The effect of 111In radionuclide distance and auger electron energy on direct induction of DNA double-strand breaks: a Monte Carlo study using Geant4 toolkit.

PURPOSE: In this study, the effect of 111In position and Auger electron energy on direct induction of DSBs was investigated. MATERIALS AND METHODS: The Geant4-DNA simulation toolkit was applied using a simple B-DNA form extracted from PDBlib library. First, the simulation was performed for electrons with energies of 111In and equal emission probabilities to find the most effective electron energies. Then, 111In Auger electrons' actual spectrum was considered and their contribution in DSB induction analysed. RESULTS: The results showed that the most effective electron energy is 183 eV, but due to the higher emission probability of 350 eV electrons, most of the DSBs were induced by the latter electrons. Also, it was observed that most of the DSBs are induced by electrons emitted within 4 nm of the central axis of the DNA and were mainly due to breaks with <4 base pairs distance in opposing strands. Whilst, when 111In atoms are very close to the DNA, 1.3 DSBs have been obtained per decay of 111In atoms. CONCLUSIONS: The results show that the most effective Auger electrons are the 350 eV electrons from 111In atoms with <4 nm distance from the central axis of the DNA which induce ∼1.3 DSBs per decay when bound to the DNA. This value seems reasonable when compared with the reported experimental data.

Dual-Receptor-Targeted Radioimmunotherapy of Human Breast Cancer Xenografts in Athymic Mice Coexpressing HER2 and EGFR Using 177Lu- or 111In-Labeled Bispecific Radioimmunoconjugates.

UNLABELLED: One mechanism of resistance to trastuzumab in human epidermal growth factor receptor-2 (HER2)-positive breast cancer (BC) is increased epidermal growth factor receptor (EGFR) expression. We have developed (111)In-labeled bispecific radioimmunoconjugates (bsRICs) that bind HER2 and EGFR on BC cells by linking trastuzumab Fab fragments through a polyethylene glycol (PEG24) spacer to epidermal growth factor (EGF). We hypothesized that tumors coexpressing HER2 and EGFR could be treated by dual-receptor-targeted radioimmunotherapy with these bsRICs labeled with the ß-particle emitter (177)Lu or the Auger electron-emitter (111)In. METHODS: The binding of (177)Lu-DOTA-Fab-PEG24-EGF to tumor cells (MDA-MB-231, SK-OV-3, MDA-MB-231/H2N, or TrR1) coexpressing HER2 and EGFR was assessed in competition assays. The clonogenic survival of these cells was measured after exposure to (177)Lu-DOTA-Fab-PEG24-EGF or (111)In-DTPA-Fab-PEG24-EGF or to monospecific (177)Lu- or (111)In-labeled trastuzumab Fab or EGF. The tumor and normal tissue biodistribution of (177)Lu-DOTA-Fab-PEG24-EGF was studied at 48 h after injection in athymic mice bearing subcutaneous MDA-MB-231/H2N tumors. Radiation-absorbed doses to tumors and normal tissues were estimated and compared for (111)In- and (177)Lu-labeled bsRICs. The maximum injected amount of (177)Lu-DOTA-Fab-PEG24-EGF that caused no observable adverse effects (NOAEL) was identified in BALB/c mice. Athymic CD1 nu/nu mice bearing subcutaneous trastuzumab-sensitive MDA-MB-231/H2N or trastuzumab-resistant TrR1 tumors were treated with (177)Lu-DOTA-Fab-PEG24-EGF or (111)In-DTPA-Fab-PEG24-EGF at the NOAEL, or with unlabeled immunoconjugates or normal saline. Tumor growth was evaluated over a period of 49 d. RESULTS: (177)Lu-DOTA-Fab-PEG24-EGF bound specifically to HER2 and EGFR on tumor cells. Monospecific (177)Lu- and (111)In-labeled trastuzumab Fab or EGF killed tumor cells that predominantly expressed HER2 or EGFR, respectively, whereas bsRICs were cytotoxic to cells that displayed either HER2 or EGFR or both receptors. bsRICs were more effective than monospecific agents. (177)Lu-DOTA-Fab-PEG24-EGF was more cytotoxic than (111)In-DTPA-Fab-PEG24-EGF. The tumor uptake of (177)Lu-DOTA-Fab-PEG24-EGF was 2-fold greater than (177)Lu-DOTA-trastuzumab Fab or (177)Lu-DOTA-EGF. The NOAEL for (177)Lu-DOTA-Fab-PEG24-EGF was 11.1 MBq (10 µg). Trastuzumab-sensitive MDA-MB-231/H2N and trastuzumab-resistant TrR1 tumors were growth-inhibited by (177)Lu-DOTA-Fab-PEG24-EGF or (111)In-DTPA-Fab-PEG24-EGF. Unlabeled immunoconjugates had no effect on tumor growth. (177)Lu-DOTA-Fab-PEG24-EGF inhibited tumor growth more effectively than (111)In-DTPA-Fab-PEG24-EGF because of a 9.3-fold-higher radiation-absorbed dose (55.0 vs. 5.9 Gy, respectively). CONCLUSION: These results are encouraging for further development of these bsRICs for dual-receptor-targeted radioimmunotherapy of BC coexpressing HER2 and EGFR, including trastuzumab-resistant tumors.

