125I Atoms Research Articles

Deposition of Iodine-125 on Silver Supports of Microsources for Prostate Cancer Brachytherapy

A method of iodine-125 deposition on a surface of microsource silver supports for brachytherapy of prostate cancer was reported, which includes preparing the support surface by sequentially treating them with nitric acid and thiourea solutions, followed by chlorination of the support surface with a chlorinating agent to form silver chloride on the support surface, and substitution of chlorine atoms for 125I atoms by placing supports containin silver chloride on the surface in a solution with 125I ions to create a 125I layer on the support surface. The method described allows fixing 125I on supports with a low activity distribution on each activity-carrying support.

How to explain the sensitivity of DNA double-strand breaks yield to 125I position?

Purpose Auger emitters exhibit interesting features due to their emission of a cascade of short-range Auger electrons. Maximum DNA breakage efficacy is achieved when decays occur near DNA. Studies of double-strand breaks (DSBs) yields in plasmids revealed cutoff distances from DNA axis of 10.5 Å–12 Å, beyond which the mechanism of DSBs moves from direct to indirect effects, and the yield decreases rapidly. Some authors suggested that the average energy deposited in a DNA cylinder could explain such cutoffs. We aimed to study this hypothesis in further detail. Materials and methods Using the Monte Carlo code CELLDOSE, we investigated the influence of the 125I atom position on energy deposits and absorbed doses per decay not only in a DNA cylinder, but also in individual strands, each modeled as 10 spheres encompassing the fragility sites for phosphodiester bond cleavage. Results The dose per decay decreased much more rapidly for a sphere in the proximal strand than for the DNA cylinder. For example, when moving the 125I source from 10.5 Å to 11.5 Å, the average dose to the sphere dropped by 43%, compared to only 13% in the case of the cylinder. Conclusions Explaining variations in DSBs yields with 125I position should consider the probability of inducing damage in the proximal strand (nearest to the 125I atom). The energy received by fragility sites in this strand is highly influenced by the isotropic (4π) emission of 125I low-energy Auger electrons. The positioning of Auger emitters for targeted radionuclide therapy can be envisioned accordingly.

Optimization of reagent concentration for radioiodination of rat C-peptide II in development of radioimmunoassay procedure for rats

Rat C-peptide is a polypeptide molecule made up of 31 amino acids and secreted from pancreas into circulation in two isoforms I and II. Quantification of rat C-peptide II in rat serum is important as it is directly related to the diagnosis of carbohydrate metabolism abnormalities, pancreatic performance analysis, monitoring of hypoglycemia, and diabetes-related illness in rat model. The aim of the present work is to develop a tracer by chloramine-T method for radioimmunoassay (RIA) procedure and to determine the optimum amount of chloramine-T required for the preparation of stable radioiodinated product with a specific activity of around 24.97 MBq/μg, corresponding to 1 125I atom per molecule of the peptide. Tyrosylated rat C-peptide II was selected for the radioiodination procedure as rat C-peptide II does not contain either tyrosine or histidine which is mandatory for the incorporation of 125I atom to the rat C-peptide II. Tyrosylated rat C-peptide II was subjected to radioiodination by chloramine-T method with different concentrations of chloramine-T and sodium metabisulfite (MBS) to obtain a stable radiolabeled compound. Optimized reaction conditions relating to the concentration of chloramine-T (10 μg) and MBS (20 μg) yielded a stable 125I-rat C-peptide II with specific activity of 21.01 MBq/μg corresponding to 0.84 125I atoms per molecule of the peptide. Preparation of high integrity tracer of rat C-peptide II was achieved by combining one molecule of oxidant (chloramine-T) and two molecule of reductant (MBS).

