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Bufadienolides are digitalis-like aglycones mainly found in skin secretions of toads. Among their biological properties, the mechanisms of antiproliferative action on tumor cells remain unclear for many compounds, including against leukemia cells. Herein, it was evaluated the mechanisms involved in the antiproliferative and genotoxic actions of hellebrigenin on tumor cell lines and in silico capacity to inhibit the human topoisomerase IIa enzyme. Firstly, its cytotoxic action was investigated by colorimetric assays in human tumor and peripheral blood mononuclear cells (PBMC). Next, biochemical and morphological studies were detailed by light microscopy (trypan blue dye exclusion), immunocytochemistry (BrdU uptake), flow cytometry and DNA/chromosomal damages (Cometa and aberrations). Finally, computational modelling was used to search for topoisomerase inhibition. Hellebrigenin reduced proliferation, BrdU incorporation, viability, and membrane integrity of HL-60 leukemia cells. Additionally, it increased G 2 /M arrest, internucleosomal DNA fragmentation, mitochondrial depolarization, and phosphatidylserine externalization in a concentration-dependent manner. In contrast to doxorubicin, hellebrigenin did not cause DNA strand breaks in HL-60 cell line and lymphocytes, and it interacts with ATPase domain residues of human topoisomerase IIa, generating a complex of hydrophobic and van der Waals interactions and hydrogen bonds. So, hellebrigenin presented potent anti-leukemic activity at concentrations as low as 0.06 μM, a value comparable to the clinical anticancer agent doxorubicin, and caused biochemical changes suggestive of apoptosis without genotoxic/clastogenic-related action, but it probably triggers catalytic inhibition of topoisomerase II. These findings also emphasize toad steroid toxins as promising lead antineoplasic compounds with relatively low cytotoxic action on human normal cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Chemical compounds from skin secretions from toads of Bufonidae family have been long-studied. In the search for new molecules with pharmacological action, the 3β-OH groups of bufadienolides are commonly derivatised using acetyl groups. This work described the isolation and/or structural elucidation of isolated and derivatised compounds from the venom of the Brazilian anuran Rhinella marina, and their evaluation in in vitro assays. In the methanolic extract of the R. marina venom, compound cholesterol (1) was isolated from the CRV-52 fraction by classic column chromatography, dehydrobufotenine (2) by Sephadex LH-20 from the CRV-28 fraction, and a mix of suberoyl arginine (3) and compound 2 was obtained from the CRV-6-33 fraction. The compounds marinobufagin (4), telocionbufagin (5) and bufalin (6) were isolated by classic column chromatography, followed by separation via HPLC in the CRV-70 fraction, and the compound marinobufotoxin (9) was isolated by classic column chromatography in the CRV-6 fraction, here being isolated for the first time in R. marina specimens. Compounds 4 and 5 were submitted for acetylation with acetic anhydride, in the presence of pyridine and 4-dimethyilaminopiridine (DMAP), in order to obtain the compounds 3-acetyl-marinobufagin (7) and 3-acetyl-telocinobufogin (8). The isolated and derivatised compounds were identified by 1 H and 13 C NMR, and their molecular mass confirmed by mass spectrometry. All compounds (except 1 and 3) were tested in cytotoxic assays by the MTT method and presented cytotoxic potential against human cancer cell lines, as well as against non-tumoral human embryonic kidney HEK-293 cells. With the exception of compound 2, all molecules presented IC 50 values < 4 μM, and none caused hemolysis of human erythrocytes, demonstrating a promising cytotoxic potential of natural and chemically-modified bufadienolides. This study presents a detailed contribution of bioactive chemicals from Brazilian Amazon Rhinella species, and indicates promising areas for further studies and pharmaceutical investments., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The use of natural products in therapeutics has been growing over the years. Lignans are compounds with large pharmaceutical use, which has aroused interest in the search for new drugs to treat diseases. The