Dynamic In Vivo SPECT Imaging of Neural Stem Cells Functionalized with Radiolabeled Nanoparticles for Tracking of Glioblastoma.

UNLABELLED: There is strong clinical interest in using neural stem cells (NSCs) as carriers for targeted delivery of therapeutics to glioblastoma. Multimodal dynamic in vivo imaging of NSC behaviors in the brain is necessary for developing such tailored therapies; however, such technology is lacking. Here we report a novel strategy for mesoporous silica nanoparticle (MSN)-facilitated NSC tracking in the brain via SPECT. METHODS: (111)In was conjugated to MSNs, taking advantage of the large surface area of their unique porous feature. A series of nanomaterial characterization assays was performed to assess the modified MSN. Loading efficiency and viability of NSCs with (111)In-MSN complex were optimized. Radiolabeled NSCs were administered to glioma-bearing mice via either intracranial or systemic injection. SPECT imaging and bioluminescence imaging were performed daily up to 48 h after NSC injection. Histology and immunocytochemistry were used to confirm the findings. RESULTS: (111)In-MSN complexes show minimal toxicity to NSCs and robust in vitro and in vivo stability. Phantom studies demonstrate feasibility of this platform for NSC imaging. Of significance, we discovered that decayed (111)In-MSN complexes exhibit strong fluorescent profiles in preloaded NSCs, allowing for ex vivo validation of the in vivo data. In vivo, SPECT visualizes actively migrating NSCs toward glioma xenografts in real time after both intracranial and systemic administrations. This is in agreement with bioluminescence live imaging, confocal microscopy, and histology. CONCLUSION: These advancements warrant further development and integration of this technology with MRI for multimodal noninvasive tracking of therapeutic NSCs toward various brain malignancies.

Peptide receptor radionuclide therapy in patients with inoperable meningiomas: our experience and review of the literature.

OBJECTIVE: Few studies describe peptide receptor radionuclide therapy (PRRT) using (90)Y- or (177)Lu-labeled peptides in patients with recurrent meningiomas. No clinical data about (111)In-Pentetreotide in such patients are available. We report on (111)In-Pentetreotide therapy in patients with inoperable meningiomas and review the literature about PRRT of meningiomas. METHODS: We reviewed clinical records of 8 patients with meningioma/meningiomatosis showing high (111)In-Pentetreotide uptake on pretherapy scintigraphy who were treated with at least one cycle of (111)In-Pentetreotide. In 2 patients, a cocktail of (111)In-Pentetreotide and beta-emitting radiolabeled peptides had been administered. RESULTS: No patient experienced acute toxicity, neurological or renal function impairment. Mild transient bone marrow toxicity was observed in 4 patients. Objective partial response was observed in 2 patients, stable disease in 5 and disease progression in one. There were no statistically significant correlations between objective response and patient age, tumor WHO grade, baseline Karnofsky performance score, (111)In-Pentetreotide tumoral uptake grade, tumor/nontumor ratio, disease state at baseline, and cumulative dose. CONCLUSIONS: In consideration of its efficacy and the lack of significant toxicity, PRRT of meningiomas using (111)In-Pentetreotide could be proposed even nowadays when the use of (177)Lu- or (90)Y-labeled peptides seems unsafe, namely in patients with renal impairment/toxicity.

Acute homing of bone marrow-derived mononuclear cells in intramyocardial vs. intracoronary transplantation.

