1-alpha- and 1-beta-D-Arabinofuranosyl-2-nitroimidazole (alpha-AZA and beta-AZ A) are synthons for a number of potential markers of tissue hypoxia. A one pot synthesis in which 2-nitroimidazole is coupled with a mixture of alpha- and beta-1-O-acetyl-2,3,5-tri-O-benzoyl-D-arabinofuranose in the presence of stannic chloride, followed by deprotection using ammonia/methanol, is described Previously reported conditions for coupling 2-nitroimidazole to 1-alpha-bromoarabinofuranose protected by base-hydrolyzable groups afforded alpha-AZA almost exclusively.

UNLABELLED The study was performed to compare the (18)F-labeled nitroimidazole compound fluoroazomycin arabinoside ((18)F-FAZA) with the standard hypoxia tracer fluoromisonidazole ((18)F-FMISO) in detection of tumor tissue hypoxia and to verify the oxygenation dependency of (18)F-FAZA uptake. METHODS Biodistribution of (18)F-FAZA was studied at various time points in EMT6 tumor-bearing BALB/c mice and in AR42J and A431 tumor-bearing nude mice and compared with that of (18)F-FMISO. The presence of tumor tissue hypoxia was verified in 5 EMT6 and 5 AR42J tumors using an oxygen-sensing needle electrode system. To evaluate the oxygenation dependency of (18)F-FAZA uptake, using the Munich prototype animal PET scanner, 2 serial PET scans were performed in 13 A431 tumor-bearing nude mice breathing pure oxygen or room air on 1 d and then selecting the other oxygen breathing condition on the following day. In addition, digital autoradiography was performed with EMT6 tumor-bearing (18)F-FAZA-dosed, nude mice breathing either room air (n = 8) or carbogen (n = 9). RESULTS Tissue partial pressure of oxygen (Po(2)) electrode measurements revealed that tumor hypoxia was present under room air breathing in EMT6 (tissue Po(2) = 2.9 +/- 2.6) and AR42J tumors (tissue Po(2) = 0.4 +/- 0.2), which was significantly lower compared with that of reference tissue (tissue Po(2) = 25.8 +/- 6.7 and tissue Po(2) = 29.0 +/- 3.0 [mean +/- SD], respectively; P < 0.01). In all tumor models, (18)F-FAZA displayed significantly higher tumor-to-muscle and tumor-to-blood ratios compared with (18)F-FMISO, indicating a faster clearance of (18)F-FAZA from normal tissues. In AR42J tumors, (18)F-FAZA tumor-to-normal ratios were found to increase over time. Serial animal (18)F-FAZA PET studies showed that the tumor-to-background ratio was significantly higher in animals breathing room air compared with that of animals breathing pure oxygen (7.3 +/- 2.3 vs. 4.2 +/- 1.2, respectively; P < 0.001). Similarly, autoradiography showed significantly higher tumor-to-muscle ratios in mice breathing room air compared with those of animals breathing carbogen (5.3 +/- 0.8 vs. 2.2 +/- 0.8; respectively; P < 0.02). CONCLUSION (18)F-FAZA shows superior biokinetics and is, thus, a promising PET tracer for the visualization of tumor hypoxia. This study also verified a hypoxia-specific uptake mechanism for (18)F-FAZA in murine tumor models.

