Translational Studies in B-cell Malignancies: Studies on TP53 and BRAF

This thesis contains two distinct parts: Current models of Chronic Lymphocytic Leukaemia (CLL) pathogenesis invoke specialised anatomical microenvironments that harbour proliferating cells. Such proliferating CLL cells are more resistant to current immuno-chemotherapeutic regimens than cells in the peripheral blood and are thought to be the cause of disease relapse. Using a system to recapitulate CLL proliferation centres in vitro, I have observed that CLL cells undergo proliferation. Unexpectedly, under these conditions an induction of wild-type TP53 protein was also observed in all cases of CLL analysed. The results reported here were undertaken to understand how CLL cells upregulate TP53 protein and proliferate. For reasons that remain unclear, TP53 is unable to transactivate its classic target genes to induce cell-cycle arrest or apoptosis. However, it remains able to trigger a full apoptotic response after further DNA damage and a higher threshold of protein levels is reached. We propose a model whereby oxidative stress induced by proliferation in CLL triggers TP53 protein expression. Hairy Cell Leukaemia (HCL) represents approximately 2% of all leukaemias, follows an indolent course and remains an incurable disease. Recently, virtually all HCL patients shown to carry the BRAFV600E mutation, thought to be a disease-defining event. The BRAF V600E mutation results in constitutive activation of the MEK-ERK pathway resulting in aberrant proliferation, and targeted inhibitors have shown efficacy in BRAFV600E positive tumours. We wanted to test whether this efficacy can be extrapolated to HCL. Here we report in vitro studies using PLX4720 and in vivo trial of Vemurafenib in a patient with refractory HCL. While BRAF inhibition showed no effect on HCL survival in vitro, it resulted in rapid loss of viability of hairy cells in vivo. The results obtained show that efficacy of BRAF inhibition achieved did not occur via the expected inhibition of MEK-ERK activation.