Virtual screening of a natural compound library at orthosteric and allosteric binding sites of the neurotensin receptor.

Molecular dynamics (MD) simulation using the AMBER force field has been performed on the neurotensin (NT) receptor, a class A type G-protein-coupled receptor in its activated conformation co-crystallized with the non-peptide agonists. For structure-based hit molecule identification via natural chemical compound library, orthosteric sites on NT receptor have been mapped by docking using AutoDock4.0 and Vina with the known agonists and antagonists SR48692, SR142948, ML301 and ML314 of the receptor. Furthermore, clustering analysis on the MD trajectories by SIMULAID has been performed to filter receptor conformations for the allosteric binders from the Otava natural compound library. Comparative mappings of contrasting binding region patterns have been done between the crystal structure orthosteric sites as well as the binding regions in the SIMULAID-based cluster center conformations from MD trajectories with the FTmap server using the small organic molecule fragments as the probes. The distinct binding region in the cluster-based conformations in the extracellular region of the receptor has been identified for targeted docking by Otava natural chemical compound library using AutoDock4.0 and Vina docking suites to obtain putative allosteric binders. A group of compounds from the Otava library has been identified as showing high free energy in both AutoDock4.0 and Vina docking suites. Biophysical assessments on the natural compound computational hit molecules will be done to identify lead structures from the hit molecules. Communicated by Ramaswamy H. Sarma.

Assessing the binding of cholinesterase inhibitors by docking and molecular dynamics studies.

In this report we assessed by docking and molecular dynamics the binding mechanisms of three FDA-approved Alzheimer drugs, inhibitors of the enzyme acetylcholinesterase (AChE): donepezil, galantamine and rivastigmine. Dockings by the softwares Autodock-Vina, PatchDock and Plant reproduced the docked conformations of the inhibitor-enzyme complexes within 2Å of RMSD of the X-ray structure. Free-energy scores show strong affinity of the inhibitors for the enzyme binding pocket. Three independent Molecular Dynamics simulation runs indicated general stability of donepezil, galantamine and rivastigmine in their respective enzyme binding pocket (also referred to as gorge) as well as the tendency to form hydrogen bonds with the water molecules. The binding of rivastigmine in the Torpedo California AChE binding pocket is interesting as it eventually undergoes carbamylation and breaks apart according to the X-ray structure of the complex. Similarity search in the ZINC database and targeted docking on the gorge region of the AChE enzyme gave new putative inhibitor molecules with high predicted binding affinity, suitable for potential biophysical and biological assessments.

Revisiting the role of nanoparticles as modulators of drug resistance and metabolism in cancer.

INTRODUCTION: Drug resistance is the major obstacle impeding the efficacy of chemotherapeutic agents. Although numerous drug delivery techniques have been developed to combat drug resistance, their limitations of non-specific targeting and inconsistent bioavailability has led to the search of novel delivering strategies, such as nanoparticles. AREAS COVERED: Nanoparticles for anti-cancer drug delivery are microscopic preparations encapsulating a chemotherapeutic and a chemosensitizer into a rationally designed drug delivery vehicle. Nano-strategies directed against multi-drug resistance (MDR) can be categorized into those inhibiting the drug efflux pumps, those effective against the cellular factors of drug resistance, and the combinational based strategies. Here, we review the most recent literature to reposition nanoparticles as chemotherapeutics and inhibitors of MDR. EXPERT OPINION: Novelty in anti-cancer drug delivery has led to the formulation of chemotherapeutics and MDR inhibitors as nano-preparations, which are multi-functional and have better tumor cell-targeting effects. Their characteristics of size and surface attachments make them readily diffusible through the tumor vasculature and increase their retention time as well. With a better understanding of the molecular mechanisms of drug resistance, more potent and multi-targeted nano-preparations can be formulated in the near future.

Advances in Theory of Solid-State Nuclear Magnetic Resonance.

