[125I/127I/131I]Iodorhodamine: synthesis, cellular localization, and biodistribution in athymic mice bearing human tumor xenografts and comparison with [99mTc]hexakis(2-methoxyisobutylisonitrile)

Molecular phosphorescence enhancement by the plasmon field of metal nanoparticles

A theoretical model is proposed that allows the estimation of the quantum yield of phosphorescence of dye molecules in the vicinity of plasmonic nanoparticles. For this purpose, the rate constants of the radiative and nonradiative intramolecular transitions for rhodamine 123 (Rh123) and brominated rhodamine (Rh123-2Br) dyes have been calculated. The plasmon effect of Ag nanoparticles on various types of luminescence processes has been studied both theoretically and experimentally. We show that in the presence of a plasmonic nanoparticle, the efficiency of the immediate and delayed fluorescence increases significantly. The phosphorescence rate of the rhodamine dyes also increases near plasmonic nanoparticles. The long-lived luminescence i.e., delayed fluorescence and phosphorescence is more enhanced for Rh123-2Br than for Rh123. The largest phosphorescence quantum yield is obtained when the dye molecule is at a distance of 4-6 nm from the nanoparticle surface. Our results can be used in the design of plasmon-enhancing nanostructures for light-emitting media, organic light-emitting diodes, photovoltaic devices, and catalysts for activation of molecular oxygen.

Radiobromine and radioiodine for medical applications

The halogens bromine and iodine have similar chemical properties and undergo similar reactions due to their closeness in Group 17 of the periodic chart. There are a number of bromine and iodine radionuclides that have properties useful for diagnosis and therapy of human diseases. The emission properties of radiobromine and radioiodine nuclides with half-lives longer than 1 h are summarized along with properties that make radionuclides useful in PET/SPECT imaging and β/Auger therapy, such that the reader can assess which of the radionuclides might be useful for medical applications. An overview of chemical approaches that have been used to radiolabel molecules with radiobromine and radioiodine nuclides is provided with examples. Further, references to a large variety of different organ/cancer-targeting agents utilizing the radiolabeling approaches described are provided.

Electrophilic reactivity of tetrabromorhodamine 123 is bromine induced: convergent interpretation through complementary molecular descriptors

Nucleophilic addition of water and of methanol to 3,6-diamino-2,4,5,7-tetrabromo-9-[2-(methoxycarbonyl) phenyl]-9H-xanthen-9-ylium, 4BrR123, yields respectively 2-(3,6-diamino-2,4,5,7-tetrabromo-9-hydroxy-9H-xanthen-9-yl)xanthyl benzoate, HO4BrR123 and 2-(3,6-diamino-2,4,5,7-tetrabromo-9-methoxy-9H-xanthen-9-yl)xanthyl benzoate, MeO4BrR123. The novel experimental results are addressed theoretically. The linear free energy relationship, LFER, second-order perturbation theory analysis of the natural bond orbital, NBO, and quantum theory of atoms in molecules, QTAIM, lead to the same conclusion: the electron-withdrawing effect of bonded Br atoms in 4BrR123 extremely enhances the molecular electrophilicity, as compared to 3,6-diamino-9-[2-(methoxycarbonyl) phenyl]-9H-xanthen-9-ylium, R123. The reactivity of these diaminoxanthylium cations is discussed in the context of local and global softness in extended conjugated systems.

Biodistribution and stability studies of [18F]fluoroethylrhodamine B, a potential PET myocardial perfusion agent

INTRODUCTION

Fluorine-18-labeled rhodamine B was developed as a potential positron emission tomography (PET) tracer for the evaluation of myocardial perfusion, but preliminary studies in mice showed no accumulation in the heart suggesting that it was rapidly hydrolyzed in vivo in mice. A study was therefore undertaken to further evaluate this hypothesis.

METHODS

[(18)F]Fluoroethylrhodamine B was equilibrated for 2 h at 37 degrees C in human, rat and mouse serum and in phosphate-buffered saline. Samples were removed periodically and assayed by high-performance liquid chromatography. Based on the results of the stability study, microPET imaging and a biodistribution study were carried out in rats.

RESULTS

In vitro stability studies demonstrated that [(18)F]fluoroethylrhodamine B much more stable in rat and human sera than in mouse serum. After 2 h, the compound was >80% intact in rat serum but <30% intact in mouse serum. The microPET imaging and biodistribution studies in rats confirmed this result showing high and persistent tracer accumulation in the myocardium compared with the absence of uptake by the myocardium in mice thereby validating our original hypothesis that (18)F-labeled rhodamines should accumulate in the heart.

CONCLUSIONS

[(18)F]Fluoroethylrhodamine B is more stable in rat and human sera than it is in mouse serum. This improved stability is demonstrated by the high uptake of the tracer in the rat heart in comparison to the absence of visible uptake in the mouse heart. These observations suggest that (18)F-labeled rhodamines are promising candidates for more extensive evaluation as PET tracers for the evaluation of myocardial perfusion.

