Targeted protein degradation technology, including proteolysis-targeting chimeras (PROTACs), offers great potential for modulating the activity of proteins that are difficult targets for conventional small molecules. Many of these proteins play key roles in the development of neurodegenerative diseases such as Alzheimer's and Parkinson's. The advantage of this technology is that a single PROTAC molecule causes the degradation of multiple molecules of the target protein requiring a lower dose of drug.
The isoforms of monoamine oxidase; monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B) play a multifaceted role in neuronal function and healthy brain. In addition, synthetic and natural inhibitors of these two isoforms have neuroprotective effects. Numerous studies confirm their efficacy in alleviating disease symptoms and progression of mood disorders, neurodegenerative disorders, and certain cancers.
As part of our master’s thesis, we designed and synthesised pomalidomide-based MAO-A proteolysis-targeting chimeras. The PROTAC molecule consists of harmine (ligand for human (h)MAO-A) and pomalidomide (ligand for E3 ligase) connected by linkers of different structures. The synthesis was based on harmine demethylated at the methoxy group under acidic conditions. The resulting phenol was alkylated with a previously prepared linker containing tert-butyloxycarbonyl protected amine moiety on one side and an electrophilic alkyl bromide on the other side of the molecule. Subsequently, the protecting group was removed by acidolysis and the amine was reacted with 4-fluorothalidomide. Four molecules with linkers of different lengths (hexyl, diethylene glycol, triethylene glycol, and tetraethylene glycol) were synthesised by the described route, ant the analytical data for the putative triethylene glycol derivative were not in accordance with the expected structure. The results of the biochemical assay on isolated hMAO-A showed that three derivatives inhibited the enzymatic activity of hMAO-A with IC50 values in the nanomolar range, whereas the triethylene glycol analogue was inactive. For the three derivatives that inhibited hMAO-A and therefore bound to the active site, we tested whether they induced hMAO-A degradation in the neuroblastoma SH-SY5Y cell line. According to the preliminary results, unfortunately, the degradation of hMAO-A was not effective.
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