Ouabain at nanomolar concentrations is cytotoxic for biliary tract cancer cells

Target Identification of Marine Natural Product Odoamide:Odoamide Induces Apoptotic Cell Death by Targeting ATPase Na+/K+ Transporting Subunit Alpha 1 (ATP1A1)

Marine natural products show a large variety of unique chemical structures and potent biological activities. Elucidating the target molecule and the mechanism of action is an essential and challenging step in drug development starting with a natural product. Odoamide, a member of aurilide-family isolated from Okinawan marine cyanobacterium, has been known to exhibit highly potent cytotoxicity against various cancer cell lines. In this study, we investigated the target protein and the cytotoxic mechanism of odoamide. Compared to existing anticancer agents, odoamide showed a unique fingerprint in the JFCR39 cancer cell panel and a characteristic pattern in gene expression profiling. Affinity chromatography utilizing a biologically active odoamide probe identified ATPase Na+/K+ transporting subunit alpha 1 (ATP1A1) as a specific binding protein. Additionally, cells resistant to odoamide were found to have mutations at Gly98 and Gly99 of the ATP1A1 protein. The apparently attenuated cytotoxic and apoptotic activities of odoamide in odoamide-resistant cells suggests that the induction of these activities by odoamide is critically dependent on its interaction with ATP1A1. We conclude that odoamide induces apoptotic cell death by targeting ATP1A1, and we discuss the impact of affinity-based target identification for natural products and the potential of ATP1A1 inhibitors for drug discovery.

Digoxin and its Na+/K+-ATPase-targeted actions on cardiovascular diseases and cancer

Na+/K+-ATPase (NKA) is a plasma membrane ion-transporting protein involved in the generation and maintenance of Na+ and K+ gradients across the cell membrane, which can produce a driving force for the secondary transport of metabolic substrates. NKA also regulates intracellular calcium that is responsible for modulating numerous cellular processes, while it interacts with many other proteins and functions as a signal transducer, with several signaling pathways being involved. Thus, NKA has become an important target for the treatment of human diseases. Cardiac glycosides are well-known NKA inhibitors, of which (+)-digoxin or digoxin has been long used for the treatment of congestive heart failure. Also, digoxin has exhibited potential antitumor activity, by targeting directly HIF-1α, NKA, and NF-κB. Thus, the function of NKA in human cardiovascular diseases and cancer and the therapeutic effects of digoxin on these diseases are summarized in the present review, with the correlations among digoxin, NKA, cardiovascular diseases, and cancer being discussed. Presented herein are also the antitumor potential of monosaccharide cardiac glycoside analogues of digoxin, including (-)-cryptanoside A, (-)-oleandrin, (-)-ouabain, and (+)-strebloside. It is hoped that this contribution will provide some helpful information for the design and discovery of new cardiac glycoside-type therapeutic agents for the treatment of cardiovascular diseases and cancer.

Combination of ethyl acetate fraction from Calotropis gigantea stem bark and sorafenib induces apoptosis in HepG2 cells

The cytotoxicity of the ethyl acetate fraction of the Calotropis gigantea (L.) Dryand. (C. gigantea) stem bark extract (CGEtOAc) has been demonstrated in many types of cancers. This study examined the improved cancer therapeutic activity of sorafenib when combined with CGEtOAc in HepG2 cells. The cell viability and cell migration assays were applied in HepG2 cells treated with varying concentrations of CGEtOAc, sorafenib, and their combination. Flow cytometry was used to determine apoptosis, which corresponded with a decline in mitochondrial membrane potential and activation of DNA fragmentation. Reactive oxygen species (ROS) levels were assessed in combination with the expression of the phosphatidylinositol-3-kinase (PI3K)/ protein kinase B (Akt)/ mammalian target of rapamycin (mTOR) pathway, which was suggested for association with ROS-induced apoptosis. Combining CGEtOAc at 400 μg/mL with sorafenib at 4 μM, which were their respective half-IC50 concentrations, significantly inhibited HepG2 viability upon 24 h of exposure in comparison with the vehicle and each single treatment. Consequently, CGEtOAc when combined with sorafenib significantly diminished HepG2 migration and induced apoptosis through a mitochondrial-correlation mechanism. ROS production was speculated to be the primary mechanism of stimulating apoptosis in HepG2 cells after exposure to a combination of CGEtOAc and sorafenib, in association with PI3K/Akt/mTOR pathway suppression. Our results present valuable knowledge to support the development of anticancer regimens derived from the CGEtOAc with the chemotherapeutic agent sorafenib, both of which were administered at half-IC50, which may minimize the toxic implications of cancer treatments while improving the therapeutic effectiveness toward future medical applications.