Anti-apoptotic proteins play a fundamental role in cell survival. Under physiological conditions, such proteins trigger apoptosis in defective or damaged cells only; under pathological conditions, however, they can be dysregulated allowing the cells to survive despite being harmful. Considering the importance of anti-apoptotic proteins in many physio-pathological roles, their specific inhibition is an attractive strategy to develop safe therapeutics. This thesis describes the inhibition of two classes of anti-apoptotic proteins:

1. Inhibition of the anti-apoptotic protein CK2 to develop novel anti-cancer molecules targeting pockets outside the well-conserved ATP-binding site: -Using a Fragment-Based-Drug-Discovery (FBDD) approach twelve small molecule inhibitors of CK2 were developed. The lead molecule, 3l, inhibited the catalytic activity of CK2α by binding in the cryptic αD pocket with a Kd of 4 μM. 3l stopped proliferation of colorectal cancer cells with a GI50 of 10 μM and presented improved drug-like properties and selectivity compared to previously reported inhibitors. Remarkably, 3l has the potential to be developed into a potent and selective anticancer drug. -Using a combination of rational-based approach and peptide stapling, twenty-two conformationally-constrained peptides were generated to target the protein-protein interaction (PPI) of CK2 and affect its function. The lead peptide, P7-F1C5, presented a novel, highly-functionalised constraint that allowed the molecule to become cell-permeable, exert its anti-proliferative activity in cancerous cells, and to become resistant to serum proteases. P7-F1C5 is the first macromolecule reported in the literature that binds to CK2α with sub-micromolar affinity (Kd 150 nM), and that can act as a chemical probe for targeting the PPI of CK2.
2. Inhibition of the anti-apoptotic Bcl-2 proteins to dissect their role in platelet activation and apoptosis. Bcl-2 proteins regulate cell lifespan; however, their role in non-nucleated platelets is not fully understood. The elucidation of these pathways in platelets is crucial to the development of selective anti-platelet therapeutics. To this end, this thesis describes the development and the first application of twenty-seven BH3-only peptides in human platelets highlighting how peptides can provide an alternative to conventional methodologies to study PPIs in platelets. The most promising peptide, P9-F5C5, engaged the anti-apoptotic protein Bcl-xL with 26 nM affinity and reviled a new role for the protein Bim in platelet activation.