Three bufadienolides induce cell death in the human lung cancer cell line CL1-5 mainly through autophagy.

The effects of 3 bufadienolides, namely kalantuboside B, kalantuboside A, and bryotoxin C, isolated from Kalanchoe tubiflora (Harvey) were evaluated and characterized in CL1-5 highly metastatic human lung cancer cells. In contrast to their apoptosis-promoting activity in other cancer cells, these bufadienolides only slight or did not induce apoptosis in CL1-5 cancer cells. Instead, they activated an autophagy pathway, as indicated by increased autophagosome formation. Autophagy induced by these bufadienolides was demonstrated to be linked to the down-regulation of p-mTOR and the up-regulation of LC3-II, ATG5, ATG7, and Beclin-1. Our findings revealed an autophagy as the alternative mechanism of drug action by bufadienolides in CL1-5 lung cancer cells and provided evidence that bufadienolides are a potential therapeutic strategy for highly metastatic human lung cancer.

Total synthesis, chemical modification and structure-activity relationship of bufadienolides.

Bufadienolides are a type of natural cardiac steroids and originally isolated from the Traditional Chinese Medicine Chan'Su, they have been used for the treatment of heart disease in traditional remedies as well as in modern medicinal therapy with potent anti-tumor activities. Due to their unique molecular structures with unsaturated six-membered lactones attached to the steroid core, bufadienolides have received great attention in the synthetic organic community. This review presents total synthetic efforts to some representative bufadienolides, chemical modification of bufadienolides will also be given to discuss their structure-activity relationship in anti-tumor.

Hybrids of arenobufagin and benzoisoselenazol reducing the cardiotoxicity of arenobufagin.

Arenobufagin is a naturally occurring bufadienolide showing promising antitumor activity accompanied however with apparent cardiac toxicity. Following the recent discovery that oxidative damage possibly be an important cause of the cardiac toxicity of cardenolides, a strategy fusing the antitumor agent arenobufagin with a benzoisoselenazol fragment, a reactive oxygen species (ROS) scavenger, has been developed. Six novel hybrids were synthesized and their ROS scavenging activities as well as their in vitro cytotoxicity against the human hepatocellular carcinoma cell line HepG2, an adriamycin-resistant subline HepG2/ADM, and the human myocardial cell line AC16 were evaluated. The results indicate that the hybrids exhibit various degrees of in vitro ROS scavenging activities, and weaker cytotoxicity than that of arenobufagin against the myocardial cell line AC16. These findings suggest the feasibility of a strategy in which the cardiotoxicity of the potential antitumor agent arenobufagin is reduced.

The synthesis of cardenolide and bufadienolide aglycones, and related steroids bearing a heterocyclic subunit.

Covering: early studies through to March 2016Cardenolides and bufadienolides constitute an attractive class of biologically active steroid derivatives which have been used for the treatment of heart disease in traditional remedies as well as in modern medicinal therapy. Due to their application as therapeutic agents and their unique molecular structures, bearing unsaturated 5- or 6-membered lactones (or other heterocycles) attached to the steroid core, cardio-active steroids have received great attention, which has intensified during the last decade, in the synthetic organic community. Advances in the field of cross-coupling reactions have provided a powerful tool for the attachment of lactone subunits to the steroid core. This current review covers a methodological analysis of synthetic efforts to cardenolide and bufadienolide aglycones. Special emphasis is given to cross-coupling reactions applied for the attachment of lactone subunits at sterically very hindered positions of the steroid core. The carefully selected partial and total syntheses of representative cardio-active steroids will also be presented to exemplify recent achievements (improvements) in the field.

Novel stereoselective bufadienolides reveal new insights into the requirements for Na(+), K(+)-ATPase inhibition by cardiotonic steroids.

Cardiotonic steroids (CTS) are clinically important drugs for the treatment of heart failure owing to their potent inhibition of cardiac Na(+), K(+)-ATPase (NKA). Bufadienolides constitute one of the two major classes of CTS, but little is known about how they interact with NKA. We report a remarkable stereoselectivity of NKA inhibition by native 3ß-hydroxy bufalin over the 3α-isomer, yet replacing the 3ß-hydroxy group with larger polar groups in the same configuration enhances inhibitory potency. Binding of the two (13)C-labelled glycosyl diastereomers to NKA were studied by solid-state NMR (SSNMR), which revealed interactions of the glucose group of the 3ß- derivative with the inhibitory site, but much weaker interactions of the 3α- derivative with the enzyme. Molecular docking simulations suggest that the polar 3ß-groups are closer to the hydrophilic amino acid residues in the entrance of the ligand-binding pocket than those with α-configuration. These first insights into the stereoselective inhibition of NKA by bufadienolides highlight the important role of the hydrophilic moieties at C3 for binding, and may explain why only 3ß-hydroxylated bufadienolides are present as a toxic chemical defence in toad venom.

Synthesis and biological evaluation of bufalin-3-yl nitrogen-containing-carbamate derivatives as anticancer agents.

