Synthesis and bioactivity studies of some carbocyclic and heterocyclic compounds as potential proteasome inhibitors

The ubiquitin proteasome system (UPS) is the main proteolytic system in the nucleus and cytosol of all eukaryotic cells. This system is important for the destruction of most of the proteins involved in many important biological processes such as cell growth, cell differentiation, apoptosis, signal transduction, DNA repair, antigen process and inflammatory response. The molecular and functional characteristics of the UPS have been investigated and it has been revealed that many disorders within this system are related with many diseases such as brain ischemia, musculer disorders, inflammation, autoimmune diseases, cystic fibrosis, viral infections, diabetes, stroke, neurodegenerative diseases, heart diseases and especially cancer. Therefore, the development of inhibitors specifically targeting the components of the ubiquitin proteasome system has been assumed as a favourable strategy for the treatment of these diseases. Proteasome, a multiprotease enzyme complex, is a major component of the ubiquitin proteasome system and it plays an important role in the protein degradation pathway. Importance of proteasome as a therapeutic target has been proved by the clinical success of Bortezomib. Bortezomib, a dipeptidyl boronic acid derivative, is the first proteasome inhibitor approved by the US Food and Drug Administration (FDA) for the treatment of multiple myeloma. Despite the clinical benefits of bortezomib in the treatment of multiple myeloma, new selective proteasome inhibitors are still required because of its crucial side effects, drug resistance potential and insufficient pharmacokinetic properties. For this purpose, research studies for the discovery of new and selective proteasome inhibitors have been going on by many research groups. As a result of these investigations, the naphthoquinone derivative encoded PI-083 has recently been reported as a proteasome inhibitor. It has been shown that PI-083 has a broader antitumor activity and is more selective against cancer cells compared to bortezomib in vitro and in vivo. Therefore, napthoquinone scaffold of PI-083 have been acknowledged as promising core structure for the development of new proteasome inhibitors. In our dissertation, PI-083-encoded proteasome inhibitor was selected as the lead compound in order to develop therapeutically effective and selective new proteasome inhibitors and the hypothetical pharmacophore structure predicted by the structure-activity relationship studies on this compound has been realized. With this purpose 41 compounds of sulfonamide and carboxamide derivatives bearing naphthoquinone core were designed and synthesized. Structural identification of the synthesized compounds were confirmed by spectral (IR, 1H NMR, MS) and elemental analysis methods. The antiproteasomal activities of the compounds on the human breast cancer cell line (MCF-7), the cytotoxic properties and the total polyubiquitinated protein accumulation levels of the compounds were determined by WST-1 cell proliferation assay and the immunoblotting technique, respectively. Morevover, inhibition of proteasomal chymotrypsin-like activity of compounds which cause high level of polyubiquitinated protein accumulation has been investigated by fluorometric method in vitro. According to the biological activity results, it has been observed that our compounds with sulfonamide and carboxamide structure cause cytotoxic activity and polyubiquitinated protein accumulation at various ratios. The evaluation of the inhibition of chymotrypsin-like activity of the selected compounds which cause high level of polyubiquitinated protein accumulation has revealed that the sulfonamide derivative bearing 2-chloro-3-pyridyl group on amide nitrogen encoded NS26 exhibited significant (p<0.05) proteasome chymotripsin-like activity inhibition compared to the lead compound. We believe that data obtained from this study will significantly contribute for the discovery of novel proteasome inhibitors, as well as provide significant contributions to the literature.