Shubhra Chaturvedi

Synthesis of oxovanadium(IV) Schiff base complexes derived from C-substituted diamines and pyridoxal-5-phosphate as antitumor agents.

Oxovanadium (IV) complexes of N,N′‐bispyridoxyl‐5, 5′‐bis (phosphate) ethylenediimine (L1) and N,N′‐bis(pyridoxyl)‐5,5′‐bis(phosphate)‐1′′‐(p‐nitrobenzyl)ethylenediimine (L2) were synthesized by condensation of optically active C‐substituted diamines and pyridoxal‐5‐phosphate. Oxovanadium (IV) complexes derived from L1 and L2 were evaluated as DNA cleavage agent (cleavage of supercoiled plasmid pBR322 DNA). Interestingly, both the oxovanadium (IV) complexes exhibited DNA nuclease activity, and the extent of oxidation of DNA by these vanadyl complexes was superior to VOSO4. The significant reduction in primary tumor and increased delay in tumor growth of 15 days was seen in the tumor regression analysis with oxovanadium (IV) complex of L1. With the preliminary studies performed with the pyridoxal‐5‐phosphate ‐based salen derivatives including the cytotoxicity and tumor regression, it is evident that the salen bifunctional chelating agent has obtained therapeutic potential if conjugated to a gene‐specific targeting molecule for the oxidation of guanine residue.

99mTc‐DTPA‐Amino Acids Conjugate as Specific SPECT Pharmaceuticals for Tumor Imaging

99mTc‐Diethylene triamine pentaacetic acid‐bis (amide) conjugates have been synthesized and evaluated as a potential radiopharmaceutical for tumor imaging. The compounds were synthesized by the condensation reaction of DTPA bis(anhydride) with different l‐amino acids (methyl tryptophan, and 5‐hydroxy tryptophan) and were characterized on the basis of IR, NMR, and Mass spectroscopy. 99mTc‐labeled compounds were found stable for about 24 h under physiological conditions with more than 95% radiolabeling yield. Blood kinetic studies of all these complexes showed a bi‐exponential pattern as well as quick wash out from the blood circulation. The biological t1/2(F) and t1/2(S) were found to be 20 ± 0.001 min for DTPA‐(Me‐Trp)2 and 18 ± 0.001 min for DTPA‐(5HT)2 and t1/2 (slow) 5 h 45 min ± 0.001, 5 h 30 ± 0.001 min for DTPA‐(Me‐Trp)2, and DTPA‐(5HT)2, respectively. Imaging and biodistribution studies were performed in mice bearing Ehrlich ascites tumor (EAT) tumors in right thigh. Radioconjugate derived from l‐5‐hydroxytryptophan exhibited remarkable localization at tumor site; whereas radiotracer derived from l‐methyl tryptophan shows relatively less accumulation at the tumor site. Tumor‐to‐muscles ratios were 5.07 ± 0.001, and 4.2 ± 0.001 at 1 and 4 h for 99mTc‐DTPA‐(Me trp)2 and 4.97 ± 0.001 and 5.8 ± 0.001 at 1 and 4 h after postinjection for 99mTc‐DTPA‐(5HT)2, respectively. The preliminary results with these amino acid based ligands are encouraging to carrying out further in vivo experiments for targeted tumor imaging.

Targeted theranostic liposomes: rifampicin and ofloxacin loaded pegylated liposomes for theranostic application in mycobacterial infections

Theranostic liposomes are effective drug delivery systems for the management of infections. With added features of targeting and stealth, theranostic liposomes can be made more effective. We report the synthesis and validation of targeted stealth theranostic liposomes for the management of mycobacterial infections. The targeted drug delivery systems for infections are devised to improve the therapeutic window of encapsulated drugs by increasing their delivery to the target area and minimizing the drug-associated toxicity. FR+ targeted pegylated liposomal formulation was developed for in vivo imaging of mycobacterial infections. The encapsulated drugs for mitigation are rifampicin and ofloxacin. The prepared liposomes were characterized for physicochemical properties and stability. In vitro release properties, mycobacterial activity, in vivo blood-kinetics, bio-distribution, and bio-efficacy of the prepared lyophilized liposomes were assessed. The mean particle size of the liposomes was 160.6 nm with considerable colloidal stability observed up to 120 days. The results of in vitro investigations indicate good encapsulation efficiency of 66.89 (±10.9)% and 40.61 (±8.7)% for rifampicin and ofloxacin respectively with excellent anti-mycobacterial activity. The pharmacokinetics data corroborate a slow biphasic pattern with a much longer terminal half-life of 19.13 h. The tissue distribution studies revealed high blood pool activity even up to 24 h post injection (p.i.) with the maximum organ localization in the spleen, liver, and kidneys at one hour p.i. Further, in vivo scintigraphic studies in the murine model of TB infection showed higher uptake at infected lesions at two hours p.i. The blocking imaging experiments showed minimized uptake, which confirms specific targeting. Therapeutic efficacy studies further confirmed that liposomal delivery of the anti-TB drugs is efficacious in the murine model of infection. In conclusion, preliminary studies demonstrated that the formulated liposomes can be an effective theranostic agent against mycobacterial infections in the mouse model.

