Potential Radiopharmaceuticals Research Articles

In vitro and in vivo evaluation of selected 68Ga-siderophores for infection imaging

IntroductionSiderophores are low-molecular-mass iron chelators serving as iron transporters for almost all bacteria, fungi and some plants. Iron is an essential element for majority of organisms and plays an important role in virulence of pathogenic organisms. 68Ga is a positron emitter with complexing properties comparable to those of Fe(III) and readily available from a generator. Initial studies with 68Ga-triacetylfusarinine C (TAFC) showed excellent targeting properties in a rat infection model. We report here on the in vitro and in vivo evaluation of other siderophores radiolabelled with 68Ga as potential radiopharmaceuticals for infection imaging.Methods68Ga labelling was performed using acetate buffer. Stability, log P and protein binding values were determined. In vitro uptake was tested using iron-deficient and iron-sufficient Aspergillus fumigatus (A.f.) cultures. Biodistribution of 68Ga-siderophores was studied in Balb/c mice.ResultsSignificant differences among studied siderophores were observed in labelling efficiency, stability and protein binding. Uptake in A.f. cultures was highly dependent on iron load and type of the siderophore. In mice, 68Ga-TAFC and 68Ga-ferrioxamine E (FOXE) showed rapid renal excretion and low blood values even at a short period after injection; in contrast, 68Ga-ferricrocin and 68Ga-ferrichrome revealed high retention in blood and 68Ga-fusarinine C showed very high kidney retention.ConclusionsSome of the studied siderophores bind 68Ga with high affinity and stability, especially 68Ga-TAFC and 68Ga-FOXE. Low values of protein binding, high and specific uptake in A.f., and excellent in vivo biodistribution make them favourable agents for Aspergillus infection imaging.

Novel radioiodinated sibutramine and fluoxetine as models for brain imaging

Brain imaging is a process which allows scientists and physicians to view and monitor the areas of the brain which allow diagnosis and following up different abnormalities in the brain. The aim of this study was to develop potential radiopharmaceuticals for the non-invasive brain imaging. Sibutramine and fluoxetine (two drugs that have the ability to cross blood–brain barrier) were successfully labeled with 125I via direct electrophilic substitution reaction at ambient temperature. The reaction parameters studied were substrate concentration, oxidizing agent concentration, pH of the reaction mixture, reaction temperature, reaction time and in vitro stability of the iodocompounds. The iodocompounds gave maximum labeling yield of 92 ± 2.77 and 93 ± 2.1%, respectively, and maintained stability throughout working period (24 h). Biodistribution studies showed that maximum in vivo uptake of the iodocompounds in the brain was 5.7 ± 0.19 and 6.14 ± 0.26% injected activity/g tissue organ, respectively, at 15 and 5 min post-injection, whereas the clearance from the mice appeared to proceed via the hepatobiliary pathway. Brain uptake of 125I-sibutramine and 125I-fluoxetine is higher than that of 99mTc-ECD and 99mTc-HMPAO (currently used radiopharmaceuticals for brain imaging) and so radioiodinated sibutramine and fluoxetine could be used instead of 99mTc-ECD and 99mTc-HMPAO for brain SPECT.

PEGylation of 99mTc-labeled bombesin analogues improves their pharmacokinetic properties

