Isolation and characterization of cytotoxic cyclotides from Viola philippica

• Published in: Peptides (New York, N.Y. : 1980) N.Y. : 1980), 2011-08, Vol.32 (8), p.1719-1723
• Main Authors: He, Wenjun, Chan, Lai Yue, Zeng, Guangzhi, Daly, Norelle L., Craik, David J., Tan, Ninghua
• Format: Article
• Language: English
• Subjects: active ingredients; Amino Acid Sequence; Antineoplastic Agents, Phytogenic - chemistry; Antineoplastic Agents, Phytogenic - isolation & purification; Antineoplastic Agents, Phytogenic - pharmacology; antiretroviral agents; Backbone; Biological and medical sciences; Cell Line, Tumor; Cyclic peptides; Cyclotides; Cyclotides - chemistry; Cyclotides - isolation & purification; Cyclotides - pharmacology; Cytotoxic activity; cytotoxicity; Digestion; disulfide bonds; drugs; enzymatic treatment; Fundamental and applied biological sciences. Psychology; HeLa Cells; hemolysis; Humans; Ingredients; Molecular Sequence Data; Oriental traditional medicine; Peptides; Plants (organisms); Reduction; Sequencing; Structure-Activity Relationship; structure-activity relationships; Surgical implants; tandem mass spectrometry; Vertebrates: endocrinology; Viola; Viola - chemistry; Viola philippica; Violaceae; Viphi A–H
• ISSN: 0196-9781; 1873-5169
• DOI: 10.1016/j.peptides.2011.06.016

• Eight new cyclotides were characterized from the Viola philippica. • All cyclotides were evaluated for their cytotoxic activity. • The novel cyclotides enhance the sequence variation observed for cyclotides. Cyclotides are a large family of plant peptides characterized by a macrocyclic backbone and knotted arrangement of three disulfide bonds. This unique structure renders cyclotides exceptionally stable to thermal, chemical and enzymatic treatments. They exhibit a variety of bioactivities, including uterotonic, anti-HIV, cytotoxic and hemolytic activity and it is these properties that make cyclotides an interesting peptide scaffold for drug design. In this study, eight new cyclotides (Viphi A–H), along with eight known cyclotides, were isolated from Viola philippica, a plant from the Violaceae family. In addition, Viba 17 and Mram 8 were isolated for the first time as peptides. The sequences of these cyclotides were elucidated primarily by using a strategy involving reduction, enzymatic digestion and tandem mass spectroscopy sequencing. Several of the cyclotides showed cytotoxic activities against the cancer cell lines MM96L, HeLa and BGC-823. The novel cyclotides reported here: (1) enhance the known sequence variation observed for cyclotides; (2) extend the number of species known to contain cyclotides; (3) provide interesting structure–activity relationships that delineate residues important for cytotoxic activity. In addition, this study provides insights into the potential active ingredients of traditional Chinese medicines.