Recent advances in theory of solid state nuclear magnetic resonance (NMR) such as Floquet-Magnus expansion and Fer expansion, address alternative methods for solving a time-dependent linear differential equation which is a central problem in quantum physics in general and solid-state NMR in particular. The power and the salient features of these theoretical approaches that are helpful to describe the time evolution of the spin system at all times are presented. This review article presents a broad view of manipulations of spin systems in solid-state NMR, based on milestones theories including the average Hamiltonian theory and the Floquet theory, and the approaches currently developing such as the Floquet-Magnus expansion and the Fer expansion. All these approaches provide procedures to control and describe the spin dynamics in solid-state NMR. Applications of these theoretical methods to stroboscopic and synchronized manipulations, non-synchronized experiments, multiple incommensurated frequencies, magic-angle spinning samples, are illustrated. We also reviewed the propagators of these theories and discussed their convergences. Note that the FME is an extension of the popular Magnus Expansion and Average Hamiltonian Theory. It aims is to bridge the AHT to the Floquet Theorem but in a more concise and efficient formalism. Calculations can then be performed in a finite-dimensional Hilbert space instead of an infinite dimensional space within the so-called Floquet theory. We expected that the FME will provide means for more accurate and efficient spin dynamics simulation and for devising new RF pulse sequence.

Biodistribution of indocyanine green-loaded nanoparticles with surface modifications of PEG and folic acid.

PURPOSE: To establish the biodistribution profile of the PLGA nanoparticles with dual surface modifications of PEG and folic acid (FA) in mice xenografted with MDA-MB-231 human breast cancer cells with high expression of folate receptor (FR); and to illustrate that the modified nanoparticles can target the loaded indocyanine green (ICG) to the tumor with high FR expression. METHODS: ICG-loaded nanoparticles were prepared with PLGA (non-modified nanoparticles, NM-NP) or mPEG-PLGA and FA-PLGA (dual modified nanoparticles, DM-NP). Biodistribution of the ICG-loaded nanoparticles (1.25 mg/kg) after i.v. injection was investigated on athymic mice transplanted with MDA-MB-231 tumor. RESULTS: ICG concentration in plasma from the DM-NP group was significantly (p<0.05) higher than the NM-NP group from 90 min to the end of the study (12 h). After 4 h, the drug concentration in the tumor tissue from the DM-NP started to be significantly (p<0.05) higher than the NM-NP until 12 h. Compared to the NM-NP, the DM-NP increased the AUC(0-12 h) in plasma by 245% and the AUC(0-12 h) in tumor by 194%, while decreased the AUC(0-12 h) in liver by 13%. CONCLUSION: The accumulation of DM-NP into the tumor was significantly higher than NM-NP due to the long circulation and FR-mediated uptake.

Polymeric nanoparticulate delivery system for Indocyanine green: biodistribution in healthy mice.

The objective of this study is to investigate the biodistribution of Indocyanine green (ICG) in healthy mice, when delivered through polymeric nanoparticles. The poly(DL-lactic-co-glycolic acid) (PLGA) nanoparticles entrapping ICG were engineered and characterized. The extraction method for ICG recovery from biological samples was developed. The biodistribution of ICG was determined in healthy C57BL/6 mice (female, 10-week old) when delivered through PLGA nanoparticles in comparison to free ICG solution, using a fluorometric assay method. The extraction method for ICG shows efficiency above 80% for various organs and plasma. When nanoparticles were used to deliver ICG, 2-8 times higher concentrations of ICG was deposited in various organs, with 5-10 times higher plasma levels till 4 h, after an i.v. dose as compared to free ICG solution. In conclusion, the nanoparticle formulation significantly increased the ICG concentration and circulation time in plasma as well as the ICG uptake, accumulation and retention in various organs. Overall, this study represents the first step in exploring and establishing the potential of nanoparticles as an ICG-delivery system for use in tumor-diagnosis and photodynamic therapy.