Radiolabeled bombesin (BN) conjugates are promising radiotracers for imaging and therapy of breast and prostate tumors in which BN(2)/gastrin-releasing peptide (GRP) receptors are overexpressed. However, the low in vivo stability of BN conjugates may limit their clinical application. In an attempt to improve their pharmacokinetics and counteract their rapid enzymatic degradation, we prepared a series of polyethylene glycol (PEG)-ylated BN(7-14) analogues for radiolabeling with (99m)Tc(CO)(3) and evaluated them in vitro and in vivo. Derivatization of a stabilized (N(α)His)Ac-BN(7-14)[Cha(13),Nle(14)] analogue with linear PEG molecules of various sizes [5 kDa (PEG(5)), 10 kDa (PEG(10)) and 20 kDa (PEG(20))] was performed by PEGylation of the ɛ-amino group of a β(3)hLys-βAla-βAla spacer between the stabilized BN sequence and the (N(α)His)Ac chelator. The analogues were then radiolabeled by employing the (99m)Tc-tricarbonyl technique. Binding affinity and internalization/externalization studies were performed in vitro in human prostate carcinoma PC-3 cells. Stability was investigated in vitro in human plasma and in vivo in Balb/c mice. Finally, single photon emission computed tomography (SPECT)/X-ray computed tomography studies were performed in nude mice bearing PC-3 tumor xenografts. PEGylation did not affect the binding affinity of BN analogues, as the binding affinity for BN(2)/GRP receptors remained high (K(d)<0.9 nM). However, in vitro binding kinetics of the PEGylated analogues were slower. Steady-state condition was reached after 4 h, and the total cell binding was 10 times lower than that for the non-PEGylated counterpart. Besides, PEGylation improved the stability of BN conjugates in vitro and in vivo. The BN derivative conjugated with a PEG(5) molecule showed the best pharmacokinetics in vivo, i.e., faster blood clearance and preferential renal excretion. The tumor uptake of the (99m)Tc-PEG(5)-Lys-BN conjugate was slightly higher compared to that of the non-PEGylated analogue (3.91%±0.44% vs. 2.80%±0.28% injected dose per gram 1 h postinjection, p.i.). Tumor retention was also increased, resulting in a threefold higher amount of radioactivity in the tumor at 24 h p.i. Furthermore, decreased hepatobiliary excretion and increased tumor-to-nontarget ratios (tumor-to-blood: 17.1 vs. 2.1; tumor-to-kidney: 1.1 vs. 0.4; tumor-to-liver: 5.8 vs. 1.0, 24 h p.i.) were observed and further confirmed via small-animal SPECT images 1 h p.i. PEGylation proved to be an effective strategy to enhance the tumor-targeting potential of (99m)Tc-labeled BN-based radiopharmaceuticals and probably other radiolabeled peptides.

Recoil and conversion electron considerations of the 166Dy/166Ho in vivo generator

Abstract The use of radionuclides as potential therapeutic radiopharmaceuticals is increasingly investigated. An important aspect is the delivery of the radionuclide to the target, i.e. the radionuclide is not lost from the chelating agent. For in vivo generators, it is not only the log K of complexation between the metal ion and the chelator that is important, but also whether the daughter radionuclide stays inside the chelator after decay of the parent radionuclide. In our previous work, we showed that the classical recoil effect is only applicable for decays with a Q value higher than 0.6 MeV (in the atomic mass range around 100). However, Zhernosekov et al. [1] published a result for140Nd/140Pr (Q = 0.222 MeV) which indicated that &gt;95% of the daughter (140Pr) was lost by a DOTA chelator upon decay of140Nd. The authors ascribed this to the &amp; ldquo;post-effect”. Their experiment was repeated with the166Dy/166Ho generator to ascertain whether our calculations were correct. It was found that 72% of the daughter (166Ho) was liberated from the DOTA chelator, indicating that the “post effect” does exist in contrast to our recoil calculations. Upon further investigation, we determined that one should not only consider recoil energy levels but also the mode of decay which was able to explain the partial recoil found for166Dy/166Ho. It is concluded for the166Dy/166Ho system that the low recoil energy of the daughter nucleus166Ho is not a sufficient reason to rule out release of the nuclide from chelators. On the other hand, we found that the ratio of the166Ho that gets released corresponds to the ratio of relaxation of Ho atoms via the Auger process.

