Preparation and evaluation of the rhenium-188-labelled anti-NCA antigen monoclonal antibody BW 250/183 for radioimmunotherapy of leukaemia

Anti-NCA antigen antibody BW 250/183 (Anti-Granulocyte) localizes more than 50% of injected antibody dose to the bone marrow. Therefore, this antibody is promising for adjuvant conditioning radioimmunotherapy of bone marrow before bone marrow transplantation. To examine its potential use for radioimmunotherapy, we developed an efficient and reproducible technical protocol for labelling anti-NCA antigen antibody BW 250/183 with generator-produced rhenium-188, aiming at both high radiochemical yield and high specific activity. ¹⁸⁸Re-labelled BW 250/183 antibody was used in 12 patients with advanced leukaemia. Labelling of BW 250/183 with ¹⁸⁸Re was accomplished by the direct radiolabelling method using tris-(2-carboxyethyl) phosphine (TCEP) as the reducing agent. Twelve patients with recurrent acute or chronic leukaemia were treated with activities of 6.5–12.4 GBq of ¹⁸⁸Re-labelled BW 250/183. Standard gamma camera scintigraphy was used to evaluate the biodistribution, and a region of interest analysis together with the MIRDOSE 3.1 software was applied to determine the radiation doses to relevant tissues. The ¹⁸⁸Re-BW 250/183 antibody was labelled in high radiochemical yield, with high radiochemical purity (94%±3%) and specific activity (5.55–7.4 GBq/mg) within 1 h. The preliminary biodistribution studies showed persistent uptake of ¹⁸⁸Re-BW 250/183 in bone marrow. The radiation absorbed doses (mGy/MBq) delivered to the total body, red marrow, liver, spleen and kidneys were 0.13±0.02, 1.45±0.71, 0.43±0.21, 1.32±0.99 and 0.71±0.17, respectively. TCEP reduction enabled the direct, fast and effective labelling of the monoclonal antibody BW 250/183 with ¹⁸⁸Re. Preliminary clinical results suggest delivery of a significant radiation dose to bone marrow and thus the potential for adjuvant conditioning therapy before BMT. Received 6 January and in revised form 10 May 1999     

Preparation and evaluation of the rhenium-188-labelled anti-NCA antigen monoclonal antibody BW 250/183 for radioimmunotherapy of leukaemia.

Anti-NCA antigen antibody BW 250/183 (Anti-Granulocyte) localizes more than 50% of injected antibody dose to the bone marrow. Therefore, this antibody is promising for adjuvant conditioning radioimmunotherapy of bone marrow before bone marrow transplantation. To examine its potential use for radioimmunotherapy, we developed an efficient and reproducible technical protocol for labelling anti-NCA antigen antibody BW 250/183 with generator-produced rhenium-188, aiming at both high radiochemical yield and high specific activity. (188)Re-labelled BW 250/183 antibody was used in 12 patients with advanced leukaemia. Labelling of BW 250/183 with (188)Re was accomplished by the direct radiolabelling method using tris-(2-carboxyethyl) phosphine (TCEP) as the reducing agent. Twelve patients with recurrent acute or chronic leukaemia were treated with activities of 6.5-12.4 GBq of (188)Re-labelled BW 250/183. Standard gamma camera scintigraphy was used to evaluate the biodistribution, and a region of interest analysis together with the MIRDOSE 3.1 software was applied to determine the radiation doses to relevant tissues. The (188)Re-BW 250/183 antibody was labelled in high radiochemical yield, with high radiochemical purity (94%+/-3%) and specific activity (5.55-7.4 GBq/mg) within 1 h. The preliminary biodistribution studies showed persistent uptake of (188)Re-BW 250/183 in bone marrow. The radiation absorbed doses (mGy/MBq) delivered to the total body, red marrow, liver, spleen and kidneys were 0.13+/-0.02, 1.45+/-0.71, 0.43+/-0.21, 1.32+/-0.99 and 0.71+/-0. 17, respectively. TCEP reduction enabled the direct, fast and effective labelling of the monoclonal antibody BW 250/183 with (188)Re. Preliminary clinical results suggest delivery of a significant radiation dose to bone marrow and thus the potential for adjuvant conditioning therapy before BMT.     

