Therapeutic radiopharmaceuticals

Superparamagnetic iron oxide nanoparticles stabilized by a poly(amidoamine)-rhenium complex as potential theranostic probe

Three-component nanocomposites, constituted by a superparamagnetic iron oxide core coated with a polymeric surfactant bearing tightly bound Re(CO)3 moieties, were prepared and fully characterized. The water soluble and biocompatible surfactant was a linear poly(amidoamine) copolymer (PAA), containing cysteamine pendants in the minority part (ISA23SH), able to coordinate Re(CO)3 fragments. For the synthesis of the nanocomposites two methods were compared, involving either (i) peptization of bare magnetite nanoparticles by interaction with the preformed ISA23SH-Re(CO)3 complex, or (ii) "one-pot" synthesis of iron oxide nanoparticles in the presence of the ISA23SH copolymer, followed by complexation of Re to the SPIO@ISA23SH nanocomposite. Full characterization by TEM, DLS, TGA, SQUID, and relaxometry showed that the second method gave better results. The magnetic cores had a roundish shape, with low dispersion (mean diameter ca. 6 nm) and a tendency to form larger aggregates (detected both by TEM and DLS), arising from multiple interactions of the polymeric coils. Aggregation did not affect the stability of the nano-suspension, found to be stable for many months without precipitate formation. The SPIO@PAA-Re nanoparticles (NPs) showed superparamagnetic behaviour and nuclear relaxivities similar or superior to commercial MRI contrast agents (CAs), which make them promising as MRI "negative" CAs. The possibility to encapsulate (186/188)Re isotopes (γ and β emitters) gives these novel NPs the potential to behave as bimodal nanostructures devoted to theranostic applications.

Radioiodinated hypericin: its biodistribution, necrosis avidity and therapeutic efficacy are influenced by formulation

PURPOSE

To study whether formulation influences biodistribution, necrosis avidity and tumoricidal effects of the radioiodinated hypericin, a necrosis avid agent for a dual-targeting anticancer radiotherapy.

METHODS

Iodine-123- and 131-labeled hypericin ((123)I-Hyp and (131)I-Hyp) were prepared with Iodogen as oxidant, and formulated in dimethyl sulfoxide (DMSO)/PEG400 (polyethylene glycol 400)/water (25/60/15, v/v/v) or DMSO/saline (20:80, v/v). The formulations with excessive Hyp were optically characterized. Biodistribution, necrosis avidity and tumoricidal effects were studied in rats (n = 42) without and with reperfused liver infarction and implanted rhabdomyosarcomas (R1). To induce tumor necrosis, R1-rats were pre-treated with a vascular disrupting agent. Magnetic resonance imaging, tissue-gamma counting, autoradiography and histology were used.

RESULTS

The two formulations differed significantly in fluorescence and precipitation. (123)I-Hyp/Hyp in DMSO/PEG400/water exhibited high uptake in necrosis but lower concentration in the lung, spleen and liver (p < 0.01). Tumor volumes of 0.9 ± 0.3 cm(3) with high radioactivity (3.1 ± 0.3% ID/g) were detected 6 days post-treatment. By contrast, (131)I-Hyp/Hypin DMSO/saline showed low uptake in necrosis but high retention in the spleen and liver (p < 0.01). Tumor volumes reached 2.6 ± 0.7 cm(3) with low tracer accumulation (0.1 ± 0.04%ID/g).

CONCLUSIONS

The formulation of radioiodinated hypericin/hypericin appears crucial for its physical property, biodistribution, necrosis avidity and tumoricidal effects.

Design, synthesis, and biological evaluation of catecholamine vehicle for studying dopaminergic system

