131^I标记抗人成骨肉瘤单抗荷瘤裸鼠体内分布和放射免疫显像研究

目的：研究131^I标记抗人成骨肉瘤单克隆抗体在荷人成骨肉瘤裸鼠体内分布和放射免疫定位显像。方法：采用Iodogen固相法标记制备131^—HOS McAb。25只荷瘤裸鼠随机分为5组，分别腹腔注射131^I—HOS McAb后，于6、12、24、48和72 h 5个时间段进行裸鼠的体内分布研究；对5只荷瘤裸鼠分别腹腔注射131^I—HOS McAb后，于6、12、24、48和72h 5个时间段进行荷瘤裸鼠的放射免疫定位显像研究。结果：在荷人成骨肉瘤裸鼠腹腔注射131^I—HOS McAb后，12h肿瘤与血的T／NT比值为1．37，24h为3．75，48h达到最高为5．24。腹腔注射131^I—HOS McAb后，12h肿瘤部位即可见明显放射性浓聚，48h本底明显降低，肿瘤呈放射性热区。结论：131^I—HOS McAb对成骨肉瘤定向性较好，对放射免疫定位显像有利，为进一步放射免疫治疗研究提供了理论基础。     

抗前列腺特异膜抗原单克隆抗体的标记及在荷瘤裸鼠体内的分布研究

目的:研究125I标记的抗前列腺特异膜抗原(PSMA)单克隆抗体(125Ⅰ-Ed-5)及正常小鼠IgG(125Ⅰ-NMIgG)在荷人前列腺癌瘤裸鼠体内的分布,探讨应用125Ⅰ-Ed-5进行放射免疫显像诊断和放射免疫治疗实验性人前列腺癌的可行性.方法:建立荷人前列腺癌裸鼠移植瘤模型,用125Ⅰ标记抗PSMA单克隆抗体Ed-5和NMIgG,125Ⅰ-Ed-5和125Ⅰ-NMIgG经尾静脉注入荷瘤裸鼠体内,于注射后24、48、72、120小时分批处死,测定肿瘤和血液、肝、肺等重要脏器的单位重量放射性比值(T/NT)、各组织摄取百分比(%ID/g),研究其在荷瘤裸鼠体内的放射性分布情况.结果:125Ⅰ-Ed-5的标记率为72.3%,放射性比活度为55.2MBq/mg,放射性化学纯度是90.2%,免疫活性分数为63%.在注射125Ⅰ-Ed-5后24～120小时内,裸鼠体内肿瘤部位出现选择性放射性浓聚:各组织的T/NT比值在72h达到最高,其中肿瘤/肌肉高达6.36.而在注射125Ⅰ-NMlgG的对照组中,裸鼠体内未见放射性浓聚,呈全身均匀性分布.结论:标记后的125Ⅰ-Ed-5免疫活性没有改变,在裸鼠体内对前列腺癌移植瘤有靶向定位作用,为进一步应用125Ⅰ-Ed-5进行前列腺癌放射免疫显像和放射免疫治疗的实验研究奠定基础.     

99mTc标记的抗CEA小分子嵌合抗体的体内分布与肿瘤显像

[目的]采用99mTc标记抗人CEA小分子嵌合抗体Rch24 F(ab')2,研究其在荷人结肠癌裸鼠体内的生物学分布及放射免疫显像的特征与应用价值.[方法]采用SnC12直接还原法标记抗体,快速薄层层析法(ITLC)测定抗体的标记效率、放化纯度和体外稳定性,ELISA检测标记抗体的免疫比活性.荷人结肠癌裸鼠尾静脉注射99mTc-Rch24 F(ab')2后,研究标记抗体在裸鼠体内的生物学分布,并进行肿瘤显像.[结果] 99mTc-Rch24 F(ab')2的标记率为90％,放化纯度＞95％.99mTc-Rch24 F(ab')2的放射比活为840MBq/mg,免疫比活性为65.7％.标记抗体24h时放射性脱落小于5％.荷瘤裸鼠注射99mTc-Rch24 F(ab')2 3h后即可观察到肿瘤影像,5～24h均可获得清晰的肿瘤影像,标记抗体在体内呈肿瘤靶向性分布,12h时肿瘤的摄取和多数脏器T/NT比值均达到最高水平.[结论]99mTc-Rch24 F(ab')2在体内靶向分布于结肠癌肿瘤组织,具有较高的T/NT比值并可在肿瘤局部滞留,注射99mTc-Rch24 F(ab')25h后肿瘤成像满意.99mTc-Rch24 F(ab')2在临床肿瘤的放射免疫分子显像诊断中具有良好的应用前景.     