In vitro and in vivo properties of human/mouse chimeric monoclonal antibody specific for common acute lymphocytic leukemia antigen

A human/mouse chimeric monoclonal antibody specific for a common acute lymphocytic leukemia antigen was efficiently obtained by ligating human heavy-chain enhancer element to the chimeric heavy- and light-chain genes. Cell binding and competitive inhibition assays of both radioiodine and indium-111- (111In) labeled chimeric antibodies demonstrated in vitro immunoreactivity identical with that of the parental murine monoclonal antibodies. The biodistribution of the radiolabeled chimeric antibody in tumor-bearing nude mice was similar to that of the parental murine antibody. Tumor accumulation of radioiodinated parental and chimeric antibodies was lower than that of 111In-labeled antibodies, probably because of dehalogenation of the radioiodinated antibodies. Indium-111-labeled chimeric antibody clearly visualized xenografted tumor. These results suggest that a human/mouse chimeric antibody can be labeled with 111In and radioiodine without the loss of its immunoreactivity, and that chimeric antibody localizes in vivo in the same way as the parental murine antibody.     

In vitro and in vivo evaluation of novel ligands for radioimmunotherapy

Novel ligands cis-2,6-bis[N,N-bis(carboxymethyl)aminomethyl]-1-piperidineacetic acid (PIP-DTPA), cis-[(1R,11S)-6,9,15-Tris-carboxymethyl-3,6,9,15-tetraazabicyclo[9.3.1]pentadec-3-yl]-acetic acid (PIP-DOTA), cis-{2,7-bis-[bis-carboxymethyl-amino)-methyl]-azepan-1-yl}-acetic acid (AZEP-DTPA), [2-(4,7-bis-carboxymethyl-[1,4,7]triazacyclononan-1-yl-ethyl]-2-carbonylmethyl-amino]-tetraacetic acid (NETA) and [{4-carboxymethyl-7-[2-(carboxymethylamino)-ethyl]-perhydro-1,4,7-triazonin-1-yl}-acetic acid (NPTA) are investigated as potential chelators of 177Lu, 90Y, 212Pb and 213Bi for radioimmunotherapy (RIT). The new ligands are radiolabeled with 177Lu, 86/88/90Y, 203Pb and 205/6Bi, and in vitro stability and in vivo stability of the radiolabeled complexes are assessed in human serum and athymic mice, respectively. In vitro studies indicate that all radiolabeled complexes with the exception of 90Y-AZEP-DTPA are stable in serum for 5-11 days. All new ligands examined herein are found to tightly hold 177Lu in vivo. Piperidine-backboned DTPA (PIP-DTPA) complexes radiolabeled with all radioisotopes examined display excellent in vivo stability, that is, excretion without dissociation. The azepane-backboned DTPA derivative, AZEP-DTPA, appears ineffective in binding all but 177Lu in vivo. NETA and NPTA radiolabeled with 86Y or 177Lu exhibit rapid blood clearance and low organ uptakes. Significant accretion in the kidney, femur and/or liver is observed with 203Pb-labeled AZEP-DTPA, PIP-DOTA and NPTA. Both 203Pb-PIP-DOTA and 205/6Bi-PIP-DOTA result in moderate to high renal accumulation of radioactivity. NETA exhibits improved renal accumulation with respect to PIP-DOTA for 205/6Bi but also shows significant liver uptake. Of all ligands studied, only PIP-DTPA appears to effectively bind 203Pb and 205/6Bi in vivo. PIP-DTPA, PIP-DOTA, NETA and NPTA all show strong evidence of rapid blood clearance and low organ uptake for 177Lu and 90Y. Serum stability and in vivo biodistribution results suggest PIP-DTPA as a potential chelating agent with broad applicability for use in 177Lu, 90Y, 212Pb and 213Bi RIT.     