present study evaluated the cytotoxicity of (-)-trachelogenin, a dibenzylbutyrolactone type lignan isolated from Combretum fruticosum, against several tumor and non-tumor cell lines using the MTT assay and its possible mechanism of action. (-)-Trachelogenin showed IC 50 values ranging of 0.8-32.4μM in SF-295 and HL-60 cell lines, respectively and IC 50 values >64μM in non-tumor cell lines. (-)-trachelogenin persistently induced autophagic cell death, with cytoplasmic vacuolization and formation of autophagosomes mediated by increasing LC3 activation and altering the expression levels of Beclin-1., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The venom of amphibians is a fascinating source of active substances. In view of their medical importance and aiming to explore the amazing Brazilian biodiversity, we conducted bioprospecting of antiproliferative activity in extracts of Rhinella marina and Rhaebo guttatus toads occurring in the Southern Amazon of Mato Grosso, Brazil. LC-MS and HPLC analysis of the venom extracts of R. marina revealed four bufadienolides (telocinobufagin, marinobufagin, bufalin and resibufogenin. R. guttatus venom extracts contained only marinobufagin. First, R. marina and R. guttatus venom extracts were evaluated for cytotoxicity against tumor cell lines by the MTT assay. All extracts revealed cytotoxicity, where R. marina extracts were comparable to doxorubicin (IC₅₀ values ranging from 0.01 to 0.23 μg/mL). Only extracts of R. guttatus toad venom caused membrane disruption of human erythrocytes. The extracts were investigated for selective activity by determining their effect on stimulated human peripheral blood mononuclear cells (PBMC) with the Alamar Blue™ assay. The extracts were up to 80-fold more selective against leukemia cells when compared to dividing leukocytes. Aiming to confirm these antiproliferative effects, BrdU incorporation into DNA was measured in HL-60 treated cells with R. marina venom extracts. These extracts decreased BrdU incorporation at both concentrations tested. In summary, nine extracts of R. marina and R. guttatus venom showed pronounced lethal and discriminating effects on tumor lines, especially those from R. marina, highlighting toad parotoid gland secretions as a promising source for novel lead anticancer chemicals., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The effects and susceptibility of donkeys to Crotalaria juncea and Crotalaria retusa poisoning were determined at high and low doses. Seeds of C. juncea containing 0.074% of dehydropyrrolizidine alkaloids (DHPAs) (isohemijunceines 0.05%, trichodesmine 0.016%, and junceine 0.008%) were administered to three donkeys at 0.3, 0.6 and 1 g/kg body weight (g/kg) daily for 365 days. No clinical signs were observed and, on liver and lung biopsies, the only lesion was a mild liver megalocytosis in the donkeys ingesting 0.6 and 1 g/kg/day. Two other donkeys that received daily doses of 3 and 5 g seed/kg showed initial respiratory signs 70 and 40 days after the start of the administration, respectively. The donkeys were euthanized following severe respiratory signs and the main lung lesions were proliferation of Clara cells and interstitial fibrosis. Three donkeys ingested seeds of C. retusa containing 5.99% of monocrotaline at daily doses of 0.025, 0.05 and 0.1 g/kg for 365 days. No clinical signs were observed and, on liver and lung biopsies, the only lesion was moderate liver megalocytosis in each of the three donkeys. One donkey that received a single dose of 5 g/kg of C. retusa seeds and another that received 1 g/kg daily for 7 days both showed severe clinical signs and died with diffuse centrilobular liver necrosis. No lung lesions were observed. Another donkey that received a single dose of 2.5 g/kg of C. retusa seeds showed no clinical signs. The hepatic and pneumotoxic effects observed are consistent with an etiology involving DHPAs. Furthermore, the occurrence of lung or liver lesions correlates with the type of DHPAs contained in the seeds. Similarly as has been reported for horses, the data herein suggest that in donkeys some DHPAs are metabolized in the liver causing liver disease, whereas others are metabolized in the lung by Clara cells causing lung disease., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Sesquiterpene lactones (SLs) are natural