OBJECTIVES: Cell homing optimisation after transplantation is critical in myocardial infarction (MI) cell therapy. DESIGN: Eight pigs were randomized to receiving autologous purified (111)indium-labeled bone marrow mononuclear cells (BMMCs) (10(8) cells/2 ml) by intramyocardial (IM) (n=4) or by intracoronary (IC) (n=4) transplantation after 90 minutes occlusion of the CX-coronary artery. Dual isotope SPECT imaging was performed 2 and 24 hours postoperatively. Two animals were additionally analyzed on the sixth postoperative day. Tissue samples from the major organs were analyzed. RESULTS: In SPECT imaging revealed that BMMCs administered using IM injection remained in the injured area. In contrast, minor proportion of IC transplanted cells remained in the myocardium, as most of the cells showed homing in the lungs. Analysis of the biopsies showed a seven-fold greater number of cells in the myocardium for the IM method and a 10-fold greater number of cells in the lungs in the IC group (p < 0.001). CONCLUSIONS: In producing persistently high cell homing at the infarction site, the IM transplantation is superior to the IC transplantation. However, the IC administration might be more specific in targeting injured capillaries and epithelial cells within the infarcted myocardium.

The role of combined imaging in metastatic medullary thyroid carcinoma: 111In-DTPA-octreotide and 131I/123I-MIBG as predictors for radionuclide therapy.

PURPOSE: The medical treatment of metastatic medullary thyroid carcinoma (MTC) is still questionable. The aim of this study was to evaluate a combined imaging protocol using 111In-DTPA-octreotide and 131I/123I-MIBG to decide whether targeted radiotherapy would be useful, and which radiopharmaceutical (90Y-DOTATOC or 131I-MIBG) would be more effective. METHODS: Eight patients (four men, four women; mean age 61 years) with metastatic MTC were included. Treatments were performed with 3,330 MBq 90Y-DOTATOC at 6-week intervals, or 11.1 GBq 131I-MIBG with a minimum interval of 3 months. RESULTS: The imaging procedure was positive in all eight patients: 111In-DTPA-octreotide imaging in five patients, 131I/123I-MIBG imaging in four patients. With respect to the number of metastatic lesions, MIBG imaging was less effective than octreotide. According to the results of combined imaging, we identified one patient to be treated with 90Y-DOTATOC, and three patients with 131I-MIBG. An overall antitumor effect was observed in all four patients, one with partial remission and three with stable disease. No relevant toxicity was observed. CONCLUSIONS: The combined imaging can increase the detection rate of metastatic foci in patients with MTC and identify more patients for effective radionuclide treatment. The treatment with 90Y-DOTATOC or 131I-MIBG is well tolerated and may improve the fate of patients with metastatic MTC.

Indium-111-pentetreotide prolongs survival in gastroenteropancreatic malignancies.

Somatostatin and its analogues bind to somatostatin receptors (sst) 1 through 5 that are overexpressed in neuroendocrine neoplasms such as gastroenteropancreatic (GEP) malignancies. After ligand-receptor binding, a fraction of the ligand-receptor complexes internalize. This internalization process is an effective means of delivering cytotoxic radiolabeled somatostatin analogues, especially those emitting short-range decay particles such as Auger electrons, to the neoplastic cell nucleus. Indium-111-pentetreotide, an sst 2 preferring somatostatin analogue with gamma and Auger electron decay characteristics, is commonly used for the scintigraphic evaluation and management of neuroendocrine cancer patients. This clinical trial was performed to determine the effectiveness and tolerability of therapeutic doses of (111)In-pentetreotide in patients with GEP tumors. GEP tumor patients who had failed all forms of conventional therapy, with worsening of tumor-related signs and symptoms and/or radiographically documented progressive disease, an expected survival less than 6 months, and sst positivity as determined by the uptake on a 6.0 mCi (111)In-pentetreotide scan (OctreoScan; Mallinckrodt Medical, Inc, St. Louis, MO), were treated with at least 2 monthly 180-mCi intravenous injections of (111)In-pentetreotide. Baseline clinical assessments, serum chemistries, and plasma pancreastatin levels were measured and repeated before each (111)In-pentetreotide treatment. From February 1997 to February 1998, 27 GEP (24 carcinoid neoplasms with carcinoid syndrome and 3 pancreatic islet cells) patients were accrued, with 26 patients evaluable for clinical and radiographic responses, 21 patients evaluable for biochemical assessments, and 27 patients evaluable for survival analysis and safety. Toxicity was evaluated by using standard National Cancer Institute (NCI) Common Toxicity Criteria guidelines. Clinical benefit occurred in 16 (62%) patients. Pancreastatin levels decreased by 50% or more in 81% of the patients. Objective partial radiographic responses occurred in 2 (8%) patients, and significant tumor necrosis (defined by 20 Hounsfield units or greater decrease from baseline) developed in 7 (27%) patients. The following transient Grades 3/4 NCI Common Toxicity Criteria side effects were observed, respectively: leukocyte: 1/1; platelets: 0/2; hemoglobin: 3/0; bilirubin: 1/3; creatinine: 1/0; neurologic: 1/0. Myeloproliferative disease and/or myelodysplastic syndrome have not been observed in the 6 patients followed-up for 48+ months. The median survival was 18 months (range, 3-54+ mo). Two doses (180 mCi) of (111)In-pentetreotide are safe, well-tolerated, and improve symptoms in 62% of patients, decrease hormonal markers in 81% of patients, decrease Hounsfield units on computed tomography (CT) scans in 27% of patients, with 8% partial radiographic responses and increased expected survival in GEP cancer patients with somatostatin receptor-expressing tumors. The maximal tolerated dose of (111)In-pentetreotide and the optimal dosing schedules remain under investigation.

