Advanced second generation inhibitors of histone deacetylases (HDAC) are currently used in clinical development. This study aimed at comparing the pharmacological properties of selected second generation HDAC inhibitors with the hydroxamate and benzamide head group, namely SAHA, LAQ824/LBH589, CI994, MS275 and MGCD0103. In biochemical assays using recombinant HDAC1, 3, 6 and 8 isoenzymes, SAHA and LAQ824/LBH589 behave as quite unselective HDAC inhibitors. In contrast, the benzamides CI994, MS275 and MGCD0103 are more selective, potent inhibitors of at least HDAC1 and HDAC3. All HDAC inhibitors induce histone H3 hyperacetylation, correlating with inhibition of proliferation, induction of cell differentiation and apoptosis. A broad cytotoxicity is seen across cell lines from different tumor entities with LAQ824/LBH589 being the most potent agents. The apoptosis inducing activity is evident in arrested and proliferating RKO colon cancer cells with inducible, heterologous p21 waf1 expression, indicative for a cell-cycle independent mode-of-action. Differentiation of MDA-MB468 breast cancer cells is induced by benzamide and hydroxamate analogs. The reversibility of drug action was evaluated by pulse treatment of A549 lung cancer cells. Whereas paclitaxel induced irreversible cell cycle alterations already after 6 hr treatment, HDAC inhibitor action was retarded and irreversible after >16 hr treatment. Interestingly, pulse treatment was equally effective as continous treatment. Finally, the efficacy of LAQ824, SAHA and MS275 in A549 nude mice xenografts was comparable to that of paclitaxel at well tolerated doses. We conclude that despite a different HDAC isoenzyme inhibition profile, hydroxamate and benzamide analogs as studied display similar cellular profiles. ' 2007 Wiley-Liss, Inc.Key words: HDAC inhibition; hydroxamate and benzamide head group; isoenzyme selectivity; protein hyperacetylation Posttranslational modification by reversible acetylation of lysine residues in histone proteins and their putative role in RNA synthesis was first described in 1964 by Allfrey et al.1 Since this landmark article, the natural antifungal antibiotic Trichostatin A (TSA) was found to act by inhibition of mammalian histone deacetylases (HDAC).2 Subsequently, the first human HDAC named HD1 (syn. HDAC1), a homolog of yeast transcriptional regulator Rpd3, was isolated.3 Since then, enormous progress was made in understanding reversible protein acetylation in general and histone modifications in particular.4,5 Chromatin condensation and transcriptional activity is regulated by acetylation of N-terminal lysine residues in core histone proteins H3 and H4 by histone acetyltransferases (HATs) and deacetylation by HDACs. HDACs are components of transcriptional silencing complexes as first described for the mRpd3/N-CoR /mSin3 complex.6 Up to now, 11 different HDAC isoenzymes belonging to the class I (HDAC 1, 2, 3, 8), class II (HDAC 4-7, 9, 10) and class IV families (HDAC11) have been described. 7 HDAC class III enzymes, also named Sirtuin...

Although the chemistry of transition metal polyphosphide anions has attracted significant attention, there are few reports of studies in which such species have been synthesized directly from white phosphorus. [K(OEt ) {Co(BIAN)(cod)}] (1, BIAN=1,2-bis(2,6-diisopropylphenylimino)acenaphthene, cod=1,5-cyclooctadiene), which is readily prepared by ligand exchange from [K(thf) {Co(cod) }], reacts with P to afford [{K(thf)} {(BIAN)Co} (μ-η :η -P )] (2 a) in 61 % yield (isolated product). [{K(OEt )} {(BIAN)Co} (μ-η :η -P )] (2 b) and [K([18]crown-6)(MeCN)] [{(BIAN)Co} (μ-η :η -P )] (2 c) were obtained by recrystallizing 2 a from diethyl ether and acetonitrile (and using [18]crown-6 in case of 2 c). Oxidation of 2 a with [Cp Fe]BAr (one equivalent) and subsequent recrystallization of the product from different solvents gave [K(OEt ){(BIAN)Co} (μ-η :η -P )] (3 a) and [K(dme) ][{(BIAN)Co} (μ-η :η -P )] (3 b; dme=1,2-dimethoxyethane). Neutral [{(BIAN)Co} (μ-η :η -P )] (4) was obtained in moderate yield by oxidizing 2 a with two equivalents of [Cp Fe]BAr . The new complexes were characterized by NMR, EPR (in the case of 3 a), and UV/Vis spectroscopy, and elemental analysis. The molecular structures revealed by X-ray crystallography display planar cyclic or open-chain P units sandwiched between {(BIAN)Co} fragments.

The activation of white phosphorus (P4) by transition‐metal complexes has been studied for several decades, but the functionalization and release of the resulting (organo)phosphorus ligands has rarely been achieved. Herein we describe the formation of rare diphosphan‐1‐ide anions from a P5 ligand by treatment with cyanide. Cobalt diorganopentaphosphido complexes have been synthesized by a stepwise reaction sequence involving a low‐valent diimine cobalt complex, white phosphorus, and diorganochlorophosphanes. The reactions of the complexes with tetraalkylammonium or potassium cyanide afford a cyclotriphosphido cobaltate anion 5 and 1‐cyanodiphosphan‐1‐ide anions [R2PPCN]− (6‐R). The molecular structure of a related product 7 suggests a novel reaction mechanism, where coordination of the cyanide anion to the cobalt center induces a ligand rearrangement. This is followed by nucleophilic attack of a second cyanide anion at a phosphorus atom and release of the P2 fragment.

Reversible lysine-specific acetylation has been described as an important posttranslational modification, regulating chromatin structure and transcriptional activity in the case of core histone proteins. Histone deacetylases (HDAC) are considered as a promising target for anticancer drug development, with 2a as pan-HDAC inhibitor approved for cutanous T-cell lymphoma therapy and several other HDAC inhibitors currently in preclinical and clinical development. Protein kinases are a well-established target for cancer therapy with the EGFR/HER2 inhibitor 5 approved for treatment of advanced, HER2 positive breast cancer as a prominent example. In the present report, we present a novel strategy for cancer drug development by combination of EGFR/HER2 kinase and HDAC inhibitory activity in one molecule. By combining the structural features of 5 with an (E)-3-(aryl)-N-hydroxyacrylamide motif known from HDAC inhibitors like 1 or 3, we obtained selective inhibitors for both targets with potent cellular activity (target inhibition and cytotoxicity) of selected compounds 6a and 6c. By combining two distinct pharmacologically properties in one molecule, we postulate a broader activity spectrum and less likelihood of drug resistance in cancer patients.

P–P condensation reactions in the coordination sphere of cobalt give access to unique organyl-substituted pentaphosphido complexes.