Biodistribution of single-walled carbon nanotubes in rats

Background: Carbon nanotube (CNT) mediated drug delivery systems have recently aroused a great deal of interest. Such delivery systems for drugs, proteins and genes have been preliminarily studied using cellular and animal models. For further study of the related biological behaviours of CNTs in vivo, a fast and convenient tracing method is particularly necessary. Methods: We adopted concentrated nitric acid/concentrated sulfuric acid oxidation combined with ultrasonication to treat SWCNTs, then detected and analyzed the samples before and after treatment by transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR), energy dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). The iodogen oxidative method was used to synthesize iodinated single-walled carbon nanotubes, followed by intratracheal instillation of 125I-labelled SWCNTs to determine their distribution in rats. Results: SWCNTs form more hydroxyl and carboxyl functional groups with no change in their essential characteristics after treatment by violet acid oxidation combined with ultrasonication. 125I can easily form C–I covalent bonds to SWCNTs. The proportion of iodine-125 labelled SWCNTs is 46.14%, the radiochemical purity is 98.95%. In order of total radioactivity concentration in the main organs/tissues and body fluids for 125I-SWCNTs, it was shown that trachea > urine > stomach > small intestine > serum > bladder > blood vessel > kidney > liver > lung > adrenal > femoral head > spleen > testis > thymus > thyroid > heart > fat > muscle > brain. Conclusions: In this paper, we developed a generally adoptable tracing method for studying the biodistribution of SWCNTs (single walled carbon nanotubes) in vivo. SWCNTs could be labelled with radioactive 125I atoms. The 125I labelling method is reliable and effective and affords a quantitative analysis of CNTs accumulated in animal tissues. This result will provide an important reference for future research into the biomedical and pharmacological applications of SWCNTs.

Effect of distance between decaying 125I and DNA on Auger-electron induced double-strand break yield

Purpose: To determine the possible effects of 125I-to-DNA distance on the magnitude and mechanism of Auger-electron induced-double-strand break (DSB) production.Materials and methods: We have synthesized a series of 125I-labeled Hoechst (H) derivatives (125IE–H, 125IB–H, 125I-C8–H and 125I-C12–H). While all four molecules share a common DNA minor groove binding bis-benzimidazole motif, they are designed to position 125I at varying distances from the DNA helix. Each Hoechst derivative was incubated at 4°C in phosphate buffered saline (PBS) together with supercoiled (SC) 3H-pUC19 plasmid DNA (ratio 3:1) ± the •OH scavenger dimethyl sulfoxide (DMSO) (0.2 M). Aliquots were analyzed on agarose gels over time and DSB yields per decay of 125I atom were determined. Docking of the iodinated compounds on a DNA molecule was carried out to determine the distance between the iodine atom and the central axis of DNA.Results: In the absence of DMSO, the results show that the DSB yields decrease monotonically as the 125I atom is distanced – by 10.5 Å to 13.9 Å – from the DNA helix (125IEH: 0.52 ± 0.01; 125IB–H: 0.24 ± 0.03; 125I-C8–H: 0.18 ± 0.02; 125I-C12–H: 0.10 ± 0.00). In the presence of DMSO, DSB yields for 125IEH (0.49 ± 0.02) and 125IB-H (0.26 ± 0.04) remain largely unchanged indicating that DSB are entirely produced by direct effects. Strikingly, 125I-C8–H or 125I-C12–H, did not produce detectable DSB in the presence of DMSO under similar conditions suggesting when 125I atom is positioned > 12 Å from the DNA, DSB are entirely produced by indirect effects.Conclusion: These results suggest that at a critical distance between the 125I atom and the DNA helix, DSB production switches from an ‘all’ direct to an ‘all’ indirect mechanism, the latter situation being comparable to the decay of 125I free in solution. These experimental findings were correlated with theoretical expectations based on microdosimetry.

Biodistribution of Carbon Single-Wall Carbon Nanotubes in Mice

Carbon nanotubes are promising for use in biomedical and pharmaceutical sciences. Therefore, it becomes imperative to know the basic biological properties of carbon nanotubes in vivo. We labeled the water-soluble hydroxylated carbon single-wall nanotubes with radioactive 125I atoms, and then the tracer was used to study the distribution of hydroxylated carbon single-wall nanotubes in mice. They moved easily among the compartments and tissues of the body, behaving as small active molecules though their apparent mean molecular weight is tremendously large. This study, for the first time, affords a quantitative analysis of carbon nanotubes accumulated in animal tissues.

