Englerin A

Bridgehead Modifications of Englerin A Reduce TRPC4 Activity and Intravenous Toxicity but not Cell Growth Inhibition.[Pubmed:32944138]

ACS Med Chem Lett. 2020 Aug 3;11(9):1711-1716.

Modifications at the bridgehead position of Englerin A were made to explore the effects of variation at this site on the molecule for biological activity, as judged by the NCI 60 screen, in which Englerin A is highly potent and selective for renal cancer cells. Replacement of the isopropyl group by other, larger substituents yielded compounds which displayed excellent selectivity and potency comparable to the natural product. Selected compounds were also evaluated for their effect on the ion channel TRPC4 as well as for intravenous toxicity in mice, and these had lower potency in both assays compared to Englerin A.

Transient Receptor Potential Canonical 4 and 5 Channel Antagonist ML204 Depolarized Pacemaker Potentials of Interstitial Cells of Cajal.[Pubmed:32321198]

J Neurogastroenterol Motil. 2020 Sep 30;26(4):521-528.

Background/Aims: To investigate an effect of ML204 (an inhibitor of transient receptor potential canonical 4 and 5 [TRPC4/5] channels) on interstitial cells of Cajal (ICCs) and therefore determine whether TRPC4/5 channels act on ICC-generated pacemaker activity. Methods: We enforced whole cell patch clamp analysis, measurements of the intracellular Ca(2+) concentration, and reverse transcription polymerase chain reaction to determine the effect of ML204 (10 muM) or Englerin A (a selective activator of TRPC4/5 channeles, 10 muM) and the existence of TRPC4/5 in mouse small intestinal ICC. Results: Treatment of ICCs with ML204 or Englerin A caused the membrane potentials to depolarize. This depolarization effect of membrane potentials by ML204 in ICCs was observed to be concentration-dependent. After treating Ca(2+)- and Na+-free solutions or flufenamic acid (a non-selective cation channel blocker), the pacemaker potentials in the ICCs were abolished. A specific anoctamin 1 channel blocker did not have any effect on the pacemaker activity in ML204-untreated control cells; however, they blocked ML204-induced pacemaker activity in ICCs. Specific primers designed against TRPC4 and TRPC5 detected the presence of TRPC4/5 in small intestinal ICCs, and the application of ML204 increased raise the frequency of Ca(2+) oscillations in ICCs, as assessed using Fluo-4 AM. Conclusion: The results implied that ML204 could not inhibit the pacemaker activity but depolarized the membrane potential of ICCs by regulating intracellular Ca(2+) oscillations and anoctamin 1 channels.

Shape Similarity by Fractal Dimensionality: An Application in the de novo Design of (-)-Englerin A Mimetics.[Pubmed:32162837]

ChemMedChem. 2020 Apr 3;15(7):566-570.

Molecular shape and pharmacological function are interconnected. To capture shape, the fractal dimensionality concept was employed, providing a natural similarity measure for the virtual screening of de novo generated small molecules mimicking the structurally complex natural product (-)-Englerin A. Two of the top-ranking designs were synthesized and tested for their ability to modulate transient receptor potential (TRP) cation channels which are cellular targets of (-)-Englerin A. Intracellular calcium assays and electrophysiological whole-cell measurements of TRPC4 and TRPM8 channels revealed potent inhibitory effects of one of the computer-generated compounds. Four derivatives of this identified hit compound had comparable effects on TRPC4 and TRPM8. The results of this study corroborate the use of fractal dimensionality as an innovative shape-based molecular representation for molecular scaffold-hopping.

Syntheses of Epoxyguaiane Sesquiterpenes (-)-Englerin A, (-)-Oxyphyllol, (+)-Orientalol E, and (+)-Orientalol F: A Synthetic Biology Approach.[Pubmed:32052978]

Org Lett. 2020 Mar 6;22(5):1976-1979.

A combined approach toward syntheses of epoxyguaiane sesquiterpenes is presented. By use of a fungus sesquiterpene cyclase, guaian-6,10(14)-diene was produced through metabolic engineering of the isoprenoid pathway in E. coli. (-)-Englerin A, (-)-oxyphyllol, (+)-orientatol E, and (+)-orientalol F have been synthesized in two to six steps. This strategy provided rapid access to the epoxyguaiane core structure and would facilitate syntheses of (-)-Englerin A and its analogues for evaluation of their therapeutic potentials in drug discovery.

