Convallatoxin

1 Antiaris sp. 2 Convallaria sp. 3 Ornithogalum sp. 4 Parquetina sp.

Anti-Tumor Effects of Cardiac Glycosides on Human Lung Cancer Cells and Lung Tumorspheres.[Pubmed:27662422]

J Cell Physiol. 2017 Sep;232(9):2497-2507.

Lung cancer is a leading cause of cancer-related death in the United States. Although several drugs have been developed that target individual biomarkers, their success has been limited due to intrinsic or acquired resistance for the specific targets of such drugs. A more effective approach is to target multiple pathways that dictate cancer progression. Cardiac glycosides demonstrate such multimodal effects on cancer cell survival, and our aim was to evaluate the effect of two naturally occurring monosaccaridic cardiac glycosides-Convallatoxin and Peruvoside on lung cancer cells. Although both drugs had significant anti-proliferative effects on H460 and Calu-3 lung cancer cells, Convallatoxin demonstrated twofold higher activity as compared to Peruvoside using both viability and colony forming assays, suggesting a role for the aglycone region in dictating drug potency. The tumor suppressor p53 was found to be important for action of both drugs-p53-underexpressing cells were less sensitive as compared to p53-positive H460 cells. Further, assessment of p53-underexpressing H460 cells showed that drugs were able to arrest cells in the G0/G1 phase of the cell cycle in a dose-dependent manner. Both drugs significantly inhibited migration and invasion of cancer cells and decreased the viability of floating tumorspheres. An assessment of intracellular pathways indicated that both drugs were able to modulate proteins that are involved in apoptosis, autophagy, cell cycle, proliferation, and EMT. Our data suggest, a promising role for cardiac glycosides in lung cancer treatment, and provides impetus for further investigation of the anti-cancer potential of this class of drugs. J. Cell. Physiol. 232: 2497-2507, 2017. (c) 2016 Wiley Periodicals, Inc.

Suppression of NRF2/ARE by convallatoxin sensitises A549 cells to 5-FU-mediated apoptosis.[Pubmed:29902094]

Free Radic Res. 2018 Dec;52(11-12):1416-1423.

NF-E2-related factor 2 (NRF2) regulates transcription of phase II cytoprotective enzymes to protect normal cells against oxidative stress. However, a high level of NRF2 offers a growth advantage, chemoresistance, and radioresistance in cancer. In the present study, we have identified Convallatoxin as a novel inhibitor of NRF2/ARE. Suppression of NRF2 by Convallatoxin was not transcriptionally mediated, but regulated at the level of proteolysis. Convallatoxin activated GSK-3beta and suppression of NRF2 by Convallatoxin required the Neh6 domain. Convallatoxin sensitised A549 cells to 5-fluorouracil-mediated cell death by promoting apoptosis. Together, our results provide evidence that Convallatoxin might be useful as a chemotherapeutic adjuvant due to its ability to suppress NRF2/ARE.

Molecular mechanisms of anti-oxidant and anti-aging effects induced by convallatoxin in Caenorhabditis elegans.[Pubmed:28503972]

Free Radic Res. 2017 May;51(5):529-544.

Convallatoxin is widely used as a cardiac glycoside in acute and chronic congestive heart-failure and paroxysmal tachycardia, with many effects and underlying protective mechanisms on inflammation and cellular proliferation. However, Convallatoxin has not been investigated in its antioxidant effects and lifespan extension in Caenorhabditis elegans. In this study, we found that Convallatoxin (20 muM) could significantly prolong the lifespan of wild-type C. elegans up to 16.3% through daf-16, but not sir-2.1 signalling and increased thermotolerance and resistance to paraquat-induced oxidative stress. Convallatoxin also improved pharyngeal pumping, locomotion, reduced lipofuscin accumulation and reactive oxygen species levels in C. elegans, which were attributed to hormesis, free radical-scavenging effects in vivo, and up-regulation of stress resistance-related proteins, such as SOD-3 and HSP-16.1. Furthermore, aging-associated genes daf-16, sod-3, and ctl-2 also appeared to contribute to the stress-resistance effect of Convallatoxin. In summary, this study demonstrates that Convallatoxin can protect against heat and oxidative stress and extend the lifespan of C. elegans, pointing it as a potential novel drug for retarding the aging process in humans.

