BACKGROUND:The preliminary characterization of [(131)I]iodoazomycin arabinoside ([(131)I]IAZA) as a potential radiotherapeutic radiopharmaceutical is described. METHODS:High-specific-activity [(131)I]IAZA was prepared in therapeutic doses (up to 3 GBq per batch) by isotope exchange in pivalic acid melt and was purified on Sep-Pak cartridges. Stability in 15% ethanol in saline at 4 degrees C was determined by high-performance liquid chromatography. IAZA cytotoxicity (IC(50), approximately 0.1 mM) against both murine (EMT-6) and human (143B, 143B-LTK) tumor cells determined by MTT test was in the range previously reported for EMT-6 cells using a clonogenic assay. Tissue radioactivity levels were measured in a murine tumor model for the 24- to 168-h postinjection period. Radiation dose estimates obtained from the tissue activity levels for this period were calculated from pharmacokinetic (WinNonlin) and dosimetry (MIRD and RAdiation Dose Assessment Resource) parameters. RESULTS:The radioiodination efficiency was >90%, but with systematic losses during Sep-Pak purification, the recovered yields of [(131)I]IAZA were approximately 75%. The product (specific activity, 4.6-6.4 GBq/micromol) was stable for at least 2 weeks, with only approximately 6% degradation over this storage period. Extended biodistribution studies in Balb/c mice bearing implanted EMT-6 tumors showed that the highest tumor/blood radioactivity ratio (T/B; 4.8) occurred 24 h after dosing; the T/B ratio was approximately 1.5 at the end of the 7-day study. The 24- to 168-h tissue radioactivity data fit a one-compartment model except for liver data, which best fit a two-compartment model. Dosimetry estimates showed a tumor self-dose of 7.4 mGy/MBq, which is several-fold higher than for the liver or the kidney. CONCLUSIONS:[(131)I]IAZA can be efficiently radiolabeled at high specific activity, purified by a simple Sep-Pak technique and stored with little radiolysis or chemical decomposition at these specific activities. Based on measured radioactivity burdens during the week following injection and on published animal ([(125)I]IAZA) and clinical ([(123)I]IAZA) dosimetry data, the current dose estimates point to selective tumor irradiation at low dose rates.

1-(2'-[F-18]-fluoroethoxy)-2,5-bi,(4'-methoxystyryl)benzene (F-18-FESB) was synthesized in similar to 76% radiochemical yield (specific activity > 58.6 GBq or 1.58 Ci/mu mol) in an Advanced Cyclotron Systems' automated synthesis unit by nucleophilic substitution of 1-(2'-toluenesulfonylethoxy)-2,5-bis(4'-methoxystyryl)benzene and purified using reversed phase column chromatography. When performed in the presence of ionic fluid, either 1-butyl-3-methylimidazolium tetrafluoroborate (Bmimtetrafluoroborate; BmimBF(4)) or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (Emimtriflate; EmimTFMS), radiochemical yields of F-18-FESB ranged from 17 to 76%. The radiochemical yields were consistently lower (similar to 3-7%) in the absence of these ionic fluids. Copyright (c) 2005 John Wiley & Sons, Ltd.

A multistep radioimmunotherapeutic (RIT) approach, exploiting the combination of a bispecific monoclonal antibody (BsMAb) with 90Y labelled biotinylated long-circulating liposomes was tested as a potential adjuvant treatment for epithelial ovarian carcinomatosis. The BsMAb, with anti-CA 125 and anti-biotin epitopes was used with PEGylated liposomes coated with biotin to deliver the cytotoxic radionuclide 90Y to tumor sites. This approach was used to overcome some of the major obstacles associated with conventional strategies, in particular, to increase the amount of radioactivity delivered to the tumor site compared with conventional monoclonal antibody (MAb) radionuclide delivery. Sequential intraperitoneal administration of the targeting and therapeutic moieties provides the basis for enhanced therapeutic ratio, according to our strategy. We report here the results of an in vivo therapy using our RIT approach with the Balb/c nude mouse model xenografted with the NIH:OVCAR-3 (CA 125+) human ovarian cancer cell line. An ongoing tumor growth delay/control study in Balb/c mice xenografted intraperitoneally with the NIH:OVCAR-3 cell line indicates a significant delay in onset of tumor and ascites development in treated vs. control populations.

To improve tumor-to-tissue ratios of anticancer agents in radioimmunotherapy, a three-step targeting approach was used to deliver biotinylated liposomes to human ovarian cancer cells (NIH:OVCAR-3, SK-OV-3) in vitro. Targeting was based upon the use of two antibodies specific for the CA-125 antigen that is highly expressed on NIH:OVCAR-3 cells but not expressed on SK-OV-3 cells. Briefly, the approach consists of prelabeling target cells with biotinylated anti-CA-125 antibody and FITC-labeled streptavidin (SAv) prior to administration of biotinylated liposomes containing a marker dye for visualization by confocal laser scanning microscopy (CLSM). In addition, the two anti-CA-125 antibodies (B27.1 and B43.13) were labeled with FITC and incubated with ovarian cancer cells at 37 degrees C from 30 min to 24 h to study binding and uptake kinetics. Shedding kinetics of bound antibody from tumor cells was performed using radiolabeled B27.1. Results demonstrated that both B27.1 and B43.13 specifically bound to the cell surface of OVCAR-3 cells but not to SK-OV-3 cells. Biotinylation, FITC-labeling and radiolabeling of the antibodies did not compromise immunoreactivity. Less than 6% of the bound B27.1 was shed from tumor cells by 4 h following incubation, and the antibody-antigen complex resided predominantly on the cell surface by 4 h at 37 degrees C with slow internalization by 12-24 h. Biotinylated, conventional liposomes were specifically and effectively delivered to OVCAR-3 cells prelabeled with biotinylated B27.1 and SAv. The slow internalization and shedding properties of these antibodies are useful for multistep pretargeting methods. Thus, a modified targeting strategy, utilizing a bispecific antibody and liposomes, may be feasible for radioimmunoliposomal therapy of ovarian cancer.