Bone marrow toxicity in mice treated with indium-114m-labelled blood cells.

Clinical trials with autologous indium-114m-labelled lymphocytes have revealed significant anti-tumour effects in chronic lymphocytic leukaemia patients with highly resistant disease. Substitution of the lymphocyte vector with heat-damaged red blood cells (HDRBC) may make this treatment more universally applicable and reduce the dose-limiting myelosuppression encountered with labelled lymphocytes. Therefore, the bone marrow localization and toxicities of indium-labelled lymphocytes or HDRBC have been investigated in BDFI mice. At 24 hours approximately 4% and 1.2% of 114In(m) administered as labelled lymphocytes or HDRBC respectively was localized within the bone marrow and remained constant for 57 days thereafter. Toxicity towards bone marrow stem cells, measured as CFU-S, was equivalent for both cellular vectors. However, at clinically relevant activities, 114In(m) HDRBC were less toxic than labelled lymphocytes towards committed progenitors, assayed as in vitro-CFC and CFU-Meg. These data suggest that substitution of HDRBC for lymphocytes as the 114In(m) vector may be beneficial in reducing the myelosuppression associated with this technique.

In situ radiotherapy with 111In-pentetreotide. State of the art and perspectives.

111In-pentetreotide (Octreoscan) and other radiolabeled somatostatin analogs are useful in the management of well differentiated neuroendocrine malignancies such as carcinoid or islet cell neoplasms. These radiopeptides bind to membrane bound somatostatin receptors (sst 1-5) which are over-expressed in a wide variety of neoplasms, especially those arising from the neuroectoderm. Imaging advances allow for the noninvasive determination of the presence of sst receptors by combining radioactivity [111Indium with a somatostatin analog, DTPA-D-phe1-octreotide (pentetreotide)]. Radiolabeled somatostatin analogs bind to membrane receptors and internalization of the complex occurs. Auger emitting somatostatin analogs offer a novel and significantly less toxic approach to controlling neoplastic diseases by delivering targeted radiation specifically to receptor bearing cells while sparing receptor negative cells. Responses of 62-69% in 85 patients with metastatic neuroendocrine tumors treated with high dose (6-19.6 GBq) 111In-pentetreotide, specifically targeting tumor somatostatin receptors, have been reported. Objective responses observed included biochemical and radiographic responses with prolonged survival. This article will discuss and review the multi-center data available to date, the mechanisms of action of radiolabeled somatostatin analogs, dosimetry, clinical response parameters, and toxicity.

The role of radioactive somatostatin and its analogues in the control of tumor growth.

