Study on the interaction between 4-(1H-indol-3-yl)-2-(p-tolyl)quinazoline-3-oxide and human serum albumin
Graphical abstract
Introduction
The interactions between bio-macromolecules and organic small-molecular compounds have attracted increasing interest in recent years.1, 2, 3, 4 Among biomacromolecules, human serum albumin (HSA) is a kind of rich source of soluble protein in plasma and play an important role in the transportation and deposition of endogenous and exogenous substances such as fatty acids, amino acids and drugs.5 Thus, HSA is usually selected as model protein for studying the interaction between ligands (organic small-molecular drugs) and macromolecules for evaluation their drug effect.6, 7 HSA is a circulating protein composed of 585 amino acid residues in heart-shaped form. The crystal structure of HSA showed that it is composed of three structural domains: IA domain is composed of 1–195 amino acid residues, IIA domain is composed of 196–383 amino acid residues, and IIIA domain is composed of 384–585 amino acids. There are two binding sites, site I and site II in IIA and IIIA. There is a large hydrophobic cavity in the IIA domain,8 which is conducive to ligand binding sites. In 1976, Sudlow et al. found that warfarin could be combined with site I and site II.9 In 1995, Theodore Peters found that digitoxin could bind to HSA, but not at site I and site II. After experimental verification, the binding site was defined as site III.10 Therefore, the subsequent researchers conducted three sites competition experiments with drugs to determine the binding sites of ligand with HSA. The interaction between ligand and protein determines the bioavailability of the ligand to serum protein, and can reasonably evaluate biological and physicochemical properties of ligand. At the same time, it can also provide more information for improving the characteristic of biological macromolecules. The relationship between drug development and human health is very close. Therefore, in the follow-up experiments, HSA is directly used as the experimental material for the study of the structure–activity relationship of small molecule drug.
Quinazoline11, 12, 13 and indole14, 15, 16 derivatives are useful nitrogen-containing heterocyclic compounds, which are core structural motifs of many natural products and pharmaceuticals. Heterocyclic compounds bearing these two skeletons most likely possess interesting biological and physicochemical properties.17 For example, indoloquinazoline derivatives have been reported to be protein kinase CK2 inhibitors18 and poly(ADP-ribose) polymerase-1(PARP-1) inhibitors.19 4-(indole-3-yl)quinazolines have been reported to be potent epidermal growth factor receptor tyrosine kinase inhibitors.20 Recently, our group has been studied the structure–activity relationship of some quinazoline compounds, with the aim of screening out a quinazoline-based pharmaceutical molecular.21, 22, 23 More recently, a serial of 4-(indole-3-yl)quinazoline-3-oxides were synthesized via a cross-dehydrogenative coupling of quinazoline-3-oxides and indoles in our laboratory (Scheme 1).24 By primary experiments, 1-H-indol-3-yl-2-(p-tolyl)quinazoline-3-oxide 1a was found had an obvious activation effect on tyrosinase, and its semi-activated mass concentration (EC50) was 0.13 ± 0.1 mM. Considering the potential medicinal use of this organic compound and the important physiological functions of HSA, here the interactions and the mechanism btween 1a and HAS were explored.
Section snippets
Reagents and materials
HSA and digitoxin were purchased from Sigma-Aldrich, USA. DMSO, anhydrous ethanol, disodium hydrogen phosphate, sodium dihydrogen phosphate, etc. were purchased from Shanghai Sinopharm group. Ultrapure water was used throughout the experiment.
1-H-indol-3-yl-2-(p-tolyl)quinazoline-3-oxide 1a was synthesized via a cross-dehydrogenative coupling of quinazoline-3-oxide and indole according to our reported (scheme 1).24 The experimental procedures are as follow: 2-(p-tolyl)quinazoline-3-oxide
Fluorescence quenching analysis the interaction between HSA and compound 1a
As shown in Fig. 1A, the fluorescence emission of HSA has the maximum value at the wavelength of 333 nm (curve 1), and curve a is the fluorescence of compound 1a itself. As the concentration of 1a increased, the fluorescence absorption at 333 nm decreased significantly. As shown in Fig. 1B, when the concentration of 1a increased from 0 to 100 μM, the fluorescence intensity decreased by 49.2%, indicating that 1a can be bind with HSA and results fluorescence quenching.
In order to elucidate the
Conclusion
The interaction and mechanism of 4-(1H-indol-3-yl)-2-(p-tolyl)quinazoline-3-oxide 1a on HSA were investigated. Fluorescence quenching experiments showed that the quenching of HSA by 1a was static quenching, the combination of 1a and HSA resulted in the fluorescence quenching of HSA. Site competition experimental and molecular docking results show that the combination site of 1a on HSA is hydrophobic interaction in the IIA structure domain and is hydrogen bonds in the IIIA structure domain. The
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Financial support from National Natural Science Foundation of China (no. 21762020 and 21362014), Jiangxi Provincial Department of Science and Technology (no. 20171BAB203006), and Key Laboratory of Functional Small Organic Molecule, Ministry of Education, Jiangxi Normal University (no. KLFS-KF-201623) is gratefully acknowledged.
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