In vitro and in vivo evaluations of THAM derived telomers bearing RGD and Ara-C for tumour neovasculature targeting

As an approach to the development of specific drug delivery systems, a new class of low macromolecular carriers called ‘telomers’ endowed with an antitumour agent, such as arabinofuranosylcytosine (Ara-C), RGDSK peptidic sequences, as tumour targeting moieties, and tyrosine groups labelled with 125I atoms allowing the in vivo scintigraphic follow up, were synthesized. Their tumour targeting ability was assessed in vivo in mice bearing a murine B16 melanoma. The biological results showed that the presence of RGDSK sequences onto the macromolecules leads to the selective targeting and the accumulation of telomers within the vascularized zone of the tumour. Moreover, such compounds exhibited in vitro a better IC50 (0.015 μM) than pure Ara-C and in vivo an oncostatic index higher than 160%.

Synthesis of photoactivable inhibitors of osteoclast vacuolar ATPase

Amides of (2 Z,4 E)-5-[(5,6-dichloroindol-2-yl)]-2-methoxy- N-[3-[4-[3-(carboxymethoxy)phenyl)] piperazin-1-yl]propyl]-2,4-pentadienamide ( 1) and of 5-(5,6-dichloro-2-indolyl)-2-methoxy-2,4-pentadienoic acid ( 2) are strong inhibitors of the vacuolar ATPase located on the plasma membrane of osteoclasts. In order to understand which V-ATPase subunit is involved in the interaction with these novel inhibitors, analogues containing a photoactivable group and an iodine atom were designed. A series of alcohols or amines containing the photoactivable trifluoroaziridinophenyl or benzophenone moiety and an iodine atom were linked to the above acids via an ester or amide group. These compounds could be thereafter used as a radioactive photoprobe to label the protein. Whereas the compounds containing the photoactivable groups maintained good inhibitory activity, the introduction of the bulky iodine atom was generally detrimental, decreasing potency significantly. Better results were obtained by linking 3-(4-aminopiperidinomethyl)-3′-iodobenzophenone to 3-ethoxy-4-(2-(5,6-dichlorobenzimidazolyl))benzoic acid to give the corresponding amide 27, that inhibited vacuolar ATP-ase with a IC 50=140 nM. The feasibility of introducing a radioactive 125I atom was ascertained by exchanging the iodine with a tributylstannyl group, that was again substituted by iodine.

Radioprobing of DNA: distribution of DNA breaks produced by decay of 125I incorporated into a triplex-forming oligonucleotide correlates with geometry of the triplex.

The distribution of breaks produced in both strands of a DNA duplex by the decay of 125I carried by a triplex-forming DNA oligonucleotide was studied at single nucleotide resolution. The 125I atom was located in the C5 position of a single cytosine residue of an oligonucleotide designed to form a triple helix with the target sequence duplex. The majority of the breaks (90%) are located within 10 bp around the decay site. The addition of the free radical scavenger DMSO produces an insignificant effect on the yield and distribution of the breaks. These results suggest that the majority of these breaks are produced by the direct action of radiation and are not mediated by diffusible free radicals. The frequency of breaks in the purine strand was two times higher that in the pyrimidine strand. This asymmetry in the yield of breaks correlates with the geometry of this type of triplex; the C5 of the cytosine in the third strand is closer to the sugar-phosphate backbone of the purine strand. Moreover, study of molecular models shows that the yield of breaks at individual bases correlates with distance from the 125I decay site. We suggest the possible use of 125I decay as a probe for the structure of nucleic acids and nucleoprotein complexes.