Catecholamine mimetic EDTA-bis(tyramide) was synthesized and characterized by various spectroscopic techniques (NMR, mass spectroscopy) and λem 310 nm for the excitation at 270 nm. Molecular docking studies were performed with human serum albumin (PDB 1E78), showing binding pattern with amino acid residues Arg218, Arg222, and Lys444, identifies the ligand-human serum albumin interaction for the transportation affinity of the ligand at the specific site of the target. Subsequently, binding study with human serum albumin at λex  = 350 nm found to be 5.847 × 10(4)  m(-1) shows effective quenching effect. Additionally, to go more insight, acetylcholinesterase binding affinity was investigated, which shows 90% binding affinity for the 10 mm concentration. IC50 value was found 18.60 μm for MAO-B inhibition. Finally, EDTA-bis(tyramide) labeled with (99m) Tc to investigate its in vivo radiopharmaceutical efficiency having 97% binding affinity with 98% radiochemical purity. In vivo studies were carried out for (99m) Tc-EDTA-bis(tyramide) included blood kinetics showed a quick wash out from the circulation via renal route, and biodistribution revealed that maximum %ID/g was found in kidney at 1 h, and its scintigraphy image shows 3.96% brain uptake with respect to whole body.

New dicoumarol sodium compound: crystal structure, theoretical study and tumoricidal activity against osteoblast cancer cells

BACKGROUND

Enormous interest had been paid to the coordination chemistry of alkali and alkaline metal ions because of their role inside body viz; their Li(+)/Na(+) exchange inside the cell lead to different diseases like neuropathy, hypertension, microalbuminuria, cardiac and vascular hypertrophy, obesity, and insulin resistance. It has been presumed that alkali metal ions (whether Na(+) or K(+)) coordinated to chelating ligands can cross the hydrophobic cell membrane easily and can function effectively for depolarizing the ion difference. This unique function was utilized for bacterial cell death in which K(+) has been found coordinated valinomycin (antibiotic).

RESULTS

Distinct sodium adduct (1) with dicoumarol ligand, 4-Hydroxy-3-[(4-hydroxy-2-oxo-4a,8a-dihydro-2H-chromen-3-yl)-phenyl-methyl]-chromen-2-one (L) is isolated from the saturated solution of sodium methoxide. Single crystal X-ray diffraction studies of the adduct reveals that sodium is in the form of cation attached to a methoxide, methanol and a dicoumarol ligand where carbonyl functional groups of the coumarin derivative are acting as bridges. The sodium compound (1) is also characterized by IR, (1)H-NMR, and (13)C{(1)H}-NMR spectroscopic techniques. The composition is confirmed by elemental analysis. DFT study for 1 has been carried out using B3LYP/6-13G calculations which shown the theoretical confirmation of the various bond lengths and bond angles. Both the compounds were studied subsequently for the U2OS tumoricidal activity and it was found that L has LD50 value of 200 μM whereas the sodium analog cytotoxicity did not drop down below 60%.

CONCLUSION

A sodium analogue (1) with medicinally important dicoumarol ligand (L) has been reported. The crystal structure and DFT study confirm the formation of cationic sodium compound with dicoumarol. The ligand was found more active than the sodium analog attributed to the instability of 1 in solution state. Coumarin compound with sodium was observed to be less cytotoxic than the ligand, its LD50 value never dropped below 60%.

Sandmeyer reaction repurposed for the site-selective, non-oxidizing radioiodination of fully-deprotected peptides: studies on the endogenous opioid peptide α-neoendorphin

Standard radioiodination methods lack site-selectivity and either mask charges (Bolton-Hunter) or involve oxidative reaction conditions (chloramine-T). Opioid peptides are very sensitive to certain structural modifications, making these labeling methods untenable. In our model opioid peptide, α-neoendorphin, we replaced a tyrosyl hydroxyl with an iodine, and in cell lines stably expressing mu, delta, or kappa opioid receptors, we saw no negative effects on binding. We then optimized a repurposed Sandmeyer reaction using copper(I) catalysts with non-redoxing/non-nucleophilic ligands, bringing the radiochemical yield up to around 30%, and site-selectively incorporated radioactive iodine into this position under non-oxidizing reaction conditions, which should be broadly compatible with most peptides. The (125)I- and (131)I-labeled versions of the compound bound with high affinity to opioid receptors in mouse brain homogenates, thus demonstrating the general utility of the labeling strategy and of the peptide for exploring opioid binding sites.