Peptide receptor scintigraphy with the radioactive somatostatin analogue [111In-DTPA-D-Phe1]octreotide is a sensitive and specific technique to show in vivo the presence and abundance of somatostatin receptors on various tumors. With this technique primary tumors and metastases of neuroendocrine cancers as well as of many other cancer types can be localized. This technique is currently used to assess the possibility of peptide receptor radionuclide therapy with repeated administration of high doses of [111In-DTPA-D-Phe1]octreotide. 111In emits Auger and conversion electrons, having a tissue penetration of 0.02-10 microns and 200-500 microns, respectively. Thirty end-stage patients with mostly neuroendocrine progressing tumors were treated with [111In-DTPA-D-Phe1]octreotide, up to a maximal cumulative patient dose of about 74 GBq, in a phase-I trial. There were no major clinical side effects after up to 2 years of treatment, except that in a few patients a transient decline in platelet counts and lymphocyte subsets occurred. Promising beneficial effects on clinical symptoms, hormone production, and tumor proliferation were found. Of the 21 patients who received a cumulative dose of more than 20 GBq, eight showed stabilization of disease and six others a reduction in tumor size. There is a tendency towards better results in patients whose tumors have a higher accumulation of the radioligand. Peptide receptor radionuclide therapy is also feasible with 111In as the radionuclide. Theoretically, depending on the homogeneity of distribution of tumor cells expressing peptide receptors and the size of the tumor, beta-emitting radionuclides, e.g., 90Y, labeled to DOTA-chelated peptides may be more effective than 111In for peptide receptor radionuclide therapy. The first peptide receptor radionuclide therapy trials with [90Y-DOTA-Tyr3]octreotide started recently.

Treatment with high dose [(111)In-DTPA-D-PHE1]-octreotide in patients with neuroendocrine tumors--evaluation of therapeutic and toxic effects.

Carcinoid tumors and endocrine pancreatic tumors often express somatostatin receptors (sst). Tumor spread may be visualized by sst scintigraphy using [(111)In-DTPA-D-Phe1]-octreotide. In this study, tumor targeting therapy with [(111)In-DTPA-D-Phe1]-octreotide at high doses (6 GBq every third week) was used to treat patients with sst-expressing tumors. Five patients entered the protocol and three were evaluable for response, while all could be evaluated for toxicity. Two patient responded with a significant reduction in tumor markers (> 50%). The third patient showed increasing levels of tumor markers. Side effects were expressed as depression of bone-marrow function. In one patient a grade 4 reduction in platelet count was observed requiring several thrombocyte transfusions. In another two patients platelet counts decreased significantly. We conclude that treatment with [(111)In-DTPA-D-Phe1]-octreotide can be used in patients with neuroendocrine tumors but blood parameters have to be carefully monitored to avoid severe side effects.

Dose escalation trial of indium-111-labeled anti-carcinoembryonic antigen chimeric monoclonal antibody (chimeric T84.66) in presurgical colorectal cancer patients.

UNLABELLED: Chimeric T84.66 (cT84.66) is a high-affinity (1.16x10(11) M(-1)) IgG1 monoclonal antibody against carcinoembryonic antigen (CEA). The purpose of this pilot trial was to evaluate the tumor-targeting properties, biodistribution, pharmacokinetics and immunogenicity of 111In-labeled cT84.66 as a function of administered antibody protein dose. METHODS: Patients with CEA-producing colorectal cancers with localized disease or limited metastatic disease who were scheduled to undergo definitive surgical resection were each administered a single intravenous dose of 5 mg of isothiocyanatobenzyl diethylenetriaminepentaacetic acid-cT84.66, labeled with 5 mCi of 111In. Before receiving the radiolabeled antibody, patients received unlabeled diethylenetriaminepentaacetic acid-cT84.66. The amount of unlabeled antibody was 0, 20 or 100 mg, with five patients at each level. Serial blood samples, 24-hr urine collections and nuclear images were collected until 7 days postinfusion. Human antichimeric antibody response was assessed up to 6 mo postinfusion. RESULTS: Imaging of at least one known tumor site was performed in all 15 patients. Fifty-two lesions were analyzed, with an imaging sensitivity rate of 50.0% and a positive predictive value of 76.9%. The antibody detected tumors that were not detected by conventional means in three patients, resulting in a modification of surgical management. Interpatient variations in serum clearance rates were observed and were secondary to differences in clearance and metabolic rates of antibody and antibody:antigen complexes by the liver. Antibody uptake in primary tumors, metastatic sites and regional metastatic lymph nodes ranged from 0.4% to 134% injected dose/kg, resulting in estimated 90Y-cT84.66 radiation doses ranging from 0.3 to 193 cGy/mCi. Thirteen patients were evaluated 1-6 mo after infusion for human antichimeric antibody, and none developed a response. No major differences in tumor imaging, tumor uptake, pharmacokinetics or organ biodistribution were observed with increasing protein doses, although a trend toward increasing blood uptake and decreasing liver uptake was observed with increasing protein dose. CONCLUSION: Chimeric T84.66 demonstrated tumor targeting comparable to other radiolabeled intact anti-CEA monoclonal antibodies. Its immunogenicity after single administration was lower than murine monoclonal antibodies. These properties make 111In-cT84.66, or a lower molecular weight derivative, attractive for further evaluation as an imaging agent. Yttrium-90 dosimetry estimates predict potentially cytotoxic radiation doses to select tumor sites, which makes 90Y-cT84.66 also appropriate for further evaluation in Phase I radioimmunotherapy trials. Although clinically important changes in biodistribution, pharmacokinetics and tumor targeting with increasing protein doses of 111In-cT84.66 were not demonstrated, the results do suggest that antibody clearance from the blood is driven by hepatic uptake and metabolism, with more rapid blood clearance seen in patients with liver metastases. These patients with rapid clearance and potentially unfavorable biodistribution for imaging and therapy may, therefore, be a more appropriate subset in which to evaluate the role of administering higher protein doses. This underscores the need to further identify, characterize and understand those factors that influence the biodistribution and clearance of radiolabeled anti-CEA antibodies, to allow for better selection of patients for therapy and rational planning of radioimmunotherapy.

