No description available.

The cyclotides are a family of naturally occurring peptides characterized by cyclic cystine knot (CCK) structural motif, which comprises a cyclic head-to-tail backbone featuring six conserved cysteine residues that form three disulfide bonds. This unique structural motif makes cyclotides exceptionally resistant to chemical, thermal and enzymatic degradation. They also exhibit a wide range of biological activities including insecticidal, cytotoxic, anti-HIV and antimicrobial effects. The cyclotides found in plants exhibit considerable sequence and structural diversity, which can be linked to their evolutionary history and that of their host plants. To clarify the evolutionary link between sequence diversity and the distribution of individual cyclotides across the genus Viola, selected known cyclotides were classified using signature sequences within their precursor proteins. By mapping the classified sequences onto the phylogenetic system of Viola, we traced the flow of cyclotide genes over evolutionary history and were able to estimate the prevalence of cyclotides in this genus. In addition, the structural diversity of the cyclotides was related to specific features of the sequences of their precursor proteins, their evolutionary selection and expression levels. A number of studies have suggested that the biological activities of the cyclotides are due to their ability to interact with and disrupt biological membranes. To better explain this behavior, quantitative structure-activity relationship (QSAR) models were developed to link the cyclotides’ biological activities to the membrane-interactive physicochemical properties of their molecular surfaces. Both scalar quantities (such as molecular surface areas) and moments (such as the distributions of specific properties over the molecular surface) were systematically taken into account in the development of these models. This approach allows the physicochemical properties of cyclotides to be geometrically interpreted, facilitating the development of guidelines for drug design using cyclotide scaffolds. Finally, an optimized microwave-assisted Fmoc-SPSS procedure for the total synthesis of cyclotides was developed. Microwave irradiation is used to accelerate and improve all the key steps in cyclotide synthesis, including the assembly of the peptide backbone by Fmoc-SPPS, the cleavage of the protected peptide, and the introduction of a thioester at the C-terminal carboxylic acid to obtain the head-to-tail cyclized cyclotide backbone by native chemical ligation.

During the last decade there has been increased interest in the cyclotide protein family, which consist of a circular chain of approximately 30 amino acids, including six cysteines that form three disulfide bonds, arranged in a cyclic cystine knot motif. This thesis gives new insights in cyclotide distribution and occurrence in the plant family Violaceae, structure-activity relationships for cytotoxic effects, membrane disruption and adsorption on lipid membranes, and evaluates toxicity and anti-tumor activity in vivo. A large-scale analysis was done on over 200 samples covering 17 of the 23 genera in Violaceae, and cyclotides were positively identified in almost 150 of approximately 900 known species. Conclusions are that the Violaceae is an extremely rich source of cyclotides, and that they are ubiquitous among all species in that plant family. After investigating the cyclotides' cytotoxicity it was evident that the effects were immediate and occurred at low micromolar concentrations. To understand the relationships between structure and activity, approximately 30 cyclotides and cyclotide derivates were assayed for cytotoxicity. Results showed that the overall charge is of minor influence on activity and revealed a strong correlation between an intact hydrophobic molecular surface and cytotoxic effect. The cytotoxic activity is mainly due to interactions between peptides and target membranes, illustrated by prototypic cyclotides' ability to induce liposome leakage and adsorb to lipid membranes. Cyclotides were strongly lytic against zwitterionic liposomes, less when cholesterol was included, while for anionic liposomes, activity depend on the net charge of cyclotide. A similar pattern was observed for the adsorption of the cyclotides to anionic bilayers, in which strong lytic activity was coupled with high adsorption. To further evaluate cyclotides cytotoxic effects, in vivo studies were conducted, both for acute toxicity and anti-tumor efficacy in mice. Two different methods were used: hollow fiber method and traditional xenografts, but no significant anti-tumor effects were detected. The results indicate that anti-tumor effects are minor or absent at tolerable doses and that cyclotides have a very abrupt in vivo toxicity profile, with lethality after single injection at 2.0 mg/kg.