^131I标记抗CD20单克隆抗体在荷瘤裸鼠体内的放射免疫显像

目的探讨^131I-anti-CD20McAb经瘤内注射后在荷人Burkitt’s淋巴瘤细胞系Raji细胞移植瘤裸鼠体内的放射免疫显像。方法^131I标记物的标记采用IODO-GEN碘化标记；注射标记物后第1、3、7、15天将荷瘤裸鼠SPECT显像后活杀，定标器测量并计算瘤、血等12种器官或组织的％ID／g值，根据MIRD委员会推荐的公式计算肿瘤累积吸收剂量。结果^131I-anti-CD20McAb瘤内注射组的SPECT显像结果优于腹腔注射组和^131I-IgG瘤内注射组，该组肿瘤％ID／g值在给药后第1、3和7天分别为后两组的1．4～17倍和1．7～3．7倍，肿瘤累及吸收剂量在给药后第3、7和15天分别为后两组的1．5～2．5倍和6．0～12．6倍。结论^131I-anti—CD20McAb经瘤内途径给药可以使肿瘤获得最高的放射性药物摄取率．为下一步运用该途径进行放射免疫治疗提供了实验依据。     

~(125)I-CEA人/鼠嵌合抗体rch24在裸鼠人结肠癌模型中的生物学分布

[目的]研究125I标记CEA人/鼠嵌合抗体rch24(125I鄄rch24)及淋巴瘤抗体IgG(125I鄄IgG)在荷人结肠癌裸鼠体内的分布,为放射免疫显像(RII)及临床应用提供依据。[方法]每鼠尾静脉注射抗体0.1ml(约100μCi),测定注射后24、48、96、168h肿瘤和血液、肝、肺等重要脏器的单位重量放射性比值(T/NT),各组织摄取百分比。[结果]125I鄄rch24注射后24～168h内,肿瘤部位出现选择性放射性浓聚;肿瘤组织在注射125I鄄rch24后,48h组织摄取百分比达到最大值28.06%;96h所有脏器T/NT比值均大于8.0;125I鄄IgG未出现放射性浓聚,呈全身分布。[结论]125I鄄rch24在荷人结肠癌裸鼠体内,可特异结合肿瘤组织,可望用于临床诊断和治疗。     

188Re～HAb18F(ab′)2肝癌放射免疫显像的研究

目的　探讨1 88Re标记的肝癌单抗片段HAb18F(ab′) 2 在荷人肝癌移植瘤裸鼠体内的放免显像和生物学分布。方法　采用 2 巯基乙醇为还原剂的直接法标记肝癌单抗片段HAb18F(ab′) 2 ,Whatman 3mm纸层析法测 1 88Re HAb18F(ab′) 2 标记率 ,活细胞放射免疫结合法测标记物的免疫活性。放免显像实验时 ,于荷肝癌裸鼠尾静脉注射标记物 11 1MBq ,SPECT低能通用型准直器显像。生物学分布实验中每只荷肝癌裸鼠尾静脉注射标记物 1 85～ 2 5 9MBq ,分别于注射后不同时间点各处死一组 ,取血及主要组织 ,称重 ,测放射性计数。结果　最佳标记率为 91 7% ,免疫活性分数为 0 78。低能通用型准直器可缓解1 88Re显像时边界模糊的问题。在显像观察中 ,3h时右下肢肿瘤区已有放射性聚集 ,19h～ 30h时肿瘤显影清晰、明确 ,45h以后整体放射性均趋于减弱。生物学分布表明 ,标记物除在肿瘤中有特异性聚集外 ,在其他正常组织中无特异性浓聚 ,尤其在血液中清除较快 ,肿瘤最佳显像时间可确定为 2 0～ 30h。结论　1 88Re HAb18F(ab′) 2 在荷人肝癌裸鼠体内可明确地定位于肿瘤部位 ,为进一步研究该标记物的抑瘤作用奠定了基础     

