Novel Approaches for the Modulation of Pin1 Prolyl Isomerase Activity

Pin1 is a peptidyl-prolyl isomerase that catalyses the cis-trans isomerisation of proteins at phosphorylated serine-proline and threonine-proline motifs (pS/pT-P). It regulates over 200 substrate proteins, influencing their catalytic and transcription activities, phosphorylation status, protein interactions, subcellular localization, and stability. Pin1 is vital for cellular processes like cell cycle, growth, motility, apoptosis, and neuronal differentiation. Its dysregulation is linked to diseases such as cancer, obesity, diabetes, inflammation, and neurodegeneration, making it a significant target for disease prevention and treatment. Despite many Pin1 inhibitors being developed, their preclinical success has been limited due to issues like poor specificity, cell permeability, solubility, and off-target effects. This thesis investigates Pin1 inhibition via dual-ligand cooperativity and examines other fundamental aspects of Pin1 structure and function.

Chapter 1 provides an introduction to Pin1 as a drug target, including its physiological role and reported inhibitors. Chapters 2 and 3 show cooperativity between Pin1 inhibitors (juglone, EGCG, and KPT-6566) using prolyl isomerase activity and ligand binding assays. Juglone and KPT-6566 demonstrated cooperative effects in Pin1 activity and substrate binding, reducing cell viability in breast cancer models. Chapter 4 discusses catalytic activity of Pin1, presenting data on the dynamic and allosteric effects of ligand binding. Chapter 5 explores sulfopin, a new covalent Pin1 inhibitor, highlighting its potential through allosteric substrate binding. Chapter 6 investigates the interaction between Pin1 and the nuclear factor-erythroid factor 2-related factor 2 (Nrf2), a transcription factor regulating genes involved in cellular protection and disease. Disrupting Pin1-Nrf2 interactions could reduce Nrf2-mediated cancer progression. Fluorescence polarisation experiments provided data on Pin1-Nrf2 interaction strength and the impact of Pin1 inhibitors. Key residues and domains, particularly the WW domain, were identified as potential drug targets.

In summary, this thesis offers diverse perspectives on modulating Pin1 activity, potentially paving the way for the development of Pin1 inhibitors in the future.