Discovery of cheap, nontoxic and readily available antiatherosclerotic drugs is an extraordinary challenge in this modern world. Atherosclerosis and cardiovascular diseases have been predicted to be the leading cause of death by the year 2030. Hence, this thesis was designed to search for plant (s) with anti-atherogenic properties, investigate its possible side effects and extrapolate its likely mechanism(s) of action. An ethnobotanical survey was employed in identification of locally important plants used for the management and treatment of cardiovascular diseases and its predisposing factors in Nkonkobe Municipality, Eastern Cape in South Africa. Information on the names of plants, their parts used and methods of preparation was collected through a questionnaire which was administered to herbalists, traditional healers and rural dwellers. The most frequently used plant (Rhizomes of Tulbaghia violacea Harv.) was investigated for toxicity using brine shrimp lethality (in vitro) and in vivo toxicity test (acute and subchronic) on rats to determine safety dosage. The in vitro antioxidant and free radical scavenging activity of the plant was investigated using models such as 1,1-diphenyl-2- picrylhydrazyl (DPPH), superoxide anions, hydrogen peroxide (H2O2), nitric oxide (NO), 2,2’- azinobis [3-ethylbenzothiazoline-6-sulfonic acid] diammonium salt (ABTS), lipid peroxidation inhibition and the ferric reducing agent. Phytochemical content and the effect of oral administration of fresh methanolic extract rhizomes of Tulbaghia violacea (250, 500 mg/kg. bwt/day) on Lipid peroxidation (TBARS), serum and tissue antioxidant enzymes in normal, hypercholesterolemic and diet induced atherogenic rats were also assessed. More so, the potential of the extract (250 and 500 mg/kg. bwt) to protect against atherogenic diet (4 percentage cholesterol 1 pecentage cholic acid and 0.5 percentage thiouracil) induced fatty streaks formation, dyslipidemia, oxidative stress and endothelial dysfunction was also investigated. Ethnobotanical study revealed that 19 plant species are used for the treatment of heart related diseases in the Municipality. 53 percentage of the plants mentioned were used for the management of chest pain, 47 percentage for high blood pressure, 42 percent for heart disease, 16 percentage for stroke and 11 percentage for the treatment of hypercholesterolemia. Tulbaghia violacea was repeatedly mentioned as the plant species used for the treatment of high blood pressure and predisposing factors in the study area. The brine shrimp cytotoxicity test revealed that fresh, dried methanolic extracts and essential oil of the T. violacea exhibited a high degree of cytotoxic activity with IC50 values of 18.18 (fresh) and 19.24 (dried) μg/ml. An IC50 value of 12. 59 μg/ml was obtained for the essential oil of the plant. The low cytotoxicity values obtained, suggested that rhizome of T. violacea may serve as a potential source of antimicrobial and anticancer agents. In vivo acute study of single oral administration of 5g/kg dose does not produce mortality or significant behavioral changes during 14 days observation. In the sub-chronic study, the extract (250, 500 mg/kg/bwt/ day) administered for a period of 28 days showed no mortality or morbidity. The weekly body and organ weight of the rats showed no significant differences between the control and the rats treated with the extract. The extract at all doses does not show any effect on of biomarkers of liver or renal damage. However, a significant decrease in the activity of ƔGT was observed in the extract treated groups. Hematological evaluation revealed that oral administration of fresh methanolic extracts of rhizomes of T. violacea does not cause anaemia or leucocytosis in the animals. Furthermore, histopathology results of the internal organs revealed no detectable inflammation. These results demonstrated that the rhizome extract of T. violacea was potentially safe for consumption orally even in chronic concentration. In vitro antioxidant evaluation showed that the essential oil, fresh and dried methanolic extracts exhibited potent antioxidant activities in a concentration dependent manner. Phytochemical investigation reveals that the fresh and the dry extract of RTV are rich in flavonoid, flavonol, phenols, tannin and proanthocyanidin, while the essential oil contained dimethy disulfide, dimethyl trisulfide, (methyl methylthio) methyl, 2,4-dithiapentane (11.35 percent) and (methylthio) acetic acid, 2- (methylthio) ethanol, 3-(methylthio) - and propanenitrile (7.20 percent). The fresh extract had higher radicals scavenging activity than the essential oil or dried extract, with 50 percentage inhibition of DPPH, hydrogen peroxide and lipid peroxidation at a concentration of 35.0 ± 0.12, 19.3 ± 0.11 and 17.9 ± 0.15 μg/ml respectively. Oral administration of methanolic extract of RTV in 125, 250 and 500 mg/kg to female Wistar rats significantly inhibited reduction of glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT). The extracts also inhibited (p< 0.05) lipid peroxidation in normal, high cholesterol and diet induced atherosclerosis fed rats in a dose dependant manner. Also the extract (250 and 500 mg/kg/bwt/day) caused a significant (p<0.05) improvement in body weight of treated animals compared with untreated hypercholesterolemia control rats. The extracts also protected significantly (p<0.05) against atherogenic diet induced liver damage or fatty streaks formation in the aorta as revealed by histological examination. The anti-cholesterolemia and anti-atherosclerotic activities of the extract compared favorably well with standard drugs Gemfibrozil and Atorvastatin respectively. Conclusively, rhizomes of T. violacea possess significant anti-atherogenic activity and its mechanism of action(s) may be due to its antioxidant and anti-hypercholesterolemia properties. The results of this study also suggested that rhizome of T. violacea is relatively safe for human consumption and it may be used as an alternative to garlic.

