Anupama Datta

Comparative evaluation of F-18 FDOPA, F-18 FDG, and F-18 FLT-PET/CT for metabolic imaging of low grade gliomas.

Introduction: We undertook this prospective study to compare amino acid metabolism, glucose metabolism, and proliferation in primary and recurrent low grade gliomas using positron emission tomography (PET)/computed tomography with F-18 FDOPA, F-18 FDG, and F-18 FLT. Methods: Fifteen patients with newly diagnosed or previously treated low grade gliomas (WHO grade I or II) were subjected to F-18-FDOPA, F-18 FDG, and F-18 FLT PET/computed tomography studies on consecutive days. This included 2 patients in remission as control subjects. Uptake of all the 3 tracers were analyzed visually and quantified using standardized uptake values and tumor to normal (T/N) ratios. The accuracy of all the 3 PET tracers in the detection of newly diagnosed and recurrent low grade gliomas was compared. Results: F-18 FDOPA was positive in all cases of primary and recurrent low grade gliomas and negative in the patients in remission. Tumor was visualized on F-18 FDG in 7 of 13 cases, F-18-FLT was positive in 4 of 13 cases. Average tumor standardized uptake values max for F-18 FDOPA (5.75 ± 4.9) and F-18 FLT (1.8 ± 0.91) was lower than that of F-18 FDG (8.5 ± 4.4). T/N ratios for F-18-FDOPA (2.3 ± 0.51) and F-18 FLT (1.8 ± 0.91) were higher than F-18 FDG (1.03 ± 0.64) providing good image contrast for tumor detection in positive cases. Conclusion: F-18 FDOPA scan is superior to both F-18 FLT and F-18 FDG for visualization of primary and recurrent low grade gliomas. F-18-FLT should not be considered for evaluation of recurrent low grade gliomas.

Synthesis of 99mTc-DOTMP and Its Preclinical Evaluation as a Multidentate Imaging Agent for Skeletal Metastases

The convenient synthetic methodology and in vivo stability of the bone-seeking gamma-radiation-emitting compound, (99m)Tc-DOTMP are described in this paper. The radiolabeling efficiency was found to be >97%, and the stability in serum indicated that (99m)Tc remained bound to the chelate, DOTMP, for up to 24 hours. Blood clearance showed a quick washout from the circulation, and biologic half-life was found to be t(1/2)(F) = 25 min; t(1/2)(S) = 6 hours 5 minutes. The LD(50) was found to be 70 mg/kg, as determined by toxicity studies in BALB/c mice. Biodistribution characteristics of (99m)Tc-DOTMP were examined in BALB/c mice. The drug was excreted mainly through renal routes and the accumulation of (99m)Tc-DOTMP in bone was 9.06 +/- 0.75 percent injected dose per gram at 1 hour. Visual image analysis of (99m)Tc-DOTMP was clinically comparable to the interpretation of imaging studies with conventional (99m)Tc-MDP and other phosphonate derivatives. (99m)Tc-DOTMP injected into Balb/c mice showed prominent bone localization and rapid clearance from blood and other organs, thereby making it a promising candidate as a diagnostic pharmaceutical of bone metastases.

Bivalent Approach for Homodimeric Estradiol Based Ligand: Synthesis and Evaluation for Targeted Theranosis of ER(+) Breast Carcinomas

The synthesis of estradiol based bivalent ligand [(EST)2DT] is reported and its potential for targeted imaging and therapy of ER(+) tumors has been evaluated. For the purpose, ethinylestradiol was functionalized with an azidoethylamine moiety via click chemistry. The resultant derivative was reacted in a bivalent mode with DTPA-dianhydride to form the multicoordinate chelating agent, (EST)2DT which displayed capability to bind (99m)Tc. The radiolabeled complex, (99m)Tc-(EST)2DT was obtained in >99% radiochemical purity and 20-48 GBq/μmol of specific activity. RBA assay revealed ∼15% binding with estrogen receptor. Evaluation of ligand on ER(+)-cell line (MCF-7) suggested enhanced and ER-mediated uptake. In vivo assays displayed early tracer accumulation in MCF-7 xenografts with tumor to muscle ratio ∼6 in 2 h and negligible uptakes in nontargeted organs. MTT assay performed on ER(+) and ER(-) cell lines displayed selective inhibition of ER(+) cancer cell growth with IC50 = 14.3 μM which was comparable to tamoxifen. The anticancer activity of the ligand is possibly due to the increase in ERβ and suppression of ERα protein levels in gene transcription. The studies reveal the potential of (EST)2DT as diagnostic imaging agent with the additional benefits in therapy.