products with a variety of biological activities. Previously, we demonstrated the cytotoxic effects of three new α-santonin derivatives on different tumor cell lines with low toxic effects upon peripheral human leukocytes. Here, we evaluated the mechanism of action triggered by these derivatives. HL-60 cell cycle determined after 24h treatment revealed a significant inhibition on cell-cycle progression and leading to an increasing of cells in G2/M [7.6% and 9.0% for compound 3% and 9.0% and 8.6% for compound 4 (1 and 2 μM, respectively)]. However, after 48 h exposure, all compounds caused G2/M reduction and a significant DNA fragmentation. Compounds 2, 3 and 4 were able to induce apoptosis on leukemia cells, which was corroborated by phosphatidyserine externalization and activation of caspases-3 and -7 after 24h exposure. None of the derivatives analyzed caused depolarization of mitochondrial membrane within 24h of incubation, suggesting the involvement of the extrinsic apoptotic pathway in the death process. The antiproliferative action of these compounds is related to the DNA synthesis inhibition and cell cycle arrest, which probably lead to apoptosis activation. Therefore, these santonin derivatives are promising lead candidates for development of new cytotoxic agents., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The antiproliferative activity of lectins Canavalia ensiformis (ConA) and Canavalia brasiliensis (ConBr) were studied using human leukemia MOLT-4 and HL-60 cell lines. It was revealed that both ConA and ConBr were markedly cytotoxic to cells using MTT and NAC assays. The IC(50) values were approximately 3 and 20 μg/mL for ConA and ConBr, respectively, for both MOLT-4 and HL-60 cells. However, in normal human peripheral blood lymphocytes, the lectins were not cytotoxic, even when tested at concentrations as high as 200 μg/ml. Using comet assay, the lectins produced a rate of DNA damage exceeding 80% in MOLT-4 and HL-60 cells. Fluorescence analysis revealed the morphology characteristic of apoptosis, with low concentrations of apoptotic bodies and fragmented DNA (5 μg/ml). Flow cytometric analysis demonstrated an accumulation of cells in the sub-G1 cell cycle that is characteristic of DNA fragmentation, and a decrease in membrane integrity at high concentrations. Lastly, we evaluated the alterations in mitochondrial potential that reduced after treatment with lectins. Our results indicate that ConA and ConBr inhibited cell proliferation selectively in tumor cells and that apoptosis was the main death mechanism. Therefore, lectins can be considered a class of molecules with a high antitumor activity potential., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In this study, the cytotoxicity, genotoxicity and early ROS generation of 2,2-dimethyl-(3H)-3-(N-3'-nitrophenylamino)naphtho[1,2-b]furan-4,5-dione (QPhNO(2)) were investigated and compared with those of its precursor, nor-beta-lapachone (nor-beta), with the main goal of proposing a mechanism of antitumor action. The results were correlated with those obtained from electrochemical experiments held in protic (acetate buffer pH 4.5) and aprotic (DMF/TBABF(4)) media in the presence and absence of oxygen and with those from dsDNA biosensors and ssDNA in solution, which provided evidence of a positive interaction with DNA in the case of QPhNO(2). QPhNO(2) caused DNA fragmentation and mitochondrial depolarization and induced apoptosis/necrosis in HL-60 cells. Pre-treatment with N-acetyl-l-cysteine partially abolished the observed effects related to the QPhNO(2) treatment, including those involving apoptosis induction, indicating a partially redox-dependent mechanism. These findings point to the potential use of the combination of pharmacology and electrochemistry in medicinal chemistry., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