DNA strand breakage by 125I-decay in a synthetic oligodeoxynucleotide--2. Quantitative analysis of fragment distribution.

The DNA breakage produced by decay of 125I in a double-stranded 41 bp oligodeoxynucleotide was investigated by DNA sequencing gel analysis. Use of both 5'- and 3'-end 32P labelling of the 125I containing strand provided the single-stranded breakage pattern at either side of the 125I-dC. The asymmetric pattern of breakage relative to the 125I-labelled nucleotide enabled deconvolution of two components of breakage. One of them declines very quickly with nucleotide number from 125I-dC and dominates within 4-5 nucleotides. We assume this component to be associated with neutralisation of charged Te atom resulted from decay, or/and with radiation damage to an initial target other than the deoxyribosyl moiety--probably the bases. The second component depends on the geometrical distance between the 125I atom and deoxyribosyl atoms. These two components are responsible for breakage under conditions limiting radical mediated damage, namely in the presence of 2M dimethylsulphoxide. The third component, associated with radical-mediated damage, contributes to the total breakage during incubation in 20 mM phosphate buffer alone, and under these incubation conditions dominates the breakage beyond 8-9 nucleotides from 125I-dC. The estimated average numbers of single-stranded breaks produced in the 125I-containing strand by each mechanism in 41-mer oligodeoxynucleotide with 125I-dC at 21st position are respectively 2.33, 0.98 and 0.63.

Dna Damage Induction by125I-Estrogen

DNA damage induced by the radioactive decay of 125I-estrogen (125I-VME2) in an estrogen receptor expressing CHO cell line, CHO-ER, was measured. 125I-VME2 targeted 125I atoms proximal to DNA estrogen response elements (EREs). 125I decays were accumulated at -135 degrees C, and thereafter assayed by alkaline and neutral filter elution techniques to measure DNA single strand break (ssb) and double strand break (dsb) induction respectively. Increasing DNA damage (both ssbs and dsbs) was detected after exposure of cells to increasing concentrations of 125I-VME2. DNA ssb and dsb dose-response curves for 125I-VME2 were multiphasic. The rates of DNA damage induction by the decay of 125I-VME2 was determined by comparing slopes of all data or by comparing initial slopes. DNA ssb induction per 125I-VME2 decay was approximately 2 times greater compared with DNA dsb induction. 125I-VME2 decay induced approximately 4-8 times more DNA dsbs than 125IUdR decay.

Amplification of Oncogenes and Integrated SV40 Sequences in Mammalian Cells by the Decay of Incorporated Iodine-125

Iodine-125, in the form of 5-[125I]iododeoxyuridine (I-UdR), was incorporated into the DNA of SV40 transformed Chinese hamster embryo cells. Disintegration of the 125I led to increased cell killing with increasing dose as measured by the colony-forming ability of single cells. The D37 (the dose at which 37% of the cells survive) amounts to 95 decays per cell, corresponding to 0.66 Gy. Variations in the copy number of specific DNA sequences was measured by using dispersed cell blotting with sensitive DNA hybridizations. A 13-fold amplification of the viral DNA sequences (SV40) and a twofold amplification of two cellular oncogenes of the ras-family (Ki-ras and Ha-ras) were found. Other cellular genes, like the alpha-actin gene, were not amplified, and no variation in gene copy number was detected after incubation of cells with cold I-UdR. We suggest the observed gene amplifications are induced by the densely ionizing radiation emitted by the decay of the incorporated 125I atoms.

Preparation of carrier free [ 125I]IodoHoechst 33258

The DNA ligand Hoechst 33258 has been iodinated with carrier-free [ 125I]iodide by the lactoperoxidase method. The product was separated from other iodination products and the uniodinated compound by preparative thin layer chromatography. 125I-labelled Hoechst 33258 is useful as a probe with DNA molecules of defined sequence since the decay of the 125I atom results in the induction of a double-strand break, the location of which can be detected by DNA-sequencing techniques.

