Dietary Natural Products as Potential Tumor Chemo-Sensitizers

P-glycoprotein (P-gp) is a membrane ATP-binding transporter that detoxifies cells from different xenobiotics. Multiple drug resistant (MDR) cells can be sensitized toward anticancer agents when treated with P-gp inhibitors/modulators (chemo-sensitizers). Regarding the requirement of high serum concentrations of P-gp inhibitors leading to potential toxicity, dietary phytochemicals are very important and they may interact with co-administered pharmaceuticals as P-gp substrates, leading to altered pharmacokinetics. In silico models for predicting probable binding mode of dietary phytochemicals to P-gp are useful in the early phase of drug discovery projects since they describe structural features in binding to P-gp and hence designing novel anti-MDR scaffolds. Introduction: As a part of our ongoing studies on virtual analysis of bioactive phytochemicals and to explore new substances that do not exhibit significant toxicity at doses required for P-gp inhibition, we aimed to get more insight into the interactions of P-gp and a few dietary natural constituents as tumor chemosensitizing agents. Methods and Results: Radiographic 3D holo structure of P-gp was retrieved from protein data bank (4XWK; www.rcsb.org). Lamarckian genetic algorithm of AutoDock 4.2 was used to simulate the binding of dietary compounds. All ab initio studies were done with functional B3LYP associated with split valence basis set using polarization functions (Def2-SVP) by ORCA quantum chemistry package. Our study proposed the dominant role of R-site in binding to Curcuminoids (Curcumin II;  -8.17 kcal/mol). In the case of black pepper, hydrophobic contacts seemed to be important in Piperine/P-gp complex. It was also proposed that Piperine carbonyl might be a good mimic of Curcumin II enone group due to the formation of H-bonds (Gln986). Among the catechins of green tea, Epicatechin gallate might not be identified as modulator/substrate since relatively similar ΔGbs were recorded within M, H and R sites. Quercetin was not preferentially docked within H-site (-4.77 kcal/mol) in accordance to the previous reports. Within the H-site, Epigallocatechin (green tea) was the weakest binder (-4.31 kcal/mol) and amino acid decomposition analysis dedicated -2.66 and -8.76 kcal/mol attractive forces for interaction with Glu180 and Lys185, respectively. Conclusions: Combined molecular docking/quantum mechanical studies revealed that among assessed phytochemicals, Bergapten (grape fruit) might be identified as P-gp modulator. Other constituents exhibited more affinity toward R-site with Curcumionoids being the top-ranked ones. Results indicated Lys185, Glu871 and Glu986 as important interacted residues with Curcuminoids due to strong hydrogen bondings

Systematic Modeling of Drug P-Glycoprotein Interactions via Combined Docking/QM Approach

Introduction: The overexpression of P-gp in cancer tumor cells results in increased efflux of chemotherapeutic compounds. This phenomenon leads to the wide-spectrum resistance of cancer cells to variant drugs or multi drug resistance (MDR). Regarding the important biological role of P-gp with regard to cancer therapy, in silico analysis of binding affinity/mode of diverse anticancer drugs toward P-gp may be an active area of research since it provides more insight into the binding interactions and key amino acid residues that were involved. Methods and Results: Ligand-flexible docking studies were performed using the molecular docking software, AutoDock 4.2. To elucidate the interactions of selected anticancer drugs, all the related structures were docked into the active site of validated P-gp target (4XWK). Quantum mechanical calculations were applied to intermolecular binding energy analysis in terms of drug-residue binding interactions via functional B3LYP in association with split valence basis set using polarization functions (Def2-SVP). Mitomycin was found to be the weakest binder with -7.29 kcal/mol energy. Bisantrene was the top-ranked binder (-10.59 kcal/mol) with H-bond and lipophilic interaction patterns. To explain more, Asn838 participated in bidentate H-bonding with nitrogen atom of imidazole ring. Another H-bond interaction was detected in the case of Ser725 within the same ring but different nitrogen atom of the drug molecule. Besides hydrogen bonding, it was revealed that 12 hydrophobic residues interacted with Bisantrene. Within the evaluated drugs, unlike Epothilone E and F, no H-bonds could be detected for Epothilone A, B, C & D. Such observation was pertained to the presence of hydroxymethyl moiety on the thiazole ring of Epothilone E and F which provided well-oriented H-bonds with Ala307. Despite observed interactive residues, lower binding affinity of Epothilone F persuaded us to run QM job in terms of drug-residue binding interactions. It was interestingly concluded that a few residues made repulsive forces with the drug, a result that might explain lower affinity of this molecule toward P-gp. Conclusions: Collective in silico exploration of a few anticancer drugs provided some insights into the binding mode toward P-gp as an interfering target in chemotherapeutic strategies. On the basis of obtained results, structure binding relationship pattern for studied anticancer drugs were developed

Response Surface Methodological Approach toward Optimization of a RP-HPLC Method to Determine Paracetamol in Tablets