Convallatoxin-Induced Reduction of Methionine Import Effectively Inhibits Human Cytomegalovirus Infection and Replication.[Pubmed:27654292]

J Virol. 2016 Nov 14;90(23):10715-10727.

Cytomegalovirus (CMV) is a ubiquitous human pathogen that increases the morbidity and mortality of immunocompromised individuals. The current FDA-approved treatments for CMV infection are intended to be virus specific, yet they have significant adverse side effects, including nephrotoxicity and hematological toxicity. Thus, there is a medical need for safer and more effective CMV therapeutics. Using a high-content screen, we identified the cardiac glycoside Convallatoxin as an effective compound that inhibits CMV infection. Using a panel of cardiac glycoside variants, we assessed the structural elements critical for anti-CMV activity by both experimental and in silico methods. Analysis of the antiviral effects, toxicities, and pharmacodynamics of different variants of cardiac glycosides identified the mechanism of inhibition as reduction of methionine import, leading to decreased immediate-early gene translation without significant toxicity. Also, Convallatoxin was found to dramatically reduce the proliferation of clinical CMV strains, implying that its mechanism of action is an effective strategy to block CMV dissemination. Our study has uncovered the mechanism and structural elements of Convallatoxin, which are important for effectively inhibiting CMV infection by targeting the expression of immediate-early genes. IMPORTANCE: Cytomegalovirus is a highly prevalent virus capable of causing severe disease in certain populations. The current FDA-approved therapeutics all target the same stage of the viral life cycle and induce toxicity and viral resistance. We identified Convallatoxin, a novel cell-targeting antiviral that inhibits CMV infection by decreasing the synthesis of viral proteins. At doses low enough for cells to tolerate, Convallatoxin was able to inhibit primary isolates of CMV, including those resistant to the anti-CMV drug ganciclovir. In addition to identifying Convallatoxin as a novel antiviral, limiting mRNA translation has a dramatic impact on CMV infection and proliferation.

Antitumor effects of naturally occurring cardiac glycosides convallatoxin and peruvoside on human ER+ and triple-negative breast cancers.[Pubmed:28250972]

Cell Death Discov. 2017 Feb 27;3:17009.

Breast cancer is second most prevalent cancer in women, and the second only to lung cancer in cancer-related deaths. It is a heterogeneous disease and has several subtypes based on the presence or absence of hormone receptors and/or human epidermal growth factor receptor 2 (HER2). Hormone receptor-positive and HER2-enriched cancers can be targeted using hormone and HER2-targeting therapies such as trastuzumab or lapatinib. However, triple-negative breast cancers (TNBCs) do not express any of the receptors and therefore are resistant to most targeted therapies, and cytotoxic chemotherapies are the only viable option available for the treatment of TNBCs. Recently, cardiac glycosides (CGs) have emerged as potential anticancer agents that impart their antiproliferative effect by targeting multiple pathways. In this study our aim was to evaluate anticancer effects of two naturally occurring CGs, Convallatoxin (CT) and Peruvoside (PS), on ER+ and TNBCs cells. CT and PS demonstrated dose- and time-dependent cytotoxic effect on MCF-7 cells, which was further supported by loss of colony formation on drug treatment. CT and PS arrested MCF-7 cells in the G0/G1 phase and reduced the viability of MCF-7-derived mammospheres (MMs). Interestingly, while CT and PS imparted cell death in TNBCs cells from both Caucasians (MDA-MB-231 cells) and African Americans (MDA-MB-468 cells) in a dose- and time-dependent manner, the drugs were much more potent in MDA-MB-468 as compared with TNBC MDA-MB-231 cells. Both drugs significantly inhibited migration and invasion of both MCF-7 and MDA-MB-468 cells. An assessment of intracellular pathways indicated that both drugs were able to modulate several key cellular pathways such as EMT, cell cycle, proliferation and cell death in both cell types. Our data suggest a promising role for CGs in breast cancer treatment specifically in targeting TNBCs derived from African Americans, and provides impetus for further investigation of the anticancer potential of this class of drugs.

Convallatoxin is a cardiac glycoside isolated from Adonis amurensis Regel et Radde. Convallatoxin ameliorates colitic inflammation via activation of PPARγ and suppression of NF-κB. Convallatoxin is a P-glycoprotein (P-gp) substrate and recognized Val982 as an important amino acid involved in its transport. Convallatoxin is an enhancer of ligand-induced MOR endocytosis with high potency and efficacy. Anti-inflammatory and anti-proliferative properties.

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