The influence of β-cyclodextrin encapsulation on the binding of 2'-hydroxyflavanone with calf thymus DNA

Inclusion complexation of 2'-hydroxyflavanone (2'HF) with β-cyclodextrin (β-CD) was studied, both in solution phase and as solid inclusion complexes, by UV-visible and fluorescence spectroscopic, scanning electron microscopic and X-ray diffractometric techniques. The interaction of 2'HF with calf thymus DNA (ctDNA) in the presence and the absence of β-CD were compared. Fluorescence enhancement was observed for 2'HF due to the formation of 1:1 complex with β-CD. The structure of 1:1 complex is proposed based on spectral observation, molecular modeling and by calculated theoretical bond lengths. The possible mode of interaction between 2'HF and DNA was analyzed by molecular modeling method. The interaction of 2'HF with calf thymus DNA (ctDNA) was investigated by absorption and fluorescence measurements in the presence and the absence of β-CD as capping agent. Both in the presence and the absence of β-CD, 2'HF showed hyper-chromic effect, red shift of absorption spectra, and quenching of fluorescence due to binding of 2'HF with ctDNA. The results reveal that the phenolic moiety is involved in inclusion complexation with β-CD and interaction with DNA. In the presence of β-CD, the phenolic moiety may be included in cyclodextrin cavity, whereas the dihydrobenzopyran-4-one moiety interacts with DNA. Further, β-CD selectively blocks a part of the 2'HF molecule binding with DNA. This renders the remaining portion of the flavanone available for interaction with DNA.

Discovery of novel human phenylethanolamine N-methyltransferase (hPNMT) inhibitors using 3D pharmacophore-based in silico, biophysical screening and enzymatic activity assays

With the aid of receptor-oriented pharmacophore-based in silico screening, we established three pharmacophore maps explaining the binding model of hPNMT and a known inhibitor, SK&F 29661 (Martin et al., 2001). The compound library was searched using these maps. Nineteen selected candidate inhibitors of hPNMT were screened using STD-NMR and fluorescence experiments. An enzymatic activity assay based on HPLC was additionally performed. Consequently, three potential hPNMT inhibitors were identified, specifically, 4-oxo-1,4-dihydroquinoline-3,7-dicarboxylic acid, 4-(benzo[d][1,3]dioxol-5-ylamino)-4-oxobutanoic acid, and 1,4-diaminonaphthalene-2,6-disulfonic acid. These novel inhibitors were retrieved using Map II comprising one hydrogen bond acceptor, one hydrogen bond donor, one lipophilic feature, and shape constraints, including a hydrogen bond between Lys57 of hPNMT and a hydrogen bond donor of the inhibitor, and stacked hydrophobic interactions between the side-chain of Phe182 and an aromatic region of the inhibitor. Water-mediated interactions between Asn267 and Asn39 of hPNMT and the amide or amine group of three potent inhibitors were additional important features for hPNMT activity. The binding model presented here may be applied to identify inhibitors with higher potency. Moreover, our novel compounds are valuable candidates for further lead optimization of PNMT inhibitors.