Synthesis of fluorine-18 labeled rhodamine B: A potential PET myocardial perfusion imaging agent

There is considerable interest in developing an (18)F-labeled PET myocardial perfusion agent. Rhodamine dyes share several properties with (99m)Tc-MIBI, the most commonly used single-photon myocardial perfusion agent, suggesting that an (18)F-labeled rhodamine dye might prove useful for this application. In addition to being lipophilic cations, like (99m)Tc-MIBI, rhodamine dyes are known to accumulate in the myocardium and are substrates for Pgp, the protein implicated in MDR1 multidrug resistance. As the first step in determining whether (18)F-labeled rhodamines might be useful as myocardial perfusion agents for PET, our objective was to develop synthetic methods for preparing the (18)F-labeled compounds so that they could be evaluated in vivo. Rhodamine B was chosen as the prototype compound for development of the synthesis because the ethyl substituents on the amine moieties of rhodamine B protect them from side reactions, thus eliminating the need to include (and subsequently remove) protecting groups. The 2'-[(18)F]fluoroethyl ester of rhodamine B was synthesized by heating rhodamine B lactone with [(18)F]fluoroethyltosylate in acetonitrile at 165 degrees C for 30min using [(18)F]fluoroethyl tosylate, which was prepared by the reaction of ethyleneglycol ditosylate with Kryptofix 2.2.2, K(2)CO(3), and [(18)F]NaF in acetonitrile for 10min at 90 degrees C. The product was purified by semi-preparative HPLC to produce the 2'-[(18)F]fluoroethylester in >97% radiochemical purity with a specific activity of 1.3GBq/mumol, an isolated decay corrected yield of 35%, and a total synthesis time of 90min.

Nanoparticles as drug delivery agents specific for CNS: in vivo biodistribution

The pharmacological treatment of neurological disorders is often complicated by the inability of drugs to pass the blood-brain barrier. Recently we discovered that polymeric nanoparticles (NPs) made of poly(D,L-lactide-co-glycolide), surface-decorated with the peptide Gly-L-Phe-D-Thr-Gly-L-Phe-L-Leu-L-Ser(O-beta-D-glucose)-CONH2 are able to deliver, after intravenous administration, the model drug loperamide into the central nervous system (CNS). This new drug delivery agent is able to ensure a strong and long-lasting pharmacological effect, far greater than that previously observed with other nanoparticulate carriers. Here we confirmed the effectiveness of this carrier for brain targeting, comparing the effect obtained by the administration of loperamide-loaded NPs with the effect of an intracerebroventricular administration of the drug; moreover, the biodistribution of these NPs showed a localization into the CNS in a quantity about two orders of magnitude greater than that found with the other known NP drug carriers. Thus, a new kind of NPs that target the CNS with very high specificity was discovered.

FROM THE CLINICAL EDITOR

This paper discusses a nanoparticle-based technique of targeted drug delivery through the blood-brain barrier. The biodistribution of these novel nanoparticles showed two orders of magnitude greater efficiency compared to other known NP drug carriers.

DMSO increases radioiodination yield of radiopharmaceuticals

A high-yield radioiodination method for various types of molecules is described. The approach employs DMSO as precursor solvent, a reaction ratio of 2-5 precursor molecules per iodine atom, 5-10 microg oxidant, and a 10-25 microl reaction volume. The solution is vortexed at room temperature for 1-5 min and progress of the reaction is assessed by HPLC. Radioiodinated products are obtained in > or = 95% yield and meet the requirements for radiotracer imaging, biodistribution studies, and molecular and cellular biology research.

Photophysical, Photochemical, and Tumor-selectivity Properties of Bromine Derivatives of Rhodamine-123

The conceptual basis for the development of mitochondrial targeting as a novel therapeutic strategy for both chemotherapy and photochemotherapy of neoplastic diseases rests on the observation that enhanced mitochondrial membrane potential is a common tumor cell phenotype. The potential of this strategy is highlighted by the fact that the toxic effects associated with a number of cationic dyes known to localize in energized cell mitochondria are much more pronounced in tumor cells than in normal cells. Here we evaluate the phototoxic properties of four bromine derivatives of rhodamine-123 toward human uterine sarcoma (MES-SA) and green monkey kidney (CV-1) cells and compare the degrees of tumor cell selectivity associated with these dyes with those associated with two model mitochondrial triarylmethanes (crystal violet and ethyl violet). Selective phototoxicity toward tumor cells was found to be highly dependent upon the lipophilic/hydrophilic character of the cationic photosensitizer. Our experimental data have indicated that the probability of success of mitochondrial targeting in (photo)chemotherapy of neoplastic diseases is higher when the octan-1-ol/water partition coefficient of the drug candidate falls within approximately two orders of magnitude from that of the prototypical mitochondria-specific dye rhodamine-123.

