Synthesis of Linear and cyclic peptides analogues of Longicalycinin A and evaluation of toxicity effects on cancerous cells HepG2 and HT-29

Abstract

In this work, linear and cyclic peptides analogues of Longicalycinin A, known as a natural cyclopeptide anticancer agent, have been designed and successfully synthesized by solid phase peptide synthesis methodology of Fmoc/t-Bu. 2-Chlorotrityl chloride resin (2-CTC) was used as solid support. The synthesized linear (Ot-Bu) Longicalycinin A analogues were cleavaged by the method of partial cleavage for the separation of the solid phase. The final deprotection was performed by treatment with TFA 95% containing scavengers to achieve deprotected linear Longicalycinin A analogues. Macrocyclization of deprotected cyclic Longicalycinin A analogues were characterized by different instrumental methods using FT-IR, LC-MS, 1H-­NMR and 13C-­NMR. Deprotected linear and cyclic analogues, synthesized as such, were evaluated for their toxic activity against cell lines of HepG2 (human liver cancer cell line) and HT-29 (human colorectal adenocarcinoma cell line) using MTT assay. The synthetic linear and cyclic analogues showed relatively good activity against cell lines of HepG2 and HT-29 with IC50 values from 8.76 to 17.2 µg/mL and 9.06 to 17.34µg/mL, respectively, in comparison to standard drug 5-fluorouracil (5-FU). Safety profile of the synthesized liner and cyclic analogues of Longicalycinin A were also examined using skin Fibroblast cells. Among the linear peptides, linear compounds 1, 8, 12, 13 and 14, showed a considerable toxicity activity on cancer cell lines HT-29 than HepG2 along with a high safety on normal cells and among the cyclic peptides, compound 5, considering the property of toxicity action good enough on cancerous cell lines along with high safety profile on normal skin cells, can be good candidates for developing new anticancer agents