Indium-111 satumomab pendetide: the first FDA-approved monoclonal antibody for tumor imaging.

OBJECTIVE: Colon cancer is the second most common cause of cancer mortality. Ovarian cancer is the most common gynecologic malignancy cause of death in women. A labeled monoclonal antibody attaches to a tumor-associated antigen and allows these tumor masses to be imaged or treated, depending on the radionuclide used. Indium-111 satumomab pendetide was the first labeled monoclonal antibody to be approved by the Food and Drug Administration (FDA) for tumor imaging. It is reactive with most colorectal and ovarian cancers, as well as other cancers. After reading this article, the technologist will understand the FDA approval process, phase trial results, safety and adverse reactions, human antimurine antibody response, indications, imaging protocol, and strengths and weaknesses of imaging with satumomab pendetide. Representative cases are presented.

Interference of patient medication in the radiolabelling of white blood cells: an update.

Evidence is now accumulating that patient medication can adversely affect the radiolabelling of white cells. We have undertaken a survey for the years 1981-97 to examine instances of unusually low labelling efficiencies of 111In-tropolone and 99Tcm-HMPAO labelled white cells. Respondents were asked to ascertain which drugs were being taken on the day of the test. Fifty adverse reports were received during that period. Many patients were taking drugs which are known to affect white cell function, including cephalosporins, azathioprine, prednisolone, cyclophosphamide, nifedipine, suphasalazine, iron salts and heparin. Using Bradford-Hill's criteria to assess whether an association between two variables is also one of causation, it was found that there was a high probability that the above drugs caused the low labelling efficiencies.

Thyroid radiation doses during radioimmunotherapy of CEA-expressing tumours with 131I-labelled monoclonal antibodies.