(4-Methoxyphenyl)(3,4,5-trimethoxyphenyl)methanone (PHT) belongs to the phenstatin family. This compound has been studied due to its potent cytotoxicity and ability to inhibit tubulin assembly. The present study aimed to evaluate the mutagenic potential of PHT in human lymphocytes. PHT displayed cytotoxicity in human lymphocytes with an IC50 value of 5.68 μM, and therefore, concentrations of 0.25, 0.5, 1.0, 2.0, and 4.0 μM were used for all protocols. The alkaline comet assay and chromosome aberration (CA) analysis were performed in different phases of the cell cycle (G1, G1/S, transition, and G2), to evaluate the DNA-damaging and clastogenic effects of PHT, respectively. CA analysis was carried out in the presence or absence of colchicine to evaluate the action of PHT in the mitotic phase. PHT was cytotoxic and significantly reduced the mitotic index with drug exposure in all phases of cell cycle. Interestingly, it induced an increase in mitotic index in experimental protocols without colchicine, corroborating its action as an antitubulin agent. It also induced DNA damage and was clastogenic with drug exposure in all phases of the cell cycle, in the presence or absence of colchicine. In conclusion, PHT induces DNA damage and exerts clastogenic effects in human lymphocytes., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

Indigofera suffruticosa causes hemolytic anemia and hemoglobinuria in cattle. The plant was administered to six groups of two guinea pigs each, at the daily dose of 10 g/kg body weight, for periods of 2, 4, 6, 8, 10 and 15 days. The guinea pigs progressively developed reduced hematocrits and hemoglobin concentrations, and finally presented anemia, without hemoglobinuria. Urine passed by guinea pigs that had ingested the plant for more than 24 h acquired a turquoise blue pigmentation 8-10 h after urination. It is suggested that the anemia is caused by the aniline contained in I. suffruticosa., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Pristimerin has been shown to be cytotoxic to several cancer cell lines. In the present work, the cytotoxicity of pristimerin was evaluated in human tumor cell lines and in human peripheral blood mononuclear cells (PBMC). This work also examined the effects of pristimerin (0.4; 0.8 and 1.7 microM) in HL-60 cells, after 6, 12 and 24h of exposure. Pristimerin reduced the number of viable cells and increased number of non-viable cells in a concentration-dependent manner by tripan blue test showing morphological changes consistent with apoptosis. Nevertheless, pristimerin was not selective to cancer cells, since it inhibited PBMC proliferation with an IC50 of 0.88 microM. DNA synthesis inhibition assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation in HL-60 cells was 70% and 83% for the concentrations of 0.4 and 0.8 microM, respectively. Pristimerin (10 and 20 microM) was not able to inhibit topoisomerase I. In AO/EB (acridine orange/ethidium bromide) staining, all tested concentrations reduced the number of HL-60 viable cells, with the occurrence of necrosis and apoptosis in a concentration-dependent manner, results in agreement with trypan blue exclusion findings. The analysis of membrane integrity and internucleosomal DNA fragmentation by flow cytometry in the presence of pristimerin indicated that treated cells underwent apoptosis. The present data point to the importance of pristimerin as representative of an emerging class of potential anticancer chemicals, exhibiting an antiproliferative effect by inhibiting DNA synthesis and triggering apoptosis.

Manganese (Mn) has a natural occurrence and is necessary during the initial periods of the development. However, in high concentrations, Mn can be related to neurodegenerative disorders. The aim of the present study was to evaluate the mutagenic potential of manganese chloride (MnCl2.4H2O). Comet assay and chromosome aberrations analysis were applied to determine the DNA-damaging and clastogenic effects of MnCl2.4H2O. Cultured human lymphocytes were treated with 15, 20 and 25 microM manganese chloride during the G1, G1/S, S (pulses of 1 and 6h), and G2 phases of the cell cycle. All tested concentrations were cytotoxic and reduced significantly the mitotic index in G1, G1/S and S (1 and 6h) treatments, while in G2 treatment only the higher concentrations (20 and 25 microM) showed cytotoxic effects. Clastogenicity and DNA damage were found only in treatments with the highest concentration (25 microM). Chromosome aberrations were found exclusively in the G2 phase of the cell cycle. The absence of polyploidy in mitosis, suggests that manganese does not affect the formation of the mitotic spindle with the concentrations tested. The genotoxicity found in G2 phase and in the comet assay can be related to the short time of treatment in both cases.