Radiosynthesis and in vitro stability evaluation of various radioiodine-labelled beta-iodoalkylether prosthetic groups linked to model compounds

A systematic comparative investigation into the in vitro radiochemical stabilities of model compounds containing radioiodinated beta-iodoethoxyl units and derivatives thereof, as well as those of similar compounds lacking a beta-oxygen to serve as control references, was undertaken. The radioiodinations were carried out in fair to modest yields by means of substitution of a tosyl group by iodide. Stability evaluations were carried out by incubating the labeled compounds in human blood serum at 37 degrees C and measuring free radioiodide by means of radio-HPLC and radio-TLC. The compounds containing beta-iodoethoxyl units displayed much superior stabilities than those without, while the presence of small alkyl or aryl groups in such a unit rendered an additional degree of stability to the carbon-iodine bond, especially over a long period.

Selenoxanthones via directed metalations in 2-arylselenobenzamide derivatives

The reaction of N, N-diethyl 4-(N', N'-dimethylamino)-2-phenylselenobenzamide (7a), N, N-diethyl 4-methoxy-2-phenylselenobenzamide (7b), N, N-diethyl 4-(N', N'-dimethylamino)-2-[(3-(N, N-dimethylamino)phenylseleno]benzamide (7c), and N, N-diethyl 4-methoxy-2-(3-methoxyphenylseleno)-benzamide (7d) with excess lithium diisopropylamide (LDA) gave 2-N, N-(dimethylamino)-9H-selenoxanthone (9a), 2-methoxy-9H-selenoxanthone (9b), 2,7-bis-N, N-(dimethylamino)-9H-selenoxanthone (9c), and 2,5-dimethoxy-9H-selenoxanthone (9d) in 70%, 59%, 23%, and 90% isolated yields, respectively. N, N-Diethyl 2-phenylselenobenzamide (2-Se) gave no reaction with LDA, t-BuLi, MeLi, or lithium 2,2,6,6-tetramethylpiperidide as base. Electron donation from the 4-substituent of benzamide derivatives 7a-7d may increase the directing ability of the carbonyl oxygen to metalate the 2-position of the arylseleno group.

Functional Near-Infrared Fluorescence Imaging for Cardiac Surgery and Targeted Gene Therapy

Cardiac revascularization is presently performed without realtime visual assessment of myocardial blood flow or perfusion. Moreover, gene therapy of the heart cannot, at present, be directed to specific territories at risk for myocardial infarction. We have developed a surgical imaging system that exploits the low autofluorescence, deep tissue penetration, low tissue scatter, and invisibility of near-infrared (NIR) fluorescent light. By completely isolating visible and NIR light paths, one is able to visualize, simultaneously, the anatomy and/or function of the heart, or any desired tissue. In rat model systems, we demonstrate that the heptamethine indocyanine-type NIR fluorophores IR-786 and the carboxylic acid form of IRDye78 can be injected intravenously in the living animal to provide real-time visual assessment of myocardial blood flow or perfusion intraoperatively. This imaging system may prove useful for the refinement of revascularization techniques, and for the administration of cardiac gene therapy.

2,4,6-triarylchalcogenopyrylium dyes related in structure to the antitumor agent AA1 as in vitro sensitizers for the photodynamic therapy of cancer

Cationic chalcogenopyrylium dyes 2-4 were synthesized in six steps from 4-(dimethylamino)phenylethyne (7), have absorption maxima in methanol of 594, 631, and 672 nm, respectively, and generate singlet oxygen with quantum yields [Phi((1)O(2))] of 0.020, 0.064, and 0.037, respectively. Dyes 2-4 are hydrolytically more stable than other chalcogenopyrylium dyes evaluated previously as sensitizers for photodynamic therapy. At 10 microM final concentration, all dyes 2-4 inhibited cytochrome c oxidase during irradiation of tumor mitochondrial suspensions treated with 10 microM dye. The degree of enzyme inhibition was abated in a reduced oxygen environment and in the presence of imidazole, a singlet oxygen trap. Superoxide dismutase, at a final concentration of 30 U, did not alter the photosensitized inhibition of mitochondrial cytochrome c oxidase by dyes 2-4. These data suggest that singlet oxygen may play a major role in the photosensitized inhibition of mitochondrial cytochrome c oxidase. Irradiation of R3230AC rat mammary adenocarcinoma cells in the presence of dyes 2-4 caused a significant loss in cell viability with thiopyrylium dye 2 displaying the greatest phototoxicity. Initial acute toxicity studies in vivo demonstrate that, at 10 mg/kg, none of the three dyes displayed overt toxicity.

Synthesis of 4'-epi-iodo-4'-deoxy-daunorubicin, a potential cancer radiotherapeutic agent

We have prepared 4'-epi-iodo-4'-deoxy-daunorubicin (IDDNR)(1), a doxorubicin analog, via a 5-step synthesis involving a protected daunorubicin triflate derivative (4). This triflate derivative will allow the facile and regiospecific nucleophilic preparation of I-125 or Br-80 m labelled analogs of IDDNR. Auger electron-emitting I-125- or Br-80 m-labelled analogs of IDDNR may have potential as cancer radiotherapeutic agents.