A number of radioimmunotherapy (RAIT) trials with iodinated antibodies have shown a high variability in the radiation doses to the thyroid. Therefore, the aim of this study was to evaluate which factors influence these thyroid doses during RAIT with 131iodinated monoclonal anti-carcinoembryonic antigen (CEA) antibodies. Data from 36 patients with CEA-expressing tumours were analysed. The patients underwent RAIT with the 131I-labelled IgG1 anti-CEA antibody, MN-14 (Ka = 10(9) l mol-1) or its F(ab')2 fragment (activity range 45.8-220.0 mCi). The thyroid was blocked with 120 mg iodine (lugol's orSSKI solution) and 400 mg perchlorate per day, starting 1 day prior to the first study. Blood clearance and molecular composition of labelled plasma compounds were determined by blood sampling and size-exclusion high-performance liquid chromatography analysis. The cumulated activities of tissues were determined from daily imaging and blood clearance data. Doses were derived from the MIRD scheme. Thyroid radiation doses showed a high variability, between 1.2 and 37.7 cGy mCi-1 (mean +/- S.D.: 11.1 +/- 8.3 cGy mCi-1), corresponding to absolute doses between 2.5 and 43.6 Gy. However, the maximal iodine uptake in the thyroid was 2.4 +/- 1.9 microCi mCi-1 (range 0.2-10.0 microCi mCi-1), which was less than 1% of the injected activity, indicating that more than 99% of the thyroid was blocked in all cases. No correlation was found between these thyroid doses and conditions leading to an enhanced exposure to free radioiodine, such as unbound I- in the mAb preparation, rapid metabolic breakdown of the labelled antibody due to human anti-mouse antibodies (HAMA), or immune complex formation with circulating antigen. However, a relationship between the thyroid doses and the patients' compliance in taking their Lugol's and perchlorate blocking medications, as well as to a relatively high variability in the biological half-life of the iodine in the thyroid (range from 31.1 h to virtual infinity), is indicated. No rising TSH titres or other signs of (latent) hypothyroidism were seen in these patients during a 2 year follow-up period. Longer follow-up was not possible because of the terminal condition of most of the patients. These data show that thyroid doses in an appropriately blocked individual given a standard, non-myeloablative dose of RAIT, are generally lower than those assumed to be required to cause late hypothyroidism. Even if higher activities are used, potential hypothyroidism may be overcome easily by hormone replacement. Thyroid doses are independent of parameters leading to an enhanced exposure of the thyroid to free radioiodine, suggesting that patient compliance in taking their blocking medication may be the most crucial factor for reducing thyroid doses in RAIT with 131I-labelled antibodies.

Hematologic side effects of radiolabeled immunoglobulin therapy.

Radiolabeled immunoglobulin therapy (RIT) is a new cancer treatment that is more selective than its predecessors. Its dose-limiting normal tissue side effect is bone marrow toxicity, and hematopoietic stem cell damage appears to be its most significant mechanism. Platelet consumption in irradiated normal liver tissues and apoptosis of circulating peripheral blood lymphocytes are other, less important, hematologic side effects. 131I and 90Y are the radioisotopes most commonly used for RIT; in addition, animal toxicology and initial clinical studies of chelate immunoglobulins radiolabeled with 111In (for diagnosis) or 90Y (for therapy) are reviewed. The bone-seeking properties of free 90Y are not considered to be a major component of the hematologic damage caused by yttrium-labeled immunoglobulins. The microenvironment of the bone marrow system is not significantly damaged by current RIT protocols. Moreover, granulocyte colony-stimulating factor (G-CSF) can open the blood-marrow barrier. Bone marrow toxicity after RIT can be corrected by bone marrow transplantation, growth factors, blood products, or fractionation of RIT. Selection of the appropriate corrective regimen depends on the severity of the bone marrow damage and will further enhance the therapeutic ratio of RIT.

Somatostatin receptor imaging with indium-111-pentetreotide in gastroenteropancreatic neuroendocrine tumors: safety, efficacy and impact on patient management.

UNLABELLED: Indium-111-pentetreotide, a radiolabeled somatostatin analog, has been proposed for imaging tumors bearing somatostatin receptors. This study evaluates the safety, efficacy and impact on patient management of this scintigraphic agent in patients with gastroenteropancreatic (GEP) neuroendocrine tumors. METHODS: We studied 47 consecutive patients with a proven or clinically suspected GEP neuroendocrine tumor who were imaged 4 and 24 hr after injection of 111In-pentetreotide. The patients were monitored for adverse reactions and changes in vital signs or clinical chemistry over 24 hr. The scintigraphic findings were compared with results from conventional imaging methods. The patients were followed over a minimal 6-mo period during which further localization procedures were performed to confirm or refute the additional tumor sites found at scintigraphy. RESULTS: No adverse reactions or clinically relevant changes in clinical chemistry were noted after injection of the radiopharmaceutical. The final diagnosis of a GEP neuroendocrine tumor was retained in 38 patients. Somatostatin receptor-positive lesions were found in 33 of these patients, whereas conventional methods were positive in 31 patients. Of the 54 sites seen by conventional procedures, 50 sites were also detected scintigraphically. CONCLUSION: Indium-111-pentetreotide is a safe, sensitive imaging agent in the detection of GEP neuroendocrine tumor sites. Indium-111-pentetreotide also provides information on the somatostatin receptor status of the tumor and may therefore aid in therapeutic decisions.

Spermatogenic and mutagenic damage after paternal exposure to systemic indium-114m.