Iron (Fe) is a common chemical element that is essential for organisms as a co-factor in oxygen transport, but that in high amounts presents a significant risk of neurodegenerative disorders. The objective of this study was to evaluate the mutagenic potential of iron sulfate. The comet assay and chromosome aberration (CA) analysis were applied to determine the DNA-damaging and clastogenic effects of iron sulfate. Human lymphocytes were treated in the quiescent phase for the comet assay and proliferative phase during the G1, G1/S, S (pulses of 1 and 6 h), and G2 phases of the cell cycle for CA analysis, with 1.25, 2.5 and 5 microg/mL concentrations of FeSO(4).7H2O. All tested concentrations were cytotoxic and reduced significantly the mitotic index (MI) in all phases of the cell cycle. They also induced CA in G1, G1/S and S (pulses of 1 and 6 h) phases. Iron sulfate also induced polyploidy in cells treated during G1. In the comet assay, this metal did not induce significant DNA damage. Our results show that Fe causes alteration and inhibition of DNA synthesis only in proliferative cells, which explain the concomitant occurrence of mutagenicity and cytotoxicity, respectively, in the lymphocytes studied.

This work evaluated the in vitro cytotoxic activity of laticifer proteins (LP) recovered from the latex of the medicinal plant Calotropis procera. The LP displayed considerable cytotoxicity with IC(50) values ranging from 0.42 to 1.36 microg/ml to SF295 and MDA-MB-435 cell lines, respectively. In healthy peripheral blood mononuclear cells exposed to LP (10 microg/ml) for 72 h, no noticeable effects on viability or cell morphology were seen. The fractionating of LP on an ion exchange chromatography gave rise to a new fraction (PI) that retained almost all cytotoxicity. The cytotoxic effects of both LP and PI were diminished when previously treated with pronase, or 2-mercaptoethanol, suggesting a protein nature of active molecules, however, pre-incubation with dithiothreitol (DTT) only reduced PI activity. PI did not exhibit cysteine proteinase activity, indicating that cysteine proteinases, abundantly found in LP, are not implicated in LP cytotoxicity. In this study, using HL-60 cell as a model, LP was shown to inhibit DNA synthesis. This is probably due to alterations in the topology of DNA, since it was observed that LP is able to interfere in topoisomerase I activity by somehow acting upon DNA. LP provoked reduction in cell number but it did not cause any significant increase in the number of non-viable cells. These findings corroborated with the morphologic analysis, where cells treated with LP showed morphology of apoptotic process with abundant vacuoles, chromatin condensation and fragmentation of the nuclei. The results of this study suggests that LP is a target for DNA topoisomerase I triggering apoptosis in cancer cell lines.

The aim of this study was to determine whether the antiproliferative effects observed for pisosterol, a cytotoxic triterpene isolated from Pisolithus tinctorius, are related to cell differentiation induction using HL-60 cell line as a model. Also, the effects of pisosterol on normal human cells were examined in peripheral blood mononuclear cells (PBMC). The effects on cell viability and morphological changes were the first indications showing that pisosterol induces HL-60 differentiation. The demonstration of blue tetrazolium reduction in HL-60 cells exposed to pisosterol demonstrated differentiation in a dose- and time-dependent manner, reaching a maximum effect after 72 h incubation at 5 microg/mL. Assays for alpha-naphthyl acetate esterase activity indicated that pisosterol triggers differentiation towards a monocytic cell-like pathway. The antiproliferative effect of pisosterol was determined by inhibition of DNA synthesis based on BrdU incorporation into HL-60 proliferating cells. It appears that pisosterol-treated cells, despite displaying a differentiated phenotype, continued to proliferate at all doses tested after 72 h, with a slightly decrease at 5 microg/mL. Apoptosis was observed in pisosterol-treated cells in a dose-dependent way. Nevertheless, after the same period of incubation, no cytotoxicity was detected in PBMC in the presence of pisosterol even at 25 microg/mL, providing some evidence that pisosterol may be selective for tumor cells. The mechanisms underlying the effect of pisosterol in leukemia cells indicates the induction of a monocytic cell-like differentiation, suggesting that this compound could be used in the development of new pharmacological tools with potential therapeutic value in the management of leukemia with fewer side effects.