131Ⅰ标记抗CD20单克隆抗体在荷瘤裸鼠体内的放射免疫显像

目的 探讨131I-anti-CD20McAb经瘤内注射后在荷人Burkitt's淋巴瘤细胞系Raji细胞移植瘤裸鼠体内的放射免疫显像.方法 131I标记物的标记采用IODO-GEN碘化标记;注射标记物后第1、3、7、15天将荷瘤裸鼠SPECT显像后活杀,定标器测量并计算瘤、血等12种器官或组织的%ID/g值,根据MIRD委员会推荐的公式计算肿瘤累积吸收剂量.结果 131I-anti-CD20McAb瘤内注射组的SPECT显像结果优于腹腔注射组和131I-IgG瘤内注射组,该组肿瘤%ID/g值在给药后第1、3和7天分别为后两组的1.4～17倍和1.7～3.7倍,肿瘤累及吸收剂量在给药后第3、7和15天分别为后两组的1.5～2.5倍和6.0～12.6倍.结论 131I-anti-CD20McAb经瘤内途径给药可以使肿瘤获得最高的放射性药物摄取率,为下一步运用该途径进行放射免疫治疗提供了实验依据.     

131I标记抗人肿瘤分泌IgG轻链单克隆抗体荷瘤裸鼠体内分布与显像初步研究

[目的]用131I标记抗人肿瘤分泌IgG轻链单克隆抗体（ATILCMcAb）进行荷瘤裸鼠体内生物分布与显像研究,探讨其在放射免疫显像及靶向治疗中的应用前景。[方法]采用氯胺-T法标记,SephadexG-25柱层析分离纯化,纸层析法测定标记率和放化纯度。BALB/c裸鼠右侧腹股沟皮下注射宫颈癌上皮细胞（HeLa MR）,待肿瘤长至1cm左右,进行荷瘤裸鼠体内生物分布与显像实验。对照组为mIgG蛋白。[结果]131I-ATILCMcAb标记率89.9%±4.72%（n=4）,放射性比活度1.26MBq/μg,放化纯度98.1%±1.24%（n=4）,于4℃冰箱及37℃正常人混合血清存放72h后,放化纯度仍〉90%。131I-ATILCMcAb在血中的清除率较131I-mIgG快（P〈0.001）;除肝、膀胱和股骨外,各组织72h T/NT比值与131I-mIgG比较有显著性差异（P〈0.05）。荷瘤裸鼠体内显像实验显示24~72h,ATILCMcAb使肿瘤部位清晰显像。[结论]ATILCMcAb能够通过与肿瘤分泌的IgG特异结合而实现对肿瘤的探测,具有较好的生物学特性,为进一步的放射免疫显像及靶向治疗研究奠定了实验基础。     

125Ⅰ-CEA人/鼠嵌合抗体rch24在裸鼠人结肠癌模型中的生物学分布

[目的]研究125I标记CEA人/鼠嵌合抗体rch24(125I-rch24)及淋巴瘤抗体IgG(125I-IgG)在荷人结肠癌裸鼠体内的分布,为放射免疫显像(RⅡ)及临床应用提供依据.[方法]每鼠尾静脉注射抗体0.1ml(约100μCi),测定注射后24、48、96、168h肿瘤和血液、肝、肺等重要脏器的单位重量放射性比值(T/NT),各组织摄取百分比.[结果]125I-rch24注射后24～168h内,肿瘤部位出现选择性放射性浓聚;肿瘤组织在注射125I-rch24后,48h组织摄取百分比达到最大值28.06%;96h所有脏器T/NT比值均大于8.0;125I-IgG未出现放射性浓聚,呈全身分布.[结论]125I-rch24在荷人结肠癌裸鼠体内,可特异结合肿瘤组织,可望用于临床诊断和治疗.     

188Re标记CEA嵌合人源化抗体在荷人结肠癌裸鼠的放射免疫显像研究

背景与目的：癌胚抗原（carcinoembbryonic antigen,CEA）在多种肿瘤,尤其是结肠癌中高表达,抗CEA抗体在人结肠癌的诊断治疗中具有良好的应用前景。本研究采用^188Re标记CEA嵌合抗体,研究其在荷人结肠癌裸鼠体内的生物分布及放射免疫显像。方法：用氯化亚锡还原法标记CEA嵌合抗体及其亲本鼠单抗C50,薄层层析法鉴定标记抗本的标记率、放化纯度及体外稳定性,ELISA鉴定标记后的免疫活性,研究^188Re-CEA嵌合抗体在荷人结肠癌裸鼠体内的分布及放射免疫显像效果,并与C50鼠单抗的显像效果进行比较。结果：^188Re-CEA嵌合抗体的放化纯度大于95%;比活为36MBq/mg;免疫活性为61%;薄层层析示其在体外稳定。^188Re-CEA嵌合抗体的生物学分布显示：注射后24h,肿瘤与肾脏、血液的放射性比值分别为0.75、0.99,与其余各脏器的放射性比值均大于1.78;48h,肿瘤与肾脏、血液的放射性比值分别为1.02、1.12,与其余各脏器的放射性比值均大于2.08。20h后,肿瘤显影清晰。CEA嵌合抗体的放射生物学特性及显像效果与C50鼠单抗基本相同。结论：^188Re-CEA嵌合抗体在裸鼠体内放射免疫显像显示出良好的肿瘤特异性,且显像速度较快,可显示的肿瘤最小可达0.5cm。CEA嵌合抗体降低了免疫原性,在人体内显像更优于其亲本鼠单抗C50。     