Localization of colorectal carcinoma by rhenium-188-labeled B72.3 antibody in xenografted mice

In order to evaluate the feasibility of¹⁸⁸Re-labeled antibodies for radioimmunotargeting, monoclonal antibody B72.3, recognizing TAG-72, expressed on the surface membranes of colorectal cancer cells, was directly labeled with¹⁸⁸Re, obtained from a¹⁸⁸W/¹⁸⁸Re generator, using stannous tartrate and compared with¹²⁵I-labeled B72.3. As a control, a human IgG was also radiolabeled with¹⁸⁸Re and^I25I. Prepared antibodies for¹⁸⁸Re labeling could be stored as kits. Biodistribution was determined in nude mice inoculated with human colorectal carcinoma LoVo. Labeling efficiency and immunoreactivity of¹⁸⁸Re-B72.3 were 80.3% and 64.7%, respectively.¹⁸⁸Re-B72.3 localized specifically in the LoVo tumors. Although the absolute tumor accumulation level of¹⁸⁸Re-B72.3 was lower than^I25I-B72.3,¹⁸⁸Re-B72.3 demonstrated higher tumor-to-blood contrast than the¹²⁵I-labeled counterpart, 2.04 ± 0.44 vs. 1.05 ± 0.28 at 96 hours, because of fast clearance from the blood.¹⁸⁸Re-B72.3 seemed efficient for the imaging and therapy of colorectal carcinoma.     

Clinical experience with rhenium-186-labeled monoclonal antibodies for radioimmunotherapy: results of phase I trials.

Rhenium is a radionuclide with physical and chemical properties suitable for radioimmunotherapy. Two Phase I trials were carried out using 186Re-labeled murine monoclonal antibodies. Patients with refractory metastatic epithelial carcinoma received single doses of either 186Re-labeled intact NR-LU-10, a pancarcinoma antibody, 25-120 mCi/m2 (n = 15) or 186Re-labeled F(ab')2 fragment of NR-CO-02, an anti-CEA variant antibody, 25-200 mCi/m2 (n = 31). Prior to radioimmunotherapy, tumor localization of antibody was confirmed by 99mTc-labeled NR-LU-10 Fab or 99mTc-labeled NR-CO-02 F(ab')2 imaging. Dose-limiting myelosuppression was observed at 120 mCi/m2 following 186Re-NR-LU-10 intact antibody and at 150 mCi/m2 following NR-CO-02 F(ab')2 fragment in heavily pretreated patients. In patients with minimal prior therapy, a maximum tolerated dose for NR-CO-02 F(ab')2 was not reached by 200 mCi/m2. Non-marrow toxicity was minimal. Human anti-mouse antibody developed in all patients receiving intact NR-LU-10, and in 86% patients receiving F(ab')2 NR-CO-02. One patient treated with 186Re NR-CO-02 achieved a partial response. We conclude that 186Re-labeled antibody can be safely administered with significant toxicity limited to marrow.     

Direct radiolabeling of monoclonal antibodies with rhenium-188 for radioimmunotherapy of solid tumors--a review of radiolabeling characteristics, quality control and in vitro stability studies.

188Re is one of the radioisotopes expected to emerge as useful for therapy. Development of new radiopharmaceuticals based on 188Re depends on the radiolabeling methods used, which would give stable complexes having predefined radiochemical properties and in vitro and in vivo stability. This paper has attempted to provide a perspective of 188Re-labeled monoclonal antibodies, their radiolabeling characteristics, methods for quality control of radioimmunoconjugates and in vitro stability for radioimmunotherapy of solid tumors. The direct method of 188Re radiolabeling of antibodies by reductive attachment of 188Re in which free sulfhydryl groups have been generated by reduction of the intramolecular S-S disulfide bonds has been shown to be a promising approach in particular. Moreover, excellent methods have been developed to test the radionuclide, radiochemical purity and stability of 188Re-radioimmunoconjugates using high performance liquid chromatography (HPLC) and paper chromatography.     

Administration guidelines for radioimmunotherapy of non-Hodgkin's lymphoma with (90)Y-labeled anti-CD20 monoclonal antibody.

