Abstract

Most clinical cytotoxic cancer therapies induce cell death through
the intrinsic apoptotic pathway, which involves mitochondrial permeabilisation
followed by activation of the caspase cascade. This leads to an immunologically
silent cell death and a lack of an inflammatory response, which can promote
oncogenesis in surviving cells and lead to recurrence. Inhibition of the
caspase cascade combined with lethal cytotoxic stimulation will lead to cells
undergoing caspase independent cell death (CICD), a more immunogenic form of
cell death. Blockade of the caspase cascade in vitro and in vivo is
suggested to lead to activation of pro-inflammatory M1 macrophages and immune
clearance of tumours. There is potential therefore for a caspase inhibitor to
be used in conjunction with conventional cytotoxic therapies, to enhance the
immune clearance of tumour cells and augment the anti-tumour effect of these
treatments. This may be particularly effective as this approach would not just
target the cells sensitive to the chemotherapy, but may result in wider
clearance of cancer cells by activating the immune system.

Through performing druggability and structural assessments of the
caspase family we have identified potential compound binding sites. Further
validation of this approach and the development of biochemical and cellular screening
assays have been carried out at the Beatson DDU. Biochemical assays have been
developed in-house for a number of caspases as potential drug targets. We have
also characterised appropriate cellular assay systems to measure caspase
inhibition and CICD in human cancer cell lines, and have developed cell assays
to measure changes in the expression of cytokines and chemokines involved in
pro-inflammatory signalling and immune cell activation. Here we report the
development of a screening cascade of biochemical and cellular assays aimed at
supporting a

c

aspase drug discovery project.