Nucleolipids as building blocks for the synthesis of 99mTc-labeled nanoparticles functionalized with folic acid

The development of drug delivery nanocarriers is emerging as a promising therapeutic tool to transport anti-cancer agents to tumors. In this contribution, preparation of nanoparticles (NPs) highly loaded with cisplatin using the bio-inspired hybrid nucleoside-lipids has been reported. The construction of these NPs using a “layer-by-layer’’ approach allows surface functionalization with polyethylene glycol and targeting moieties. Uridine moieties were pegylated for folic acid (FA) functionalisation to render specificity for active targeting. The uridine moieties at the surface of the nanoparticle act as ligands for 99mTc radiolabeling, whereas the lipid chains maintain the structure of the nanoparticle. In vitro, these hybrid NPs are stable and actively internalize in two different cell lines overexpressing the folic acid receptor. In vivo scintigraphy shows that nucleolipid functionalized NPs notably improved the pharmacokinetic profile of cisplatin (enhanced blood circulation time) and accumulated in the tumor xenografted mice model.

Small Molecule Radiopharmaceuticals - A Review of Current Approaches

Radiopharmaceuticals are an integral component of nuclear medicine and are widely applied in diagnostics and therapy. Though widely applied, the development of an “ideal” radiopharmaceutical can be challenging. Issues such as specificity, selectivity, sensitivity, and feasible chemistry challenge the design and synthesis of radiopharmaceuticals. Over time, strategies to address the issues have evolved by making use of new technological advances in the fields of biology and chemistry. This review presents the application of few advances in design and synthesis of radiopharmaceuticals. The topics covered are bivalent ligand approach and lipidization as part of design modifications for enhanced selectivity and sensitivity and novel synthetic strategies for optimized chemistry and radiolabeling of radiopharmaceuticals.

Synthesis, docking and preliminary in vivo evaluation of serotonin dithiocarbamate as novel SPECT neuroimaging agent

Functional imaging, for understanding the pathophysiology of neuropsychiatric disorders and neurocognition pathways, can be achieved by targeting receptors in the central neural system (CNS). The multitude of physiological functions elicited by the interaction of serotonin with its receptors and the relation between the level and ‘state’ of the serotonin receptor (5-HT1A) and neuropsychiatric diseases makes this receptor an attractive target for imaging and therapeutics. Thus, for imaging of “active” 5-HT1A a ligand with an agonistic mode of binding has been designed and evaluated as a SPECT radiotracer. In this study, serotonin, the natural ligand, has been modified as the dithiocarbamate and radiolabelled with 99mTc. The efficacy of the complex as an imaging agent has been evaluated in terms of radiochemical purity, stability, lipophilicity, biodistribution pattern and scintigraphy. For understanding the binding mode, the ligand has been docked on the 5-HT1A receptor homology models built using the crystal structure of the human β2-adrenergic receptor in the presence (PDB 3D4S) and absence (PDB 2RH1) of cholesterol. The docking results are in line with the agonist mode of binding for the ligand and strongly supported by the experimental data. Preliminary results indicate excellent radiolabelling above 95%, a biphasic blood clearance pattern with t1/2 (fast) of 45 minutes and t1/2 (slow) of 5.9 hours and a predominantly hepatobiliary excretion route. The regional brain uptake studies indicate localization of the complex in the hippocampus region. Thus, a novel dithiocarbamate based on the scaffold of serotonin has been synthesized and evaluated as a potential neuroimaging agent.

New Trends and Current Status of Positron-Emission Tomography and Single-Photon-Emission Computerized Tomography Radioligands for Neuronal Serotonin Receptors and Serotonin Transporter

The critical role of serotonin (5-hydroxytryptamine; 5-HT) and its receptors (5-HTRs) in the pathophysiology of diverse neuropsychiatric and neurodegenerative disorders render them attractive diagnostic and therapeutic targets for brain disorders. Therefore, the in vivo assessment of binding of 5-HT receptor ligands under a multitude of physiologic and pathologic scenarios may support more-accurate identification of disease and its progression and the patients response to therapy as well as the screening of novel therapeutic strategies. The present Review aims to focus on the current status of radioligands used for positron-emission tomography (PET) and single-photon-emission computerized tomography (SPECT) imaging of human brain serotonin receptors. We further elaborate upon and emphasize the attributes that qualify a radioligand for theranostics on the basis of its frequency of use in clinics, its benefit to risk assessment in humans, and its continuous evolution, along with the major limitations.