The Km and Vmax of [14C]-radiolabeled polyamines were determined for PC-3 and AT3B-1 cell lines. With PC-3 Km values are in the following order: ornithine> spermidine> spermine> putrescine, while with AT3B-1 it was spermidine> ornithine> spermine> putrescine. To determine which of these polyamines exhibit higher accumulation, the relative uptake of all the four amines was studied with prostate (PC-3, AT3B-1, LNCaP) and non-prostate (MCF-7, KLN-205, OVCAR) cell lines at 10 and 20 microM after 1 hour. Spermine and spermidine accumulated at higher levels in prostate (AT3B-1 and LNCaP) over non-prostate cell lines (p < 0.01). Putrescine accumulated more in PC-3 and LNCaP than the non-prostate cancer cells.

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.

A review of published data on some of the problems associated in treating cancer using radioimmunotherapy is presented. Potential improvements for this type of therapy using pretargeting strategies are discussed and preliminary results on a novel multistep regimen to treat human ovarian cancer are presented. A pretargeting strategy using a biotinylated, anti-CA125 monoclonal antibody (MAb) to attract biotinylated long-circulating liposomes to the surface of CA125-expressing ovarian cancer cells, was employed. Confocal laser scanning microscopy and fluorescent labels were used to establish the biodistribution patterns in NIH:OVCAR-3 (CA-125 positive) and SK-OV-3 (CA-125 negative) human ovarian cancer cells. Shedding kinetics of the pretargeted stage were measured using 125I labeled MAbs. No significant internalization of the MAb used in the pretargeting step was observed by 4 hrs. The antibody was gradually internalized starting at 6 hrs, and most of the labelled MAb was detected in cytoplasm by 24 hrs. Shedding and exocytosis of the antigen-MAb complex was not significant for up to 6-hours following administration of the iodinated MAb. Biotinylated liposomes were shown to specifically target the biotinylated MAb/streptavidin complex on the cell surface. We have demonstrated that by a three-step pretargeting approach, biotinylated liposomes can be specifically delivered to cells pretargeted with biotinylated MAb/SAv complex. The slow internalization and shedding properties of the two MAbs are ideal for multistep pretargeting methods. A successful multistep linkage was established with the biotinylated MAb B27.1, streptavidin and biotinylated liposomes to OVCAR-3 cells, but not to SK-OV-3 cells.

The radionuclide 41Ar has many ideal properties as a gas flow tracer. However, the modest cross-section of 40Ar for thermal neutron activation makes preparation of suitable activities of 41Ar technically difficult particularly for low flux reactors. Argon can however be trapped in a molecular complex called a clathrate that can then be irradiated. We prepared argon clathrate and explored its irradiation and stability characteristics. Argon clathrate can be used to provide gigabecquerel quantities of 41Ar even with low power reactors.

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.

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.

A novel method for generating monoclonal antibodies against synthetic tumour-associated glycoconjugates has been developed. One of these monoclonal antibodies, designated 170H.82, was derived against the TF antigen and has been shown in vitro to have a wide range of reactivity with adenocarcinoma. This antibody has been labelled with 111In and 99Tcm and has been evaluated in pilot clinical trials involving 48 patients with a range of adenocarcinoma. Overall clinical accuracy with the radiolabelled antibody was 92%, with the antibody appearing to have particular clinical utility in gynaecological and breast cancers. Single photon emission computed tomographic (SPECT) imaging was shown to improve the quality of the images and to improve the diagnostic sensitivity. We believe that this unique antibody, labelled with 99Tcm, appears to offer promise for routine clinical use in the evaluation of patients with a range of primary and metastatic adenocarcinoma.

S of the Society of Nuclear Medicine in Canada and Prairie Provinces Chapter, SNM Conjoint Meeting: PDF Only

A multichannel scaling (MCS) system has been developed to monitor the biological distribution of radiotracers in vivo. The design of this system permits the simultaneous collection of data from up to four radiation detectors. The evolution of detected count rates is displayed in real time as a histogram with a minimum channel width of 1 s. Each point in the data arrays can accommodate more than 16 million counts. The low-power Schottky integrated circuits used can readily process the maximum count rates that sodium iodide detectors can produce. The four counting units together with control circuitry were constructed on a single custom IBM PC expansion board.

Commercially available liquid scintillation (LS) counters are usually designed so that they can automatically count a large number of samples focusing attention on only a few of the most frequently used radionuclides. A single-sample LS counter has been developed incorporating features that allow a more flexible analysis of the signals generated by a pair of photomultiplier (PM) tubes. This instrument has been applied to the measurement of radioactivity contained in moderator water samples obtained from a small nuclear reactor.

Three examples of modern liquid scintillation counters were tested and several of their performance characteristics measured. Color and chemical quenched samples were counted in a Beckman LS 9000, a Packard 460C and a Tracor Mark III to test the reproductbility of different quench monitoring techniques. Instrumental differences and similarities are discussed and related to the performance of these counters. All three counters operated reliably over a wide range of sample quenching.

A photon absorbing quencher (PAQ) has been developed to facilitate the testing of liquid scintillation counting systems. The components of this mixture have been selected so that all wavelengths of light emitted by a toluene based flour are uniformly absorbed. The use of dried filter paper carrier discs greatly simplifies the addition of this colour quencher to counting vials.