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Phenotypic screening of drug molecules relies on the generation of a specific response; however the means by which this is elicited often remains unknown. Affinity chromatography is a valuable tool in the discovery of drug binding partners and may even allow the elucidation of the wider interactome of the initial drug target. The introduction of easily cleavable linkers and affinity-independent elution protocols to affinity chromatography is of current interest, since they render the technique much more adaptable with respect to the characterisation of biologically active species of interest. This thesis details the application of a novel azobenzene linker developed by the Hulme group for use in affinity-independent chromatography. The first chapter reviews recent developments in affinity chromatography and describes the synthesis of an affinity linker toolbox with both affinity-dependent and affinity-independent linkers. These linkers are functionalised with an azide moiety for use in CuAAC coupling to alkynyl derivatives of bioactive small molecules and have been modified to include photoreactive groups giving a series of linkers for use in the identification of less abundant, or low affinity, proteins. The first drug investigated, anisomycin (ANS), is a small molecule which was initially introduced as an antibiotic drug (Flagecidin). At nanomolar concentrations ANS has been shown to affect the mitogen activated protein kinase (MAPK) pathways; downstream effects of these pathways are thought to play a role in a range of pathological disorders such as Alzheimer’s disease, cancer and spinal muscular atrophy (SMA). ANS is thus a candidate for drug repurposing. Although the downstream effects of MAPK/SAPK pathway activation induced by anisomycin are well-documented, the cellular target has yet to be revealed. Previous work by the Hulme group has shown that the N-propargyl anisomycin derivative (I) retains the biological activity of the lead compound ANS. Thus to evaluate the cellular protein targets, N-propargyl ANS (I) was coupled onto the linker toolbox to create an ANS affinity probe library as described in chapter 2. The second drug investigated, fingolimod, was introduced as an immunomodulating drug (Glienya) for the treatment of multiple sclerosis (MS). This small molecule has also been shown to have anti-cancer properties in a range of cancer cell lines; however the precise mechanism by which this is effected is unknown. Literature precedent shows that terminal modification of fingolimod generates analogues which still retain biological activity. Thus a novel fingolimod alkyne derivative (II) was synthesised and used to create an affinity probe library as described in chapter 3. Chapter 4 describes affinity pull-down experiments conducted with the aim of finding the protein target(s) of ANS and fingolimod, using the affinity probe libraries generated in chapters 2 and 3. This chapter concludes with a discussion of the implications of these findings and directions for future study.

Diabetic cardiomyopathy is a distinct pathological condition characterized by myocardial fibrosis and cardiac dysfunction in diabetic patients. The resolution of myocardial fibrosis to improve cardiac function in diabetes is an active area of research. Notably, increased T lymphocyte infiltration into myocardium has been attributed to increased cardiac fibrosis and dysfunction in diabetes. However, the experimental data on the role of T lymphocyte modulation in diabetic myocardial fibrosis is scarce. To this end, sphingosine 1-phosphate receptor 1 (S1P1) regulates the egress of mature T lymphocytes from lymphoid organs to blood and peripheral organs. Thus, the inhibition of T cells trafficking through S1P1 receptor modulation is a potential translational approach to protect the heart in diabetes. We hypothesized that inhibition of T lymphocyte trafficking by modulating S1P1 receptor protects diabetic heart and ameliorates fibrosis. To accomplish this overarching objective, we conducted three related studies: (1) assess the effects of fingolimod (S1P1 receptor modulator) treatment in diabetes-induced myocardial fibrosis in mice; (2) study cardiac fibrosis and dysfunction in diabetes using conditional T-cell S1P1 knockout (TS1P1KO) mice; (3) evaluate the effects of CD4+ T cells transfer to TS1P1KO mice in diabetes-induced myocardial fibrosis and dysfunction.

Fingolimod is the first oral disease-modifying therapy approved for relapsing forms of multiple sclerosis (MS). Following phosphorylation in vivo, the active agent, fingolimod phosphate (fingolimod-P), acts as a sphingosine 1- phosphate (S1P) receptor modulator, binding with high affinity to four of the five known S1P receptors (S1P1, S1P3, S1P4 and S1P5). The mechanism of action of fingolimod in MS has primarily been considered as immunomodulatory, whereby fingolimod-P modulates S1P1 on lymphocytes, selectively retaining autoreactive lymphocytes in lymph nodes to reduce damaging infiltration into the central nervous system (CNS). However, emerging evidence indicates that fingolimod has direct effects in the CNS on MS relevant neural cell types including astrocytes, oligodendrocytes, neurons, and microglia. To study the roles of fingolimod and S1P signaling in MS, a transgenic activity reporter mouse was used in experimental autoimmune encephalomyelitis (EAE) to identify and characterize active cells during the disease process that may be altered by relevant S1P signaling. A subset of astrocytes is robustly activated at EAE sign onset in clusters that progressively expand along white matter tracts. The extent of astrocyte activation is highly correlated with disease severity and is limited by the loss of astrocytic S1P1. Transcriptome analyses of these EAE-activated astrocytes reveal several pathways that are both independently changed by astrocyte S1P1 knockouts and by fingolimod administration and concurrently changed by these S1P modulations. Among the pathways that have shared transcript differences in EAE-activated astrocytes from astrocyte S1P1 knockouts and by fingolimod administration, and control EAE-activated astrocytes, direct CNS effects of fingolimod may be uncovered.