Radio-protective potential of lipoic acid free and nano-capsule against 99mTc-MIBI induced injury in cardio vascular tissue

BACKGROUND

SPECT MPI (Single photon emission computed tomography myocardial perfusion imaging) is an essential tool for diagnosis of cardiovascular disease, but it also involves considerable exposure to ionizing radiation.

OBJECTIVE

To determine the radioprotective potential of lipoic acid free and nano-capsule against 99mTc-MIBI-induced injury in cardiovascular tissue.

METHODS

The radioprotective ability was assessed by blood count, histopathology and heart enzymes in different groups of mice. Hearts of mice from all groups were dissected and prepared for oxidative stress analysis of superoxide dismutase (SOD) and malondialdehyde (MDA). Furthermore, levels of DNA damage in heart and bone marrow cells were evaluated by alkaline comet assay technique. The same measurements were estimated after treating the mice with lipoic acid.

RESULTS

Comparing mice injected by radiopharmaceutics with control group showed a significant depression in the count of white blood cells (WBC) by about 40 % at 24 &72 hrs post-radiopharmaceutical administration. Moreover, platelets count was decreased by 27% at 72 hrs post-radiopharmaceutical administration. Radiation also dropped in super oxide dismutase (SOD) and increased in activity of heart enzymes and level of MDA (Malondialdehyde). Additionally, histopathological observation was characterized by focal necrosis of cardiac myocytes. 99mTc-MIBI induced DNA damage had significant increase. Nevertheless, pretreatment with free and lipoic acid nano-capsules (LANC's) prevented the reduction induced in WBCs and platelets, and improved their counts significantly. Conversely pre-treatment with lipoic acid free and nano-capsule significantly increased the activity of SOD and decreased the level of MDA and therefore protected the cardiovascular tissues and reduced DNA strand-break, consequently and enhanced the body weight of the mice.

CONCLUSIONS

These findings highlight the efficacy of lipoic acid free and nano-capsule as a radio protector.

Direct and Auger Electron-Induced, Single- and Double-Strand Breaks on Plasmid DNA Caused by 99mTc-Labeled Pyrene Derivatives and the Effect of Bonding Distance

It is evident that ^99mTc causes radical-mediated DNA damage due to Auger electrons, which were emitted simultaneously with the known γ-emission of ^99mTc. We have synthesized a series of new ^99mTc-labeled pyrene derivatives with varied distances between the pyrene moiety and the radionuclide. The pyrene motif is a common DNA intercalator and allowed us to test the influence of the radionuclide distance on damages of the DNA helix. In general, pUC 19 plasmid DNA enables the investigation of the unprotected interactions between the radiotracers and DNA that results in single-strand breaks (SSB) or double-strand breaks (DSB). The resulting DNA fragments were separated by gel electrophoresis and quantified by fluorescent staining. Direct DNA damage and radical-induced indirect DNA damage by radiolysis products of water were evaluated in the presence or absence of the radical scavenger DMSO. We demonstrated that Auger electrons directly induced both SSB and DSB in high efficiency when ^99mTc was tightly bound to the plasmid DNA and this damage could not be completely prevented by DMSO, a free radical scavenger. For the first time, we were able to minimize this effect by increasing the carbon chain lengths between the pyrene moiety and the ^99mTc nuclide. However, a critical distance between the ^99mTc atom and the DNA helix could not be determined due to the significantly lowered DSB generation resulting from the interaction which is dependent on the type of the ^99mTc binding motif. The effect of variable DNA damage caused by the different chain length between the pyrene residue and the Tc-core as well as the possible conformations of the applied Tc-complexes was supplemented with molecular dynamics (MD) calculations. The effectiveness of the DNA-binding ^99mTc-labeled pyrene derivatives was demonstrated by comparison to non-DNA-binding ^99mTcO₄^–, since nearly all DNA damage caused by ^99mTcO₄^– was prevented by incubating with DMSO.