Heterogeneity of 125I-labeled epidermal growth factor

Highly purified epidermal growth factor (EGF) was iodinated, and the labeled product with the same isoelectric point as underivatized EGF was isolated by isoelectric focusing. When the 125I-labeled EGF was analyzed by reverse-phase chromatography, the resulting profile of 125I activity was much broader than the profile obtained with underivatized EGF. Rechromatography of 125I-EGF fractions indicated that our highly-purified labelled EGF was indeed heterogenous. Analysis of each HPLC column fraction demonstrated that degradation of EGF had not occurred. The column fractions containing 125I-EGF were pooled into five groups for analysis of cell binding characteristics. Scatchard plot analysis of the five 125I-EGF pools revealed markedly different binding behaviors. In contrast, they had equal potency in stimulating DNA synthesis, within the sensitivity of our assay. Specific activity measurements indicated that the five HPLC pools of 125I-EGF had varying numbers of 125I atoms per EGF molecule. The heterogeneity of the highly purified 125I-EGF and the binding characteristics of the 125I-EGF subfractions pose serious implications for all workers who use iodinated ligands for receptor binding studies.

A sensitive radioimmunoassay for corticotropin using a fully biologically active 125I-labeled ligand.

The human corticotropin (ACTH) analog, Phe2,Nle4-ACTH-(1-38) was iodinated by the chloramine-T procedure and the product was purified by reverse phase high performance liquid chromatography. The specific radioactivity of [125I]Tyr23,Phe2,Nle4-ACTH-(1-38) was determined by comparing the antiserum binding curves of the iodinated peptide and [3H]ACTH of known specific activity. This method gave a value of 1800 +/- 75 Ci/mmol, which is close to the theoretical radioactivity expected for the introduction of a single 125I atom into the peptide. [125I]Tyr23,Phe2,Nle4-ACTH-(1-38) was as potent as ACTH in stimulating corticosterone production in isolated rat adrenocortical cells. The concentrations for half-maximal steroidogenesis were 36.5 +/- 6.1 pM for the 125I derivative and 37.6 +/- 6.7 pM for ACTH. By the use of this 125I-labeled ligand, a highly sensitive RIA capable of detecting 1 pg aCTH was developed.l The antiserum employed in this study appeared to be directed against residues 11-13 of ACTH.

Preparation, purification, and stability of high specific activity 125I-labeled thyronines.

A modified chloramine-T method is described for the preparation of several radioiodothyronines by an exchange reaction, which results in low specific activity preparations, or by an addition reaction, which yields radioiodothyronines with specific activities up to 7 mCi/microgram. Purification by paper chromatography is shown to be more convenient than by LH-20 chromatography and provides better resolution among the various thyronines. Radioiodothyronines with only a single iodine atom in the outer (3,5,3'-triiodothyronine and 3,3'-diiodothyronine) are stable for several months when stored in organic solvents. The least stable radioiodothyronines are those with two 125I atoms in the outer ring (3,3',5'-triiodothyronine (rT3) produced from 3-iodothyronine and thyroxine (T4) from 3,5-diiodothyronine). The stability of rT3 and T4 stored in human plasma at 4 C is much greater than when stored in buffer at the same pH. The use of high specific activity [125I]rT3 has permitted the development of a radioimmunoassay with a sensitivity of 1 pg rT3/ml incubation volume.

Prolonged retention of high specific activity by 125I-labeled angiotensin II — a consequence of ‘decay catastrophe’

Angiotensin II labeled with a single atom of 125I per moleculed had been shown to retain 80% of the original specific activity of the radioiodinated peptide during storage for up to 5 months. This phenomenon is attributable to destruction of the angiotensin II molecule during the radioactive decay process, so that the immunoreactive peptide effectively desappears at the same rate as the incorporated 125I atom. For this reason, monoiodinated angiotensin II can be employed for prolonged periods in radioimmunoassay and binding studies, with retention of high specific activity in the absence of formation of free iodide or interfering peptide fragments.