Orientador: Vanderlan da Silva Bolzani / Co-orientador: Alberto José Cavalheiro / Banca: Humberto Márcio Santos Milagre / Banca: Alessandra Regina Pepe Ambrozin / Resumo: Os ciclotídeos são produtos natura is de estrutura polipeptídica, contendo de 2 8 a 37 resíduos de aminoácidos, sendo seis deles resíduos de cisteína, altamente conservados e formados por ligações dissulfeto as quais exib em ciclização tipo "cabeça - cauda". Ess e arranjo estrutura l característico co nfere aos ciclotí deos uma estabilidade excepcional e resistência à proteólise . Devido a estas peculiaridades moleculares os ciclotídeos são substâncias com importante s funç ões biológica s, entre elas, de stacam - se as de defesa e adaptação dos organismos que as acumulam . São de gran de interesse para agricultura, agindo como inseticida s e, no uso medicinal p or apresentarem atividades anti - HIV, anti - helmíntic a, antimicrobian a e efeitos uterotônicos . A presente dis sertação trata d o estudo de ciclotídeos isolados d a planta Noisettia orchidiflora (Rudge) Gingins, pertencente à família Violaceae, um táxon de ocorrência frequente n a Mata Atlântica . Já existem dados na literatura sobre o estudo de ciclotídeos das raíze s e o presente estudo é importante na medida que registra a ocorrência desta classe de substâncias e a sua caracterização nas folhas e galhos desta espécie, levando a informações mais completas sobre a ocorrência de ciclotídeos em Violaceae . A extração de c iclotídeos do material vegetal ( galhos e folhas secos e moído s ) foi feita mediante maceração hidrometanólica até esgotamento do material vegetal, seguid a de partição líquido - líquido com diclorometano. A fase polar foi concentrada e submetida à crom atografia em coluna, empregando octadecilsilano (C 18 ) como fase estacioná ria, obtendo - se frações ricas em peptídeos. O processo de purificação foi realizado p or HPLC preparativ o e/ou analític o com eluição gradiente, empregando - se acetonitrila e ág ua como fase móv e l, o que permitiu a obt... / Abstract: C yclotides are pol ypeptide str uctures, c omprise 2 8 - 37 amino acid residues, six of the m, are cysteine residues, highly conserved and formed by disulfide bonds, which exhibit "head - tail" cyclization type. This structural feature gives to cyclotides remarkable stability and resistance to proteolysis. Due to these singularities, such compound s have disclosed important biological functions . A mong the m ; the literature has highlighted important ecological properties as defense and adaptation of the organisms, which accumulate these natural products. Accordingly, they are of great interest to agri culture, acting as insecticide, and to medicine, since some compounds have displayed anti - HIV activity, anthelmintic, antimicrobial and uterotonic properties. This research deals with the study of cyclotides isolated Noisettia orchidiflora (Rudge) Gingins, belonging to the taxon Violaceae, which frequently occurs in the Atlantic Forest. There are several studies in the literature on the occurr ence of this class of compounds and their characterization in the leaves and branches of Violaceae plant species, le ading to more complete information on the occurrence of cyclotides, and their biological significance for these plants. The cyclotides extraction of plant material (dried and ground branches and leaves) was carried out by maceration with methanol/water, fo llowed by a liquid - liquid partition with dichloromethane. The polar phase was concentrated and subjected to chromatographic column using octadecylsilane (C 18 ) as stationary phase, achieving several fractions rich in peptides. The purification process was p erformed by analytical and/or preparative HPLC, in gradient of acetonitrile and water as mobile phase, which led to the isolation of the cyclotides. The amino acid sequence (primary structure) of the isolated compounds was established by MALDI - TOF /TOF by r eduction and alkylation re... / Mestre

No description available.