In vivo transfer of the herpes simplex virus type-1 thymidine kinase (HSV-1 TK) gene, with subsequent administration of antiviral drugs such as ganciclovir, has emerged as a promising gene therapy protocol for treating proliferative disorders. The in vitro cytotoxicities (IC50) for two series of 5-iodo- and (E)-5-(2-iodovinyl)-substituted 2′-deoxy- and 2′-deoxy-2′-fluoro-pyrimidine nucleosides ranged from millimolar to low nanomolar concentrations in mammalian tumor cell lines (KBALB; R-970-5; 143B; EMT-6) and their counterparts engineered to express HSV-1 TK (KBALB-STK; 143B-LTK). Their HSV-1 TK selectivity indices ranged from one (nonselective) to one million (highly selective) based on cytotoxicity, with FIRU being the least toxic to all cell lines, and FIAU being most toxic. HSV-1 TK selectivity, based on uptake, ranged from 10 to 140, with IVDU being most selective for HSV-1 TK expressing cells, followed by IVFRU, FIRU, FIAU, IVFAU and finally IUDR. Phosphorylation of [125I]FIAU led to incorporation of the radiolabel into nucleic acids, whereas IVFRU and FIRU radioactivity was trapped primarily in the nucleotide pool. These data indicate that cytotoxicity does not depend on initial metabolic trapping (e.g., phosphorylation), but on elaboration of the mononucleotides to more cytotoxic anabolites. Lipophilicities and nucleoside transport rates of the six nucleosides tested were within narrow ranges. This supports the premise that cellular biochemistry, and not cellular bioavailability, is responsible for the observed broad range of cytotoxicity and trapping. In vivo biodistribution studies with 5-[125I]iodo-2′-fluoro-2′-deoxyribouridine (FIRU), 5-[125I]iodo-2′-fluoro-2′-deoxyarabinouridine (FIAU) and (E)-5-(2-[125I]iodovinyl)-2′-fluoro-2′-deoxyuridine (IVFRU) demonstrate selective accumulation of all three radiotracers in HSV-1 TK-expressing KBABK-STK tumors, compared to their very low accumulation in the non-HSV-1 TK-expressing KBALB tumors, in Balb/c mice. In summary, these nucleosides are unpredictably cytotoxic to the various cell lines studied, and this unpredictability extends across the HSV-1 TK expression characteristic; their uptake by cells engineered to express HSV-1 TK is also dependent on the molecular construction of the gene cassette carrying the viral TK gene.

The title compound, C6H8N+.C5H9O6P2−, has been prepared via hydro­lysis of 3-methyl-1,2-buta­diene-1,1-di­phospho­nic tetrakis­(tri­methyl­silyl) ester, and stabilization of the di­phospho­nic acid thus formed as an anilinium salt. Both ions possess mirror symmetry, with all the C atoms of the anion and the N, ipso-C and para-C atoms of the cation being situated in the mirror plane. Adjacent anionic units form associations through cyclic dimeric {P(=O)(OH)}2 and chain-propagating P—OH⋯O=P interactions, with the anilinium ion being hydrogen bonded to three adjacent di­phospho­nate anions.

Radioisotope therapy (RIT) is one of the oldest interventions in nuclear medicine. Radioiodine has been used to treat thyrotoxicosis since 1941 ( 1 ), and 89Sr was first reported as an effective palliative treatment in patients with painful bone metastases in 1942 ( 2 ). Yet despite this long

UNLABELLED123I-Labeled iodoazomycin arabinoside (IAZA) is a marker of hypoxia in vivo. It has been used clinically to image hypoxic tissue in solid tumors, peripheral vascular disease of diabetic origin, blunt brain trauma, and rheumatoid joints and in an animal model of cerebrovascular disease. The radiation dose biodistribution for 123I-IAZA was studied to assess and characterize its suitability as a clinical radiopharmaceutical.METHODSSix healthy volunteers each received a nominal 185-MBq (5 mCi) dose of 123I-IAZA administered as a slow (1-3 min) intravenous injection in the arm. Anterior and posterior whole-body planar images were acquired for each volunteer beginning immediately after injection and at 1-2, 3-4, 6-8, and 20-24 h after injection. Venous blood samples (0 h predose through 28 h after dosing) and 28-h cumulative urine samples were taken from each volunteer for pharmacokinetic analysis. Radiation dose estimates were performed for all volunteers, with "reference adult" (for men) and "adult female" (for women) phantoms, and both the International Commission on Radiological Protection 30 gastrointestinal tract model and the dynamic bladder model, using the MIRDOSE3 program. Two sets of estimates, 1 using a pharmacokinetic analysis of total serum radioactivity and 1 based on scintigraphic image data, were obtained for each volunteer after 123I-IAZA administration.RESULTSTwo compartments were discernible by pharmacokinetic analysis, and 4 compartments were discernible by image analysis. The urinary bladder wall received the greatest radiation dose (6.3E-02 +/- 8.7E-03 mGy/MBq), followed by the upper large intestinal wall (5.6E-02 +/- 1.2E-02 mGy/MBq), the lower large intestinal wall (5.0E-02 +/- 1.2E-02 mGy/MBq), and the thyroid (4.4E-02 +/- 1.4E-02 mGy/MBq). Approximately 90% of physiologically eliminated radioactivity was excreted through the kidneys. Radioactivity entering the intestinal tract from the gallbladder constituted <10% of biologically eliminated activity.CONCLUSIONThe dosimetric analysis of 123I-IAZA in 6 healthy volunteers indicated that both disposition kinetics and radiation dosimetry support its clinical use for imaging tissue hypoxia.