Semisynthesis of Plant-Derived Englerin A Enabled by Microbe Engineering of Guaia-6,10(14)-diene as Building Block.[Pubmed:31999448]

J Am Chem Soc. 2020 Feb 12;142(6):2760-2765.

Herein, we report a short semisynthesis of the potent transient receptor potential canonical (TRPC) channel agonist Englerin A (EA) and the related guaianes oxyphyllol and orientalol E. The guaia-6,10(14)-diene starting material was systematically engineered in Escherichia coli and Saccharomyces cerevisiae using the CRISPR/Cas9 system and was produced with high titers. The potentially scalable approach combines the advantages of synthetic biology and chemical synthesis providing an efficient and economical method for producing EA and analogues.

Potent, selective, and subunit-dependent activation of TRPC5 channels by a xanthine derivative.[Pubmed:31277085]

Br J Pharmacol. 2019 Oct;176(20):3924-3938.

BACKGROUND AND PURPOSE: The TRPC1, TRPC4, and TRPC5 proteins form homotetrameric or heterotetrameric, calcium-permeable cation channels that are involved in various disease states. Recent research has yielded specific and potent xanthine-based TRPC1/4/5 inhibitors. Here, we investigated the possibility of xanthine-based activators of these channels. EXPERIMENTAL APPROACH: An analogue of the TRPC1/4/5 inhibitor Pico145, AM237, was synthesized and its activity was investigated using HEK cells overexpressing TRPC4, TRPC5, TRPC4-C1, TRPC5-C1, TRPC1:C4 or TRPC1:C5 channels, and in A498 cells expressing native TRPC1:C4 channels. TRPC1/4/5 channel activities were assayed by measuring intracellular concentration of Ca(2+) ([Ca(2+) ]i ) and by patch-clamp electrophysiology. Selectivity of AM237 was tested against TRPC3, TRPC6, TRPV4, or TRPM2 channels. KEY RESULTS: AM237 potently activated TRPC5:C5 channels (EC50 15-20 nM in [Ca(2+) ]i assay) and potentiated their activation by sphingosine-1-phosphate but suppressed activation evoked by (-)-Englerin A (EA). In patch-clamp studies, AM237 activated TRPC5:C5 channels, with greater effect at positive voltages, but with lower efficacy than EA. Pico145 competitively inhibited AM237-induced TRPC5:C5 activation. AM237 did not activate TRPC4:C4, TRPC4-C1, TRPC5-C1, TRPC1:C5, and TRPC1:C4 channels, or native TRPC1:C4 channels in A498 cells, but potently inhibited EA-dependent activation of these channels with IC50 values ranging from 0.9 to 7 nM. AM237 (300 nM) did not activate or inhibit TRPC3, TRPC6, TRPV4, or TRPM2 channels. CONCLUSIONS AND IMPLICATIONS: This study suggests the possibility for selective activation of TRPC5 channels by xanthine derivatives and supports the general principle that xanthine-based compounds can activate, potentiate, or inhibit these channels depending on subunit composition.

Triple-negative breast cancer cell line sensitivity to englerin A identifies a new, targetable subtype.[Pubmed:31230251]

Breast Cancer Res Treat. 2019 Sep;177(2):345-355.

PURPOSE: Triple-negative breast cancers (TNBCs) represent a heterogeneous group of tumors. The lack of targeted therapies combined with the inherently aggressive nature of TNBCs results in a higher relapse rate and poorer overall survival. We evaluated the heterogeneity of TNBC cell lines for TRPC channel expression and sensitivity to cation-disrupting drugs. METHODS: The TRPC1/4/5 agonist Englerin A was used to identify a group of TNBC cell lines sensitive to TRPC1/4/5 activation and intracellular cation disruption. Quantitative RT-PCR, the sulforhodamine B assay, pharmacological inhibition, and siRNA-mediated knockdown approaches were employed. Epifluorescence imaging was performed to measure intracellular Ca(2+) and Na(+) levels. Mitochondrial membrane potential changes were monitored by confocal imaging. RESULTS: BT-549 and Hs578T cells express high levels of TRPC4 and TRPC1/4, respectively, and are exquisitely, 2000- and 430-fold, more sensitive to Englerin A than other TNBC cell lines. While Englerin A caused a slow Na(+) and nominal Ca(2+) accumulation in Hs578T cells, it elicited rapid increases in cytosolic Ca(2+) levels that triggered mitochondrial depolarization in BT-549 cells. Interestingly, BT-549 and Hs578T cells were also more sensitive to digoxin as compared to other TNBC cell lines. Collectively, these data reveal TRPC1/4 channels as potential biomarkers of TNBC cell lines with dysfunctional mechanisms of cation homeostasis and therefore sensitivity to cardiac glycosides. CONCLUSIONS: The sensitivity of BT-549 and Hs578T cells to Englerin A and digoxin suggests a subset of TNBCs are highly susceptible to cation disruption and encourages investigation of TRPC1 and TRPC4 as potential new biomarkers of sensitivity to cardiac glycosides.