Study on biodistribution and radioimmunoimaging of (131)iodine-labeled monoclonal antibody D-D3 against progastrin-releasing peptide31-98 in tumor-bearing mouse

This study was aimed at investigating the biodistribution and radioimmunoimaging of (131)I-D-D3 in nude mice bearing different types of tumor xenografts. Radioiodination of the D-D3 antibody was performed with the chloramine-T method. The radiochemical purity was determined through thin-layer chromotography. (131)I-D-D3 was injected into healthy Kunming mice via a tail vein, and the %ID/g for various organs was obtained. Similarly, the %ID/g and tumor/nontumor tissue ratio of (131)I-D-D3 in nude mice bearing small cell lung cancer (SCLC) xenografts were obtained. Planar images of (131)I-D-D3 in tumor-bearing nude mice were acquired at different times after injection. The (131)I-D-D3 labeling rate was 86.56% ± 3.8%. The radiochemical purity of (131)I-D-D3 was 99.27% ± 0.6%. After 12 hours of incubation in 37°C water bath, the radiochemical purity was 97.64% ± 0.5% and remained at 88.38%?± 0.4% after 48 hours. After being mixed with healthy human serum for 24 hours, the radiochemical purity was more than 64%. The metabolism of (131)I-D-D3 in healthy Kunming mice was consistent with a two-compartment model with first-order absorption; T(1/2α) and T(1/2β) were 0.25 and 37.89 hours, respectively. The %ID/g of (131)I-D-D3 in SCLC xenografts was much higher than those of other tissues at 48 hours after injection, and the tumor/nontumor tissue ratio also gradually increased with time. After 24 hours of injection, planar imaging was obtained, which clearly showed a contrasting tumor on the right armpit of nude mice bearing SCLC with high concentrations of radioactivity. Also, nude mice bearing gastric cancer showed similar results as that of the SCLC with a lower radioactivity level. No observable accumulation was observed in nude mice bearing pancreatic cancer or lung adenocarcinoma. The labeling rate and radiochemical purity of (131)I-D-D3 were high and stable. (131)I-D-D3 selectively accumulated at tumors that highly expressed progastrin-releasing peptide; therefore, it is a promising radioimmunoimaging reagent for SCLC.     

Radioimmunodetection of gliomas by administration of radiolabelled monoclonal antibodies. Experimental data

Radiolabelled monoclonal antibodies (McAbs) raised against membrane components of an experimental rat glioma (79FR-G-41) were administered parenterally to immunodeficient mice bearing glioma grafts for tumor radioimmunodetection by external imaging. Purified McAbs (14AC1) of IgG2a isotype were labelled with Na131I (2mCi/50ml) using the Chloramin-T method. As control, for non-specific uptake of proteins in the tumor, normal mouse IgG were also iodinated. For radioimaging, nude mice bearing gliomas in the thigh muscle were injected intravenously with 15 micrograms of the 131I-McAb with an activity of approximately 150 mu Ci. Control tumor-bearing animals received the same amount of mouse 131I-IgG. Scans obtained immediately after injecting the intact 131I-14AC1 antibody and at 24, 48, 72, and 96 hours demonstrated accumulation in the tumor. The tumor was clearly visible 48 hours following injection of 131I-labelled antibody. At 96 hours after injection, the McAb showed a clearly higher uptake into the tumor as the control IgG. The biodistribution of the injected antibody was studied at 96 hours after injection following the last gamma-imaging. At this time the blood activity was still high, but the maximum activity was found in the tumor for the specific McAb. Using the 131I-14AC1 to image glioma transplants, it could be shown that grafts are permeable for the McAb. The time-course experiments administering 131I-14AC1 antibody and normal mouse 131I-IgG, demonstrated that the localization of 131I-I4AC1 antibody in glioma grafts is the result of specific antigen binding. The scintigrams using intact antibody without background subtraction provided adequate tumor visualization, but the activity in the blood was high even 96 hours after injection. More rapid clearance of blood - pool radioactivity would possibly be achieved with F(ab')2 fragments. These in vivo glioma imaging studies, together with related in vitro binding tests, indicate the potential value of monoclonal antiglioma antibodies not only for clinical tumor radioimmunodetection, but also for the evaluation of immunotherapeutic approaches to the glioma disease of man.     

