Jenny Felth

Cytotoxic effects of cardiac glycosides in colon cancer cells, alone and in combination with standard chemotherapeutic drugs

Cardiac glycosides have been reported to exhibit cytotoxic activity against several different cancer types, but studies against colorectal cancer are lacking. In a screening procedure aimed at identifying natural products with activity against colon cancer, several cardiac glycosides were shown to be of interest, and five of these were further evaluated in different colorectal cancer cell lines and primary cells from patients. Convallatoxin (1), oleandrin (4), and proscillaridin A (5) were identified as the most potent compounds (submicromolar IC50 values), and digitoxin (2) and digoxin (3), which are used in cardiac disease, exhibited somewhat lower activity (IC50 values 0.27-4.1 microM). Selected cardiac glycosides were tested in combination with four clinically relevant cytotoxic drugs (5-fluorouracil, oxaliplatin, cisplatin, irinotecan). The combination of 2 and oxaliplatin exhibited synergism including the otherwise highly drug-resistant HT29 cell line. A ChemGPS-NP application comparing modes of action of anticancer drugs identified cardiac glycosides as a separate cluster. These findings demonstrate that such substances may exhibit significant activity against colorectal cancer cell lines, by mechanisms disparate from currently used anticancer drugs, but at concentrations generally considered not achievable in patient plasma.

Evaluation of toxicity and antitumor activity of cycloviolacin O2 in mice

Cycloviolacin O2 is a small cyclic cysteine-rich protein belonging to the group of plant proteins called cyclotides. This cyclotide has been previously shown to exert cytotoxic activity against a variety of human tumor cell lines as well as primary cultures of human tumor cells in vitro. This study is the first evaluation of its tolerability and antitumor activity in vivo. Maximal-tolerated doses were estimated to 1.5 mg/kg for single intravenous (i.v.) dosing and 0.5 mg/kg for daily repeated dosing, respectively. Two different in vivo methods were used: the hollow fiber method with single dosing (i.v., 1.0 mg/kg) and traditional xenografts with repeated dosing over 2 weeks (i.v., 0.5 mg/kg daily, 5 days a week). The human tumor cell lines used displayed dose-dependent in vitro sensitivity (including growth in hollow fibers to confirm passage of cycloviolacin O2 through the polyvinylidene fluoride fibers), with IC5o values in the micromolar range. Despite this sensitivity in vitro, no significant antitumor effects were detected in vivo, neither with single dosing in the hollow fiber method nor with repeated dosing in xenografts. In summary, the results indicate that antitumor effects are minor or absent at tolerable (sublethal) doses, and cycloviolacin O2 has a very abrupt in vivo toxicity profile, with lethality after single injection at 2 mg/kg, but no signs of discomfort to the animals at 1.5 mg/kg. Repeated dosing of 1 mg/kg gave a local-inflammatory reaction at the site of injection after 2-3 days; lower doses were without complications.

Novel activity of acriflavine against colorectal cancer tumor cells

A high‐throughput screen of the cytotoxic activity of 2000 molecules from a commercial library in three human colon cancer cell lines and two normal cell types identified the acridine acriflavin to be a colorectal cancer (CRC) active drug. Acriflavine was active in cell spheroids, indicating good drug penetration and activity against hypoxic cells. In a validation step based on primary cultures of patient tumor cells, acriflavine was found to be more active against CRC than ovarian cancer and chronic lymphocytic leukemia. This contrasted to the activity pattern of the CRC active standard drugs 5‐fluorouracil, irinotecan and oxaliplatin. Mechanistic studies indicated acriflavine to be a dual topoisomerase I and II inhibitor. In conclusion, the strategy used seems promising for identification of new diagnosis‐specific cancer drugs. (Cancer Sci 2011; 102: 2206–2213)

Ex Vivo Activity of Cardiac Glycosides in Acute Leukaemia

Background Despite years of interest in the anti-cancerous effects of cardiac glycosides (CGs), and numerous studies in vitro and in animals, it has not yet been possible to utilize this potential clinically. Reports have demonstrated promising in vitro effects on different targets as well as a possible therapeutic index/selectivity in vitro and in experimental animals. Recently, however, general inhibition of protein synthesis was suggested as the main mechanism of the anti-cancerous effects of CGs. In addition, evidence of species differences of a magnitude sufficient to explain the results of many studies called for reconsideration of earlier results. Principal Findings In this report we identified primary B-precursor and T-ALL cells as being particularly susceptible to the cytotoxic effects of CGs. Digitoxin appeared most potent and IC50 values for several patient samples were at concentrations that may be achieved in the clinic. Significant protein synthesis inhibition at concentrations corresponding to IC50 was demonstrated in colorectal tumour cell lines moderately resistant to the cytotoxic effects of digoxin and digitoxin, but not in highly sensitive leukaemia cell lines. Conclusion It is suggested that further investigation regarding CGs may be focused on diagnoses like T- and B-precursor ALL.

