Competitive Binding Of Drugs Research Articles

Adamantane-Substituted Purines and Their β-Cyclodextrin Complexes: Synthesis and Biological Activity.

Cyclin-dependent kinases (CDKs) play an important role in the cell-division cycle. Synthetic inhibitors of CDKs are based on 2,6,9-trisubstituted purines and are developed as potential anticancer drugs; however, they have low solubility in water. In this study, we proved that the pharmaco-chemical properties of purine-based inhibitors can be improved by appropriate substitution with the adamantane moiety. We prepared ten new purine derivatives with adamantane skeletons that were linked at position 6 using phenylene spacers of variable geometry and polarity. We demonstrated that the adamantane skeleton does not compromise the biological activity, and some of the new purines displayed even higher inhibition activity towards CDK2/cyclin E than the parental compounds. These findings were supported by a docking study, which showed an adamantane scaffold inside the binding pocket participating in the complex stabilisation with non-polar interactions. In addition, we demonstrated that β-cyclodextrin (CD) increases the drug’s solubility in water, although this is at the cost of reducing the biochemical and cellular effect. Most likely, the drug concentration, which is necessary for target engagement, was decreased by competitive drug binding within the complex with β-CD.

Exploring the interaction between tyrphostin 9 and human serum albumin using biophysical and computational methods

Tyrphostin 9 (Tyr 9) is a potent platelet-derived growth factor receptor (PDGFR) inhibitor, which induces apoptosis in various cancer cell types. The binding of Tyr 9 to the major transport protein, human serum albumin (HSA) was investigated using several spectroscopic techniques and molecular docking method. Fluorescence quenching titration results showed progressive decrease in the protein fluorescence with increasing drug concentrations. A decreasing trend of the Stern-Volmer constant, K sv with increasing temperature characterized the drug-induced quenching as static quenching, thus pointed towards the formation of Tyr 9–HSA complex. The binding constant of Tyr 9–HSA interaction was found to lie within the range 3.48–1.69 × 105 M−1 at three different temperatures, i.e. 15 °C, 25 °C and 35 °C, respectively and suggested intermediate binding affinity between Tyr 9 and HSA. The drug–HSA complex seems to be stabilized by hydrophobic forces, van der Waals forces and hydrogen bonds, as suggested from the thermodynamic data as well as molecular docking results. The far-UV and the near-UV CD spectral results showed slight alteration in the secondary and tertiary structures, respectively, of the protein upon Tyr 9 binding. Interaction of Tyr 9 with HSA also produced microenvironmental perturbations around protein fluorophores, as evident from the three-dimensional fluorescence spectral results but increased protein’s thermal stability. Both competitive drug binding results and molecular docking analysis suggested Sudlow’s Site I of HSA as the preferred Tyr 9 binding site. Communicated by Ramaswamy H. Sarma

EPR studies of intermolecular interactions and competitive binding of drugs in a drug-BSA binding model.

Understanding intermolecular interactions between drugs and proteins is very important in drug delivery studies. Here, we studied different binding interactions between salicylic acid and bovine serum albumin (BSA) using electron paramagnetic resonance (EPR) spectroscopy. Salicylic acid was labeled with a stable radical (spin label) in order to monitor its mobilized (free) or immobilized (bound to BSA) states. In addition to spin labeled salicylic acid (SL-salicylic acid), its derivatives including SL-benzoic acid, SL-phenol, SL-benzene, SL-cyclohexane and SL-hexane were synthesized to reveal the effects of various drug binding interactions. EPR results of these SL-molecules showed that hydrophobic interaction is the main driving force. Whereas each of the two functional groups (-COOH and -OH) on the benzene ring has a minute but detectable effect on the drug-protein complex formation. In order to investigate the effect of electrostatic interaction on drug binding, cationic BSA (cBSA) was synthesized, altering the negative net charge of BSA to positive. The salicylic acid loading capacity of cBSA is significantly higher compared to that of BSA, indicating the importance of electrostatic interaction in drug binding. Moreover, the competitive binding properties of salicylic acid, ibuprofen and aspirin to BSA were studied. The combined EPR results of SL-salicylic acid/ibuprofen and SL-ibuprofen/salicylic acid showed that ibuprofen is able to replace up to ∼83% of bound SL-salicylic acid, and salicylic acid can replace only ∼14% of the bound SL-ibuprofen. This indicates that ∼97% of all salicylic acid and ibuprofen binding sites are shared. On the other hand, aspirin replaces only ∼23% of bound SL-salicylic acid, and salicylic acid replaces ∼50% of bound SL-aspirin, indicating that ∼73% of all salicylic acid and aspirin binding sites are shared. These results show that EPR spectroscopy in combination with the spin labeling technique is a very powerful method to investigate drug binding dynamics in detail.

Competitive binding of drugs to the multiple binding sites on human serum albumin : A calorimetric study

A multiple-site competitive model has been developed to evaluate quantitatively the equilibrium competition of drugs that bind to multiple classes of binding sites on human serum albumin (HSA). The equations, which are based on the multiple-class binding site model, assume that competition exists at individual sites, that the binding parameters for drug or drug competitor pertain to individual sites, and also that the binding parameters for drug or competitor at any given site are independent of drug or competitor bound at other sites. For the drug-competitor pairs, ethacrynic acid (EA) -caproic acid (C6), -lauric acid (C12), and -palmitic acid (C16), the reaction heat of EA binding to HSA was measured in the absence and the presence of fatty acids at the molar ratio of 3:1 with HSA at pH 7.4 and 37°C by isothermal titration microcalorimetry. The calorimetric titration data induced by the presence of fatty acids were directly compaired to the computer simulation curves by the corresponding multiple-site competititve models, which were precedently calculated from binding parameters of EA and fatty acids. In the case of EA-C12 or -C16 competitive binding, EA binding at the first and the second classes of binding sites on HSA were instantaneously inhibited by C12 or C16, resulting that the binding constant of the first class of binding sites of EA were decreased and that the second class of binding sites on HSA entirely disappeared. In the competition between EA and C6, the first class of binding sites of EA was diminished by C6, resulting in the decrease of the binding constants and the number of binding sites in the first class of EA, whereas, the second class of binding sites was unaffected. The multiple-site competitive model assuming site-site competition could be directly comparable to the calorimetric data and be suitable to account for the competitive processes for drugs bound to the multiple-class of binding sites on HSA.

Microdialysis- liquid chromatographic study on competitive binding of drugs to protein

Microdialysis- liquid chromatographic study on competitive binding of drugs to protein

Microdialysis- liquid chromatographic study on competitive binding of drugs to protein

A new method to determine the interaction between drug and protein has been developed by utilizing the technique of microdialysis sampling with the ketoprofen and the human serum albumin (HSA) as the model of drug and protein. Two kinds of binding sites of HSA to ketoprofen have been observed. The binding constants and number of binding sites obtained by the Scatchard equation are 0.799, 3.18×lo6 mol-1 ·L and 2.15, 2.01×105 mol-1 ·L, respectively. The displacement binding of drugs to HSA has also been studied. The strong displacement of competitive binding of ibuprofen with ketoprofen to HSA was observed, which means that the primary binding site of HSA to ketoprofen and that to ibuprofen are the same. However, only a weaker displacement of warfarin for the association of ketoprofen with HSA was observed, which may suggest that the primary binding site of HSA to ketoprofen is different from that to warfarin. Such a displacement effect for competitive binding of drugs to HSA was explained by the displacement model in the liquid-solid adsorption chromatography.