Englerin A-sensing charged residues for transient receptor potential canonical 5 channel activation.[Pubmed:31080350]

Korean J Physiol Pharmacol. 2019 May;23(3):191-201.

The transient receptor potential canonical (TRPC) 5 channel, known as a nonselective cation channel, has a crucial role in calcium influx. TRPC5 has been reported to be activated by muscarinic receptor activation and extracellular pH change and inhibited by the protein kinase C pathway. Recent studies have also suggested that TRPC5 is extracellularly activated by Englerin A (EA), but the mechanism remains unclear. The purpose of this study is to identify the EA-interaction sites in TRPC5 and thereby clarify the mechanism of TRPC5 activation. TRPC5 channels are over-expressed in human embryonic kidney (HEK293) cells. TRPC5 mutants were generated by site-directed mutagenesis. The whole-cell patch-clamp configuration was used to record TRPC5 currents. Western analysis was also performed to observe the expression of TRPC5 mutants. To identify the EA-interaction site in TRPC5, we first generated pore mutants. When screening the mutants with EA, we observed the EA-induced current increases of TRPC5 abolished in K554N, H594N, and E598Q mutants. The current increases of other mutants were reduced in different levels. We also examined the functional intactness of the mutants that had no effect by EA with TRPC5 agonists, such as carbachol or GTPgammaS. Our results suggest that the three residues, Lys-554, His-594, and Glu-598, in TRPC5 might be responsible for direct interaction with EA, inducing the channel activation. We also suggest that although other pore residues are not critical, they could partly contribute to the EA-induced channel activation.

beta-Ketoesters as Mono- or Bisnucleophiles: A Concise Enantioselective Total Synthesis of (-)-Englerin A and B.[Pubmed:30938023]

Angew Chem Int Ed Engl. 2019 Jun 17;58(25):8346-8350.

A short enantioselective total synthesis of Englerin A, a guaiane sesquiterpene with significant in vitro antitumor activity, is reported. Key features of this total synthesis are an organocatalytic asymmetric decarboxylative aldol reaction, a neighboring-group-participating [4+3] cycloaddition, a novel one-pot Heck coupling/regioselective 1,4-hydrosilylation/Tamao-Fleming oxidation cascade, and a kinetic CBS reduction, generating the optically pure natural product in 6.7 % overall yield over twelve steps starting from methylglyoxal. Selective saponification of the more reactive glycolic ester moiety of Englerin A also gave (-)-englerin B.

Treasure troves of pharmacological tools to study transient receptor potential canonical 1/4/5 channels.[Pubmed:30656647]

Br J Pharmacol. 2019 Apr;176(7):832-846.

Canonical or classical transient receptor potential 4 and 5 proteins (TRPC4 and TRPC5) assemble as homomers or heteromerize with TRPC1 protein to form functional nonselective cationic channels with high calcium permeability. These channel complexes, TRPC1/4/5, are widely expressed in nervous and cardiovascular systems, also in other human tissues and cell types. It is debatable that TRPC1 protein is able to form a functional ion channel on its own. A recent explosion of molecular information about TRPC1/4/5 has emerged including knowledge of their distribution, function, and regulation suggesting these three members of the TRPC subfamily of TRP channels play crucial roles in human physiology and pathology. Therefore, these ion channels represent potential drug targets for cancer, epilepsy, anxiety, pain, and cardiac remodelling. In recent years, a number of highly selective small-molecule modulators of TRPC1/4/5 channels have been identified as being potent with improved pharmacological properties. This review will focus on recent remarkable small-molecule agonists: (-)-Englerin A and tonantzitlolone and antagonists: Pico145 and HC7090, of TPRC1/4/5 channels. In addition, this work highlights other recently identified modulators of these channels such as the benzothiadiazine derivative, riluzole, ML204, clemizole, and AC1903. Together, these treasure troves of agonists and antagonists of TRPC1/4/5 channels provide valuable hints to comprehend the functional importance of these ion channels in native cells and in vivo animal models. Importantly, human diseases and disorders mediated by these proteins can be studied using these compounds to perhaps initiate drug discovery efforts to develop novel therapeutic agents.

