Apoptosis is of utmost importance in eliminating damaged and cancerous cells. Absence or impaired function of apoptosis can lead to various neurodegenerative, autoimmune, or cancerous diseases. One of the key proteins that inhibits apoptosis and thus promotes cell survival is Bcl-2. Many Bcl-2 inhibitors have been designed, but most showed poor solubility, unfavorable pharmacokinetics, and toxic effects. One of the well-tolerated BH3-mimetics proved to be the orally bioavailable compound S55746, which induces apoptosis even in low concentrations. However, such approaches for traditional inhibitor design are inadequate for targeting the vast majority of the human proteome which is pharmacologically difficult to access. Additionally, resistance to anticancer drug therapy can rapidly develop. Targeted protein degradation represents a new therapeutic alternative, which utilizes the cell's own endogenous mechanisms for inducing protein degradation. The development of chimeric molecules or proteolysis-targeted chimeras (PROTACs), which achieve proteolytic degradation by hijacking the ubiquitin-proteasome system has garnered immense interest in the last 20 years. The successful operation of PROTAC molecules depends on the appropriate selection of all three parts of the molecule: the ligand that binds to the protein of interest, the ligand for the E3 ligase, and the linker that connects the two ligands. These molecules are able to target proteins that have long been out of pharmacological reach and can achieve the desired effect even in very low concentrations due to their catalytic mechanism of action.
We synthesized the Bcl-2 ligand based on the compound S55746, modified in such a way that enabled linker attachment. To achieve the highest possible yield, a crucial synthetic step was optimized with an appropriate combination of variables (type and amount of catalyst, reaction time). The ligand for Bcl-2 was incorporated into a PROTAC by linking it with a rigid piperidine linker and the ligand for cereblon as the E3 ligase. The PROTAC molecule was tested on the HeLa cell line, and it was found that it did not induce degradation of the Bcl-2 protein.
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