90Y-ibritumomab tiuxetan is a novel radioimmunotherapeutic agent recently approved for the treatment of relapsed or refractory low-grade, follicular, or CD20+ transformed non-Hodgkin's lymphoma (NHL). (90)Y-ibritumomab tiuxetan consists of a murine monoclonal antibody covalently attached to a metal chelator, which stably chelates (111)In for imaging and (90)Y for therapy. Both health care workers and patients receiving this therapy need to become familiar with how it differs from conventional chemotherapy and what, if any, safety precautions are necessary. Because (90)Y is a pure beta-emitter, the requisite safety precautions are not overly burdensome for health care workers or for patients and their families. (90)Y-ibritumomab tiuxetan is dosed on the basis of the patient's body weight and baseline platelet count; dosimetry is not required for determining the therapeutic dose in patients meeting eligibility criteria similar to those used in clinical trials, such as <25% lymphomatous involvement of the bone marrow. (111)In- and (90)Y-ibritumomab tiuxetan are labeled at commercial radiopharmacies and delivered for on-site dose preparation and administration. Plastic and acrylic materials are appropriate for shielding during dose preparation and administration; primary lead shielding should be avoided because of the potential exposure risk from bremsstrahlung. Because there are no penetrating gamma-emissions associated with the therapy, (90)Y-ibritumomab tiuxetan is routinely administered on an outpatient basis. Furthermore, the risk of radiation exposure to patients' family members has been shown to be in the range of background radiation, even without restrictions on contact. There is therefore no need to determine activity limits or dose rate limits before patients who have been treated with (90)Y radioimmunotherapy are released, as is necessary with patients who have been treated with radiopharmaceuticals that contain (131)I. Standard universal precautions for handling body fluids are recommended for health care workers and patients and their family members after (90)Y-ibritumomab tiuxetan administration. In summary, (90)Y-ibritumomab tiuxetan introduces (90)Y into clinical practice and expands the role nuclear medicine plays in the care of patients with cancer. Understanding the unique properties of this novel radioimmunoconjugate will facilitate its safe and effective use.     

In vivo evaluation of a lead-labeled monoclonal antibody using the DOTA ligand

The aim of this study was to assess the utility of a radioimmunoconjugate containing a lead radionuclide for therapy and scintigraphy applications. The radioimmunoconjugate evaluated consisted of a bifunctional DOTA ligand and monoclonal antibody (MAb) B72.3 using athymic mice bearing LS-174T tumors, human colon carcinoma xenografts. In the studies reported here, the lead-203-DOTA complex itself was first demonstrated to have in vivo stability. MAb B72.3 was then conjugated with the DOTA ligand and labeled with ²⁰³Pb, and the immunoreactivity of B72.3 was maintained. The localization of the radioimmunoconjugate to tumor tissue and other select organs paralleled that of DOTA-¹²⁵I-B72.3, suggesting a similar metabolic pattern of the two radioimmunoconjugates. Thus, the DOTA-metal complex does not alter the behavior of the radioimmunoconjugate. Tumor localization of the ²⁰³Pb-DOTA-B72.3 conjugate was demonstrated with biodistribution studies as well as immunoscintigraphy studies. Such data highlight the stability of a lead radionuclide in the DOTA ligand. The suitability of this chelation chemistry for labeling radioimmunoconjugates with a lead radionuclide now makes its application in nuclear medicine a feasible proposition. Received 25 October 1997 and in revised form 23 January 1998     

In vivo and in vitro characterizations of three 99mTc-labeled monoclonal antibody G250 preparations.

