Synthesis of chlorotoxin and its derivatives as enzyme inhibitors

Kesici, Mehmet Seçkin
Over the last decades, peptides have been heavily studied and proven beneficial in drug industry due to their high selectivity and potency compared to small organic molecules. A biologically and pharmaceutically significant peptide, chlorotoxin (CLTX), is one of the important peptide used in cancer studies. It is a neurotoxin, isolated from the venom matrix of Israeli Scorpion, Leirius quinquestriatus and it contains 36 amino acids and four disulfide bridges at a molecular mass of about 4 kDa. CLTX is mostly known for having strong interaction and inhibition with the matrix metalloproteinase-2 (MMP-2) enzyme, which is a zinc dependent enzyme and able to cleave all constituents in extracellular matrix. In this thesis, CLTX and its derivatives were synthesized with the microwave assisted solid phase peptide synthesis (SPPS) based on 9-fluorenylmethyloxy-carbonyl (Fmoc) chemistry strategy in order to explain and improve inhibition of CLTX on MMP-2. Based on the preliminary docking results, lysine-15 position has a close proximity to catalytic zinc ion of MMP-2. In the light of these findings, two more positions (lysine-23 and histidine-10) were included to amino acid residues that will be modified because they were amenable to chemical modifications and located in protein interaction loop regions. In the modifications of lysine residues, elongation reactions were performed with three different amino acids with different number of carbons (glycine, methionine and cysteine). Methyltrityl (Mtt) protected lysine was used in the synthesis of CLTX in order to make the modifications on the solid support by the selective deprotection of Mtt group. In the modification of histidine-10 residue, Fmoc-Dap(N3)-OH were used instead of histidine and modified by using copper(I) catalyzed azide-alkyne cycloaddition on solid phase (CuAAC-SP) with propargyl alcohol and propargyl amine. At the end of this reaction triazole ring was formed as a histidine analogue with an extra binding site. Biologic activity assays were applied on finalized modified CLTXs. As a result, it was planned to synthesize eight different CLTX modifications (three for two of lysines and two for histidine). Synthesis and activity tests of two of lysine-15 modifications were completed. Unexpectedly, lysine modified CLTX derivatives increased MMP-2 activity, 2 fold for P8F and 1.5 fold for P7F, rather than inhibition. Four modified CLTXs at lysine residue (one of them at lysine-15 and three of them at lysine-23) were successfully synthesized and activity assays will be completed. Optimization studies for the histidine-10 modifications were successfully completed on a short test peptide (6 amino acid sequenced). The optimized modification procedures will be applied to CLTX.  


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Citation Formats
M. S. Kesici, “Synthesis of chlorotoxin and its derivatives as enzyme inhibitors,” M.S. - Master of Science, Middle East Technical University, 2017.