Cyclotides as templates in drug design

doi:10.1016/j.drudis.2009.10.007

Drug Discovery Today

Volume 15, Issues 1–2, January 2010, Pages 57-64

https://doi.org/10.1016/j.drudis.2009.10.007 Get rights and content

Cyclotides are remarkably stable proteins from plants that have a range of pharmaceutical and agricultural applications based on both their various bioactivities and their potential for use as stable protein-engineering templates. This article discusses literature on pharmaceutically relevant activities of cyclotides, including anti-HIV, antimicrobial and cytotoxic activities, and evaluates their potential therapeutic applications. Their applications as templates for the design of antiangiogenic agents for the treatment of cancer and as anti-infective agents are also described. Toxic effects of cyclotides, whose native function is as insecticidal agents, can be removed by simple mutagenesis, thus rationalizing the apparent conundrum of proposing insecticidal agents as leads for human therapeutics.

Section snippets

Anti-HIV activity

The most extensively investigated biological activity of cyclotides is their anti-HIV activity, which was first reported by Gustafson et al. [14] as part of a screening program at the U.S. National Cancer Institute for novel anti-HIV natural products. In this study, two macrocyclic peptides (circulin A and B) from the bark of an African tree were shown to inhibit the HIV infection of different host cell lines [14]. Subsequent reports showed that a range of other cyclotides, belonging to

Toxicity

Some cyclotides have been reported to have several toxic effects, not least of which is their insecticidal activity 2, 3, 54, as well as activity against a range of other organisms, including mollusks [55], barnacles [56] and nematodes 57, 58, 59. Because none of these toxic activities are directed at mammals, they are not necessarily of concern for the development of cyclotides as human therapeutics, although the existence of any degree of toxicity needs to be taken into consideration for

Bioengineering of cyclotides

In our view, the most promising application of cyclotides as therapeutics will probably derive not from the exploitation of the bioactivities of naturally occurring examples but from the use of cyclotide structures as peptide templates for the stabilization of bioactive peptide epitopes. The potential use of cyclotides as a scaffold for therapeutic purposes has emerged, not only because of their high resistance to thermal, enzymatic and chemical degradation [5] but also because of the rapidly

Concluding remarks

Cyclotides are still at an early stage of development as therapeutics, but there are promising indications that they might prove useful in the not-too-distant future. So far, several therapeutically relevant bioactivities have been reported for a range of naturally occurring cyclotides but, in all cases, the potencies are not sufficient to justify progression into human trials, and combined with residual toxicity concerns, native cyclotides have not yet reached the clinic. A much more promising

Acknowledgements

Studies in our laboratory on cyclotides are supported by grants from the Australian Research Council (DP0880105) and the National Health and Medical Research Council (NHMRC). D.J.C. is an NHMRC Professorial Fellow. S.T.H. is a Marie Curie Postdoctoral Fellow awarded by European Commission (PIOF-GA-2008-220318).

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Cyclotides are plant-derived peptides characterized by an ∼30-amino acid–long cyclic backbone and a cystine knot motif. Cyclotides have diverse bioactivities, and their cytotoxicity has attracted significant attention for its potential anticancer applications. Hybanthus enneaspermus (Linn) F. Muell is a medicinal herb widely used in India as a libido enhancer, and a previous study has reported that it may contain cyclotides. In the current study, we isolated 11 novel cyclotides and 1 known cyclotide (cycloviolacin O2) from H. enneaspermus and used tandem MS to determine their amino acid sequences. We found that among these cyclotides, hyen C comprises a unique sequence in loops 1, 2, 3, 4, and 6 compared with known cyclotides. The most abundant cyclotide in this plant, hyen D, had anticancer activity comparable to that of cycloviolacin O2, one of the most cytotoxic known cyclotides. We also provide mechanistic insights into how these novel cyclotides interact with and permeabilize cell membranes. Results from surface plasmon resonance experiments revealed that hyen D, E, L, and M and cycloviolacin O2 preferentially interact with model lipid membranes that contain phospholipids with phosphatidyl-ethanolamine headgroups. The results of a lactate dehydrogenase assay indicated that exposure to these cyclotides compromises cell membrane integrity. Using live-cell imaging, we show that hyen D induces rapid membrane blebbing and cell necrosis. Cyclotide–membrane interactions correlated with the observed cytotoxicity, suggesting that membrane permeabilization and disintegration underpin cyclotide cytotoxicity. These findings broaden our knowledge on the indigenous Indian herb H. enneaspermus and have uncovered cyclotides with potential anticancer activity.
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ReviewPost ScreenCyclotides as templates in drug design

Section snippets

Anti-HIV activity

Toxicity

Bioengineering of cyclotides

Concluding remarks

Acknowledgements

J. Mol. Biol.

J. Ethnopharmacol.

Toxicon

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

FEBS Lett.

J. Biol. Chem.

Anal. Biochem.

J. Inorg. Biochem.

J. Biol. Chem.

Phytochemistry

Biochim. Biophys. Acta

Biophys. J.

Arch. Biochem. Biophys.

Acta Trop.

Int. J. Biochem. Cell Biol.

Biophys. J.

Biosynthesis and insecticidal properties of plant cyclotides: the cyclic knotted proteins from Oldenlandia affinis

Proc. Natl. Acad. Sci. U. S. A.

Plant cyclotides disrupt epithelial cells in the midgut of lepidopteran larvae

Proc. Natl. Acad. Sci. U. S. A.

Isolation of oxytocic peptides from Oldenlandia affinis by solvent extraction of tetraphenylborate complexes and chromatography on sephadex LH-20

Lloydia

Thermal, chemical, and enzymatic stability of the cyclotide kalata B1: the importance of the cyclic cystine knot

Biochemistry

Some molecular properties of kalata peptide B-1. A uterotonic polypeptide isolated from Oldenlandia affinis DC

Medd. Nor. Farm. Selsk.

An oxytocic principle found in Oldenlandia affinis DC

Medd. Nor. Farm. Selsk.

Elucidation of the primary and three-dimensional structure of the uterotonic polypeptide kalata B1

Biochemistry

A common structural motif incorporating a cystine knot and a triple-stranded β-sheet in toxic and inhibitory polypeptides

Protein Sci.

Hämolytisch aktive komponenten aus Viola tricolor L. und Viola arvensis Murray

Sci. Pharm.

Cyclopsychotride A, a biologically active, 31-residue cyclic peptide isolated from Psychotria longipes

J. Nat. Prod.

Circulins A and B: novel HIV-inhibitory macrocyclic peptides from the tropical tree Chassalia parvifolia

J. Am. Chem. Soc.

Seven novel macrocyclic polypeptides from Viola arvensis

J. Nat. Prod.

Fractionation protocol for the isolation of polypeptides from plant biomass

J. Nat. Prod.

Discovery, structure and biological activities of the cyclotides

Curr. Protein Pept. Sci.

Solution structure of the squash trypsin inhibitor MCoTI-II. A new family for cyclic knottins

Biochemistry

Review
Post Screen
Cyclotides as templates in drug design