Indocyanine green-loaded biodegradable nanoparticles: preparation, physicochemical characterization and in vitro release.

PURPOSE: The objective of this study is to develop indocyanine green (ICG)-loaded biodegradable nanoparticles by using biodegradable polymer, poly(DL-lactic-co-glycolic acid) (PLGA). METHOD: PLGA nanoparticles entrapping ICG were prepared by a modified spontaneous emulsification solvent diffusion method. To optimize the nanoparticle formulation, the influence of formulation parameters such as types of ICG, amount of ICG and the polymer were investigated. The ICG entrapment in nanoparticles, nanoparticle size and zeta potential were determined. The surface characterization was performed by atomic force microscopy (AFM) and the release of ICG from nanoparticles was determined. RESULTS: All PLGA nanoparticle formulations were found to have the mean diameter within the range of 300-410 nm with polydispersity index (PI) within the range of 0.01-0.06. Indocyanine green showed more efficient entrapment as compared to indocyanine green sodium iodide salt. All indocyanine green-loaded nanoparticle formulations were found to have almost similar ICG content of nanoparticles and showed increase in ICG entrapment with increase in the amount of polymer. The ICG entrapment reached 74% when ICG: PLGA weight ratio in the formulation reached 1:800. AFM images indicated that the nanoparticles were almost spherical in shape and had numerous pores on their surfaces. The release pattern consisted of two phases, with initial exponential phase releasing about 78% of ICG (within 8 h) followed by a slow phase releasing about 2% of ICG (within next 16 h). CONCLUSIONS: ICG-loaded PLGA nanoparticles were prepared and the formulation was optimized. The increase in amount of polymer in formulation leads to higher ICG entrapment. Nanoparticles formed were spherical and had porous surfaces and exhibited the characteristic release pattern of a monolithic matrix based system.

Enhanced photo-stability, thermal-stability and aqueous-stability of indocyanine green in polymeric nanoparticulate systems.

Photo-degradation, thermal-degradation and aqueous-instability of indocyanine green (ICG) limits its application as a fluorescence contrast agent for imaging purposes. Thus, the objective of this study is to develop polymeric nanoparticles entrapping ICG and to establish its effectiveness in providing photo-stability, thermal stability and aqueous stability to ICG. Nanoparticles entrapping ICG were engineered, characterized and the degradation kinetics of ICG in the nanoparticles was investigated in aqueous media. The entrapment of ICG in the nanoparticles causes a shift in its wavelength of peak fluorescence and a decrease in its peak fluorescence intensity. The degradation of ICG in aqueous nanoparticle suspension followed first-order kinetics for the time period studied. ICG entrapment in the nanoparticles enhanced aqueous-stability of ICG (half-life, t(1/2) was 72.2+/-6.1 h for ICG in the nanoparticles as compared to 16.8+/-1.5 h for free ICG solution), photo-stability of ICG (t(1/2) was 73.7+/-7.5 h for ICG in the nanoparticles as compared to 14.4+/-2.4 h for free ICG solution when exposed to room light from two 32 W normal fluorescent tubes) and thermal-stability of ICG (t(1/2) of ICG at 42 degrees C was 62.4+/-1.7 h for ICG in the nanoparticles as compared to 10.1+/-0.6 h for free ICG solution).

Degradation kinetics of indocyanine green in aqueous solution.

The degradation kinetics of a near-infrared fluorescent, diagnostic, and photodynamic agent, indocyanine green (ICG), was investigated in aqueous solution by steady-state fluorescence technique. The influence of ICG concentration on its fluorescence spectrum was determined. The degradation kinetics of ICG in aqueous solution was studied as a function of light exposure, type of light exposed, temperature, and ICG concentration. The degradation of ICG was found to follow first-order kinetics. Exposure to light and high temperatures caused acceleration in the degradation. The type and intensity of exposed light also affected degradation. ICG aqueous solutions were found to be more stable in dark, at low temperatures, and at higher ICG concentrations.