Perfusion, hypoxia and nucleoside uptake during ganciclovir therapy were determined in a murine HSV-1 TK-expressing tumour model (KBALB-STK). HSV-1 TK mRNA transcription in this cell line was confirmed by RT-PCR. BALB/c mice bearing KBALB-STK tumours accumulated (E)-5-(2-[125I]iodovinyl)-2′-fluoro-2′-deoxyuridine ([125I]IVFRU) (2.54% injected dose·g−1) and could be readily detected with planar imaging following administration of [131I]IVFRU. However, a single dose of ganciclovir (100 mg·kg−1 intraperitoneally) decreased tumour uptake of [125I]IVFRU to 0.33% injected dose·g−1. Subsequent single daily doses of ganciclovir over 3 consecutive days had a negligible effect on [125I]IVFRU uptake, which remained low. Tumour perfusion during 3 days of ganciclovir treatment was monitored with intravenous [99Tcm]HMPAO. Tumour perfusion increased from day 0 (no ganciclovir treatment) with 1.83% injected dose·g−1 tumour, to a maximum at day 2 (3.77% injected dose·g−1). In the same animals, accumulation of [3H]misonidazole decreased from 0.70% injected dose·g−1 at day 0 to a minimum at day 3 (0.24% injected dose·g−1), indicating that tumour tissue had become less hypoxic over the ganciclovir regimen. The uptake of [125I]IVFRU into the acid insoluble fraction of KBALB-STK cells in vitro in the presence of ganciclovir (2.0 μM) was completely inhibited, leading to a 57% decrease in total cellular accumulation of radioactivity. However, cytosolic entrapment of [125I]IVFRU was not affected by the presence of ganciclovir. These results indicate that the mechanisms leading to IVFRU exclusion during ganciclovir treatment of HSV-1 TK-expressing tumours can be attributed, at least partially, to inhibition of [125I]IVFRU-nucleotide incorporation into DNA.

Gender differences in schizophrenia include a later disease onset and second peri-menopausal peak in women, and evidence that psychopathology varies according to the menstrual cycle phase. Possible mechanisms for these gender differences include hypotheses based on animal studies demonstrating that estrogen increases striatal dopamine D2 receptors. We retrospectively investigated the relationship between gender and striatal dopamine in humans using SPECT imaging and the post-synaptic D2 radioligand epidepride. A total of 15 males (mean age = 35.0 ± 7.5 yrs) and 7 females (mean age = 32.3 ± 6.4 yrs) were evaluated from a database consisting of 10 healthy controls (7 males, 3 females), and 12 patients with social phobia (8 males, and 4 females). Multivariate analysis was performed using input variables of gender, group (control vs. social phobia), time of imaging; and an output variable of D2 receptor density (striatal to frontal cortex ratio). Findings revealed that, independent of being a patient or control, females had significantly higher values than males in all measures of striatal D2 receptor density (p = 0.0014). Furthermore, greater variability in D2 receptor density was observed in females compared to males. Consequently, post-synaptic D2 receptor density appears to be highly dependent on gender, and this should be taken into account in future studies of striatal dopamine. Increased striatal D2 receptor density in females may be secondary to the effects of estrogen, while increased D2 receptor variability may reflect estrogen changes over the menstrual cycle. These results suggest possible mechanisms for gender differences in psychiatric disorders like schizophrenia.

Effects of methoxyflurane anesthesia on the pharmacokinetics of intravenous 125I-IAZA in rats are reported. No significant differences in t1/2α, t1/2β, Vss, and ClTB for total radioactivity (125I-IAZA and metabolites) were observed between the anesthetized (Group 1, n = 4) and nonanesthetized (Group 2, n = 3) animals. For 125I-IAZA, ClTB increased from 646 ± 52 mL/h/kg to 2250 ± 351 mL/h/kg and t1/2β decreased from 97.7 ± 17.5 min to 35.6 ± 5.4 min, for Groups 1 and 2, respectively. There were no differences in Vss or t1/2α between the two groups. These findings support literature reports of anesthetic effects on xenobiotic pharmacokinetics, and indicate a need for caution in the evaluation of preclinical imaging studies in which animals are immobilized with anesthetics.