Synthesis and characterization of well-defined lactic acid-PEG cooligomers and its tricarbonyl rhenium conjugates

This article describes the synthesis and characterization of hydroxyl tailored, molecularly defined biodegradable cooligomers capable of chelating rhenium for potential radiopharmaceuticals. New insights were gained during the synthesis of lactide based on dimethylaminopyridine-catalyzed transesterification. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Utility of γH2AX as a Molecular Marker of DNA Double-Strand Breaks in Nuclear Medicine: Applications to Radionuclide Therapy Employing Auger Electron-Emitting Isotopes

There is an intense interest in the development of radiopharmaceuticals for cancer therapy. In particular, radiopharmaceuticals which involve targeting radionuclides specifically to cancer cells with the use of monoclonal antibodies (radioimmunotherapy) or peptides (targeted radiotherapy) are being widely investigated. For example, the ultra-short range Auger electron-emitting isotopes, which are discussed in this review, are being considered in the context of DNAtargeted radiotherapy. The efficient quantitative evaluation of the levels of damage caused by such potential radiopharmaceuticals is required for assessment of therapeutic efficacy and determination of relevant doses for successful treatment. The DNA double-strand break surrogate marker, γH2AX, has emerged as a useful biomonitor of damage and thus effectiveness of treatment, offering a highly specific and sensitive means of assessment. This review will cover the potential applications of γH2AX in nuclear medicine, in particular radionuclide therapy.

Triaryl (Z)-olefins suitable for radiolabeling with iodine-124 or fluorine-18 radionuclides for positron emission tomography imaging of estrogen positive breast tumors

A group of (Z)-1,2-diphenyl-1-[4-[2-(4-methylpiperazin-1-yl)ethoxy]phenyl]but-1-enes were synthesized using methodologies that will allow incorporation of a [(124)I]iodine substituent at the para-position of either the C-1 phenyl ring or the C-2 phenyl ring, or a [(18)F]OCH(2)CH(2)F substituent at the para-position of the C-2 phenyl ring. These [(124)I] and [(18)F] radiotracers are designed as potential radiopharmaceuticals to image estrogen positive breast tumors using positron emission tomography (PET).

Triaryl ( Z)-olefins suitable for radiolabeling with carbon-11 or fluorine-18 radionuclides for positron emission tomography imaging of cyclooxygenase-2 expression in pathological disease

A group of ( Z)-1,1-diphenyl-2-(4-methylsulfonylphenyl)alk-1-enes were synthesized using methodologies that will allow incorporation of a [ 11C]OCH 3 substituent at the para-position of the C-1 phenyl ring, a [ 11C]SO 2CH 3 substituent at the para-position of the C-2 phenyl ring, a [ 18F]OCH 2CH 2F substituent at the para-position of the C-1 phenyl ring, and a [ 18F]CH 2CH 2F substituent at the C-2 position of the olefinic bond. The [ 11C] and [ 18F] radiotracers are designed as potential radiopharmaceuticals to image cyclooxygenase-2 (COX-2) expression in any organ where COX-2 is upregulated. The COX-1/COX-2 inhibition data acquired suggest that compounds having a [ 11C]OMe or [ 18F]OCH 2CH 2F substituent at the para-position of the C-1 phenyl ring may be more suitable for imaging COX-2 expression in view of their ability to exclusively inhibit the COX-2 isozyme.

Preparation and characterization of new Sm(III) complexes with some bidentate ligands contains (N,N), (S,N), (O,O) and (N,O) donor atoms

New Sm(III) complexes with heterocyclic bidentate ligands namely imidazole, oxothioazolidine-4-carboxylic acid, N,N-ethylene thiourea, l-cystien, thiobarbituric acid, and thenoyltrifluroacetone have been synthesized. The new complexes have been subjected to characterization using combination of different physico-chemical techniques including spectroscopic (IR, NMR, Ms, UV–Vis), thermogravimetric methods. Electrophoresis and micro-analytical techniques have also used. The charge densities on the ligand atoms were calculated via DFT calculations. The complexes were synthesized by direct reaction between SmCl3 and bidentate ligands contains (N,N), (S,N), (O,O) and (N,O) donor atoms. The investigated complexes were soluble in polar solvents, and could be use as potential radiopharmaceuticals complexes. The antibacterial activities of the investigated complexes have been tested and evaluated.