Development of a Radiolabeled Peptide-Based Probe Targeting MT1-MMP for Breast Cancer Detection

Breast cancer is one of the most frequent and aggressive primary tumors among women of all races. Matrix metalloproteinase (MMPs), a family of zinc- and calcium-dependent secreted or membrane anchored endopeptidases, is overexpressed in varieties of diseases including breast cancer. Therefore, noninvasive visualization and quantification of MMP in vivo are of great interest in basic research and clinical application for breast cancer early diagnosis. Herein, we developed a 99mTc labeled membrane type I matrix metalloproteinase (MT1-MMP) specific binding peptide, [99mTc]-(HYNIC-AF7p)(tricine)(TPPTS), for in vivo detection of MDA-MB-231 breast tumor by single photon emission computed tomography (SPECT). [99mTc]-(HYNIC-AF7p)(tricine)(TPPTS) demonstrated nice biostability and high MT1-MMP binding affinity in vitro and in vivo. Tumor-to-muscle ratio was found to reach to the highest (4.17±0.49) at 2 hour after intravenously administration of [99mTc]-(HYNIC-AF7P)(tricine)(TPPTS) into MDA-MB-231 tumor bearing mice. Overall, [99mTc]-(HYNIC-AF7P)(tricine)(TPPTS) demonstrated great potential for MT1-MMP targeted detection in vivo and it would be a promising molecular imaging probe that are probably beneficial to breast cancer early diagnoses.

Preliminary biological evaluation of novel (99m)Tc-Cys-annexin A5 as a apoptosis imaging agent

A novel annexin A5 derivative (cys-annexin A5) with a single cysteine residue at its C-terminal has been developed and successfully labeled in high labeling yield with (99m)Tc by a ligand exchange reaction. Like the 1st generation (99m)Tc-HYNIC-annexin A5, the novel (99m)Tc-cys-annexin A5 derivative shows in normal mice mainly renal and, to a lesser extent, hepatobiliary excretion. In rat models of hepatic apoptosis there was 283% increase in hepatic uptake of (99m)Tc-cys-annexin A5 as compared to normal mice. The results indicate that the novel (99m)Tc-cys-annexin A5 is a potential apoptosis imaging agent.

In-vivo biodistribution and safety of 99mTc-LLP2A-HYNIC in canine non-Hodgkin lymphoma

Theranostic agents are critical for improving the diagnosis and treatment of non-Hodgkin Lymphoma (NHL). The peptidomimetic LLP2A is a novel peptide receptor radiotherapy candidate for treating NHL that expresses the activated α4β1 integrin. Tumor-bearing dogs are an excellent model of human NHL with similar clinical characteristics, behavior, and compressed clinical course. Canine in vivo imaging studies will provide valuable biodistribution and affinity information that reflects a diverse clinical population of lymphoma. This may also help to determine potential dose-limiting radiotoxicity to organs in human clinical trials. To validate this construct in a naturally occurring model of NHL, we performed in-vivo molecular targeted imaging and biodistribution in 3 normal dogs and 5 NHL bearing dogs. ^99mTc-LLP2A-HYNIC-PEG and ^99mTc-LLP2A-HYNIC were successfully synthesized and had very good labeling efficiency and radiochemical purity. ^99mTc-LLP2A-HYNIC and ^99mTc-LLP2A-HYNIC-PEG had biodistribution in keeping with their molecular size, with ^99mTc-LLP2A-HYNIC-PEG remaining longer in the circulation, having higher tissue uptake, and having more activity in the liver compared to ^99mTc-LLP2A-HYNIC. ^99mTc-LLP2A-HYNIC was mainly eliminated through the kidneys with some residual activity. Radioactivity was reduced to near-background levels at 6 hours after injection. In NHL dogs, tumor showed moderately increased activity over background, with tumor activity in B-cell lymphoma dogs decreasing after chemotherapy. This compound is promising in the development of targeted drug-delivery radiopharmaceuticals and may contribute to translational work in people affected by non-Hodgkin lymphoma.

