Functional Disruption of Gli1-DNA Recognition via a Cobalt(III) Complex.

The aberrant activation of the Gli family of zinc finger transcription factors (ZFTFs) is associated with several types of human cancer, including medulloblastoma and basal cell carcinoma. We have reported the use of cobalt(III) Schiff-base complexes (Co(III)-sb) as potent inhibitors of ZFTFs in vivo. These complexes inhibit transcription by displacing the zinc finger domain's structural Zn(II) ion, destabilizing the alpha helix necessary for DNA recognition. Here, we describe the use of Co(III)-sb complexes for the selective inhibition of Gli1. Spectroscopic and computational studies of the Gli1 DNA binding domain found that Co(III)-sb displaced Zn(II) through direct coordination with the His residues of the Cys2 His2 Zn(II) binding site. As a result, there is a dose-dependent degradation of the alpha-helix content in the DNA binding domain of Gli1 and corresponding inhibition of consensus sequence recognition. We conclude that this strategy is well suited for the development of new and potent inhibitors of Gli1.

Cobalt(III) Schiff base complexes stabilize non-fibrillar amyloid-ß aggregates with reduced toxicity.

The aggregation of amyloid-ß (Aß) is believed to be foundational to the pathogenesis of Alzheimer's disease (AD). In vitro aggregation kinetics have been shown to correlate with rates of disease progression in both AD patients and animal models, thus proving to be a useful metric for testing Aß-targeted therapeutics. Here we present evidence of cobalt(III) Schiff base complex ([Co(acetylacetonate)(NH3)2]Cl; Co(III)-sb) modulation of Aß aggregation kinetics by a variety of complementary techniques. These include Thioflavin T (ThT) fluorescence, circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM). Our data was fitted to kinetic rate laws using a mathematical model developed by Knowles et al. in order to extract mechanistic information about the effect of Co(III)-sb on aggregation kinetics. Our analysis revealed that Co(III)-sb alters Aß aggregation by decreasing the polymerization rate and increasing the nucleation rate, suggesting that Co(III)-sb causes Aß to rapidly stabilize oligomeric species with reduced elongation into mature fibrils. This result was corroborated by TEM and AFM of Aß aggregates in vitro. We also demonstrate that Aß aggregate mixtures produced in the presence of Co(III)-sb exhibit decreased cytotoxicity compared to untreated samples.

A Ln(III)-3-hydroxypyridine pH responsive probe optimized by DFT.

Differences in tissue pH can be diagnostic of cancer and other conditions that shift cell metabolism. Paramagnetic probes are promising tools for pH mapping in vivo using magnetic resonance spectroscopy (MRS) as they provide uniquely shifted MR signals that change with pH. Here, we demonstrate a 3-hydroxy-6-methylpyridyl coordinating group as a new pH-responsive reporter group for Ln(III) MRS probes. The pH response of the complex was observed by UV-Vis, fluorescence, and NMR spectroscopies, and modeled using DFT. These results provide insight into the observed pH-dependent NMR spectrum of the complex. The protonation state of the hydroxypyridine changes the coordinating ability of the ligand, affecting the dipolar field of the lanthanide and the chemical shift of nearby reporter nuclei. The favorable pH response and coordination properties of the 3-hydroxypyridyl group indicates its potential for further development as a dual responsive-reporter group. Incorporation into optimized scaffolds for MRS detection may enable sensitive pH-mapping in vivo.

Inhibition of Amyloid-ß Aggregation by Cobalt(III) Schiff Base Complexes: A Computational and Experimental Approach.

Coordination complexes have emerged as prominent modulators of amyloid aggregation via their interaction with the N-terminal histidine residues of amyloid-ß (Aß). Herein, we report the synthesis and characterization of a novel cobalt(III) Schiff base complex with methylamine axial ligands, and we present both computational and experimental data demonstrating the reduction of ß-sheet formation by this complex. The computations include molecular dynamics simulations of both monomeric and pentameric Aß, which demonstrate decreased formation of ß-sheet structures, destabilization of preformed ß-sheets, and suppression of aggregation. These results are consistent with a dose dependence in experimental bulk aggregation data using thioflavin T fluorescence, and overall this study demonstrates useful drug activity of the cobalt complex.

N,N'-diethyl-4-nitrobenzene-1,3-diamine, 2,6-bis(ethylamino)-3-nitrobenzonitrile and bis(4-ethylamino-3-nitrophenyl) sulfone.

N,N'-diethyl-4-nitrobenzene-1,3-diamine, C(10)H(15)N(3)O(2), (I), crystallizes with two independent molecules in the asymmetric unit, both of which are nearly planar. The molecules differ in the conformation of the ethylamine group trans to the nitro group. Both molecules contain intramolecular N-H...O hydrogen bonds between the adjacent amine and nitro groups and are linked into one-dimensional chains by intermolecular N-H...O hydrogen bonds. The chains are organized in layers parallel to (101) with separations of ca 3.4 A between adjacent sheets. The packing is quite different from what was observed in isomeric 1,3-bis(ethylamino)-2-nitrobenzene. 2,6-Bis(ethylamino)-3-nitrobenzonitrile, C(11)H(14)N(4)O(2), (II), differs from (I) only in the presence of the nitrile functionality between the two ethylamine groups. Compound (II) crystallizes with one unique molecule in the asymmetric unit. In contrast with (I), one of the ethylamine groups, which is disordered over two sites with occupancies of 0.75 and 0.25, is positioned so that the methyl group is directed out of the plane of the ring by approximately 85 degrees. This ethylamine group forms an intramolecular N-H...O hydrogen bond with the adjacent nitro group. The packing in (II) is very different from that in (I). Molecules of (II) are linked by both intermolecular amine-nitro N-H...O and amine-nitrile N-H...N hydrogen bonds into a two-dimensional network in the (10 2) plane. Alternating molecules are approximately orthogonal to one another, indicating that pi-pi interactions are not a significant factor in the packing. Bis(4-ethylamino-3-nitrophenyl) sulfone, C(16)H(18)N(4)O(6)S, (III), contains the same ortho nitro/ethylamine pairing as in (I), with the position para to the nitro group occupied by the sulfone instead of a second ethylamine group. Each 4-ethylamino-3-nitrobenzene moiety is nearly planar and contains the typical intramolecular N-H...O hydrogen bond. Due to the tetrahedral geometry about the S atom, the molecules of (III) adopt an overall V shape. There are no intermolecular amine-nitro hydrogen bonds. Rather, each amine H atom has a long (H...O ca 2.8 A) interaction with one of the sulfone O atoms. Molecules of (III) are thus linked by amine-sulfone N-H...O hydrogen bonds into zigzag double chains running along [001]. Taken together, these structures demonstrate that small changes in the functionalization of ethylamine-nitroarenes cause significant differences in the intermolecular interactions and packing.