1-α-D-(5-Fluoro-5-deoxyarabinofuranosyl)-2-nitroimidazole (fluoroazomycin arabinoside, FAZA) 6, a putative PET imaging agent when labelled with 18F, was synthesized by fluorination of 1-α-D-(2,3-di-O-acetylarabinofuranosyl)-2-nitroimidazole 3 with DAST followed by deprotection. The C-5′-deuterated and tritiated analogues were prepared by NaCNBD3 or NaCNBT3 reduction of the protected C-5′-carbonyl intermediate 5, followed by C-5′ fluorination and deprotection, to afford C-5′ deuterated and C-5′ tritiated FAZA, respectively. Preliminary in vivo biodistribution studies in a murine tumour model, and pharmacokinetic studies in rats indicated that 3H-FAZA has biodistribution, tumour uptake and pharmacokinetic properties similar to those of 123I-IAZA, a clinically-proven radiopharmaceutical for SPECT-imaging of hypoxic tissues. Copyright © 1999 John Wiley & Sons, Ltd.

This study examined the relationship between magnetic resonance diffusion imaging and autoradiographic markers of cerebral blood flow ((99m)Tc-hexamethylpropylene amine oxime) and cerebral hypoxia ((125)I-iodoazomycin arabinoside) in a rat model of stroke. Middle cerebral artery occlusion in the rat was performed using an intraluminal suture approach. Diffusion, hypoxia, and blood flow maps were acquired 2 hr following occlusion, and were compared with T2 images and histology at 7 hr, Two hours following middle cerebral artery occlusion the lesion distributions from the diffusion maps and hypoxic autoradiographs were similar. The blood flow threshold for increased uptake of the hypoxic marker was approximately 34 +/- 7% of the normal flow. The combination of diffusion or hypoxic images with perfusion maps allowed differentiation between four regions: 1) normal tissue; 2) a region of decreased perfusion but normal diffusion and normal uptake of hypoxic marker; 3) a region of decreased perfusion, decreased diffusion and increased uptake of hypoxic marker; 4) a region of decreased perfusion, decreased diffusion and low uptake of hypoxic marker. The areas for increased uptake of hypoxic marker and decreased diffusion are equivalent, indicating similar blood flow thresholds. Regions of oligaemic misery perfusion, ischaemic misery perfusion and lesion core may be delineated with the combination of diffusion or hypoxic images and perfusion maps. (C) 1999 Wiley-Liss, Inc.

Purpose: Iodine-125 induces cell death by a mechanism similar to that of high linear energy transfer (high-LET) radiation. This study investigates the cytotoxicity of high-specific-activity [I-125]meta-iodobenzylguanidine (I-125-mIBG) in human SK-N-MC neuroblastoma cells grown as three-dimensional multicellular spheroids.Materials and Methods: Spheroids were incubated with high-specific-activity I-125-mIBG (6 mCi/mu g, 1000 times that of the conventional specific activity used for autoradiography). Cytotoxicity was assessed by fluorescence viability markers and confocal microscopy for intact spheroids, fluorescence-activated cell sorting and clonogenic assay, and clonogenic assays for dispersed whole spheroids. Distribution of radioactive mIBG was determined by quantitative light-microscope autoradiography of spheroid cryostat sections. Dose estimation was based on temporal knowledge of the retained radioactivity inside spheroids, and of the radiolabel's emission characteristics. Findings were compared with those of spheroids treated under the same conditions with I-131-mIBG, cold mIBG, and free iodine-125.Results: I-125-mIBG exerted significant cell killing. Complete spheroids were eradicated when they were treated with 500 mu Ci of I-125-mIBG, while those treated with 500 mu Ci or 1000 mu Ci of I-131-mIBG were not, The observed difference in cytotoxicity between treatments with I-125- and I-131-mIBG could not be accounted for by the absorbed dose of spheroid alone. The peripheral, proliferating cell layer of the spheroids remained viable at the moderate radioactivity of 100 mu Ci for both isotopes. Cytotoxicity induced by I-125-mIBG was quantitatively comparable by the peripheral rim thickness to that of I-131-mIBG at the dose of 100 mu Ci. The peripheral rim thickness decreased most significantly in the first 17 hours after initial treatment, There was no statistical decrease in the rim thickness identified afterwards for the second, third, and fourth days of incubation.Conclusion: The cytotoxic effect of high-specific-activity I-125-mIBG appears to be comparable to, if not more efficient than that of conventionally used I-131-mIBG at the same level of total radioactivity. I-125-mIBG may improve the therapeutic index over that of I-131-mIBG in the clinical management of metastatic neuroblastoma due to the short range of Auger electrons. (C) 1998 Elsevier Science Inc.