荷人前列腺癌裸鼠移植瘤模型的建立及其应用研究

目的 应用人前列腺癌细胞株LNCaP接种裸鼠,鼠间移植传代,建立人前列腺癌裸鼠移植瘤模型.方法 观察移植瘤大体形态和组织病理学检查,并应用免疫组织化学方法观察肿瘤组织细胞中前列腺特异膜抗原（PSMA）的表达以及125I标记抗PSMA单抗的荷瘤裸鼠体内放射免疫显像.结果 移植瘤的形态和功能特性与原发肿瘤基本相似,移植瘤的移植成功率为100%;放免显像显示标记抗体能浓聚于肿瘤部位,经尾静脉注射标记抗体后96 h,肿瘤显像清晰,肿瘤组织/非肿瘤组织放射性比值（T/NT）均大于2.8.结论 本动物模型的建立为今后前列腺癌放射免疫治疗的实验研究提供1个理想的模型.     

Imaging and biodistribution of 111In-labeled anti-carcinoembryonic antigen monoclonal antibodies in nude mice bearing human colon cancer xenografts

Anti-CEA monoclonal antibody was labeled with 111In using DTPA cyclic anhydride. The radiochemical purity of the product was more than 99% and specific binding was 38%. Imaging and biodistribution of this radiopharmaceutical in nude mice bearing human colon cancer xenografts were investigated. The results showed that a clear image of tumor was obtained by gamma camera between 24 to 120 hrs, best in 72 hrs, after injection. A high uptake of 111In-labeled monoclonal antibodies in tumor tissue was also observed, although the radioactivity in liver was considerable.     

抗人肺腺癌单克隆抗体在荷瘤裸鼠体内的分布及肿瘤放射免疫显象

Biodistribution and radioimmunoimaging of monoclonal antibody, 5F11, against human lung adenocarcinoma (LTEP-a2) in tumor-bearing nude mice were studied. The binding rate of radioiodinated 5F11 with LTEP-a2, as determined by in vitro binding assay, was 27.64 +/- 5.01%, while the control was less than 5.0%, suggesting that 5F11 reacted specifically with LTEP-a2. Seventy-two, 96 and 120 hr after injection of 125I-5F11, the percentage of dose taken per gram tumor tissue was 4.84%, 6.29% and 6.60%, higher than those of all normal organs. From 48 to 120 hr on, the ratio of tumor to normal tissue (T/NT) in the liver, spleen, kidney, stomach and intestine was more than 2; T/NT in the lung was 3.1-4.7; T/NT in the blood increased gradually and was 1.87 at 96 after injection. Tumor location index was 4.16, while that of the normal tissue was only 1.21. These results showed that human lung adenocarcinoma xenografts in nude mice were specifically located by radioiodinated 5F11. Radioimmunoimaging was performed in tumor-bearing nude mice. The tumors were clearly visualized 72 hr after injection of 131I-5F11. Radioactivity was higher in tumor region than in other regions. The optimal imaging time was 72-96 hr after injection of radioiodinated 5F11.     