Synthesis, characterization, and in vivo skeletal localization of a new 99mTc-based multidentate phosphonate chelate: 5-Amino-1,3-bis(ethylamine-(N,N dimethyl diphosphonic acid) acetamido) benzene

The tetraphosphonate ligand, 5-amino-1,3-bis(ethylamine-(N,N-dimethyl diphosphonic acid) acetamido) benzene (IPTMP) used in the present study was prepared from 5-nitroisophthalate dimethylester to label with radionuclide for targeted diagnosis and therapy. The synthesized multidentate phosphonate ligand was characterized on the basis of spectroscopic techniques, which exhibited good metal ion control properties when complexed to (99m)Tc with high in vitro and in vivo stability. Excellent quality bone images of rabbit were imaged showing rapid clearance of background activity and visualization of skeleton at 1h.

Cell Uptake and Radiotoxicity Studies of an Nuclear Localization Signal Peptide−Intercalator Conjugate Labeled with [99mTc(CO)3]+

A trifunctional bioconjugate consisting of the SV40 nuclear localization signal (NLS) peptide, an aliphatic triamine ligand, and the DNA intercalating pyrene has been synthesized and quantitatively labeled with [(99m)Tc(OH(2))(3)(CO)(3)](+). The radiotoxicity of the resulting nucleus-targeting radiopharmaceutical on B16F1 mouse melanoma cells has been investigated to evaluate the activity of Auger and Coster-Kronig electrons on the viability of cells. We found a dose-dependent significant radiotoxicity of the nucleus-targeting radiopharmaceutical clearly related to the low energy decay of (99m)Tc. These principal results imply a possible therapeutic strategy based on the use of the low-energy Auger electron-emitting (99m)Tc radionuclide attached to nucleus-targeting molecules and comprising an intercalator. Highly efficient DNA targeting vectors could complement the usual role of (99m)Tc in diagnostic applications. The Auger electrons emitted by the (99m)Tc nuclide induce DNA damage leading ultimately, through a mitotic catastrophe pathway, to necrotic cell death. Non-DNA-targeting (99m)Tc complexes display much lower radiotoxicity.

Preclinical studies of [(99m)Tc]DTPA-mannosyl-dextran

We report the preclinical testing of a synthetic receptor-binding macromolecule, [(99m)Tc]DTPA-mannosyl-dextran (36 kDa, 8 DTPA and 55 mannosyl units per dextran, K(D) = 0.12 nM), for sentinel node detection. Nonclinical safety studies included cardiac pharmacology safety studies, acute toxicology and pathology studies at 50 and 500 times the scaled human dose in both rats and rabbits after foot pad administration, and perivascular irritation studies in rabbits following intra-muscular administration at 100 and 1000 times the scaled human dose. Biodistribution studies in rabbits at 15 m, 1 h, and 3 h indicated that [(99m)Tc]DTPA-mannosyl-dextran cleared the hind foot pad with a biological half-life of 2.21 +/- 0.27 h. Other than mild hepatocyte hypertrophy in rabbits, no abnormalities in toxicology or pathology were found. Intravenous administration had no effect on survival, any clinical observations, electrocardiograms, or blood pressures. Intramuscular injection had no effect on survival, clinical observations, injection site observations, or injection site histopathology. The estimated absorbed radiation dose to the affected breast was 0.15 mGy/MBq and the effective dose was 1.06 x 10(-2) mSv/MBq. This preclinical study demonstrates that [(99m)Tc]DTPA-mannosyl-dextran has no toxicities and has an acceptable biodistribution and radiation dose.

