Marine cyclic peptides

Dear Colleagues,

Marine organisms have proven to be a rich source of bioactive metabolites yielding diverse structural classes. Bioactive peptides are among the most abundantly present marine secondary metabolites. A number of these peptides have successfully found their way to clinical studies. Kahalalide F (KF), is an example of cytotoxic depsipeptide isolated from the sacoglossan mollusk Elysia rufescens and its food the green alga Bryopsis sp. KF showed, selectivity against solid tumor cell lines with an IC₅₀ < 1.0 μg/mL. KF is currently undergoing phase II clinical trials under development by PharmaMar as a potential treatment for solid tumors. Aplidin (APL), is a new antitumoral drug from marine origin isolated from the tunicate Aplidium albicans, and currently in phase II clinical trials against a wide range of cancers. Dolatstatin-10 is a potent antimitotic pentapeptide isolated from the marine mollusk Dolabella auricularia that inhibits microtubule assembly. It is currently in phase II trials in patients with advanced hepatobiliary cancers and pancreatic adenocarcinoma.

Structurally marine peptides are greatly varied. They may be cyclic, linear, or depsipeptides. Numerous marine peptides possess the rare D-amino acids, or modified features like fatty acids or hydroxy amino acids. A large number of cyclic peptides have been identified from marine invertebrates, with the greatest number isolated from marine sponges. 

The IUPAC system for nomenclature identified a peptide as a molecule that contains at least one amide bond between two amino acid residues. Cyclic peptides were classified into homodetic cyclic peptides or heterodetic cyclic peptides. A homodetic cyclic peptide ring contains only eupeptide bonds, which are amide bonds between the a-carboxylic group of one amino acid and the a-amino group of another. A heterodetic cyclic peptide consists of amino acids residues but the amide bonds are not only eupeptide bonds but also contains at least one isopeptide bond, which is an amide bond but not between two amino acids.

Cyclic peptides have been isolated from number of marine taxa, and have shown several bioactivities with remarkable cytotoxicty against number of tumor cell lines. In this review, we are discussing cyclic peptides isolated from marine origin, focusing on the structural features and the biological activities.

Prof. Rabab Mohammed

Section Editor