The usefulness of 123I-epidepride as a single photon emission computed tomography (SPECT) scan D2 receptor ligand was examined in vivo in 13 medicated patients with schizophrenia and age- and sex-matched normal controls. To establish the effect of endogenous dopamine on 123I-epidepride binding, 4 of the 13 controls also received 20 mg D-amphetamine. The results showed that 123I-epidepride had high specific binding to the striatum in both patients with schizophrenia and normal controls. There was a trend for the total striatal binding of medicated patients with schizophrenia, as measured by total basal ganglia: frontal cortex (TBG:FC) ratios, to be less than the binding of controls (P = 0.053). This trend confirms previous work showing that antipsychotic medication decreases the number of D2 receptors available for binding to the radioligand. Interestingly, there was also a significant relationship between 123I-epidepride binding ratios and global functioning scales (Global Assessment of Functioning scale [GAF]) for schizophrenia (r = 0.56, P = 0.045), although there was no such relationship with the Brief Psychiatric Rating Scale (BPRS). In addition, our results showed that amphetamine-induced dopamine release did not alter 123I-epidepride binding, confirming the high specific binding of 123I-epidepride to the D2 receptor. We conclude that 123I-epidepride appears to be a very useful SPECT ligand for imaging the D2 receptor.

OVAREX MAb B43.13 is a new radiopharmaceutical based on a monoclonal antibody (MAb-B43.13) known to recognize CA 125, a tumour antigen associated with epithelial ovarian cancer. This MAb is capable of facile radiolabelling with 99Tcm and has been shown previously to localize in the tumours of ovarian cancer patients. The present study was initiated to measure the pharmacokinetics of this MAb in the serum of 10 patients with primary or metastatic ovarian cancer. A two-compartment model was found to be best at representing the biodistribution of the 99Tcm-labelled MAb, yielding a 2.6 h distribution phase half-life and a 31.3 h elimination phase half-life. The serum and renal clearances for 99Tcm-MAb-B43.13 were 121 and 53 ml h-1 respectively. These parameters were compared with a similar model developed from the serum values of the MAb itself (determined using an ELISA detection method). Based on the serum pharmacokinetics of 99Tcm-MAb-B43.13 and whole-body planar gamma camera images, an estimate of the radiation dose from 99Tcm was calculated using standard MIRD schema. The organs demonstrating significant 99Tcm uptake included the liver, kidneys, heart and spleen. The whole-body dose was similar to other 99Tcm-labelled MAbs.

Pain in patients with cancer metastatic to bone is a significant cause of morbidity and of referrals from general practice and specialist physicians. Management typically utilizes radiation therapy and the graduated use of opiate analgesics. Bone-seeking radiopharmaceuticals have provided a new option to these management strategies, which is effective and cost effective. Strontium 89 is now in routine clinical use, while rhenium 186 hydroxyethylidene diphosphonate (HEDP) and samarium 153 ethylenediaminetetramethylene phosphonate (EDTMP) are in Phase III trials and tin 117m (4+) diethylene triaminepentacetic acid (DTPA) is in Phase I trials. Evidence taken primarily from the Strontium 89 trial, shows unsealed source therapy with these bone-seeking radiopharmaceuticals to be effective in palliating pain, improving quality of life, reducing the rate at which new painful sites develop, reducing requirements for additional radiation therapy, and reducing lifetime management costs. Indications and contraindications to therapy have now been defined, and retreatment is an option with all radiopharmaceuticals.