Dicoumarol complexes of Cu(II) based on 1,10-phenanthroline: synthesis, X-ray diffraction studies, thermal behavior and biological evaluation

A series of Cu(II) complexes containing dicoumarol derivatives and 1, 10-phenanthroline have been synthesized. Structural and spectroscopic properties of ligands were studied on the basis of mass spectra, NMR ((1)H and (13)C) spectra, FT-IR spectrophotometry and elemental analysis, while physico-chemical, spectroscopic and thermal properties of mixed ligand complexes have been studied on the basis of infrared spectra, mass spectra, electronic spectra, powder X-ray diffraction, elemental analysis and thermogravimetric analysis. X-ray diffraction study suggested the suitable octahedral geometry for hexa-coordinated state. The kinetic parameters such as order of reaction (n), energy of activation (Ea), entropy (S(*)), pre-exponential factor (A), enthalpy (H(*)) and Gibbs free energy (G(*)) have been calculated using Freeman-Carroll method. Ferric-reducing antioxidant power (FRAP) of all complexes were measured. All the compounds were screened for their antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Streptococcus pyogenes and Bacillus subtilis, while antifungal activity against Candida albicans and Aspergillus niger have been carried out. Also compounds against Mycobacterium tuberculosis shows clear enhancement in the anti-tubercular activity upon copper complexation.

Oxorhenium complexes bearing the water-soluble tris(pyrazol-1-yl)methanesulfonate, 1,3,5-triaza-7-phosphaadamantane, or related ligands, as catalysts for Baeyer-Villiger oxidation of ketones

New rhenium(VII or III) complexes [ReO3(PTA)2][ReO4] (1) (PTA = 1,3,5-triaza-7-phosphaadamantane), [ReO3(mPTA)][ReO4]I (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation), [ReO3(HMT)2][ReO4] (3) (HMT = hexamethylenetetramine), [ReO3(η(2)-Tpm)(PTA)][ReO4] (4) [Tpm = hydrotris(pyrazol-1-yl)methane, HC(pz)3, pz = pyrazolyl], [ReO3(Hpz)(HMT)][ReO4] (5) (Hpz = pyrazole), [ReO(Tpms)(HMT)] (6) [Tpms = tris(pyrazol-1-yl)methanesulfonate, O3SC(pz)3(-)] and [ReCl2{N2C(O)Ph}(PTA)3] (7) have been prepared from the Re(VII) oxide Re2O7 (1-6) or, in the case of 7, by ligand exchange from the benzoyldiazenido complex [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2], and characterized by IR and NMR spectroscopies, elemental analysis and electrochemical properties. Theoretical calculations at the density functional theory (DFT) level of theory indicated that the coordination of PTA to both Re(III) and Re(VII) centers by the P atom is preferable compared to the coordination by the N atom. This is interpreted in terms of the Re-PTA bond energy and hard-soft acid-base theory. The oxo-rhenium complexes 1-6 act as selective catalysts for the Baeyer-Villiger oxidation of cyclic and linear ketones (e.g., 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone, and 3,3-dimethyl-2-butanone or pinacolone) to the corresponding lactones or esters, in the presence of aqueous H2O2. The effects of a variety of factors are studied toward the optimization of the process.

Synthesis and application of a novel cysteine-based DTPA-NCS for targeted radioimmunotherapy

INTRODUCTION

For the development of safe and effective protein-based radiolabeled complexes such as radioimmunotherapy (RIT), the selection of the radionuclides and the chelating agents used for the radiolabeling of tumor-targeting molecules is a critical factor. We aim to synthesize a novel bifunctional chelating agent containing the isothiocyanate group for easy conjugation with antibodies having the characteristics of high stable chelation with therapeutic radionuclides.

METHODS

We have synthesized the DTPA analogue retaining L-cysteine as a core ligand of the thiol group. The chelating power of cysteine-based DTPA-NCS (cys-DTPA-NCS) was compared with that of commercial ρ-SCN-Bn-DTPA. In an application, the cetuximab was radioimmunoconjugated with (177)Lu using cys-DTPA-NCS. The affinity was tested in a cell line overexpressing EGFR. A therapy study was conducted in nude mice with subcutaneous HT-29 xenografts.

RESULTS

The cys-DTPA-NCS presents an excellent ability to chelate as compared to the ρ-SCN-Bn-DTPA. For mean ratio chemical labeling yields of 95%, the result was 0.97. (177)Lu-cys-DTPA-NCS-cetuximab was prepared under ambient condition with a high radiolabeling yield and the radiochemical purity was sustained for at least 6days. The IC50 value of the (177)Lu-labeled cetuximab was 10nM (95% confidence). The stability and therapeutic efficacy of the candidate radiopharmaceutical were verified.