Zinc complex of tryptophan appended 1,4,7,10-tetraazacyclododecane as potential anticancer agent: Synthesis and evaluation

With the rising incidences of cancer cases, the quest for new metal based anticancer drugs has led to extensive research in cancer biology. Zinc complexes of amino acid residue side chains are well recognized for hydrolysis of phosphodiester bond in DNA at faster rate. In the presented work, a Zn(II) complex of cyclen substituted with two l-tryptophan units, Zn(II)-Cyclen-(Trp)2 has been synthesized and evaluated for antiproliferative activity. Zn(II)-Cyclen-(Trp)2 was synthesized in ∼70% yield and its DNA binding potential was evaluated through QM/MM study which suggested good binding (G=-9.426) with B-DNA. The decrease in intensity of the positive and negative bands of CT-DNA at 278nm and 240nm, respectively demonstrated an effective unwinding of the DNA helix with loss of helicity. The complex was identified as an antiproliferative agent against U-87MG cells with 5 fold increase in apoptosis with respect to control (2h post incubation, IC50 25µM). Electrophoresis and comet assay studies exhibited an increase in DNA breakage after treatment with complex while caspase-3/β-actin cleavage established a caspase-3 dependent apoptosis pathway in U-87 MG cells after triggering DNA damage. In vivo tumor specificity of the developed ligand was validated after radiocomplexation with 99mTc (>98% radiochemical yield and specific activity of 2.56GBq/µmol). Avid tumor/muscle ratio of >6 was depicted in biodistribution and SPECT imaging studies in U-87 MG xenograft model nude mice.

Design and docking studies of [diethylenetriaminepentaacetic acid-(amino acid)2] with acetylcholine receptor as a molecular imaging agent for single-photon emission computed tomographic application.

The acetylcholine receptor is an essential link between the brain and the muscles, so it is a sensitive location for attack. In this study, some reversible [diethylenetriaminepentaacetic acid–(amino acid)2] have been docked computationally to the active site of the acetylcholine receptor. The induced fit method was employed to perform the automolecular docking for these systems. The result of docking studies generated thermodynamic properties, such as free energy of bindings (Glide score) and their weak electrostatic interactions. On the basis of these results, scintigraphic imaging studies were performed in mice. Among the radiotracers evaluated in this study, compound derived from 5-hydroxytryptophan/tryptophan exhibited remarkable localization in the brain, whereas radiotracer derived from L-histidine shows moderate accumulation in the brain. Preliminary studies with these amino acid–based ligands are encouraging to carrying out further in vivo experiments for targeted imaging.

Design, Synthesis, and Antimycobacterial Property of PEG–bis(INH) Conjugates

Poly(ethylene glycol) derivatives of isoniazid with varying molecular weight of poly(ethylene glycol) were designed as antimycobacterial agents. Poly(ethylene glycol)‐diacrylate of three different molecular weights (MW 258, 575, and 700) was conjugated with isoniazid by the Michael addition approach. The poly(ethylene glycol)–bis(isoniazid) conjugates thus obtained were completely characterized by FT‐IR, 1H and 13C NMR, and ESI‐MS spectroscopic techniques. Comparative MTT assay of the poly(ethylene glycol)–bis(isoniazid) conjugates showed much lower cytotoxicity than the neat isoniazid. MIC studies on Mycobaterium tuberculosis H37Rv showed potential antimycobacterial activity than the free isoniazid on a molar basis. The poly(ethylene glycol)–bis(isoniazid) conjugates were successfully radiolabeled with 99m‐Technetium with more than 97% efficiency and stability to assess their in vivo fate. The 99mTc labeled poly(ethylene glycol)–bis(isoniazid) conjugates showed higher blood retention time in New Zealand rabbits which increased with increasing molecular weight of poly(ethylene glycol). Biodistribution studies in infection‐induced murine models (BALB/c mice) showed significant retention of these conjugates at the site of infection for 72 h. The results of this study illustrate the potential utility of the PEGylated isoniazid conjugates as long circulating carriers for improved antitubercular drug therapy.

Kinetics of Formation for Lanthanide (III) Complexes of DTPA‐(Me‐Trp)2 used as Imaging Agent

Diethlenetriamine‐N,N,N′N′′N′′‐pentaacetic acid (DTPA)‐bis (amide) analogs have been synthesized and evaluated as a potential biomedical imaging agents. Imaging and biodistribution studies were performed in mice that showed a significant accumulation of DTPA analogs in brain. The stability and protonation constants of the complexes formed between the ligand [DTPA‐(Me‐Trp)2] and Gd3+, Eu3+, and Cu2+ have been determined by pH potentiometry (Gd3+, Eu3+) and spectrophotometry (Cu2+) at 25 °C and at constant ionic strength maintained by 0.10 m KCl. The kinetic inertness of Gd [DTPA‐(Me‐Trp)2] was characterized by the rates of exchange reactions with Zn2+ and Eu3+. In the Eu3+ exchange, a second‐order [H+] dependence was found for the pseudo‐first‐order rate constant [k0 = (4.5 ± 1.2) × 10−6/s; k1 = 0.58 ± 0.1 /m/s, k2 = (6.6 ± 0.2) × 104 /m2/s, k3 = (4.8 ± 0.8) × 10−4/m/s]. In the Eu3+ exchange, at pH <5.0, the rate decreases with increasing concentration of the exchanging ion. At physiological pH, the kinetic inertness of [DTPA‐(Me‐Trp)2] is more inert than GdDTPA2−, the most commonly used MRI contrast agent (t1/2 = 127 h). High kinetic stability is an important requirement for the Gd complexes used as contrast enhancement agents in magnetic resonance imaging.