In previous clinical studies, excellent visualization of tumor lesions has been observed with 131I-labeled monoclonal antibody (mAb) G250 in patients with renal cell carcinoma (RCC). In several cases, 131I-cG250 immunoscintigraphy disclosed tumor lesions that were not visualized by radiography or CT. To improve image quality, we aimed to develop a 99mTc-labeled mAb G250 preparation for radioimmunodetection of RCC. We studied in vitro stability, biodistribution and imaging potential of three 99mTc-labeled G250 preparations in nude mice with subcutaneous RCC xenografts.125I-G250 and the nonspecific mAb 131I-MN14 were used as control antibodies. METHODS: The mAb G250 was labeled with 99mTc according to three methods using: (a) S-hydrazinonicotinamide (HYNIC), (b) S-benzoylmercaptoacetyltriglycine (MAG3) and (c) a direct labeling method (Schwarz method). The stability of all preparations was tested in serum at 37 degrees C during 48 h. In addition, diethylenetriamine pentaacetic acid, cysteine and glutathione challenge assays were performed. RESULTS: All preparations showed good stability in serum during the 48-h incubation period. 99mTc-G250 (Schwarz) showed release of the radiolabel at a 100-fold or higher molar excess of cysteine and at a 10,000-fold or higher molar excess of glutathione. 99mTc-MAG3-G250 showed release of the radiolabel at a 10,000-fold molar excess of cysteine. 99mTc-HYNIC-G250 was stable under all conditions. Tumors were clearly visualized with all preparations. 99mTc-G250 (Schwarz) showed significantly lower blood levels (3.8 %ID/g) compared with all other preparations (11.2, 13.4 and 13.4 %ID/g for 99mTc-HYNIC-G250, 99mTc-MAG3-G250 and 125I-G250, respectively, 48 h postinjection). At 48-h postinjection, mean tumor uptake was very high with all mAb G250 preparations: 92.4 (99mTc-HYNIC-G250), 125.9 (99mTc-MAG3-G250), 29.4 (99mTc-G250 Schwarz) and 75.4 (125I-G250) %ID/g. Mean tumor uptake of the nonspecific 131I-MN14 mAb was 6.6 %ID/g. CONCLUSION: In this study, 99mTc-HYNIC-G250 showed excellent in vitro stability and tumor targeting. Moreover, this preparation could be labeled with high efficiency (>95%) at room temperature within 15 min. Therefore, 99mTc-HYNIC-G250 seems to be an ideal candidate for radioimmunodetection of RCC.     

Correlation of marrow dose estimates based on serial pretreatment radiopharmaceutical imaging and blood data with actual marrow toxicity in anti-CD20 yttrium-90 monoclonal antibody radioimmunotherapy of non-Hodgkin's B-cell lymphoma

The purpose of this study was to investigate whether marrow radiation absorbed dose estimates predict haematotoxicity following radioimmunotherapy with an yttrium-90 labelled anti-CD20 monoclonal antibody in non-Hodgkin's B-cell lymphoma (NHL). Radiopharmaceutical data from 12 NHL radioimmunotherapy patients were analysed retrospectively using three methods of marrow radiation absorbed dose estimation based on serial pretreatment indium-111 labelled anti-CD20 monoclonal antibody activity versus time data (0-144 h): (i) lumbar spine (LS) image counts; (ii) blood clearance (BL); and (iii) whole body (WB) activity. Linear regressions were performed between the methods, and between each method and the 0-6 month post-treatment platelet and white blood cell count nadir and absolute drop in count (ADC). For the range of yttrium-90 activities (740-1547 MBq), absorbed dose estimates (mean +/- sigma) were: LS, 142+/-50 cGy (range 62-233 cGy); BL, 89+/-21 cGy (range 63-140 cGy); and WB, 54+/-10 cGy (range 36-63 cGy). The LS and BL marrow estimates differed significantly (P <0.003), with a correlation coefficient r of 0.36 (P = NS), while WB correlated significantly with both LS (r = 0.50, P < 0.05) and BL (r = 0.58, P < 0.05). The range of r with platelet nadir and ADC was -0.20 < or = r < or = 0.01, except for WB with ADC (r = 0.38) (all P = NS). Values of r for white blood cell nadir were unexpectedly positive, being 0.13 for BL and 0.29 for LS (P = NS), and 0.60 for WB (P < 0.025). Values of r for white blood cell ADC were 0.36 for BL and -0.26 for LS (P = NS), and 0.50 for WB (P < 0.05). These results indicate that different commonly employed methods of estimating marrow radiation absorbed dose may yield significantly differing results, which may not correlate with actual radiation toxicity. Therefore, caution must be exercised in relying on these results to predict haematotoxicity.     

