Anjani K. Tiwari

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.

Synthesis, conjugation and relaxation studies of gadolinium(III)-4-benzothiazol-2-yl-phenylamine as a potential brain specific MR contrast agent

Magnetic resonance (MR) imaging is widely used in clinical research to map the structural and functional organization of the brain. We have designed and synthesized a Gd-based specific MR contrast agent that binds to regions in the brain. The presented compound {4-[(4-benzothiazol-2-yl-phenylcarbamoyl)-methyl]-7,10-bis-carboxymethyl-1,4,7,10-tetraazacyclododec-1-yl} acetic acid (DO3A-BT) was synthesized by conjugating the chloroacetylated product of 4-benzothiazol-2-yl-phenylamine with a trisubstituted cyclen. The lanthanide complex (Ln-DO3A-BT) was evaluated in vitro for both MR (Gd-DO3A-BT) and optical (Eu-DO3A-BT) imaging applications. The complex Gd-DO3A-BT displays a relaxivity of r1 = 4.18 mM(-1) s(-1) at 4.7 T which is 1.2 times greater than Dotarem and significantly higher than the brain specific MR contrast agent Luxol Fast Blue (LFB). The protonation constant of the ligand (pKa1 = 9.91, pKa2 = 8.22, pKa3 = 5.01) and the stability constant of the complex formed between Gd(III), Eu(III) and Ca(II) and ligand DO3A-BT (log βGdL = 18.4, log βEuL = 18.3, log βZn2L = 7.1, log βCa2L = 6.3) were recorded by potentiometric titration. The constants reflect the high stability of the ligand with lanthanides compared with endogenous metal ions. The transmetalation stability of Gd-DO3A-BT toward Zn proved to be excellent with a rate constant of 3.07 × 10(-5) s(-1) which is in line with other tetraazatetraacetic acid (DOTA)-monoamide complexes. The hydration number (q) was found to be 0.92, and is calculated from the difference in the luminescence lifetime of Eu-DO3A-BT in H2O and D2O solutions to determine the coordination state of this complex. The in vivo biodistribution of (99m)Tc-DO3A-BT in BALB/c mice showed a brain uptake of 1.2% ID g(-1) at 2 min post injection when injected with mannitol which disrupts the blood-brain-barrier (BBB) due to osmotic shock. In vitro binding on the brain homogenate revealed a high uptake by the neuronal/glial cells for in vivo applications.

Design, synthesis, and in vitro antiproliferative activity of benzimidazole analogues for radiopharmaceutical efficacy.

The synthesis of eight ligands by using 2-amino benzimidazole with different mono/bis aldehydes is described herein. The final products were characterized by spectral techniques such as FT-IR, (1)H NMR, and EI-Mass. The structure-activity relationships of the benzimidazole derivatives are also reported. Studies on the complexation of the ligands with (99m)Tc were optimized by using stannous tartrate as reducing agent under various reaction conditions. The radiochemical stability was >or=95% for all the complexes, and they were to be stable for 12-14 hours in serum. Most of the ligands showed fast blood clearance. Biodistribution studies of the (99m)Tc complexes of these ligands showed no significant uptake in the brain or in the heart, and the clearance was mainly through the hepatobiliary system. Among the eight compounds evaluated for their antiproliferative activity in vitro, L(8) produced good activity against the cancer cell lines A549 and PC-3.

Effect of a Novel Series of Benzothiazolo-Quinazolones on Epidermal Growth Factor Receptor (EGFR) and Biological Evaluations

A newly designed benzothiazolo‐quinazolone series was synthesized by an aromatic amine and potassium thiocyanate in the presence of bromine in glacial acetic acid, and the final product was obtained by subsequent reaction with 5‐arylamido/imidoalkyl‐2‐chlorobenzoic acid in the presence of potassium carbonate and further cyclization with sulphuric acid. A preliminary radiolabelling study with technetium shows a promising potential for further in vivo evaluation. Anti‐bacterial, anti‐viral and anti‐tumor activities were evaluated for biological properties. Lead compounds are able to block epidermal growth factor receptor (EGFR) in human breast adenocarcinoma cell line, MCF‐7.

Synthesis and biological evaluation of newly designed phosphonate based bone-seeking agent.

A cyclic tetraaza based bifunctional triphosphonate ligand 10-(2-aminoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-tris(methylenephosphonic acid) (DO3MP-EA) was synthesized as bone-seeking theranostic agent. The compound was characterized by spectroscopic techniques and labelled with (99m)Tc with more than 97% purity. Blood clearance of 99mTc labelled compound a quick wash out from the circulation. The compound was excreted mainly via kidneys and accumulation of (99m)Tc-DO3MP-EA in bone was 9.53 ± 1.06% of injected dose per gram of bone at 1 h. The preliminary CADD analysis confirms the efficacy of DO3MP-EA (G Score -7.005) as better binding agent for osteocalcin (pdb 1Q8H) rather than other known clinical agents. Subsequently stability constant of chelate with Ga(III) was found to be 18.6 which confirms its efficacy as (68)Ga labelled PET radiopharmaceutical for bone.