Cyclotides are plant proteins with a unique topology, defined as the cyclic cystine knot motif. The motif endows cyclotides with exceptional chemical and biological stability. They also exhibit a wide range of biological activities including insecticidal, cytotoxic, anti-HIV and antimicrobial effects. Hence, cyclotides have become potential candidates in the development of peptide-based drugs; either as scaffolds to stabilize susceptible peptide sequences or as drugs by their own right. In this thesis, important parameters that could be inputs toward this development have been tuned. An extraction protocol that can be extended to industrial scale production of the cyclotides from natural sources was developed; accordingly, a single maceration with hydroalcoholic solutions of medium polarity represented an optimum extraction method. Moreover, it was shown that investigating the cyclotide content of cyclotide-bearing plants from diverse environments is a promising approach for extending the knowledge of both structural and biological diversity of these proteins. Five novel cyclotides with new sequence diversity were isolated and characterized from a violet that grows on Ethiopian highlands at an altitude of 3400 m. One of the areas where the cyclotide framework has attracted interest is the development of stable antimicrobial peptides. A stability study was carried out to determine the stability of the cyclotide framework in a cocktail of bacterial proteases and serum where the native forms of tested cyclotides exhibited high stability profile. Understanding the modes of cyclotide-cell interaction is certainly an important factor for the potential development of cyclotide-based drugs. Cellular studies were carried out using the comet assay and microautoradiography. A bell-shaped dose response curve was obtained for the DNA damaging effect of the cyclotides in the comet assay, which was the first toxicological assay of its kind on this class of proteins. The microautoradiography study revealed that the cyclotides penetrate into the cells even at cytotoxic concentrations. From previous reports, it was known that the cyclotides interact with membranes; the cellular studies in this thesis added to this knowledge by clearly demonstrating that these proteins have multiple modes of action.

Submitted by ANTONIO FERNANDEZ BOBEY null (antoniofernandezbobey86@yahoo.es) on 2016-04-12T19:44:51Z No. of bitstreams: 1 Dissertação_Versão Final_ Repositorio Unesp.pdf: 2495633 bytes, checksum: f7ff8d9ec49134a24d9a1082b09926dc (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-04-15T17:37:25Z (GMT) No. of bitstreams: 1 fernandezbobey_a_me_araiq_par.pdf: 909965 bytes, checksum: 12ae7f0b3b5f6a97678bcbd7f2a70506 (MD5) / Made available in DSpace on 2016-04-15T17:37:25Z (GMT). No. of bitstreams: 1 fernandezbobey_a_me_araiq_par.pdf: 909965 bytes, checksum: 12ae7f0b3b5f6a97678bcbd7f2a70506 (MD5) Previous issue date: 2016-02-24 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Os ciclotídeos são produtos naturais de estrutura polipeptídica, contendo de 28 a 37 resíduos de aminoácidos, sendo seis deles resíduos de cisteína, altamente conservados e formados por ligações dissulfeto as quais exibem ciclização tipo "cabeça-cauda". Esse arranjo estrutural característico confere aos ciclotídeos uma estabilidade excepcional e resistência à proteólise. Devido a estas peculiaridades moleculares os ciclotídeos são substâncias com importantes funções biológicas, entre elas, destacam-se as de defesa e adaptação dos organismos que as acumulam. São de grande interesse para agricultura, agindo como inseticidas e, no uso medicinal por apresentarem atividades anti-HIV, anti-helmíntica, antimicrobiana e efeitos uterotônicos. A presente dissertação trata do estudo de ciclotídeos isolados da planta Noisettia orchidiflora (Rudge) Gingins, pertencente à família Violaceae, um táxon de ocorrência frequente na Mata Atlântica. Já existem dados na literatura sobre o estudo de ciclotídeos das raízes e o presente estudo é importante na medida que registra a ocorrência desta classe de substâncias e a sua caracterização nas folhas e galhos desta espécie, levando a informações mais completas sobre a ocorrência de ciclotídeos em Violaceae. A extração de ciclotídeos do material vegetal (galhos e folhas secos e moídos) foi feita mediante maceração hidrometanólica até esgotamento do material vegetal, seguida de partição líquido-líquido com diclorometano. A fase polar foi concentrada e submetida à cromatografia em coluna, empregando octadecilsilano (C18) como fase estacionária, obtendo-se frações ricas em peptídeos. O