Engineered Nanoparticles Associated Metabolomics

AbstractNanotechnology is of great economic importance due to rapid growth in industrial and household applications and their continuous release into environmental matrices has increased the concerns regarding its potential impact on human and environment. To evaluate the potential toxicity of nanoparticles (NPs), the impact on humans and ecosystems needs to be understood from mechanistic insight by metabolomics. The analytical methods and omics technologies are particularly well-suited to evaluate these two dimensions in environment and both in vitro and in vivo systems, respectively. In this paper, the currently most effective methods for sampling and detection are presented together for future standardization of protocols providing profiles of NPs and associated metabolomics. All these approaches are designed without compromising the reliability and quality of the analytical results for their application in understanding the metabolomics and chemistry of NPs in the environmental matrices. Among samplin...

Improvising 5-HT7R homology model for design of high affinity ligands: model validation with docking, embrace minimization, MM-GBSA, and molecular dynamic simulations

The subtype, 5-HT7R has been implicated in neurological disorders and presents itself as a promising target for antidepressant drugs. Design of targeted selective ligands, require a sound knowledge of 3D-receptor structure. In absence of receptor structure, structure-based design of targeted ligands relies on generation of 5-HT7R homology model. In this study, the impact of template choice, alignment, and model building methods on the homology model of 5-HT7R is addressed. The compactness and model quality due to the presence of cholesterol (lipidic receptor) have also been observed. The results suggest good stereochemical quality of the final model. Ramachandran Plot Analysis indicated more than 97.5% amino acid residues in the favorable region. The overall quality factor was 91.8% using ERRAT. The Z-score for backbone confirmation and packing quality were −1.248 and −1.427, respectively, using WHATCHECK. The RMS Z-score for side chain planarity was .711. Other validation results for the final model include binding site analysis in which Asp162, Val163, Phe343, Phe344, Arg350, Arg367, and Leu370 conserved residues were found in the active site, correlation coefficient of .82 in ligand-based screening and .85 in embrace minimization. Further, the model showed good correlation for agonist and antagonist in docking ( ≈ .76, ≈ .82), embrace minimization ( ≈ .73, ≈ .72), and MM-GBSA ( ≈ .69, ≈ .75) studies. The model was subjected to Molecular Dynamics (MD) simulation of 20 ns both in ligand-free and ligand-bound receptor (agonist and antagonist) system in order to assess its stability.

Design, physico-chemical and pre-clinical evaluation of a homo-bivalent 99mTc-(BTZ)2DTPA radioligand for targeting dimeric 5-HT1A/5-HT7 receptors

A mixed affinity dimeric radioligand 99mTc-(BTZ)2DTPA was designed using a “bivalent ligand approach” and evaluated as an SPECT imaging agent for targeting 5-HT1A/5-HT7 dimeric receptors in the central nervous system. In silico studies reflected high affinity for dimeric 5-HT1A/5-HT7 receptors. Following multi-step synthesis, the ligand was obtained in 87.5% yield. Detailed physico-chemical analysis included pKa evaluation and optimization of radiolabeling parameters (>98% radiolabeling efficiency). The in vitro serum-stability test of the 99mTc-complex showed ≤8.7% dissociation and appreciable stability when challenged with excess cysteine (≤4.4% dissociation). Cyto-compatibility (4.8–0.6% cell death at 100 μM to 1 pM) and haemo-compatibility (1.05% erythrocyte destruction) suggested optimum biocompatibility. Blood kinetics revealed biphasic clearance. The brain/blood ratio of 0.66 assured the CNS penetration ability and BBB permeability of the developed radioligand. Bio-distribution and in vivo SPECT imaging revealed a maximum brain uptake of 2.08 ± 0.08% ID per g at 10 min p.i. followed by major activity accumulation in 5-HT1A/5-HT7 receptor-rich regions viz., the hippocampus (41.83% ID per g) and the cortex (23.56% ID per g) of mouse brains ascertaining selective targeting of 99mTc-(BTZ)2DTPA. The radiotracer was excreted majorly through the renal route. These preclinical studies reveal that the 99mTc-(BTZ)2DTPA radiotracer shows promise as an effective diagnostic agent for neurological disorders.