Alzheimer's disease (AD) is a neurodegenerative disease that leads to gradual loss of memory and cognitive functions – dementia. Its main pathological characteristics include the buildup of amyloid plaques and neurofibrillary tangles in the brain. Lately, the role of neuroinflammation has been increasingly recognized as an important factor in AD onset and progression. In response to pathological signals, immune cells of the central nervous system activate the inflammasome, which initiates the immune response: it activates caspase-1, a cysteine protease that activates pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18), which promote the inflammatory response. Additionally, caspase-1 cleaves gasdermin D, leading to pyroptosis, an inflammatory form of programmed cell death that results in neuronal loss.
In this master's thesis, we designed and synthesized covalent inhibitors of caspase-1 intended to suppress inflammation and pyroptosis, thereby contributing to reducing neurodegeneration. The aim of our work is therefore to synthesize new caspase-1 inhibitors that will be able to fill this gap in the promising field of designing drugs that affect the neuroinflammation process. We used the principle of fragment-based drug discovery and the fragment growing technique to synthesize and evaluate 16 caspase-1 inhibitors using in vitro biochemical assay on human, recombinant caspase-1. To a previously identified caspase-1 inhibitor, indoline-1-carbonyl fluoride, additional substituents were attached at various positions on the indoline ring. We observed that substituents at positions 5 and 6 of the indoline ring have a crucial impact on the inhibitory potency, with smaller substituents, such as nitro (27) and cyano (29) groups, being particularly favourable. Compound 27 was identified as the most potent caspase-1 inhibitor. Compounds with larger substituents at position 3, such as tert-butyl propanoate (25) and tert-butyl butanoate (26), are potent caspase-1 inhibitors, while their carboxylate derivatives 43 and 44 inhibit caspase-1 to a lesser extent. Substituents at position 7 are also unfavourable, leading to weaker inhibitors. We can conclude that the most favourable modifications for inhibitory activity include small substituents at position 5, larger lipophilic fragments at position 3, and also substituents at position 6 (methyl carboxylate) of indoline core. By exploring the chemical space of indoline-1-carbonyl fluoride, we obtained additional information that will be valuable for the further development of caspase-1 inhibitors of this chemical subtype.
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