放射性碘-131在荷乳腺癌裸鼠体内分布与显像的实验研究

背景与目的近年发现约85%的雌激素受体阳性乳腺癌及其转移组织细胞表面存在大量碘转运体(sodium/iodidesymporter,NIS),可主动将血液中的碘转运到乳腺癌组织,其碘浓度远高于其他组织。本实验观察放射性131I在乳腺癌荷瘤裸鼠体内生物分布及核素显像,探讨131I对雌激素受体阳性乳腺癌的特异性亲和作用。方法制备MCF-7/ER(+)与MCF-7/ER(-)人乳腺癌裸鼠模型,当肿瘤长至0.8～1.0cm时腹腔注射131I37～55.5MBq,分别于注射后6、12、24h处死裸鼠,取血标本和心、肺、肝、肾、胃、小肠、肌肉、肿瘤组织,分别测量每克组织每分钟的放射性计数,计算每克组织摄取的放射性占总注入量的百分比(%ID/g)及肿瘤与非肿瘤组织之比(T/NT)。同时于不同时段对裸鼠行核素显像,观察131I在裸鼠体内的分布。结果注射131I后6hMCF-7/ER(+)组裸鼠肿瘤组织放射性浓度已较高,与MCF-7/ER(-)组相比有显著性差异(P<0.05),甲状腺、血液、肝脏、胃、肾放射性浓度也相对较高。12h时MCF-7/ER(+)组血、心、肺、小肠、肌肉的T/NT分别为2.39、3.06、3.94、7.69、7.60,24h时分别为5.15、5.47、5.29、11.44、10.99,而12h时放射性较高的肝、肾、胃T/NT也达到1.82、2.65、2.60。显像结果示12h时MCF-7/ER(+)裸鼠肿瘤部位可看到明显的放射性浓聚灶,24h仍可清     

131I人源抗HBs Fab在裸鼠人肝癌模型定位的研究

目的在人源抗HBsFab表达载体构建、抗体片段表达及纯化成功后,进行放射免疫显像研究,以评价其在动物模型中的免疫导向活性。方法用131I标记人源抗HBsFab,经腹腔注射l,3,5,7d后行裸鼠人肝癌模型放射免疫显像,于第7天作组织分布测定,并以鼠源抗HBsAg单抗为对照进行比较。结果实验组在标记抗体注入后第3天即获阳性显像,第5天更加清晰,此时人源抗HBsFab、鼠源单抗及无关Fab的瘤／肝放射性比值分别为5＞4,4＞0和0＞9。结论人源抗HBsFab具有良好的导向活性,为其用于肝癌的导向治疗提供了实验依据。     

乳腺癌单链抗体制备及其在荷人乳腺癌裸鼠中的放免显像

目的：制备抗乳腺癌单链抗体,用于荷瘤裸鼠的放免显像研究。方法：提取乳腺癌膜抗原,制备抗乳腺癌单克隆抗体M4G3,用Pharmacia噬菌体单链抗体制备系统得到可溶性具有抗乳腺癌活性的ScFv抗体,利用环DTPA法标记核素99^mTc,进行体外培养的乳腺癌细胞系MCF-7和荷瘤小鼠体内定位显像。结果：免疫组化显示单链抗体与乳腺癌膜抗原有较强的亲和力,并在体外培养的乳腺癌细胞及荷瘤小鼠体内显像成功,且在抗体注射第3-5天显像最清晰。结论：提示M4G3的ScFv可在乳腺癌的放射免疫显像和定位诊断研究中发挥作用,值得进一步研究。     

Biodistribution and efficacy of [131I]A33scFv::CDy, a recombinant antibody-enzyme protein for colon cancer

In antibody-directed enzyme-prodrug therapy (ADEPT), an antibody-bound enzyme localizes to tumor tissue, where it selectively converts a subsequently administered non-toxic prodrug into a cytotoxic drug. A33scFv::CDy is a bifunctional fusion construct comprising a single chain antibody against the gpA33 antigen and the prodrug-converting enzyme cytosine deaminase. gpA33 is highly and homogeneously expressed in >95% of all colorectal cancers. Here we describe the biodistribution and tumor-targeting capacity of 131I labeled A33scFv::CDy. 131I labeling of A33scFv::CDy was performed by the chloramine-T method, and the properties of the resulting [131I]A33scFv::CDy conjugate were determined in vivo and in vitro, including biodistribution studies in nude mice bearing human LIM1215 colon carcinoma xenografts. The [131I]A33scFv::CDy conjugate bound specifically to colorectal cancer cells in vitro with KD = 15.8 nM as determined by a saturation assay. in vivo, the tumor uptake of [131I]A33scFv::CDy peaked at 87% injected dose/g 47 h post injection. Normal tissue uptake was low, and activity in blood was lower than in tumor at all time-points studied (6-92 h). The tumor-to-blood ratio increased over time with a maximum of 8.1 at 67 h post injection. [131I]A33scFv::CDy thus shows a biodistribution that makes it attractive for both radioimmunotherapy (RIT) and ADEPT. Preliminary therapeutic experiments showed a significant reduction of tumor size in mice treated with the A33scFv::CDy-5-fluorocytosine/5-fluorouracil ADEPT system. This work demonstrates the feasibility of ADEPT and RIT based on the A33scFv::CDy recombinant construct.