Piplartine {5,6-dihydro-1-[1-oxo-3-(3,4,5-trimethoxyphenyl)-2-propenyl]-2(1H)pyridinone} is an alkaloid/amide component of Piper species. The purpose of the present study was to examine the antiproliferative effects of piplartine on human leukemia cell lines HL-60, K562, Jukart, and Molt-4 using the trypan blue exclusion method, as well as the effect of piplartine on DNA synthesis. The viability of all human leukemia cell lines were not affected by piplartine after 6 h, 9 h, and 12 h exposure, whereas a steady decline was seen after an exposure time of 24 h. The antiproliferative activity of piplartine seemed to be related to the inhibition of DNA synthesis, as revealed by the reduction of 5-bromo-2'-deoxyuridine (BrdU) incorporation after 24h of incubation. Piplartine-mediated reduction in cell number was associated with an increasing number of dead cells at a concentration of 10 microg/ml. These findings were corroborated by morphologic analysis. However, at the lowest concentration (2.5 microg/ml), piplartine-treated cells exhibited typical apoptotic morphological changes. The increase in caspase-3 activity was also observed in lysates of piplartine-treated cells (2.5 microg/ml). Our findings suggest that piplartine can suppress leukemia growth and reduce cell survival, triggering both apoptosis and/or necrosis, depending on the concentration used.

In this work, we studied the effects of kaurenoic acid, a diterpene isolated from the oleo-resin of Copaifera langsdorffii in developing sea urchin (Lytechinus variegatus) embryos, on tumor cell growth in microculture tetrazolium (MTT) test and on mouse and human erythrocytes in hemolysis assay. Continuous exposure of embryos to kaurenoic acid starting immediately after fertilization inhibited the first cleavage (IC(50): 84.2 microM) and progressively induced embryo destruction (IC(50): 44.7 microM and < 10 microM for blastulae and larvae stages, respectively). In MTT assay, kaurenoic acid at a concentration of 78 microM produced growth inhibition of CEM leukemic cells by 95%, MCF-7 breast and HCT-8 colon cancer cells by 45% each. Further, kaurenoic acid induced a dose-dependent hemolysis of mouse and human erythrocytes with an EC(50) of 74.0 and 56.4 microM, respectively. The destruction of sea urchin embryos, the inhibition of tumor cell growth and the hemolysis of mouse and human erythrocytes indicate the potential cytotoxicity of kaurenoic acid.

Arenosclerins A-C and haliclonacyclamine E, new tetracyclic alkylpiperidine alkaloids isolated from the marine sponge Arenosclera brasiliensis, were subjected to antimicrobial and cytotoxic bioassays. Fourteen samples of microorganisms were used: Candida albicans, Staphylococcus aureus, Escherichia coli, and 12 antibiotic-resistant bacteria isolated from hospital environment. The minimum inhibitory concentration activity of each alkaloid was determined. The four compounds displayed antibacterial activity, but no antifungal activity against C. albicans. Haliclonacyclamine E and arenosclerins A and C were active against a larger number of bacteria strains than arenosclerin B. However, arenosclerins B and C presented more potent antibacterial activity. The alkaloids displayed inhibitory activity against both Gram positive and Gram negative bacteria. Cytotoxicity bioassays using the MTT method showed that these compounds present cytotoxic activity against human HL-60 (leukemia), L929 (fibrosarcoma), B16 (melanoma) and U138 (colon) cancer cell lines at concentrations between 1.5 and 7.0microg/ml. The results obtained indicated that A. brasiliensis alkaloids have a potent toxic activity. The broad cytotoxic and antimicrobial activities presented by A. brasiliensis alkaloids suggest a defensive role of arenosclerins and haliclonacyclamine E against microbial infection and/or the action of potential predators at the sponge's natural habitat.