Calcimycin (syn. A23187) is a potent Ca2+ ionophore and carboxylic acid antibiotic isolated from the soil bacterium Streptomyces chartreusis (NRRL 3882) in 1974. It was isolated from the bacterial culture as a mixed calcium-magnesium salt, which can be converted to the free acid form.
Calcimycin is a spiroketal substituted by pyrollic and benzoxazolyl groups which allow its high affinity and selectivity for calcium. It also has high affinity for Mg2+ and Mn2+. It is used as a research tool for calcium regulation. A mobile ion-carrier, it forms complexes with divalent cations, thus equilibrating the inter- and intracellular concentrations. It allows Mn2+ into the cell to quench intracellular dye fluorescence and can be used in flow cytometry. It can be used with visible light-excitable indicators including calcium green, magnesium green and calcium orange and others. Calcimycin has activity against bacteria, fungi, protozoa, and Mycobacteria. Calcimycin can be used as a research tool to study the role of divalent cations in biological systems, such as increasing the levels of intracellular Ca2+ in intact cells. It can also be used for in-situ calibrations of fluorescent Ca2+ indicators.
Calcimycin is soluble in ethanol, methanol, DMSO and DMF. It is slightly soluble in water. Dissolve in in DMSO or ethanol prior to preparing low concentrations of aqueous solutions.
|Mechanism of Action||Calcimycin is a divalent cation ionophore, allowing ions to cross cell membranes. It is highly selective for Ca2+. It can act as an uncoupler of oxidative phosphorylation. It is an inhibitor of mitochondrial ATPase activity. In mycobacteria, Calcimycin induces P2RX7-dependent, calcium-regulated autophagy.|
|Spectrum||Gram-positive bacteria (low activity), fungi, protozoa, Mycobacteria.|
|Microbiology Applications||Calcimycin is a potent inhibitor of Mycobacterium bovis BCG in vitro and in THP-1 cells. Calcimycin binding with purinergic receptor P2X7 (P2RX7) leads to an increase in intracellular calcium level that regulates the extracellular release of ATP. ATP was able to regulate Calcimycin-induced autophagy through P2RX7 in an autocrine fashion (Mawatwal et al, 2017).
Calcimycin is effective against the protozoan parasite Leishmania major, the casual agent of leishmaniasis. Promatigotes were treated with the compound (0.5, 1 and 2 µM) and cell viability was assessed using resazurin assay. It exhibited a dose-dependent effect with IC50 of 0.16 µM. Cell death is accompanied by loss of mitochondrial polarization and plasma membrane integrity. Authors found it activated nitric oxide synthase and caused the death of the parasite, suggesting that nitric oxide synthase activation could be used as a therapeutic approach (Grekov et al, 2017).
|Eukaryotic Cell Culture Applications||When undifferentiated HL-60 cells were treated with Calcimycin, the intracellular concentration of Ca2+ became elevated, reactive oxygen species (ROS) were generated both intra- and extracellularly, and apoptosis was induced. Aoptosis could be prevented by cyclosporin A, an inhibitor of mitochondrial permeability transition (MPT). Intracellular ROS was associated with the opening of MPT pores that led to apoptotic cell death. Understanding how ROS are generated from mitochondria can provide insights into the mitochondrial electron transport chain and using MTP as a potential approach for diseases with disturbed Ca2+ homeostasis (Kajitani et al, 2007).
Calcimycin is able to induce cataract formation in lens epithelial cells. During treatment with 5 µM Calcimycin, apoptotic epithelial cells were found after 2 hours via terminal deoxynucleotidyl transferase (TdT) labeling. After 12 hours > 60% of the lens epithelial cells underwent apoptosis. Since the vertebrate lens only has a single layer of epithelial cells, apoptosis destroys the epithelium, interferes with homeostasis of the fiber cells underneath, and initiates lens opacification (Wan-Cheng et al, 1995).
|Cancer Applications||Calcimycin can be used to make artificial liposomes loaded with anti-cancer agents like topotecan (Tardi et al, 2000). The Calcimycin ionophore is used to induce an ion gradient to create an acidic carrier interior to encapsulate topotecan in the aqueous liposome interior. Protected topotecan is the lactone form, while the form released at the tumor site is the active form (Tardi et al, 2000).
A high-throughput screen was performed to identify small molecules targeting the S100A4-promoter activity, as this calcium-binding protein mediates metastasis in colon cancer. S100A4 is a target gene of the Wnt/β-catenin pathway. Calcimycin was found to be a transcriptional inhibitor of S100A4, reducing S100A4 mRNA/protein expression in a dose-dependent way. It inhibited Wnt/β-catenin pathway activity. These results provide a functional strategy to restrict mortality of colon cancer cells (Sack et al, 2011).
|Solubility||Soluble in ethanol, methanol, DMSO and DMF. Slightly soluble in water. Dissolve in in DMSO or ethanol prior to preparing low concentrations of aqueous solutions.|
Chaney MO, Demarco PV, Jones ND and Occolowitz JL (1974) Letter: The structure of A23187, a divalent cation ionophore. J. Am. Chem. Soc. 96(6):1932-1933 PMID 4815763
Grekov I et al (2017) Calcium ionophore, Calcimycin, kills Leishmania promastigotes by activating parasite nitric oxide synthase. BioMed. Res. Intl. 2017. Article ID 1309485:1-6 PMID 29181385
Kajitani N et al (2007) Mechanism of A23187-induced apoptosis in HL-60 cells: Dependency on mitochondrial permeability transition but not on NADPH oxidase. Biosci. Biotechnol. Biochem. 71(11):2701-2711 PMID 17986779
Mawatwal S et al (2017) Calcimycin mediates mycobacterial killing by inducing intracellular calcium-regulated autophagy in a P2RX7 dependent manner. Biochim Biophys Acta Gen Subj. 1861(12):3190-3200 PMID 28935606
Pressman BC et al (1976) Biological applications of ionophores. Ann. Rev. Biochem. 45:501Reed PW and Lardy HAJ (1972) A23187: A divalent cation ionophore. Biol. Chem. 247:6970
Tardi P et al (2000) Liposomal encapsulation of topotecan enhances anticancer efficacy in murine and human xenograft models. 60(13) PMID 10910044