Tricarbonyltechnetium(I) and tricarbonylrhenium(I) complexed with N-methyl-2-pyridinecarboxyamide as potential radiopharmaceuticals: a computational study

The electronic and thermodynamic properties of the ‘2 + 1’ tricarbonyltechnetium(I) and -rhenium(I) mixed ligand complexes with N-methylpyridine-2-carboxyamide (MPCA) as a bidentate ligand and chloride, water, or tert-butyl-3-isocyanopropanoate (BCP), were investigated within the framework of Density Functional Theory. The atomic charges of all complexes, polarization of the CO groups, as well as the effect of transfer of π-electron density between the ligands through the metal were calculated and compared. The free energies of the reaction of formation of the isocyanide complexes in aqueous solution were calculated based on calculated total free energies in aqueous solution of the products and the substrates. The dissociation energies of the complexes were also determined in order to rationalize the experimentally observed higher resistance of the rhenium compared to the technetium complexes in the challenge experiments with the standard sulfur-containing amino acids.

Synthesis, Biodistribution, and Microsingle Photon Emission Computed Tomography (SPECT) Imaging Study of Technetium-99m Labeled PEGylated Dendrimer Poly(amidoamine) (PAMAM)−Folic Acid Conjugates

Three conjugates based on dendrimer PAMAM generation five were synthesized and radiolabeled successfully. To investigate their tumor targeting, the in vitro and in vivo stability, cell uptake, in vivo biodistribution, and micro-SPECT imaging were evaluated, respectively. The conjugate of (99m)Tc labeled PEGylated dendrimer PAMAM folic acid conjugate ((99m)Tc-G5-Ac-pegFA-DTPA) shows much higher uptake in KB cancer cells and accumulated more in the tumor area than that of the other two conjugates. The uptake in KB cells depends on the incubation time. The results of in vivo biodistribution agree with the data obtained from micro-SPECT imaging. These studies show that PEGylation of PAMAM dendrimer folic acid conjugate improves the tumor targeting. Folate-conjugated dendrimer maybe developed to be potential radiopharmaceuticals and targeted drug delivery systems.

Study of magnetic ferrite nanoparticles labeled with 99mTc-pertechnetate

This study examined the applications of novel non-polymer magnetic ferrite nanoparticles (Fe3O4 NPs) labeled with 99mTc-pertechnetate (99mTcO4 −). The radiochemistry, chemistry, and biodistribution of Fe3O4 NPs labeled with 9mTcO4 − were analyzed. This paper employed instant thin layer chromatography and magnetic adsorption to evaluate the labeling efficiency and stability of 99mTc-Fe3O4 at various reaction conditions. A scanning electron microscope, X-ray diffractometer, Fourier transform infrared spectrometer, laser particle size analyzer, and superconducting quantum interference device magnetometer were used to analyze the physical and chemical properties of the Fe3O4 and 99Tc-Fe3O4 nanoparticles. The biodistribution and excretion of 99mTc-Fe3O4 were also investigated. Radiochemical analyses showed that the labeling efficiency was over 92% after 1 min in the presence of a reducing agent. Hydroxyl and amine groups covered the surface of the Fe3O4 particles. Therefore, 99Tc (VII) reduced to lower oxidation states and might bind to Fe3O4 NPs. The sizes of the 99Tc-Fe3O4 NPs were about 600 nm without ultrasound vibrations, and the particle sizes were reduced to 250 nm under ultrasound vibration conditions. Nonetheless, Fe3O4 NPs and 99Tc-Fe3O4 NPs exhibited superparamagnetic properties, and the saturation magnetization values were about 55 and 47 emu/g, respectively. The biodistribution showed that a portion of the 99mTc-Fe3O4 nanoparticles might embolize in a pulmonary capillary initially; the embolism radioactivity was cleared from the lungs and was then taken up by the liver. 99mTc-Fe3O4 metabolized very slowly only 1–2% of the injected dose (ID) was excreted in urine and about 2.37% ID/g was retained in the liver 4 h after injection. Radiopharmaceutically, 99mTc-Fe3O4 NPs displayed long-term retention, and only 99mTc-Fe3O4 NPs that dissociated to free pertechnetate could be excreted in urine. This research evaluated the feasibility of non-polymer magnetic ferrite NPs labeled with technetium as potential radiopharmaceuticals in nuclear medicine.