Assessment of radiation-induced DNA damage caused by the incorporation of 99mTc-radiopharmaceuticals in murine lymphocytes using single cell gel electrophoresis

The DNA damage induced by the 99mTc-radiopharmaceuticals incorporation to the cell was determined by the single-cell gel electrophoresis in murine lymphocytes in vitro. The 99mTc-hexamethyl-propylene amine oxime (99mTc-HMPAO) and 99mTc-2, 5-dihydroxybenzoic acid (99mTc-gentisic acid) induced nearly 100% of cells with breaks and/or alkali labile sites, which is explained by the action of the Auger electrons produced by the decay of the 99mTc. These results agree with the doses of 1.6 and 1.0 Gy estimated by subcellular dosimetry for 99mTc-HMPAO that is incorporated in the cytoplasm, and the 99mTc-gentisic acid, which remains bonded to the cell membrane, respectively. The results imply that Auger electrons are able to cause important DNA damage, when the radionuclide is incorporated in the range of a few microns from the nuclei.

Relative biological effectiveness of 99mTc radiopharmaceuticals

The radiotoxicity of three 99mTc-labeled compounds is investigated using spermatogenesis in mouse testis as the experimental model, and spermatogonial cell survival as the biological end point. The radiopharmaceuticals studied are pertechnetate (99mTcO4-), pyrophosphate (99mTc-PYP), and hydroxyethylene diphosphate (99mTc-HDP). The mean lethal doses at 37% survival (D37) are 0.70 +/- 0.06, 0.84 +/- 0.13, and 0.59 +/- 0.08 Gy for 99mTcO4-, 99mTc-PYP, and 99mTc-HDP, respectively. When these results are compared with the D37 value obtained with external x rays or internal gamma rays, the relative biological effectiveness (RBE) of these compounds are 0.94 +/- 0.09, 0.79 +/- 0.13, and 1.1 +/- 0.16, respectively. These results show that the radiotoxicity of 99mTc in mouse testis is essentially similar to that of low-LET radiations (i.e., RBE approximately 1). To understand these results, the distribution of these radiocompounds in the testis is determined and correlated with the observed RBE values. The expected range of RBE values for 99mTc radiopharmaceuticals in organs is 0.95 to 1.5, depending on the fraction of organ activity that is bound to DNA. This suggests that the Auger electrons emitted in the decay of 99mTc are not capable of causing extreme toxicity in vivo. These results provide further support for 99mTc as the radionuclide of choice for imaging in nuclear medicine.

First experience in healthy volunteers with technetium-99m L,L-ethylenedicysteine, a new renal imaging agent

Animal studies have indicated that technetium-99m L,L-ethylenedicysteine (99mTc-L,L-EC) may be a promising tracer agent for renal function studies. We have performed a paired study with 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) and 99mTc-L,L-EC in six male volunteers. In both cases, iodine-131-labelled o-iodohippurate was co-injected as an internal biological standard. The analog images between 0 and 30 min p.i. were of identical diagnostic value for both tracer agents. The two renograms were similar in all volunteers. The mean 1-h plasma clearance for 99mTc-MAG3 and 99mTc-L,L-EC was significantly different, respectively 382.9 +/- 17.1 ml/min per 1.73 m2 versus 460.2 +/- 47.7 ml/min per 1.73 m2 (P < 0.003). The urinary excretion after 30 min p.i. was 69.4% +/- 5.6% of the injected dose for 99mTc-MAG3 versus 66.5% +/- 2.5% for 99mTc-L,L-EC (P > 0.05) and after 60 min p.i. respectively 83.1% +/- 3.9% versus 79.8% +/- 4.3% (P > 0.05). 99mTc-L,L-EC has a very low plasma protein binding (31% +/- 6.8%) as compared to 99mTc-MAG3 (88% +/- 5.2%) and a larger volume of distribution. Although the exact mechanism responsible for the high plasma clearance of 99mTc-L,L-EC is not yet fully known, we conclude that this new agent merits further clinical evaluation in patients to establish its value as a renal radiopharmaceutical.