CONCLUSION

The new DTPA derivative, cys-DTPA-NCS, is a good bifunctional chelating agent that can be used for protein-based radiopharmaceutical using lanthanides such as (177)Lu and (90)Y. The prepared (177)Lu-cys-DTPA-NCS-cetuximab can be used for the diagnosis and treatment of human colorectal tumor.

(68)Ga-labeled bombesin analogs for receptor-mediated imaging

Targeted receptor-mediated imaging techniques have become crucial tools in present targeted diagnosis and radiotherapy as they provide accurate and specific diagnosis of disease information. Peptide-based pharmaceuticals are gaining popularity, and there has been vast interest in developing (68)Ga-labeled bombesin (Bn) analogs. The gastrin-releasing peptide (GRP) family and its Bn analog have been implicated in the biology of several human cancers. The three bombesin receptors GRP, NMB, and BRS-3 receptor are most frequently ectopically expressed by common, important malignancies. The low expression of Bn/GRP receptors in normal tissue and relatively high expression in a variety of human tumors can be of biological importance and form a molecular basis for Bn/GRP receptor-mediated imaging. To develop a Bn-like peptide with favorable tumor targeting and pharmacokinetic characteristics for possible clinical use, several modifications in the Bn-like peptides, such as the use of a variety of chelating agents, i.e., acyclic and macrocyclic agents with different spacer groups and with different metal ions (gallium), have been performed in recent years without significant disturbance of the vital binding scaffold. The favorable physical properties of (68)Ga, i.e., short half-life, and the fast localization of small peptides make this an ideal combination to study receptor-mediated imaging in patients.

Thermal Degradation Behaviour of Ni(II) Complex of 3,4-Methylenedioxaphenylaminoglyoxime

Thermal degradation behaviour of the Ni(II) complex of 3,4-methylenedioxaphenylaminoglyoxime was investigated by TG, DTA, and DTG at a heating rate of 10°C min−1under dinitrogen. The acquired experimental data shows that the complex is thermally stable up to 541 K. The pyrolytic decomposition process occurs by melting metal complex and metal oxide remains as final product. The energies of the reactions involved and the mechanism of decomposition at each stage have been examined. The values of kinetic parameters such as activation energy (E), preexponential factor (A) and thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) are also evaluated.

Dosimetric aspects of 166Ho brachytherapy biodegradable glass seed

The purpose of this study is to perform absorbed dose calculations based on Monte Carlo simulations for a novel beta emitter bioglass Ho-166 seed which is proposed for treating small hepatocellular carcinomas (HCCs). The bioactive glass seed has been developed by use of the sol-gel method. Monte Carlo simulations were carried out for the seed using the version 5 of the (MCNP) Monte Carlo radiation transport code to investigate the dosimetric parameters recommended by the AAPM Task Group 60 (TG-60). Dose distributions due to the beta and photon radiation were obtained at different radial distances surrounding the source. The dose rate in water at the reference point was calculated to be 6.71 ± 0.4 cGy h(-1) μCi(-1). The anisotropy function values ranging from 0.745 to 1.928 were obtained for radial distances of 0.3-8 mm and polar angles of 0°-90°. The (166)Ho seed source can deliver high radiation doses to the tumor, while the short range of the beta particles limits damage to the adjacent normal tissue.

Inorganic chemistry in nuclear imaging and radiotherapy: current and future directions

Radiometals play an important role in diagnostic and therapeutic radiopharmaceuticals. This field of radiochemistry is multidisciplinary, involving radiometal production, separation of the radiometal from its target, chelate design for complexing the radiometal in a biologically stable environment, specific targeting of the radiometal to its in vivo site, and nuclear imaging and/or radiotherapy applications of the resultant radiopharmaceutical. The critical importance of inorganic chemistry in the design and application of radiometal-containing imaging and therapy agents is described from a historical perspective to future directions.