Chalcone Based Homodimeric PET Agent, 11C-(Chal)2DEA-Me, for Beta Amyloid Imaging: Synthesis and Bioevaluation

Homodimeric chalcone based 11C-PET radiotracer, 11C-(Chal)2DEA-Me, was synthesized, and binding affinity toward beta amyloid (Aβ) was evaluated. The computational studies revealed multiple binding of the tracer at the recognition sites of Aβ fibrils. The bivalent ligand 11C-(Chal)2DEA-Me displayed higher binding affinity compared to the corresponding monomer, 11C-Chal-Me, and classical Aβ agents. The radiolabeling yield with carbon-11 was 40-55% (decay corrected) with specific activity of 65-90 GBq/μmol. A significant ( p < 0.0001) improvement in the binding affinity of 11C-(Chal)2DEA-Me with synthetic Aβ42 aggregates over the monomer, 11C-Chal-Me, demonstrates the utility of the bivalent approach. The PET imaging and biodistribution data displayed suitable brain pharmacokinetics of both ligands with higher brain uptake in the case of the bivalent ligand. Metabolite analysis of healthy ddY mouse brain homogenates exhibited high stability of the radiotracers in the brain with >93% intact tracer at 30 min post injection. Both chalcone derivatives were fluorescent in nature and demonstrated significant changes in the emission properties after binding with Aβ42. The preliminary analysis indicates high potential of 11C-(Chal)2DEA-Me as in vivo Aβ42 imaging tracer and highlights the significance of the bivalent approach to achieve a higher biological response for detection of early stages of amyloidosis.

Can 18F-Fluoroestradiol positron emission tomography become a new imaging standard in the estrogen receptor-positive breast cancer patient: A prospective comparative study with 18F-Fluorodeoxyglucose positron emission tomography?

Correct staging is the most crucial for the treatment outcome in cancer management. Molecular imaging with 18F-fluoroestradiol (FES) positron emission tomography-computed tomography (PET-CT) targets estrogen receptor (ER) and may have a higher incremental value in diagnosis by aiding specificity. We enrolled 12 female breast cancer patients prospectively and did 18F-FES PET-CT and 18F-fluorodeoxyglucose (FDG) PET-CT within 1 week interval time. Lesion detection sensitivity was compared for a total number of lesions and for nonhepatic lesions only by McNemar test. 18F-FES PET-CT was taken as reference in case of indeterminate lesions. The incremental value reported by identifying 18F-FES exclusive lesions and by characterization of 18F-FDG indeterminate lesions. Spearman rank test was used to correlate ER expression and maximum standardized uptake value (SUVmax). Two ER-negative patients with no 18F-FES uptake were excluded. Ten ER-positive patients with 154 disease lesions were finally analyzed. 18F-FDG picked-up 142 lesions (sensitivity 92.21%), whereas 18F-FES picked-up 116 lesions (sensitivity 75.32%) and this difference was statistically significant. For nonhepatic lesions (n = 136) detectability, 18F-FDG picked-up 124 (sensitivity 91.18%), whereas 18F-FES picked-up 116 (sensitivity 85.29%) lesions and this difference was not statistically significant. Beside 12 exclusive lesions, 18F-FES characterized 41 (27.5%) 18F-FDG indeterminate lesions. Overall 18F-FES impacted 20% patient management. The positive trend was also seen with 18F-FES SUVmax with ER expression and negative with 18F-FDG SUVmax. We conclude, 18F-FDG has overall better sensitivity than 18F-FES PET-CT, however for nonhepatic metastasis difference was not significant. 18F-FES PET-CT better-characterized lesions and impacted 20% patient management. Therefore, 18F-FES PET-CT should be used with 18F-FDG PET-CT in strongly ER expressing patients for better specificity.

Picolinic acid based acyclic bifunctional chelating agent and its methionine conjugate as potential SPECT imaging agents: syntheses and preclinical evaluation

Bifunctional chelate, 6,6′-(2-aminoethylazanediyl)bis(methylene)dipicolinic acid (H2pentapa-en-NH2), has been synthesized and labeled with 99mTc with a specific activity of 135–140 MBq μmol−1 in >95% yield. The in vitro stability of the labeled chelate in both PBS and human serum shows only 85% yield and labeled with 99mTc in 96.2% radiochemical yield with a specific activity of 110–125 MBq μmol−1. The conjugate probe exhibited high serum stability (>94% at 24 h). The in vivo blood kinetic studies of radiocomplexes of H2pentapa-en-NH2 and its methionine conjugated derivative exhibited fast clearance with t1/2(F) = 32 ± 0.14 min, t1/2(S) = 4 h 20 min ± 0.21 min and t1/2(F) = 27 ± 0.3 min, t1/2(S) = 4 h 01 min ± 0.11 min, respectively. In vivo scintigraphy and ex vivo biodistribution studies in EAT tumor bearing mice demonstrated a high retention of H2pentapa-en-met2 at the site of the tumor with tumor to muscle ratio of 6.52 at 1 h, indicating the high specificity of 99mTc-pentapa-en-met2 toward tumors.