Antimycin A induced apoptosis in HCT-116 colorectal cancer cells through the up- and downregulation of multiple signaling pathways.

Colorectal cancer is the third most life-threatening cancer in the western countries. For the treatment, several chemotherapeutic drugs are using those that have severe side effects on the patient. So, finding alternative drugs is important. In the present research antimycin A was selected to evaluate the anticancer properties on the HCT-116 colorectal cancer cells. Antimycin A inhibited HCT-116 cells proliferation with the IC50 value of 29 µg/mL concentration. As a long-term effect, HCT-116 cells were incubated with 10-40 µg/mL concentration of antimycin A for 7 days. No colony was observed in the treated wells. Apoptotic features in HCT-116 cells were observed in antimycin A treated cells after being stained with Hoechst 33342 dye. Apoptosis was further confirmed by FITC-annexin V/PI. Role of caspase-3 protein in the apoptosis process was also confirmed by the caspase-3 inhibitor. After treatment of HCT-116 cells with antimycin A, apoptotic related gene expression was checked by reverse transcription polymerase chain reaction. p53 and caspase-9 genes were upregulated consequently mitogen-activated protein kinases (MAPK), poly(ADP-Ribose) polymerase (PARP), and nuclear factor kappa B (NF-κB) genes were downregulated. Molecular docking simulation indicated significant binding affinity of antimycin A with the five proteins. The results indicated antimycin A would be a promising anticancer agent for further anticancer research.

Discovery of potent broad spectrum antivirals derived from marine actinobacteria.

Natural products provide a vast array of chemical structures to explore in the discovery of new medicines. Although secondary metabolites produced by microbes have been developed to treat a variety of diseases, including bacterial and fungal infections, to date there has been limited investigation of natural products with antiviral activity. In this report, we used a phenotypic cell-based replicon assay coupled with an iterative biochemical fractionation process to identify, purify, and characterize antiviral compounds produced by marine microbes. We isolated a compound from Streptomyces kaviengensis, a novel actinomycetes isolated from marine sediments obtained off the coast of New Ireland, Papua New Guinea, which we identified as antimycin A1a. This compound displays potent activity against western equine encephalitis virus in cultured cells with half-maximal inhibitory concentrations of less than 4 nM and a selectivity index of greater than 550. Our efforts also revealed that several antimycin A analogues display antiviral activity, and mechanism of action studies confirmed that these Streptomyces-derived secondary metabolites function by inhibiting the cellular mitochondrial electron transport chain, thereby suppressing de novo pyrimidine synthesis. Furthermore, we found that antimycin A functions as a broad spectrum agent with activity against a wide range of RNA viruses in cultured cells, including members of the Togaviridae, Flaviviridae, Bunyaviridae, Picornaviridae, and Paramyxoviridae families. Finally, we demonstrate that antimycin A reduces central nervous system viral titers, improves clinical disease severity, and enhances survival in mice given a lethal challenge with western equine encephalitis virus. Our results provide conclusive validation for using natural product resources derived from marine microbes as source material for antiviral drug discovery, and they indicate that host mitochondrial electron transport is a viable target for the continued development of broadly active antiviral compounds.

Antimycin A as a mitochondrial electron transport inhibitor prevents the growth of human lung cancer A549 cells.

Antimycin A (AMA) inhibits mitochondrial electron transport between cytochromes b and c. We evaluated the effects of AMA on the growth of human pulmonary adenocarcinoma A549 cells in relation to cell cycle and apoptosis. Treatment with 2-100 microM AMA significantly inhibited the cell growth of A549 for 72 h. DNA flow cytometry indicated that AMA slightly induced a G1 phase arrest of the cell cycle for 72 h. Treatment with 50 microM AMA induced apoptosis of approximately 17% in view of annexin V-staining cells. The dose of 50 microM AMA also induced loss of the mitochondrial membrane potential (DeltaPsi(m)) of approximately 38%. The intracellular reactive oxygen species (ROS) levels including O2(.-) were significantly increased in AMA-treated A549 cells. In conclusion, AMA inhibited the growth of A549 cells via inducing cell cycle arrest as well as triggering apoptosis. Growth inhibition in AMA-treated A549 cells was accompanied by an increase in ROS levels.

Bcl2/bcl-xL inhibitor engenders apoptosis and increases chemosensitivity in mesothelioma.

Mesothelioma is a neoplasm of the pleura that is currently incurable by conventional therapies. Previously, we demonstrated that mesothelioma overexpresses BCL-X(L), an anti-apoptotic member of the BCL-2 family. In addition, we have shown that down regulation of BCL-X(L) using a BCL-X(L) antisense oligonucleotide engenders mesothelioma apoptotic cell death in vitro and in vivo. The purpose of this study is to evaluate the efficacy of bcl2/bcl-x(L) inhibitor, 2-methoxy antimycin A3, in inducing apoptosis and increasing chemo-sensitivity in vitro and in vivo. Several bcl-x(L) high-expression tumor cell lines and one normal human cell line were exposed to 2-methoxy antimycin A3. 2-methoxy antimycin A3 demonstrated significant growth inhibition only in these tumor cell lines, with little effect on normal human cells. Treatment with 2-methoxy antimycin A3 alone resulted in a dramatic increase in the induction of apoptosis in the cancer cells. Apoptosis occurs through decreasing mitochondrial membrane potential and caspase activation. Notably, treatment with 2-methoxy antimycin A3 does not alter BCL-2 family protein expression. Synergistic inhibition of tumor growth by the coadministration of cisplatin and 2-methoxy antimycin A3 was observed in both in vitro and in vivo experiments. Together, these findings indicate that exposure of cancer cells to small molecule Bcl-2/x(L) inhibitors such as 2-methoxy antimycin A3 alone, or in the combination with other chemotherapeutics, may represent a novel therapeutic strategy in treatment of cancer, especially mesothelioma.

Antimycin A induced cardioprotection is dependent on pre-ischemic p38-MAPK activation but independent of MKK3.

To examine the role of mitogen-activated protein kinase kinase 3 (MKK3) and p38 mitogen-activated protein kinase (p38-MAPK) in the cardioprotection afforded by antimycin A. Langendorff perfused murine hearts exposed to antimycin A or vehicle prior to global ischemia with p38-MAPK and HSP27 phosphorylation examined in the presence and absence of SB203580 or the presence (mkk3(+/+)) and absence (mkk3(-/-)) of MKK3. Infarct size was determined after 30 or 40 min of global ischemia and 2 h reperfusion. p38-MAPK dual phosphorylation in response to antimycin A was attenuated by co-administration of the antioxidant mercaptopropyonyl-glycine but unaffected by the absence of MKK3 or the presence of SB203580 at a concentration that inhibited the downstream phosphorylation of HSP27. Pre-ischemic exposure to antimycin A caused a significant reduction in subsequent infarction (I:R%) compared to vehicle on both the mkk3(-/-) and mkk3(+/+) background (23.7+/-2.9 and 22.8+/-4.6 compared to 50.7+/-4.0 and 49.6+/-5.4 P=0.001, respectively). In C57Bl6 mice, antimycin A prior to ischemia reduced infarct size compared to vehicle (22.8 +/- 6.1 vs. 48.3+/-5.2 P=0.01, respectively), an effect abolished by coincident SB203580. The cardiac protection initiated by antimycin A is dependent on the activation of p38-MAPK which occurs, at least in part, in response to oxygen-derived free radicals. The mechanism of this protective form of p38-MAPK activation is independent of the upstream kinase MKK3 and does not involve autophosphorylation.