The cytotoxic and mutagenic consequences of systemic administration of 114mIn have been examined. Adult male rats were dosed intraperitoneally with 14.8 or 3.7 MBq/kg 114mIn. Approximately 0.25% of the injected radioactivity was localized within the testis by 24 h and was retained with an effective half-life of 49.5 days. Breeding studies were started 3 days after injection, males being housed with two females for seven consecutive mating trials of 19 days, separated by 2 days. Indium-114m caused a reduction in litter size and an increase in the incidence of pre- and postimplantation losses and dominant lethal mutations. These effects became evident from 24 days but were most marked between 87-126 days after treatment and persisted up to 147 days. When animals were mated 200 days after treatment, no significant changes were observed. In a parallel study, administration of 14.8 MBq/kg 114mIn resulted in decreased testis and epididymal weight and sperm reserves. Maximal reduction occurred between 87-108 days after injection followed by recovery toward control values, but neither organ had reached normal levels at 200 days. A single dose of 3.7 MBq/kg, however, had no effect on reproductive organ weight or sperm content. Male F1 progeny from the 14.8 MBq/kg group of the second mating period (commencing at 24 days) displayed decreased testis weights and sperm content and provoked a higher incidence of dominant lethal mutations. This effect was not observed in male progeny from any other time or the alternative dose level.

Quantitation of thrombogenicity of hemodialyzer with technetium-99m and indium-111 labeled platelets.

The platelet thrombogenicity of a hemodialyzer was quantified with 99mTc- and 111In-labeled platelets. The platelets collected from blood of Beagle dogs, Yorkshire pigs and human volunteers were labeled with 111In-tropolone (detergent-free) and 99mTc-HMPAO. Hemodialysis was performed with a hollow-fiber dialyzer (HFD) in a flow-loop, the temperature of which was maintained at 37 degrees C, with flow-rates of 7, 150 and 270 mL/min; after dialysis, the HFD radioactivity was measured with an ionization chamber and imaged with a gamma-camera. The radioactivity of samples of hollow-fibers taken from the top, middle and bottom of the dialyzer was determined with a gamma-counter. The mean values of hemodialyzer-adherent platelet radioactivity were calculated for both radionuclides. The canine platelets were found to be more thrombogenic than porcine and human platelets. The adhesivity of porcine platelets to the biomaterial (cellulose-acetate) of the dialyzer approximated that of human platelets. The 99mTc label underestimated the thrombus formation (P < 0.01). The dynamic processes of thrombosis and embolization from the hemodialyzer resulted in the large standard deviations around the mean values of the adherent thrombus. In spite of this limitation of the dynamic pathology, the quantitation of comparative thrombogenicity with 111In- and 99mTc-labeled platelets suggests that both radionuclides could be used for measurement of device-induced thrombogenicity and may provide an estimation of prosthesis-induced thrombogenicity of human platelets from animal studies.

Clinical assessment of 111In-CYT-103 immunoscintigraphy in ovarian cancer.

The ability of 111In-CYT-103 immunoscintigraphy to aid in the diagnosis of patients with primary or recurrent/residual ovarian cancer was evaluated in a multicenter trial. The 111In-labeled immunoconjugate of the monoclonal antibody B72.3 was prepared using a site-specific conjugation method. A total of 103 patients received a 1 mg infusion of 111In-CYT-103 and subsequently underwent surgery or biopsy. The infusion of 111In-CYT-103 was well tolerated; only 1 patient experienced a modest elevation in blood pressure that was likely related to the infusion. 111In-CYT-103 immunoscintigraphy correctly identified surgically confirmed tumor in 68% of patients with ovarian adenocarcinoma. The sensitivity of 111In-CYT-103 immunoscintigraphy was positively influenced both by the size of the tumor lesion and the tumor TAG-72 antigen expression. The overall sensitivity of 111In-CYT-103 immunoscintigraphy was greater than that of CT imaging (44%). Antibody imaging detected occult disease in 20 of 71 patients with surgically documented ovarian adenocarcinoma; 6 patients being evaluated after initial surgery and chemotherapy had an otherwise negative presurgical workup and a normal CA 125 serum level. The results of this trial also indicate that 111In-CYT-103 immunoscintigraphy can contribute to the medical and surgical management of some patients with ovarian cancer. The results of this trial indicate that 111In-CYT-103 immunoscintigraphy should be a valuable addition to the presurgical evaluation of patients with suspected persistent or recurrent ovarian cancer.