The Hedgehog (Hh) signalling pathway plays a pivotal role in the spatial and temporal regulation of cell proliferation and differentiation. By controlling the correct maturation of developing tissues and ensuring attainment of the correct size, position and the presence of fully functioning cellular structures, the Hh plays a pivotal role in development. Conversely aberrant Hh signalling is involved in Grolin syndrome, basal cell carcinoma (the most common cancer in the world), and more than one third of all human medulloblastoma cases. In all of these cases, it is believed that deregulated Hh signalling leads to increased cell proliferation and tumour formation. Inhibition of the Hedgehog signalling pathway, is a recently validated anti-cancer drug target, with Vismodegib (Erivedge™), approved by the U.S. Food and Drug Administration for the treatment of adult basal cell carcinoma. 1 In this perspective we outline the current state of Hh pathway inhibitors with a particular focus on potential limitations of upstream Hh pathway inhibition in relation to resistance mutations and crosstalk pathways. Together, these limitations indicate that inhibition of downstream components, specifically the Gli family of transcription factors, may represent a next generation approach to suppress tumours associated with aberrant Hh pathway signalling. 65 including active transport 29 and passive diffusion. 30 In the absence of Hh ligands, the 'off state' for receiving cells, Ptch catalytically inhibits Smo and prevents entry to the cilium where it is believed to inhibit various protein kinases, including PKA, GSK-3β and CK1 (Figure 1). 31 As a result, the Gli family of 70 transcription factors (Gli1, 2, and 3), which are the effectors of the system, in complex with SuFu (a negative inhibitor of the vertebrate Hh pathway) are phosphorylated stepwise by a number of protein kinases (PKA, GSK-3β and CK1). 32 These phosphorylation events results in proteosomal cleavage where 75 Gli-2 is degraded to Gli2-R, 33 Gli3 is degraded to Gli3-R (limited proteolysis) while Gli1 remains full length. 34 Simultaneously, the
Suzuki cross-couplings of 5-formyl-2-furanylboronic acid with activated or neutral aryl bromides were performed under continuous flow conditions in the presence of (Bu)4N(+)F(-) and the immobilised t-butyl based palladium catalyst CatCart™ FC1032™. Deactivated aryl bromides and activated aryl chlorides were cross-coupled with 5-formyl-2-furanylboronic in the presence of (Bu)4N(+)OAc(-) using the bis-triphenylphosphine CatCart™ PdCl2(PPh3)2-DVB. Initial evidence indicates the latter method may serve as a universal approach to conduct Suzuki cross-couplings with the protocol successfully employed in the synthesis of the current gold standard Hedgehog pathway inhibitor LDE225.
The NusB–NusE protein–protein interaction (PPI) is critical to the formation of stable antitermination complexes required for stable RNA transcription in all bacteria. This PPI is an emerging antibacterial drug target. Pharmacophore-based screening of the mini-Maybridge compound library (56 000 molecules) identified N,N′-[1,4-butanediylbis(oxy-4,1-phenylene)]bis(N-ethyl)urea 1 as a lead of interest. Competitive enzyme-linked immunosorbent assay screening validated 1 as a 20 μM potent inhibitor of NusB–NusE. Four focused compound libraries based on 1, comprising 34 compounds in total were designed, synthesized, and evaluated as NusB–NusE PPI inhibitors. Ten analogues displayed NusB–NusE PPI inhibition ≥50% at 25 μM concentration in vitro. In contrast to representative Gram-negative Escherichia coli and Gram-positive Bacillus subtilis species, these analogues showed up to 100% growth inhibition at 200 μM. 2-((Z)-4-(((Z)-4-(4-((E)-(Carbamimidoylimino)methyl)phenoxy)but-2-en-1-yl)oxy)benzylidene)hydrazine-1-carboximidamide 22 showed excellent activity against important pathogens. With minimum inhibitory concentration values of ≤3 μg/mL for Gram-positive Streptococcus pneumoniae and methicillin-resistant Staphylococcus aureus and ≤51 μg/mL for Gram-negative Pseudomonas aeruginosa and Acinetobacter baumannii, 22 is a potent lead for a novel antibacterial target. Epifluorescence studies in live bacteria were consistent with 22, inhibiting the NusB–NusE PPI as proposed.
Leveraging our quinolone-1-(2H)-one based Hedgehog signalling pathway (HSP) inhibitors we have developed two new classes of HSP inhibitors based on: l-tryptophan and benzo[1,3]dioxol-5-ylmethyl-[2-(1H-indol-3-yl)-ethyl]-amine. Synthesis of focused compound libraries identified six l-tryptophan based inhibitors, and two stimulators, of Gli at 10 μM compound concentration. 2,4-Dichloro-13 and indole 16 suppressed mRNA expression of Ptch in Shh LIGHT2 cells, with 13 suppressing and 16 stimulating Gli mRNA expression. Focused library development of the benzo[1,3]dioxol-5-ylmethyl-[2-(1H-indol-3-yl)-ethyl]-amine scaffold afforded two sub-micro molar potent inhibitors of Gli expression with 5-methoxy-1H-indole-2-carboxylic acid benzo[1,3]dioxol-5-ylmethyl-[2-(1H-indol-3-yl)-ethyl]-amide 29 and 5-chloro-1H-indole-2-carboxylic acid benzo[1,3]dioxol-5-ylmethyl-[2-(1H-indol-3-yl)-ethyl]-amide 30 returning IC values of 0.5 and 0.24 μM, respectively. Neither 29 nor 30 acted directly on Smo with our data supporting inhibition of the HSP downstream of Smo.
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