TRPC4/TRPC5 channels mediate adverse reaction to the cancer cell cytotoxic agent (-)-Englerin A.[Pubmed:30038709]

Oncotarget. 2018 Jul 3;9(51):29634-29643.

(-)-Englerin A (EA) is a natural product which has potent cytotoxic effects on renal cell carcinoma cells and other types of cancer cell but not non-cancer cells. Although selectively cytotoxic to cancer cells, adverse reaction in mice and rats has been suggested. EA is a remarkably potent activator of ion channels formed by Transient Receptor Potential Canonical 4 and 5 proteins (TRPC4 and TRPC5) and TRPC4 is essential for EA-mediated cancer cell cytotoxicity. Here we specifically investigated the relevance of TRPC4 and TRPC5 to the adverse reaction. Injection of EA (2 mg.kg(-1) i.p.) adversely affected mice for about 1 hour, manifesting as a marked reduction in locomotor activity, after which they fully recovered. TRPC4 and TRPC5 single knockout mice were partially protected and double knockout mice fully protected. TRPC4/TRPC5 double knockout mice were also protected against intravenous injection of EA. Importance of TRPC4/TRPC5 channels was further suggested by pre-administration of Compound 31 (Pico145), a potent and selective small-molecule inhibitor of TRPC4/TRPC5 channels which did not cause adverse reaction itself but prevented adverse reaction to EA. EA was detected in the plasma but not the brain and so peripheral mechanisms were implicated but not identified. The data confirm the existence of adverse reaction to EA in mice and suggest that it depends on a combination of TRPC4 and TRPC5 which therefore overlaps partially with TRPC4-dependent cancer cell cytotoxicity. The underlying nature of the observed adverse reaction to EA, as a consequence of TRPC4/TRPC5 channel activation, remains unclear and warrants further investigation.

Tonantzitlolone is a nanomolar potency activator of transient receptor potential canonical 1/4/5 channels.[Pubmed:29859013]

Br J Pharmacol. 2018 Aug;175(16):3361-3368.

BACKGROUND AND PURPOSE: The diterpene ester tonantzitlolone (TZL) is a natural product, which displays cytotoxicity towards certain types of cancer cell such as renal cell carcinoma cells. The effect is similar to that of (-)-Englerin A, and so, although it is chemically distinct, we investigated whether TZL also targets transient receptor potential canonical (TRPC) channels of the 1, 4 and 5 type (TRPC1/4/5 channels). EXPERIMENTAL APPROACH: The effects of TZL on renal cell carcinoma A498 cells natively expressing TRPC1 and TRPC4, modified HEK293 cells overexpressing TRPC4, TRPC5, TRPC4-TRPC1 or TRPC5-TRPC1 concatemer, TRPC3 or TRPM2, or CHO cells overexpressing TRPV4 were studied by determining changes in intracellular Ca(2+) , or whole-cell or excised membrane patch-clamp electrophysiology. KEY RESULTS: TZL induced an elevation of intracellular Ca(2+) in A498 cells, similar to that evoked by Englerin A. TZL activated overexpressed channels with EC50 values of 123 nM (TRPC4), 83 nM (TRPC5), 140 nM (TRPC4-TRPC1) and 61 nM (TRPC5-TRPC1). These effects of TZL were reversible on wash-out and potently inhibited by the TRPC1/4/5 inhibitor Pico145. TZL activated TRPC5 channels when bath-applied to excised outside-out but not inside-out patches. TZL failed to activate endogenous store-operated Ca(2+) entry or overexpressed TRPC3, TRPV4 or TRPM2 channels in HEK 293 cells. CONCLUSIONS AND IMPLICATIONS: TZL is a novel potent agonist for TRPC1/4/5 channels, which should be useful for testing the functionality of this type of ion channel and understanding how TRPC1/4/5 agonists achieve selective cytotoxicity against certain types of cancer cell.