processo de purificação foi realizado por HPLC preparativo e/ou analítico com eluição gradiente, empregando-se acetonitrila e água como fase móvel, o que permitiu a obtenção das substâncias. A sequência de aminoácidos (estrutura primária) dos ciclotídeos isolados foi estabelecida por Espectrometria de Massas MALDI-TOF/TOF com o auxílio das reações de redução, alquilação e digestão enzimática empregando as enzimas: endoproteinase de ácido glutâmico (endoGlu-C), tripsina e quimiotripsina. Também, foi realizada a análise de aminoácidos das substâncias, permitindo a quantificação de cada aminoácido presente. A presente pesquisa resultou no isolamento de seis compostos de galhos e três oriundos de folhas, totalizando sete diferentes possíveis ciclotídeos, visto que dois deles foram comuns para ambos os tecidos. Até o momento foi possível determinar a estrutura primária de quatro deles: Os ciclotídeos Nor B (substância F20-2), massa molecular 3180,416 Da, Nor C (substância F20-3), massa molecular 3282,472 Da, Nor D (substância F17-1), massa molecular 3249,474 Da e Nor E (substância F21-1), massa molecular 3170,472 Da. Todos eles reportados pela primeira vez no presente estudo. As demais substâncias isoladas se encontram em processo caracterização estrutural. / Cyclotides are polypeptide structures, comprise 28-37 amino acid residues, six of them, are cysteine residues, highly conserved and formed by disulfide bonds, which exhibit "head-tail" cyclization type. This structural feature gives to cyclotides remarkable stability and resistance to proteolysis. Due to these singularities, such compounds have disclosed important biological functions. Among them; the literature has highlighted important ecological properties as defense and adaptation of the organisms, which accumulate these natural products. Accordingly, they are of great interest to agriculture, acting as insecticide, and to medicine, since some compounds have displayed anti-HIV activity, anthelmintic, antimicrobial and uterotonic properties. This research deals with the study of cyclotides isolated Noisettia orchidiflora (Rudge) Gingins, belonging to the taxon Violaceae, which frequently occurs in the Atlantic Forest. There are several studies in the literature on the occurrence of this class of compounds and their characterization in the leaves and branches of Violaceae plant species, leading to more complete information on the occurrence of cyclotides, and their biological significance for these plants. The cyclotides extraction of plant material (dried and ground branches and leaves) was carried out by maceration with methanol/water, followed by a liquid-liquid partition with dichloromethane. The polar phase was concentrated and subjected to chromatographic column using octadecylsilane (C18) as stationary phase, achieving several fractions rich in peptides. The purification process was performed by analytical and/or preparative HPLC, in gradient of acetonitrile and water as mobile phase, which led to the isolation of the cyclotides. The amino acid sequence (primary structure) of the isolated compounds was established by MALDI-TOF/TOF by reduction and alkylation reactions as well as enzymatic digestion using the enzymes: endoproteinase glutamic acid (endoGlu-C), trypsin and chymotrypsin. Also, the quantification of each amino acid present in the cyclotide structures was performed, and this amino acid analysis was fundamental for the characterization of these substances. Therefore, this research resulted in the isolation of the six compounds accumulated in the branches, and 3 of them were also found in the leaves. A complete analysis of all peptides suggested that seven are cyclotides, while two of them were common for both twigs and leaves tissues. Until now it was possible to determine the primary structure of four cyclotides, which is being described in plants for the first time: The cyclotides Nor B (F20-2 substance), molecular weight 3180.416 Da, Nor C (F20-3 substance), molecular weight 3282.472 Da, Nor D (substance F17-1), molecular mass 3249.474 Da Nor E (F21-1 substance), molecular weight 3170.472 Da. All these cyclotides are being reported for the first time in this study, however, 3 of these are currently under further analytical studies aimed at the complete structural characterization. / CNPq: 133418/2014-6

