies.
Additionally, it has been demonstrated that CLL cells in poor prognosis subgroups transmit survival signals through their B-cell antigen receptor (BCR), with significant cell division occurring in tissue ‘proliferation centres‘. Therefore, tyrosine kinase inhibitors that target the non-receptor tyrosine-kinases Abl and Lyn, which are activated downstream of the BCR, have the potential to disrupt these survival signals.
Utilising multi-parameter flow-cytometry and classical molecular and biochemical techniques we aim to investigate the ability of these two groups of drugs to target the molecular pathways responsible for mediating CLL cell survival, either alone or in combination. To achieve this, we have collected primary human CLL samples and relevant clinical information (Zap-70 expression and cytogenetics). CLL cells, and normal B lymphocytes as a control, will be treated with increasing concentrations of BCL-2Is or the TKI dasatinib, to assess whether selective apoptosis of malignanant lymphocytes occurs. Selected experiments will be repeated using CLL cells co-cultured with stromal cells +/- CLL cell mitogens, to assess whether these agents preferentially target cycling or quiescent CLL cells. Bcl-2Is and dasatinib will also be assessed in combination with established chemotherapeutic agents and with each other, in vitro. Ultimately, promising treatment schedules will be assessed in vivo using in a novel mouse model system of CLL developed in our laboratory. This translational project has the potential to inform future clinical trials of treatment of patients with CLL.