Lower ligand denticity leading to improved thermodynamic and kinetic stability of the Gd3+ complex: the strange case of OBETA

OBETA, OBETA, you bet: Thermodynamic and kinetic measurements show an apparent paradox. The stability of complexes of lanthanide trivalent ions is higher with the heptadentate ligand OBETA (ethylene glycol-bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid) than with its octadentate homologue EGTA (2,2'-oxybis(ethylamine)-N,N,N',N'-tetraacetic acid). The unusual properties of Gd(OBETA)(-) (see structure), combined with the presence of two fast exchanging coordinated water molecules, candidates this complex as an MRI contrast agent.

New separation method of no-carrier-added 47Sc from titanium targets

Radionuclides with medium energy beta emission and a several day half-life are attractive candidates for radioimmunotherapy. Among the most promising in this category is 47Sc produced by fast neutron irradiation (E n>1 MeV) of titanium target with high energy neutrons in 47Ti(n,p) 47Sc nuclear reaction. In the previously reported production scheme the dissolution of the TiO2 target in hot concentrated H2SO4 and evaporation of the resulting solution were the most time-consuming steps. The present paper describes new, simple and efficient production method of 47Sc, where the slow dissolution of the target is avoided. After irradiation in fast neutron flux 47TiO2 and Li2 47TiF6 targets were dissolved in HF solutions. Next 47Sc was separated from the target using anion exchange resin Dowex 1 with 0.4 M HF + 0.06 M HNO3 solution as eluent. The eluted 47Sc was adsorbed on cation exchange resin and eluted with 0.5 M of ammonium acetate. The 47Sc separation yield in the proposed procedure is about 90% with the separation time less than 2 h. The obtained no-carrier-added 47Sc was used to label DOTATATE conjugate with 96% labeling yield.

An electro-amalgamation approach to produce 175Yb suitable for radiopharmaceutical applications

175Yb is a prospective reactor produced radionuclide suitable for preparation of therapeutic radiopharmaceuticals. However, a major restraint in the use of 175Yb produced via the (n, γ) reaction, for therapeutic applications, is the presence of longer-lived 177Lu impurity which is co-produced along with 175Yb on irradiation of natural Yb2O3 target. A radiochemical separation procedure adopting electro-amalgamation approach for the removal of 177Lu impurity from 175Yb has been critically evaluated. The experimental parameters such as applied potential, electrolysis time and the pH of the electrolyte, affecting the electrochemical separation process, were studied and optimized. The developed radiochemical procedure was extensively tested for purification of up to 15 GBq of 175Yb. The purified 175Yb could be obtained in HCl medium with ∼95% yield. The 177Lu impurity could not be detected in the purified product and 175Yb was found suitable for the preparation of potential radiotherapeutic agents.

Preparation of patient doses of (177)Lu-DOTA-TATE using indigenously produced (177)Lu: the Indian experience

PURPOSE

(177)Lu (T(1/2) = 6.73 days, E(β(max)) = 0.497 MeV, E(γ) = 113 KeV [6.4%] and 208 KeV [11%])-labeled DOTA-TATE, a somatostatin analog, is presently being considered a promising agent for the treatment of patients suffering from inoperable neuroendocrine tumors, which overexpress somatostatin receptors. The objective of the present work was to develop an optimized protocol for the preparation of therapeutic dose of (177)Lu-DOTA-TATE with as high as achievable specific activity at the time of its administration, taking into account the variable specific activity of (177)Lu available during the preparation of the agent.

METHODS

(177)Lu labeling of DOTA-TATE was carried out using a precalculated amount of DOTA-TATE based on the available specific activity of (177)Lu at the time of preparation, keeping a minimum molar ratio of [DOTA-TATE]:[Lu] = 4:1, so that (177)Lu-DOTA-TATE could be obtained with highest possible specific activity without compromising its radiochemical purity and stability.

RESULTS

One hundred (100) batches of (177)Lu-DOTA-TATE were prepared following this protocol till date at five different nuclear medicine centers of India, with a radiochemical purity of 98.25% ± 1.1% and specific activity of 32.74-65.49 GBq/μmol (885-1770 mCi/μmol). Till date, 250 patient doses of (177)Lu-DOTA-TATE have been dispensed and administered in 150 patients suffering from various types of neuroendocrine-originated tumors.

CONCLUSIONS

The developed method ensures that patient doses of (177)Lu-DOTA-TATE could be prepared with highest possible specific activity depending upon the available specific activity of (177)Lu at the hospital radio-pharmacy.