Secondary metabolites derived from plants, especially those used by traditional healers, are at the forefront of new drug development in combating diseases such as cancer and diabetes. Garlic is employed in indigenous medicine all over the world for the treatment of a variety of diseases. Dietary garlic has been recognized for its beneficial health effects. In particular, garlic consumption has been correlated with (i) reduction of risk factors for cardiovascular diseases and cancer, (ii) stimulation of immune function, (iii) enhanced detoxification of foreign compounds, (iv) hepatoprotection, (v) antimicrobial effects, (vi) antioxidant effects, and most importantly (vii) its hypoglycemic and anticoagulant properties. Due to these beneficial properties, garlic and its closely related genera which includes Tulbaghia violacea, may be useful as coadjuvant therapy in the treatment of type 2 diabetes and some of its physiological complications. The aim of this study was to determine if T. violacea has antidiabetic and anticoagulant properties. This was performed in vitro using both aqueous and organic extracts of the roots, leaves and bulbs. An organic extract was able to improve glucose-stimulated insulin secretion (GSIS) in INS-1 pancreatic β-cells and glucose uptake in Chang liver cells. The BO extract had no effect on the glucose uptake in 3T3-L1 an adipose cell line and reduced glucose utilisation in C2C12, a skeletal muscle cell line. Some of the properties displayed by T. violacea in this study are consistent with those found in similar studies with garlic extracts. It was observed that the BO extract increased the membrane potential and Glut-2 expression in INS-1 cells cultured at hyperglycemic levels, however, at normoglycemic levels a reduction was observed. The oxygen consumption increased at both glycemic levels due to treatment with the BO extract. Platelets were exposed to the extracts to determine their effects upon platelet aggregation, adhesion and protein secretion. Since the BO extract displayed the highest potential at inhibiting platelet aggregation and adhesion. A rat model was used in ex vivo studies to determine if the extract exhibited the same effect in a physiological model. It was noted that the BO extract exhibited a higher degree of inhibition on platelet aggregation and adhesion than the positive control, aspirin. The BO extract reduced clotting times in the prothrombin time (PT) test, but prolonged the clotting time in the actived partial thromboplastin time (APTT) assay in the ex vivo model; however, it had no affect on these clotting assays in the in vitro model using human blood. The BO extract increased the D-dimer and Fibrinogen-C levels in the in vitro model, but had no effect on the D-dimer concentrations and lowered the Fibrinogen-C levels in the ex vivo model. The active compounds in the extract remain to be elucidated.

Cyclotides are small cyclic plant proteins, and this thesis addresses their cytotoxic structure-activity properties and their mode of action on human cancer cell lines. Cyclotides were isolated from Viola odorata and Viola tricolor; three novel cyclotide sequences and two known sequences, but of new origin, were identified using mass spectrometry, amino acid analysis, and Edman degradation. The cyclotide structure includes three disulphide bonds in a knotted arrangement, which forces hydrophobic amino acid residues to be exposed on the surface of the molecule; 3-D homology models of cyclotides have revealed an amphipathic surface and charged residues located at similar positions in the molecules. The charged amino acid residues were shown to play a key role in the cytotoxicity of the cyclotide cycloviolacinO2 on a human lymphoma cell line. Methylation of Glu caused a dramatic change in cytotoxicity, lowering the potency 48 times, whereas concealing the charge of Arg with 1,2-cyclohexanedione caused virtually no change in potency. Acetylation of the two Lys caused a 3-fold reduction in potency, and masking all positive charges caused a 7-fold reduction. Additionally, disturbing the amphipathic structure by reducing and alkylating the disulphide bonds abolished the cytotoxicity. The time dependency of cytotoxicity and cell gross morphology after cyclotide exposure were investigated on the lymphoma cell line. Cells exposed to 4 µM of cycloviolacinO2 showed necrotic characteristics, such as membrane disintegration, within 5 min; a membrane disruptive effect of cycloviolacinO2 was also observed in a functional assay based on liposomes at a peptide-to-lipid molar ratio of 6.5. The anti-tumour properties of cycloviolacinO2 were evaluated on three human cancer cell lines using the hollow fibre assay in vitro and in vivo. The cyclotide exhibited potent anti-tumour activity in the micro-molar concentration range on all cell lines in vitro, but no effect on tumour growth could be established in vivo.