Synthesis and biological evaluation of biotin conjugates of (±)-(4bS,8aR,10aS)-10a-ethynyl-4b,8,8-trimethyl-3,7-dioxo-3,4b,7,8,8a,9,10,10a-octahydro-phenanthrene-2,6-dicarbonitrile, an activator of the Keap1/Nrf2/ARE pathway, for the isolation of its protein targets

Synthesis of the Phormidolide A Macrocycle Supports the Proposed Configurational Reassignment

We describe the successful synthesis of the phormidolide A macrocycle as a crucial step toward its total synthesis and configurational assignment. Exhaustive exploration of macrocyclization strategies revealed the detrimental effects of a bulky protecting group on the C17 hydroxyl function, leading to the successful use of a C17 p-methoxybenzyloxymethyl (PMBM) ether in the macrolactonization reaction. Further elaboration of the macrocycle with a truncated C18-C23 side chain afforded an advanced C1-C23 fragment of phormidolide A. Detailed comparison of spectroscopic data with those of phormidolide A supports the proposed configurational reassignment.

Acetylenic tricyclic bis-(cyano enone) interacts with Cys 374 of actin, a residue necessary for stress fiber formation and cell migration

The migratory and invasive potential of tumour cells relies on the actin cytoskeleton. We previously demonstrated that the tricyclic compound, TBE-31, inhibits actin polymerization and here we further examine the precise interaction between TBE-31 and actin. We demonstrate that iodoacetamide, a cysteine (Cys) alkylating agent, interferes with the ability of TBE-31 to interact with actin. In addition, in silico analysis identified Cys 217, Cys 272, Cys 285 and Cys 374 as potential binding sites for TBE-31. Using mass spectrometry analysis, we determined that TBE-31 associates with actin with a stoichiometric ratio of 1:1. We mutated the identified cysteines of actin to alanine and performed a pull-down analysis with a biotin labeled TBE-31 and demonstrated that by mutating Cys 374 to alanine the association between TBE-31 and actin was significantly reduced, suggesting that TBE-31 binds to Cys 374. A characterization of the NIH3T3 cells overexpressing eGFP-actin-C374A showed reduced stress fiber formation, suggesting Cys 374 is necessary for efficient incorporation into filamentous actin. Furthermore, migration of eGFP-Actin-WT expressing cells were observed to be inhibited by TBE-31, however fewer eGFP-Actin-C374A expressing cells were observed to migrate compared to the cells expressing eGFP-Actin-WT in the presence or absence of TBE-31. Taken together, our results suggest that TBE-31 binds to Cys 374 of actin to inhibit actin stress fiber formation and may potentially be a mechanism through which TBE-31 inhibits cell migration.

Biotinylation of an acetylenic tricyclic bis(cyanoenone) lowers its potency as an NRF2 activator while creating a novel activity against BACH1

The transcription factor BACH1 regulates the expression of a variety of genes including genes involved in oxidative stress responses, inflammation, cell motility, cancer cell invasion and cancer metabolism. Based on this, BACH1 has become a promising therapeutic target in cancer (as anti-metastatic target) and also in chronic conditions linked to oxidative stress and inflammation, where BACH1 inhibitors share a therapeutic space with activators of transcription factor NRF2. However, while there is a growing number of NRF2 activators, there are only a few described BACH1 inhibitors/degraders. The synthetic acetylenic tricyclic bis(cyanoenone),(±)-(4bS,8aR,10aS)-10a-ethynyl-4b,8,8-trimethyl-3,7-dioxo-3.4b,7,8,8a,9,10, 10a-octahydrophenanthrene-2,6-dicarbonitrile, TBE31 is a potent activator of NRF2 without any BACH1 activity. Herein we found that biotinylation of TBE31 greatly reduces its potency as NRF2 activator (50-75-fold less active) while acquiring a novel activity as a BACH1 degrader (100-200-fold more active). We demonstrate that TBE56, the biotinylated TBE31, interacts and promotes the degradation of BACH1 via a mechanism involving the E3 ligase FBXO22. TBE56 is a potent and sustained BACH1 degrader (50-fold more potent than hemin) and accordingly a powerful HMOX1 inducer. TBE56 degrades BACH1 in lung and breast cancer cells, impairing breast cancer cell migration and invasion in a BACH1-dependent manner, while TBE31 has no significant effect. Altogether, our study identifies that the biotinylation of TBE31 provides novel activities with potential therapeutic value, providing a rationale for further characterisation of this and related compounds.

Design and synthesis of 28-hydroxy protopanaxadiol as a novel probe template

To explore the antitumour mechanism of 20(S)-protopanaxadiol (PPD) while maintaining its uncovered pharmacological active site 3-hydroxyl, 28-hydroxy protopanaxadiol (17), a small molecular probe template of PPD was first designed and synthesised based on the Baldwin's reaction. Thus, 28-hydroxyl of 17 was built successfully as a derivatized site of molecular probe's functional and report groups. The important intermediates and final product were confirmed by ESI-MS and nuclear magnetic resonance spectra with good yield. These studies provided a valuable basis for probe research of PPD.

The acetylenic tricyclic bis(cyano enone), TBE-31 inhibits non-small cell lung cancer cell migration through direct binding with actin

The migratory and invasive potential of the epithelial-derived tumor cells depends on epithelial-to-mesenchymal transition (EMT) as well as the reorganization of the cell cytoskeleton. Here, we show that the tricyclic compound acetylenic tricyclic bis(cyano enone), TBE-31, directly binds to actin and inhibits linear and branched actin polymerization in vitro. Furthermore, we observed that TBE-31 inhibits stress fiber formation in fibroblasts as well as in non-small cell lung cancer cells during TGFβ-dependent EMT. Interestingly, TBE-31 does not interfere with TGFβ-dependent signaling or changes in E-cadherin and N-cadherin protein levels during EMT. Finally, we observed that TBE-31 inhibits fibroblast and non-small cell lung tumor cell migration with an IC50 of 1.0 and 2.5 μmol/L, respectively. Taken together, our results suggest that TBE-31 targets linear actin polymerization to alter cell morphology and inhibit cell migration.