The Resorcylic Acid Lactone Hypothemycin Selectively Inhibits the Mitogen-Activated Protein Kinase Kinase-Extracellular Signal-Regulated Kinase Pathway in Cells

Abstract

Resorcylic acid lactones (RALs) constitute a family of polyketide mycotoxins with a variety of biological activities.1) Representative examples are the heat shock protein 90 inhibitor radicicol and the estrogen agonist zearalenone. Hypothemycin ( Fig. 1), a RAL containing a cis-enone moiety that initially did not reveal any particularly interesting activity, was later shown to inhibit ras-transformation and T cell activation. [2][3][4] Hypothemycin and other closely related cis-enone RALs gained attention as compounds that irreversibly inhibit certain protein kinases such as mitogen-activated protein kinase kinase (MEK), extracellular signalf-regulated kinase (ERK) and TAK1, but not RAF, protein kinase C (PKC) or protein kinase A (PKA). [5][6][7][8] From their structures and irreversible mode of action, cis-enone RALs were predicted to form stable Michael addition products with cysteine residues of protein kinases. Bioinformatics studies revealed that a cysteine residue that immediately precedes the highly conserved Asp-Phe-Gly (DFG) motif is the cis-enone RAL binding site.9) This cysteine is conserved in 9% (46/ 510) of the protein kinases in the human kinome.Although different kinases contain the RAL target cysteine, cis-enone RALs have been isolated as selective inhibitors of MEK. 7,8) Furthermore, cis-enone RALs share various biological properties with MEK inhibitors. Sonoda et al. identified hypothemycin as a ras-signaling inhibitor.3) We reported that the MEK inhibitor U0126 reverses ras-mediated transformation.10) Hypothemycin and MEK inhibitors showed strong activity in cell lines with the activating BRAF V600E mutation.11) Sonoda et al. reported that the suppression of ras-induced transformation was associated with accelerated cyclin D1 degradation, 3) and a MEK inhibitor caused a loss of cyclin D expression in BRAF mutants. 11)Here, we compared the effects of hypothemycin and MEK inhibitors on signaling pathways in cells. Our results show that even though the RAL target cysteine is not confined to the components of the MEK-ERK pathway, in cellular settings hypothemycin preferentially blocks the MEK-ERK axis with sufficient selectivity to impair transformed phenotypes of cancer cells requiring this pathway. The resorcylic acid lactone hypothemycin has been shown to inactivate protein kinases by binding to a cysteine conserved in 46 protein kinases, including mitogen-activated protein kinase kinase (MEK), extracellular signal-regulated kinase (ERK) and platelet-derived growth factor receptor (PDGFR). We assessed the selectivity of hypothemycin in cellular contexts. Hypothemycin normalized the morphology and inhibited anchorage-independent growth of Ki-ras transformed normal rat kidney (NRK) cells with selectivity and potency comparable to or greater than that of the MEK inhibitor U0126. In Ki-ras-transformed and phorbol 12-myristate 13-acetate (PMA)-treated NRK cells, hypothemycin blocked ERK activation but showed a minimal effect on autophosphorylation of protein kinase D1 (PKD1), another kinase contain...

Resorcylic Acid Lactones Produced by an Endophytic Penicillium ochrochloron Strain from Kadsura angustifolia

“…Four new compounds (2,(4)(5)(6), two new natural products (1,3), and six known compounds (7)(8)(9)(10)(11)(12) were isolated from the mycelial solid culture of an endophytic fungus P. ochrochloron SWUKD4.1850 from the medicinal plant K. angustifolia after successive separation steps using various column chromatography (CC) methods (▶ Fig. 1).…”

“…1). The known compounds were identified as aigialomycin F (7) [3], aigialomycin A (8) [18], aigialomycin B (9) [18], aigialomycin D (10) [18], zeaenol (11) [19], and oxozeaenol (12) [20] by comparison of their spectroscopic data with those reported in the literature.…”

Synthesis and Biological Evaluation of New Madecassic Acid Derivatives Targeting ERK Cascade Signaling

“…Cobimetinib is a MEK inhibitor, recently approved by the FDA for treatment of patients with B-Raf V600E mutation-positive melanoma in combination with vemurafenib (Garnock-Jones, 2015 ). Hypothemycin is a resorcylic acid lactone that has been reported to selectively and irreversibly inhibit protein kinases that contain a conserved cysteine residue (Cys 166 ) in the ATP-binding site, including the mitogen-activated protein kinase (MEK) and the extracellular signal-regulated kinase (ERK) (Fukazawa et al, 2010 ). These CellMiner TM results suggested that the new MEA analogs might impact signal transduction through the ERK cascade.…”

Anticancer activities, structure–activity relationship, and mechanism of action of 12‐, 14‐, and 16‐membered macrolactones

“…Hypothemycin ( 16 ), a resorcylic acid lactone polyketide isolated from a fungal culture Setophoma terrestris (MSX45109), could inactivate protein kinases by binding to a cysteine conserved in 46 protein kinases, including MEK, extracellular signal‐regulated kinase (ERK), and platelet‐derived growth factor receptor (PDGFR). [ 51–53 ] Hypothemycin (IC 50 : 0.58 and 2.14 µM, MTT assay) showed promising activity against MDA‐MB‐435 and SW‐620 cancer cell lines, demonstrating its potential for the development of novel anti‐breast cancer agents. [ 54 ]…”