A series of bufalin-3-yl nitrogen-containing-carbamate derivatives 3 were designed, synthesized, and evaluated for their proliferation inhibition activities against human cervical epithelial adenocarcinoma (HeLa) cell line. The structure-activity relationships (SARs) of this new series are described in this paper. Cytotoxicity data revealed that the C3 moiety had an important influence on cytotoxic activity. Compound 3i-HCl exhibited significant in vitro antiproliferative activity against the ten tested tumor cell lines, with IC50 values ranging from 0.30 to 1.09 nM. Furthermore, 3i-HCl can significantly inhibit tumor growth by 100% at the dose 2 mg/kg by iv, or 4 mg/kg by ig.

Alkaloids from the Traditional Chinese Medicine ChanSu: synthesis-enabled structural reassignment of bufopyramide to bufoserotonin C.

A synthesis of putative bufopyramide has shown the structure assigned to the natural product to be incorrect. The spectroscopic data for the natural product bufopyramide matches that obtained from a synthetic sample of bufoserotonin C, confirming that the two natural products are not distinct, but instead the same compound.

Synthetic and structure-activity relationship of insecticidal bufadienolides.

A new synthetic analog of bufadienolide, methyl isobryophyllinate A (1), and a known synthetic analog, methyl isobersaldegenate-1,3,5-orthoacetate (2), were obtained by methanolysis of bryophyllin A (3) and bersaldegenin-1,3,5-orthoacetate (5) in basic solution. Structure-insecticidal activity relationship studies revealed both orthoacetate and alpha-pyrone moieties seemed to be essential structural elements for exhibiting insecticidal activity, whereas oxygenated substituents in the C ring enhanced the insecticidal activity against the third instar larvae of silkworm (Bombyx mori).

Synthesis of bufalin derivatives with inhibitory activity against prostate cancer cells.

Bufalin possesses a strong anti-cancer effect, but the cardiac toxicity targeting the Na(+), K(+)-ATPase limits its application. Here, two bufalin derivatives, bufadienolactam (1) and secobufalinamide (2), were synthesised by treating bufalin with ammonium acetate in dimethylformamide solution. Their structures were elucidated by extensive spectroscopic methods. The structure of compound 2 was further confirmed by single-crystal X-ray diffraction analysis. Compounds 1 and 2 expressed strong inhibitory activities against androgen-dependent prostate cancer cells (IC50 values about 10 µM), but only weak inhibition on Na(+), K(+)-ATPase (Ki about 70 µM), indicating that they might be potential anti-prostate cancer agents without severe cardiac toxicity.

Synthesis and structure-activity relationships study of cytotoxic bufalin 3-nitrogen-containing-ester derivatives.

A series of bufalin 3-nitrogen-containing-ester derivatives (2-6) were designed, synthesized, and evaluated for their proliferation inhibition activities against human cervical epithelial adenocarcinoma (HeLa) and non-small-cell lung cancer (A549) cell lines. The structure-activity relationships (SARs) of this new series were described in this paper. Cytotoxicity data revealed that C3 moiety had important influence on cytotoxic activity. On two cell lines, the bufalin-3-piperidinyl-4-carboxylate compound 2 (IC50 values on HeLa and A549 cell lines were 0.76 nM and 0.34 nM, respectively) displayed a significant cytotoxic potency compared to the parent compound bufalin.

Configurational reassignment and improved preparation of the competitive IL-6 receptor antagonist 20R,21R-epoxyresibufogenin-3-formate.

20R,21R-Epoxyresibufogenin-3-formate (1) and 20S,21S-epoxyresibufogenin-3-formate (2) were synthesized from commercial resibufogenin (3) using known procedures. The major product (1) was dextrorotatory, as was the major product from the reported synthesis of epoxyresibufogenin-3-formate; however, the literature (+)-compound was assigned the 20S,21S-configuration on the basis of NMR data. We have now unequivocally determined, using single-crystal X-ray structure analyses of the major and minor products of the synthesis and of their derivatives, that the major product from the synthesis was (+)-20R,21R-epoxyresibufogenin-3-formate (1). Our minor synthetic product was determined to have the (-)-20S,21S-configuration (2). The (+)-20R,21R-compound 1 has been found to have high affinity for the IL-6 receptor and to act as an IL-6 antagonist. A greatly improved synthesis of 1 was achieved through oxidation of preformed resibufogenin-3-formate. This has enabled us to prepare, from the very expensive commercial resibufogenin, considerably larger quantities of 1, the only known nonpeptide small-molecule IL-6 antagonist.

Synthesis of orally active cardiosteroid derivatives.

Starting from hellebrigenin, orally cardiotonic active acylcardiosteroid derivatives have been synthesized. D 12316 (acrihellin), the hellebrigenin-3 beta-dimethylacrylate, has been chosen for clinical evaluation.

[Meproscillarin, a new semisynthetic cardiac glycoside/chemistry and physical properties (author's transl)]. / Meproscillarin, ein neues halbsynthetisches Herzglykosid. Chemie und physikalische Eigenschaften.

14-Hydroxy-3beta-[4-O-methyl-alpha-L-rhamnopyranosyl)oxy]-14beta-bufa-4,20,22-trienolide (meproscillarin) is a new semisynthetic glycoside for the therapy of cardiac insufficiency. The preparation from proscillaridin and the chemical and physical properties are described.