Technetium-99m-tetrofosmin as a new radiopharmaceutical for myocardial perfusion imaging

A new cationic complex, [99mTc(tetrofosmin)2O2]+, where tetrofosmin is the ether functionalized diphosphine ligand 1,2-bis[bis(2-ethoxyethyl)phosphino]ethane, has been synthesized and evaluated for potential use in myocardial perfusion imaging. The structure of the complex has been determined by x-ray crystallography of the 99Tc analog. In comparison with previously reported 99mTc complexes of alkyl-phosphines, the tetrofosmin species shows substantially increased clearance from nontarget tissue, especially blood and liver. A freeze-dried kit formulation has been developed. The kit provides a product of high radiochemical purity up to 8 hr after reconstitution at room temperature.

Lymphocyte labeling with technetium-99m-HMPAO: a radiotoxicity study using the micronucleus assay

The cytogenetic radiation damage to lymphocytes after in-vitro labeling of mixed leukocytes and isolated lymphocytes with 99mTc-hexamethylpropyleneamine oxime (HMPAO) was evaluated using the cytokinesis-blocked micronucleus assay. A direct assessment of the radiation damage to the lymphocytes after a labeling procedure of leukocytes separated from 46 ml blood with 740 MBq of 99mTc-HMPAO was not possible due to an almost complete impairment of the proliferative capacity. By starting with isolated lymphocytes, the number of micronuclei was studied versus the intracellular activity concentration in the range 0-3 MBq/10(7) lymphocytes for three donors. A comparison of these results with the dose response of the micronucleus incidence in lymphocytes after in-vitro irradiation with x-rays allowed an individual assessment of the x-ray dose, inducing the equivalent amount of clastogenic damage as the intracellular activity after 99mTc-HMPAO labeling. Based on an extrapolation of these data, the radiation damage of the lymphocytes due to self-irradiation in a labeling procedure of leukocytes with 740 MBq of 99mTc-HMPAO was estimated to be equivalent to 26 Gy of x-rays. Due to the observed almost complete inhibition of the proliferative capacity at this high dose level, the increased risk for a lymphoid malignancy after administration of isolated lymphocytes or mixed leukocytes labeled with 99mTc-HMPAO activities sufficient for scintigraphy can be regarded as small.

Preparation and evaluation of 99mTc-t-butylisonitrile (99mTc-TBI) for myocardial imaging: a kit for hospital radiopharmacy

A previous method was modified to obtain [99mTc(TBI)6]+ by reacting Zn(TBI)2Br2 directly with 99mTcO4- in the presence of Sn2+ ions. [Cu(TBI)4]Cl was next used as a source of TBI. On reaction with 99mTcO4- and Sn2+ ions for 3 min at 100 degrees C, [99mTc(TBI)6]+ product of radiochemical purity greater than 90% and yield greater than 70% was obtained. Data of biodistribution in rats (2-2.5% in heart) and biokinetics in rabbits were satisfactory. The kit formulation was found to be stable and also safe for administration.

Characterization of technetium-99m-L,L-ECD for brain perfusion imaging, Part 1: Pharmacology of technetium-99m ECD in nonhuman primates

Technetium-99m ethyl cysteinate dimer ([99mTc]ECD) is a neutral, lipophilic complex which rapidly crosses the blood-brain barrier. Brain retention and tissue metabolism of [99mTc]ECD is dependent upon the stereochemical configuration of the complex. While both L,L and D,D enantiomers are extracted by the brain, only the L,L but not the D,D form, is metabolized and retained in the monkey brain (4.7% injected dose initially, T 1/2 greater than 24 hr). Dynamic single photon emission computed tomography imaging studies in one monkey indicates 99mTc-L,L-ECD to be distributed in a pattern consistent with regional cerebral blood flow for up to 16 hr postinjection. Dual-labeled 99mTc-L,L-ECD and [14C]iodoantipyrine autoradiography studies performed 1 hr after administration show cortical gray to white matter ratios of both isotopes to be equivalent (approximately 4-5:1). These data suggest that 99mTc-L,L-ECD will be useful for the scintigraphic assessment of cerebral perfusion in humans.