The application of class I HDAC inhibitors as cancer therapies is well established, but more recently their development for nononcological indications has increased. We report here on the generation of improved class I selective human HDAC inhibitors based on an ethylketone zinc binding group (ZBG) in place of the hydroxamic acid that features the majority of HDAC inhibitors. We also describe a novel set of HDAC3 isoform selective inhibitors that show stronger potency and selectivity than the most commonly used HDAC3 selective tool compound RGFP966. These compounds are again based on an alternative ZBG with respect to the ortho-anilide that is featured in HDAC3 selective compounds reported to date.
A series of bay-substituted perylene derivatives is reported as a new class of G-quadruplex ligands. The synthesized compounds have differing N-cyclic substituents on the bay area and differing side chains on the perylene major axis. ESI-MS and FRET measurements highlighted the strongest quadruplex binders in this series and those showing the highest quadruplex/duplex selectivity. Several biological assays were performed on these compounds, which showed that compound 5 (PPL3C) triggered a DNA damage response in transformed cells with the formation of telomeric foci containing phosphorylated γ-H2AX and 53BP1. This effect mainly occurred in replicating cells and was consistent with Pot1 dissociation. Compound 5 does not induce telomere damage in normal cells, which are unaffected by treatment with the compound, suggesting that this agent preferentially kills cancer cells. These results reinforce the notion that G-quadruplex binding compounds can act as broad inhibitors of telomere-related processes and have potential as selective antineoplastic drugs.
A “frozen” electron donor–acceptor array that bears porphyrin and fullerene units covalently linked through the ortho position of a phenyl ring and the nitrogen of a pyrrolidine ring, respectively, is reported. Electrochemical and photophysical features suggest that the chosen linkage supports both through‐space and through‐bond interactions. In particular, it has been found that the porphyrin singlet excited state decays within a few picoseconds by means of a photoinduced electron transfer to give the rapid formation of a long‐lived charge‐separated state. Density functional theory (DFT) calculations show HOMO and LUMO to be localized on the electron‐donating porphyrin and the electron‐accepting fullerene moiety, respectively, at this level of theory. More specifically, semiempirical molecular orbital (MO) configuration interaction (CI) and unrestricted natural orbital (UNO)‐CI methods shed light on the nature of the charge‐transfer states and emphasize the importance of the close proximity of donor and acceptor for effective electron transfer.
Based on previous work on both perylene and coronene derivatives as G-quadruplex binders, a novel chimeric compound was designed: N,N'-bis[2-(1-piperidino)-ethyl]-1-(1-piperidinyl)-6-[2-(1-piperidino)-ethyl]-benzo[ghi]perylene-3,4:9,10-tetracarboxylic diimide (EMICORON), having one piperidinyl group bound to the perylene bay area (positions 1, 12 and 6, 7 of the aromatic core), sufficient to guarantee good selectivity, and an extended aromatic core able to increase the stacking interactions with the terminal tetrad of the G-quadruplex. The obtained "chimera" molecule, EMICORON, rapidly triggers extensive DNA damage of telomeres, associated with the delocalization of telomeric protein protection of telomeres 1 (POT1), and efficiently limits the growth of both telomerase-positive and -negative tumor cells. Notably, the biological effects of EMICORON are more potent than those of the previously described perylene derivative (PPL3C), and more interestingly, EMICORON appears to be detrimental to transformed and tumor cells, while normal fibroblasts expressing telomerase remain unaffected. These results identify a new promising G-quadruplex ligand, structurally and biologically similar on one side to coronene and on the other side to a bay-monosubstituted perylene, that warrants further studies.
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