Recoil effect on β-decaying in vivo generators, interpreted for 103Pd/ 103mRh

The use of Auger emitters as potential radiopharmaceuticals is being increasingly investigated. One of the radionuclides of interest is 103mRh, which can be produced from 103Ru or 103Pd in an in vivo generator. A potential problem, however, is the recoil of the 103mRh out of the carrier molecule and even out of the target cell. In order to determine the likelihood of this happening in the 103Pd/ 103mRh, case calculations were made to prove that this does not happen. The equations were generalised for all radionuclides with an atomic mass of 10–240 as a tool for determining the recoil threshold of any β-emitting radionuclide.

Synthesis and radiolabelling of Re(CO)3‐β‐elemene derivatives as potential therapeutic radiopharmaceuticals

Abstractβ‐Elemene, (1S, 2S, 4R)‐(−)‐(1‐methy‐1‐vinyl‐2,4‐diisopropenyl cyclohexane) is an anticancer agent from the Traditional Chinese Herb Medicinal. Three novel Re(CO)3‐β‐elemene derivatives including their radioactive conjugates containing N,N,N tridentate ligands and tricarbonyl rhenium (complex 12, 13, 14) were synthesized. Their structures were characterized by infrared (IR), 1H‐NMR and HRMS. Good radioactive yield (above 90%) and radioactive chemical purity with Re‐188 (above 95%) were obtained for all of the three derivatives (complex 15, 16, 17). The antiproliferative activity of non‐radioactive β‐elemene‐Re(CO)3 derivatives on Lewis lung cancer cells and HeLa cell lines were evaluated by WST‐1 methods. The result shows substantial decrease in IC50 values compared with the parent compound β‐elemene. The synthesis and radiosynthesis of β‐elemene tricarbonyl rhenium conjugates provide the possibility to find a new kind of potential radiopharmaceuticals on β‐elemene. Copyright © 2009 John Wiley &amp; Sons, Ltd.

18F-labelling of A-ring substituted 16α-fluoro-estradiols as potential radiopharmaceuticals for PET imaging

The 2-methoxy derivative of estradiol is currently in Phase II clinical trial as an anticancer agent while the 4-methyl derivative has been shown to interact with cytoplasmic and nuclear estrogen receptors in rat pituitary gland and hypothalamus. We hypothesize that the 16α- 18F-analogs of these estrogens could be suitable radiotracers to evaluate action mechanisms of the parent compounds. In this study we report the synthesis of the 16α- 18F and 16α- 19F-analogs of the A-ring substituted estradiols in high yield via stereoselective opening of the intermediate 16β,17β-O-cyclic sulfones with [ 18F]F − or F − followed by deprotection.

Complexation and biodistribution study of 111In and 90Y complexes of bifunctional phosphinic acid analogs of H 4dota

In this study, the complexation rates of two new phosphinate H 4dota (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) analogs, H 5do3ap PrA and H 4do3ap ABn, and H 4dota itself were compared under identical conditions (H 5do3ap PrA=10-{[(2-carboxyethyl)hydroxyphosphoryl]methyl}-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid; H 4do3ap ABn=10-{[(4-aminophenyl)hydroxyphosphoryl]methyl}-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). The biodistribution of their 111In and 90Y complexes in healthy rats was also studied. Unlike the observation obtained under “chemical” conditions where differences between the ligands were observed no such differences in complexation rates were found under radiochemical conditions. The ligands bind the radiometals similarly to H 4dota. So, “chemical” formation kinetic data should be transferred into radiochemical conditions only with high care and “radiochemical” complexation experiments should be run as part of standard in vitro studies with new ligands considered as potential radiopharmaceuticals. Pharmacokinetic studies in rats showed similar distribution characteristics for both phosphinate H 4dota analogs radiolabelled with 111In and 90Y when compared with that of the 111In–H 4dota complex. No specific uptake in any organ and tissue of rats was determined. The phosphinate complexes are not accumulated in calcified tissues.