Response surface methodology (RSM) was applied to develop an RP-HPLC method in which paracetamol was analyzed and determined on a C18 column with UV detection. To explain more, RSM was used to statistically model the impact of flow rate (ml.min-1) (A), column temperature (°C) (B) and mobile phase composition (H2O: MeOH) (C)on the retention time (RT) of Paracetamol within tablets. Introduction: The major goal of this investigation was to optimize an RP-HPLC method which is simple, linear, accurate, sensitive and selective in determination of Paracetamol in solid dosage forms. Methods and Results:Three distinctive levels were dedicated to each evaluated factor.Box-Behnken experimental design including seventeen independent runs within a range of 25-50% MeOH ratio (mobile phase), 25-45 ºC and 0.7-1.3 mL. min-1 flow rate were carried out to explore the effectivefactors onRT of Paracetamol using RP-HPLC method. ANOVA results revealed that quadratic model was significant (Model F-value of 225.65) and could best describe the relationship between dependent variable (RT) and independent ones: RT= 3.30 - 1.2A - 0.38B - 0.80C + 0.30AC + 0.43BC + 0.53A2 As can be understood from the model terms, the most significant term was the solvent ratio and all the factor levels were indirectly proportional to the Rt. Moreover, the interaction of column temperature and solvent ration seemed to be more important. It was also predicted that optimum assay condition included 1:2 ratio of methanol to water, column temperature of 35ºC and mobile phase flow rate of 1.3 mL.min−1. Using this optimum condition, baseline separation of the drug was achieved with a good resolution and a run time of 2.1 min. The optimized method was validated in terms of linearity, accuracy, limit of detection and limit of quantification of paracetamol within a few commercially available Paracetamol tablets. Conclusions:The optimized RP-HPLC technique provided a convenient and efficient method toward qualitative/quantitative analysis of Paracetamol in its tablets. The improved method is also rapid and sensitive enough to be used for single tablet analysis

Hypoglycemic activity of curcumin synthetic analogues in alloxan-induced diabetic rats.

The currently available therapies for type 2 diabetes have been unable to achieve normoglycemic status in the majority of patients. The reason may be attributed to the limitations of the drug itself or its side effects. In an effort to develop potent and safe oral antidiabetic agents, we evaluated the in vitro and in vivo hypoglycemic effects of 10 synthetic polyphenolic curcumin analogues on alloxan-induced male diabetic albino rats. In vitro studies showed 7-bis(3,4-dimethoxyphenyl)hepta-1,6-diene-3,5-dione (4) to be the most potential hypoglycemic agent followed by 1,5-bis(4-hydroxy-3-methoxyphenyl)penta-1,4-dien-3-one (10). Structure activity relationship (SAR) of the tested compounds was elucidated and the results were interpreted in terms of in vitro hypoglycemic activities. Furthermore, oral glucose tolerance test (OGTT) with compounds 4, 10 and reference hypoglycemic drug glipizide showed that compound 4 and glipizide had relatively similar effects on the reduction of blood glucose levels within 2 h. Thus, compound 4 might be regarded as a potential hypoglycemic agent being able to reduce glucose concentration both in vitro and in vivo

Molecular Modeling of Drug-Albumin Interactions: A case Study on Antifungal Agents

Background & objectives: the interaction of albumin- the most important plasma protein- with various drugs leads to variations in the pharmacokinetics of drugs. Since interaction of different pharmaceuticals with albumin is determinant in the estimation of dose and prediction of drug-drug and drug-food interferences, studying the binding ability of different drugs with albumin is an active area of research. Methods: Docking studies were performed by Lamarckian Genetic Algorithm of AutoDock 4.2 program. The three-dimensional structures of albumin were obtained from Brookhaven protein data bank (2BXD & 2BXF; www.rcsb.org). Pre-processing of molecules was done using AM1 method and AutoDock Tools 1.5.4 software. AM1 optimization method was performed using Polak-Ribiere (conjugate gradient) algorithm with termination condition as RMS gradient of 0.1 Kcal/Å mol. Schematic representation of drug-albumin complexes were obtained by Ligplot. Results: Oxiconazole and fenticonazole were top-ranked drugs in binding to site 1 (subdomain IIA) and 2 (subdomain IIIA) of albumin, respectively (∆Gb -9.01 and -9.89 kcal.mol-1). Leu238 and Ala291 were the key residues of site 1 due to hydrophobic contacts with all of the antifungals, while Ile388, Asn391 and Leu430 were the key residues of site 2. A few structure binding relationship rules could be extracted from the binding pattern of antifungal drugs. Conclusion: It was found that antifungal agents might have higher affinity toward site 2 of albumin rather than site 1. Estimated high albumin affinities of antifungals provided the possibility of drug-drug or drug-food interactions. It seemed that hydrophobic contacts were more significant in binding antifungals to albumin. &nbsp

Comparative Amino Acid Decomposition Analysis of Potent Type I P38α Inhibitors

Background and purpose of the study:p38α is a member of mitogen-activated protein kinases (MAPK) considered as a prominent target in development of anti-inflammatory agents. Any abnormality in the phosphorylation process leads to the different human diseases such as cancer, diabetes and inflammatory diseases. Several small molecule p38α inhibitors have been developed up to now. In this regard, structural elucidation of p38 inhibitors needs to be done enabling us in rational lead development strategies.Methods:Various interactions of three potent inhibitors with p38α active site have been evaluated in terms of binding energies and bond lengths via density function theory and MD simulations.Results:Our comparative study showed that both ab initio and MD simulation led to the relatively similar results in pharmacophore discrimination of p38α inhibitors.Conclusion:The results of the present study may find their usefulness in pharmacophore based modification of p38α inhibitors