Comparative Evaluation of Glutamate-Sensitive Radiopharmaceuticals: Technetium-99m–Glutamic Acid and Technetium-99m–Diethylenetriaminepentaacetic Acid–bis(Glutamate) Conjugate for Tumor Imaging

Single-photon emission computed tomography has become a significant imaging modality with huge potential to visualize and provide information of anatomic dysfunctions that are predictive of future diseases. This imaging tool is complimented by radiopharmaceuticals/radiosubstrates that help in imaging specific physiological aspects of the human body. The present study was undertaken to explore the utility of technetium-99m (⁹⁹(m)Tc)-labeled glutamate conjugates for tumor scintigraphy. As part of our efforts to further utilize the application of chelating agents, glutamic acid was conjugated with a multidentate ligand, diethylenetriaminepentaacetic acid (DTPA). The DTPA-glutamate conjugate [DTPA-bis(Glu)] was well characterized by IR, NMR, and mass spectroscopy. The biological activity of glutamic acid was compared with its DTPA conjugate by radiocomplexation with ⁹⁹(m)Tc (labeling efficiency ≥98%). In vivo studies of both the radiolabeled complexes ⁹⁹(m)Tc-Glu and ⁹⁹(m)Tc-DTPA-bis(Glu) were then carried out, followed by gamma scintigraphy in New Zealand albino rabbits. Improved serum stability of ⁹⁹(m)Tc-labeled DTPA conjugate indicated that ⁹⁹(m)Tc remained bound to the conjugate up to 24 hours. Blood clearance showed a relatively slow washout of the DTPA conjugate when compared with the labeled glutamate. Biodistribution characteristics of the conjugate in Balb/c mice revealed that DTPA conjugation of glutamic acid favors less accumulation in the liver and bone and rapid renal clearance. Tumor scintigraphy in mice showed increasing tumor accumulation, stable up to 4 hours. These preliminary studies show that ⁹⁹(m)Tc-DTPA-bis(Glu) can be a useful radiopharmaceutical for diagnostic applications in single-photon emission computed tomography imaging.

Quantitative Structure–Property Relationship (Correlation Analysis) of Phosphonic Acid-Based Chelates in Design of MRI Contrast Agent

Nuclear magnetic resonance imaging is a very useful tool in modern medical diagnostics, especially when gadolinium (III)‐based contrast agents are administered to the patient with the aim of increasing the image contrast between normal and diseased tissues. With the use of soft modelling techniques such as quantitative structure–activity relationship/quantitative structure–property relationship after a suitable description of their molecular structure, we have studied a series of phosphonic acid for designing new MRI contrast agent. Quantitative structure–property relationship studies with multiple linear regression analysis were applied to find correlation between different calculated molecular descriptors of the phosphonic acid‐based chelating agent and their stability constants. The final quantitative structure–property relationship mathematical models were found as – quantitative structure–property relationship Model for phosphonic acid series (Model 1) − log KML = {5.00243(±0.7102)}− MR {0.0263(±0.540)}n = 12 l r l = 0.942 s = 0.183 F = 99.165 quantitative structure–property relationship Model for phosphonic acid series (Model 2) − log KML = {5.06280(±0.3418)}− MR {0.0252(± .198)}n = 12 l r l = 0.956 s = 0.186 F = 99.256.

Disubstituted 4(3H) Quinazolones: A Novel Class of Antitumor Agents

A series of disubstituted 4(3H) quinazolines were designed for potential application in tumors. Firstly, N‐benzoyl anthranilic acid is formed, which undergoes cyclization in the presence of pyridine. Subsequently, nucleophilic attack by semicarbazide on the carbonyl carbon gives 2‐substituted 3‐carbamido 4(3H) quinazolones, which gives final compound with appropriate substitution. The final as well as intermediate products were confirmed by NMR, FT‐IR, and mass spectrometry. In vitro toxicity was performed with different cell lines and showed that the connection of hydrophilic styryl to quinazoline moiety increases its efficacy.

Synthesis and assessment of 99mTc chelate-conjugated alendronate for development of specific radiopharmaceuticals.

Indole-based alendronate (AI) was derived from the condensation reaction of indole 3-carboxaldehyde with sodium alendronate (ALN) and was characterized by various spectroscopic methods (e.g., ultraviolet, fourier-transform-infrared, and liquid chromatography mass spectrometry). The AI was labeled with (99m)Tc and radiochemical purity was above 97%, which was ascertained by instant thin-layer chromatography, using different solvent conditions, with a specific activity 2-5 mCi/mg. The receptor ligand assay on human bone cell line Soas-2 showed K(D) = 0.55 nM. The derivative (AI) was stable, which was determined under physiologic conditions up to 24 hours The blood kinetic study showed a biexponential pattern as well as quick wash-out from the circulation with varying biologic t(1/2)(F) and t(1/2)(S). Excellent-quality radio images were recorded of bone, showing a rapid clearance of background activity, at an early visualization at 1.5 hours. The excretory pathway of the derivative was through the kidneys, which was evidenced by biodistribution studies. Thus, the newly synthesized derivative can be considered as a specific bone-seeking agent.