In vitro and in vivo comparison of DTPA- and DOTA-conjugated antiferritin monoclonal antibody for imaging and therapy of pancreatic cancer

Pancreatic cancer has a very poor prognosis with a less than 5% survival rate at 5 years. Neither external beam radiation nor chemotherapy, alone or in combination, have given encouraging results so far. A possible solution might come from the use of targeted therapy such as radioimmunotherapy. We present here the results obtained from the preclinical development of a new monoclonal antiferritin antibody (Ab), AMB8LK. Ferritin is overexpressed in pancreatic cancer and could thus be used as a target for the delivery of radioactivity at the tumour sites. The AMB8LK Ab was conjugated to three chelating agents: the 2-(4-isothiocyanatobenzyl)-diethylenetriamine pentaacetic acid (PSCN-Bz-DTPA), the (R)-2-amino-3-(4-isothiocyanatophenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-pentaacetic acid (p5CN-Bz-CHX-A"-DTPA) and the 2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (pSCN-Bz-DOTA). Radiolabelling of the three immunoconjugates with indium 111 and yttrium 90 as well as in vitro stability and immunoreactivity against pure ferritin and cells expressing ferritin were analysed. In vivo biodistribution studies were conducted on normal and on human pancreatic adenocarcinoma CAPAN-1 tumour bearing mice. These experiments demonstrated good radiolabelling (>95%), stability and immunoreactivity of the three compounds. In the biodistribution studies, differences between the three immunoconjugates were apparent in the rate of blood clearance and in tumour, liver and bone uptake. A very good pancreatic adenocarcinoma tumour targeting was observed especially with the Bz-DTPA-AMB8LK: 20% of the injected dose of the indium-labelled compound 3 days after injection; 15% of the injected dose 5 days after that of the yttrium-labelled Ab. Altogether, these results in animal models suggest that (90)Y-Bz-DTPA-AMB8LK is a good candidate for further therapeutic efficacy studies.     

In vivo study of spontaneous and therapy-induced apoptosis in patients with chronic lymphocytic leukemia treated with chlorambucil]

The efficiency of Chlorambucil in the induction of apoptosis was investigated in the study, and measurable apoptosis parameters were compared to the other prognostic factors with the aim of possible prediction of clinical response to the therapy in the patients with CD5 + B-cell chronic lymphocytic leukemia (B-CLL). Seven newly diagnosed patients, initially treated with daily high-doses of Chlorambucil (HD-CLB) were analyzed. Quantitative analysis of apoptosis parameters on semi-fine sections obtained from peripheral blood was performed prior and during the first five days of therapy. The level of spontaneous apoptosis (SA) was determined, as well as the maximal response by apoptosis (MAR), and the time needed to establish maximal response by apoptosis (TMAR), respectively. The results revealed that the level of SA in the studied group of patients was 11.39%-20.50%. In three patients with achieved criteria for complete remission (CR) was observed high level of SA, TMAR 2-4 days and MAR 23.42-26.36%, respectively. All patients with CR were with negative LDT, non-diffuse involvement of bone marrow and clinical stage B. Criteria for partial remission (PR) were achieved in 4 patients. Within this group, all three measurable parameters of apoptosis could have been determined in only one patient, while in the rest was noticed the increased percentage of apoptotic cells on the last day of follow-up. In all patients was observed negative LDT, diffuse bone marrow involvement, and 2 out of 4 patients had CLPL of cytomorphological type and clinical stage B. By comparing the obtained values of measurable apoptotic parameters with the clinical response to the applied therapy with HD-CLB, it is possible to divide our patients into two groups: patients who have achieved CR have the highest percentage of cells dying due to the therapy-induced apoptosis, as well as the higher values of measurable parameters compared to the certain parameters of the patients with the criteria for PR. Our preliminary results of therapeutic response to the apoptosis might be useful for the timely decision upon the duration of therapy and change of modality of treatment for every patient during the follow-up period.     

Production and characterization of 188Re-C595 antibody for radioimmunotherapy of transitional cell bladder cancer.