Gambogic acid is cytotoxic to cancer cells through inhibition of the ubiquitin-proteasome system

SummaryGambogic acid (GA), displays cytotoxicity towards a wide variety of tumor cells and has been shown to affect many important cell-signaling pathways. In the present work, we investigated the mechanism of action of GA by analysis of drug-induced changes in gene expression profiles and identified GA and the derivative dihydro GA as possible inhibitors of the ubiquitin-proteasome system (UPS). Both GA and dihydro GA inhibited proteasome function in cells resulting in the accumulation of polyubiquitin complexes. In vitro experiments showed that both GA and dihydro GA inhibited 20S chymotrypsin activity and the inhibitory effects of GA and dihydro GA on proteasome function corresponded with apoptosis induction and cell death. In conclusion, our results show that GA and dihydro GA exert their cytotoxic activity through inhibition of the UPS, specifically by acting as inhibitors of the chymotrypsin activity of the 20S proteasome.

Antimicrobial and Antineoplastic Activities of Agelasine Analogs Modified in the Purine 2-Position

Agelasines are 7,9‐dialkylpurinium salts found in marine sponges (Agelas sp.), which display a variety of antimicrobial and cytotoxic effects. We have synthesized simplified agelasine analogs modified in the purine 2‐position and examined their antimicrobial and anticancer activities. The compounds were screened against Staphylococcus aureus, Escherichia coli, Mycobacterium tuberculosis, Candida krusei, and Candida albicans, protozoa causing tropical diseases (Plasmodium falciparum, Leishmania infantum, Trypanosoma cruzi, and Trypanosoma brucei), a panel of human cancer cell lines (U‐937 GTB, RPMI 8226/s, CEM/s, and ACHN) as well as VERO and/or MRC‐5 cells. The results indicate that the introduction of a methyl group in the purine 2‐position is beneficial for antimycobacterial and antiprotozoal activity, and that amino groups may enhance activity against several cancer cell lines.

Bioassays in natural product research - strategies and methods in the search for anti-inflammatory and antimicrobial activity.

INTRODUCTION Identifying bioactive molecules from complex biomasses requires careful selection and execution of relevant bioassays in the various stages of the discovery process of potential leads and targets. OBJECTIVE The aim of this review is to share our long-term experience in bioassay-guided isolation, and mechanistic studies, of bioactive compounds from different organisms in nature with emphasis on anti-inflammatory and antimicrobial activity. METHODS In the search for anti-inflammatory activity, in vivo and in vitro model combinations with enzymes and cells involved in the inflammatory process have been used, such as cyclooxygenases, human neutrophils and human cancer cell lines. Methods concerning adsorption and perforation of bacteria, fungi, human cells and model membranes, have been developed and optimised, with emphasis on antimicrobial peptides and their interaction with the membrane target, in particular their ability to distinguish host from pathogen. RESULTS A long-term research has provided experience of selection and combination of bioassay models, which has led to an increased understanding of ethnopharmacological and ecological observations, together with in-depth knowledge of mode of action of isolated compounds. CONCLUSION A more multidisciplinary approach and a higher degree of fundamental research in development of bioassays are often necessary to identify and to fully understand the mode of action of bioactive molecules with novel structure-activity relationships from natural sources.

2-Substituted agelasine analogs : synthesis and biological activity, and structure and reactivity of synthetic intermediates

2-Substituted N-methoxy-9-methyl-9H-purin-6-amines were synthesized either from their corresponding 6-chloro-9-methyl-9H-purines or 2-chloro-N-methoxy-9-methyl-9H-purin-6-amine. Great diversity in the amino/imino tautomeric ratios was observed and calculated based on 1H NMR. The tautomers were identified by 1D and 2D 1H, 13C, and 15N NMR techniques, and showed significant variation both in 13C and 15N shift values. Comparison of the tautomeric ratios with Hammett F values revealed that as the field/inductive withdrawing abilities of the 2-substituent increased, the ratio of amino:imino tautomers was shifted toward the amino tautomer. Computational chemistry exposed the significance of hydrogen bonding between solvent and the compound in question to reach accurate predictions for tautomeric ratios. B3LYP/def2-TZVP density functional theory (DFT) calculations resulted in quantitatively more accurate predictions than when employing the less expensive BP86 functional. N-7-Alkylation of the 2-substituted N-methoxy-9-methyl-9H-purin-6-amines showed that when the field/inductive withdrawing ability of the 2-substituent reached a certain point the reactivity drastically dropped. This correlated with the atomic charges on N-7 calculated using a natural bond orbital (NBO) analysis. Biological screening of the final 2-substituted agelasine analogs indicated that the introduction of a methyl group in the 2-position is advantageous for antimycobacterial and antiprotozoal activity, and that an amino function may improve activity against several cancer cell lines.

Bioassays in natural product research - Strategies and methods in the search for bioactive natural products

Bioassays in natural product research - Strategies and methods in the search for bioactive natural products