Novel Chemically Modified Analogues of Neuropeptide Y for Tumor Targeting

The successful use of peptides as potential radiopharmaceuticals essentially requires the modification of the bioactive peptide hormones to introduce chelators for radiolabeling. In this study, four Y 1/Y 2 receptor-selective NPY analogues with different receptor subtype specificities have been investigated. For in vitro studies, the cold metal surrogate was used. Gallium and indium complexes were introduced by using 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid as bifunctional chelator. The peptides were synthesized by solid-phase peptide synthesis (SPPS), the chelator was coupled either at the N-terminus or at the N(epsilon) side chain of Lys(4) of the resin-bound peptide, and the labeling was performed in solution after cleavage. Competitive binding assays showed high binding affinity of the receptor-selective analogues at NPY receptor expressing cells. To test internalization of the novel peptide analogues and the metabolic stability in human blood plasma, the corresponding 5(6)-carboxyfluorescein (CF) analogues were prepared and investigated. One of the most promising analogues, the Y 1-receptor selective [Lys(DOTA)(4), Phe(7), Pro(34)]NPY was labeled with (111)In and injected into nude mice that bear MCF-7 breast cancer xenografts, and biodistribution studies were performed. In vitro and in vivo studies suggest that receptor-selective analogues of NPY have promising characteristics for future applications in nuclear medicine for breast tumor diagnosis and therapy.

A possible in vivo generator 103Pd/ 103mRh—Recoil considerations

The use of Auger emitters as potential radiopharmaceuticals is increasingly investigated. One such radionuclide of interest is 103mRh. This can be produced from 103Ru or from 103Pd in an in vivo generator. A potential problem with this concept is the recoil of the 103mRh out of the carrier molecule and even out of the target cell. In order to determine whether this would happen in the 103Pd/ 103mRh case calculations were done to prove that this does not happen. From theoretical considerations it seems that the 103Pd/ 103mRh in vivo generator system would be possible.

DOTA-Tyr3-Octreotate: Labeling with β-emitting radionuclides for the preparation of potential therapeutic radiopharmaceuticals

Radiolabeled somatostatin analogues, including octreotate have been used for targeted radiotherapy of neuroendocrine tumors such as lymphoma, breast cancer, small-cell lung cancer and melanoma. In this paper, studies on the optimization of the production of 177Lu, 166Ho and 153Sm radionuclides in Pakistan Atomic Research Reactor (PARR-I) and the investigations on the labeling of DOTA-Tyr-3 Octreotate with 131I, 177Lu, 166Ho and 153Sm have been reported. The labeled DOTA-Tyr3-Octreotate complexes were found to be stable in acetate/ascorbate buffer and saline at room temperature (18–22°C). The biodistribution studies of 177Lu-DOTA-Tyr-3 Octreotate in rat model indicated that the critical organ for this complex was the pancreas and the excretion route was through kidney.

Two novel procedures of preparation for [Tc(CO)2(NO)]2+labeled by EHIDA and its biodistribution

To develop potential new Tc radiopharmaceuticals, a novel compound [99mTc(CO)2(NO)(EHIDA)]0 (EHIDA: 2,6-diethylphenylcarbamoylmethyliminodiacetic acid) has been prepared by reacting [99mTc(CO)3)(EHIDA)]− with NOBF4 both in water and acetonitrile. The conversion of [99mTc(CO)3)(EHIDA)]− to [99mTc(CO)2(NO)(EHIDA)]0 was supported by TLC, HPLC and eletrophoresis. The radiochemical purity (more than 99%) was proved by TLC and HPLC. The biodistribution in mice demonstrated that [Tc(CO)2(NO)(EHIDA)]0 showed higher uptake in blood, kidney and lung (15 min, blood: 19.24±2.95; kidney: 13.61±3.49; lung: 10.81±1.09.) but a lower uptake in liver (15 min, 5.73±0.74). The slower clearances (120 min, blood: 12.75±1.34; kidney: 13.61±3.49) from blood and kidney were also found. This research describes two methods for the conversion of [99mTc(CO)3]+ into [99mTc(CO)2)(NO)]2+ by using NOBF4 as the source of NO+ both in organic solvent and water. The latter method offers the possibility to introduce the NO-group in high yield in water.