Bladder cancer was responsible for >12,000 deaths in the United States in 1999. The high-molecular-weight glycoprotein MUC1 mucin is overexpressed on bladder tumors and represents a useful target for radioimmunoscintigraphy and radioimmunotherapy. We report on the production and initial tracer studies of a 188Re-antibody complex directed against this target and intended for intravesical radioimmunotherapy of superficial bladder cancer. METHODS: 188Re perrhenate was eluted from a 188W/188Re generator. C595 antibody was reduced with 2-mercaptoethanol and was labeled in the presence of stannous tartrate. The final reaction mixture contained high-molecular-weight contamination, which was removed from the complex using an affinity separation technique. The specificity and integrity of the antibody complex were tested by radioimmunoassay and size exclusion chromatography. Tumor localization was investigated using an ex vivo model in human cystectomy specimens. Tracer amounts of the complex were also administered intravesically to three patients with bladder cancer, who were then imaged by gamma scintigraphy. RESULTS: The complex was immunoreactive (70% +/- 17%) and specific for MUC1 antigens. A peak corresponding to a protein of 150 kDa was observed on size exclusion chromatography, showing that the complex was homogeneous. Binding to bladder tumors was observed in an ex vivo model in which tumors were successfully imaged in four specimens. The mean tumor-to-normal tissue ratio in ex vivo bladders was 7:1. Tumor uptake after intravesical administration was confirmed in three patients with bladder cancer (mean tumor-to-normal tissue ratio, 4:1). CONCLUSION: The C595 antibody was labeled with 188Re, providing a radioimmunoconjugate with high immunoreactivity and specificity. Its ability to localize in tumors both in an ex vivo model and after intravesical administration to patients has been shown. This approach will now be extended for the therapy of superficial bladder cancer.     

CD45单抗及188Re-亲和素二步法预定位对淋巴瘤Raji细胞的放射免疫效应研究

目的 探讨CD45单抗及¹⁸⁸Re-亲和素(Avidin)二步法预定位对人淋巴瘤Raji细胞的放射免疫效应。方法 ¹⁸⁸Re对CD45单抗及Avidin的标记采用直接标记法,采用纸层析法测定标记率及放化纯度。分析¹⁸⁸Re-CD45单抗与Raji细胞的体外结合能力,并进行体外竞争结合实验,采用CCK-8法测定二步法预定位组、¹⁸⁸Re-CD45单抗组、¹⁸⁸Re-Avidin组和¹⁸⁸ReO₄^-组对Raji细胞的增殖抑制效应,计算Raji细胞存活率和抑制率。结果 ¹⁸⁸Re-CD45单抗与Raji细胞的特异性结合率为(70.92±1.91)%,同时加入¹⁸⁸Re-CD45单抗和过量的CD45单抗,则细胞结合率平均为(7.96±0.87)%。二步法预定位组、¹⁸⁸Re-CD45单抗组、¹⁸⁸Re-Avidin组和¹⁸⁸ReO₄^-组对Raji细胞的增殖均有抑制作用,抑制率与放射性活度呈正相关(r=0.907~0.992,P<0.05);在相同放射性活度下,二步法预定位组在各时间点的抑制作用均高于¹⁸⁸Re-CD45单抗组、¹⁸⁸Re-Avidin组和¹⁸⁸ReO₄^-组(t=124.76~607.98,P<0.05)。结论 ¹⁸⁸Re-CD45单抗可特异性地与Raji细胞结合,CD45单抗及¹⁸⁸Re-Avidin二步法预定位对人淋巴瘤Raji细胞具有明显的抑制作用。     

In vitro and in vivo evaluation of a 99mTc(I)-labeled bombesin analogue for imaging of gastrin releasing peptide receptor-positive tumors

A new radiolabeled bombesin analogue, [99mTc(I)-PADA-AVA]bombesin (7-14), was synthesized and in vitro and in vivo characterized. High affinity and rapid internalization were obtained in binding assays. A specific binding towards gastrin releasing peptide receptors-positive tissues, pancreas and tumor, was observed in CD-1 nu/nu mice bearing PC-3 prostate adenocarcinoma xenografts. We therefore conclude that [99mTc(I)-PADA-AVA]bombesin (7-14) might have promising characteristics for applications in nuclear medicine, namely for diagnosis of GRP receptor overexpressing tumors.