99Tcm-RGD环肽二聚体的制备及其体内外评价

目的评价^99Tc^m标记的精氨酸-甘氨酸-天冬氨酸（RGD）环肽二聚体E[c（RGDfK）]：的体内外特性及其用于整合素α，B，阳性肿瘤显像的可行性。方法以三羟甲基甘氨酸（tricine）和三苯基膦三磺酸钠（TPPTS）作为协同配体，以联肼尼克酰胺（HYNIC）作为双功能连接剂，采用无亚锡一步法制备^99Tc^m-HYNIC—E[c（RGDfK）]：，通过U87人神经胶质瘤细胞测定其半数抑制浓度（IC50），观察其体外与整合素α，B，受体的结合解离动力学、细胞内化及外化，评价其在荷人神经胶质瘤裸鼠的生物分布。结果^99Tc^m-HYNIC-E[c（RGDfK）]，的标记率〉95％，经Sep-PekC18柱纯化后其放化纯〉99％。与RGD环肽单体C（RGDyK）相比，HYNIC偶联的E[C（RGDfK）]：二聚体具有更高的整合素α，β3亲和力，IC50分别为80．0和9．07nmol／L。细胞实验显示，^99Tc^m-HYNIC—E[C（RGDfK）]：与整合素α，β，结合较快，并迅速被受体介导内化。生物分布实验显示，^99Tc^m -HYNIC—E[C（RGDfK）]：主要经肾脏排泄，在注射后0．5和4h，标记物在肿瘤的每克组织百分注射剂量率（％ID／g）分别为（2．46±0．66）和（3．10±0．35）％ID／g，标记物在肿瘤中的滞留时间足够长。1显像示注射后1h肿瘤清晰可见，注射后4h显像效果更佳。结论^99 Tc^mHYNIC-E[C（RGDfK）]：是一种有前景的用于整合素α，β3，阳性肿瘤显像的显像剂。     

99Tcm标记RGD环肽二聚体人神经胶质瘤显像及重组人血管内皮细胞抑制素对其影响的实验研究

目的 研究新型含RGD的环肽二聚体探针99Tcm-HYNIC-2聚乙二醇(PEG)4-Dimer { Dimer:E-[c(RGDfK)2]}作为整合素αvβ3受体显像剂的可行性,并观察重组人血管内皮细胞抑制素注射液(恩度)对标记探针在荷瘤裸鼠体内生物学分布及γ显像的影响.方法 选取整合素αvβ3受体表达阳性的人神经胶质瘤细胞株U87MG,免疫荧光检测U87MG经恩度处理后的整合素αvβ3受体表达情况.制备99Tcm-HYNIC-2PEG4-Dimer.建立荷U87MG神经胶质瘤裸鼠模型,并按简单随机法将其分为2组,恩度组给予200μl(1 mg)恩度,对照组给予同等体积的生理盐水,6h后注射99Tcm-HYNIC-2PEG4-Dimer,评价探针在2组荷瘤裸鼠体内的生物学分布.另取荷瘤裸鼠16只,分为恩度处理组和生理盐水组,分别按体质量给予20 mg/kg恩度和同等体积的生理盐水,给药后行γ显像.采用两样本t检验对实验数据进行统计分析.结果 99 Tcm-HYNIC-2PEG4-Dimer的放化纯大于95％.U87MG细胞高表达整合素αvβ3受体,经恩度处理后整合素αvβ3受体表达逐渐减低,恩度质量浓度为400 μg/ml时,表达程度最低.荷瘤裸鼠注射99Tcm-HYNIC-2PEG4-Dimer后90 min,肿瘤组织有较高摄取,给予恩度后肿瘤摄取减低,恩度组和对照组肿瘤摄取分别为(1.50±0.08) ％ID/g和(6.27±0.33) ％ID/g(t=40.23,P＜0.05);γ显像示2组T/NT比值分别为1.02±0.11和2.58±0.36(t=10.25,P＜0.05);免疫组织化学检查结果显示2组整合素αvβ3受体阳性表达率分别为(33.1±2.7)％与(81.5±3.2)％(t=32.60,P＜0.05).结论 99Tcm-HYNIC-2PEG4-Dimer可用于整合素αvβ3受体阳性肿瘤的显像,并可用于监测恩度疗效,有望用于筛选恩度治疗病例.     

99Tcm标记新型RGD环肽在神经胶质瘤动物模型的实验研究

目的 评价引入2个聚乙二醇（PEG4）对精氨酸-甘氨酸-天冬氨酸（RGD）环肽二聚体（Dimer：E[c（RGDfK）]2）体外受体结合亲和力和体内药代动力学特征的影响,以及99Tcm标记2PEG4-Dimer用于整合素αvβ3阳性肿瘤显像的前景.方法 用免疫组织化学实验测定U87MG人神经胶质瘤细胞以及肿瘤组织中整合素αvβ3的表达.通过U87MG细胞受体竞争结合实验测定RGD环肽单体c（RGDyK）、联肼尼克酰胺（HYNIC）-Dimer和HYNIC-2PEG4-Dimer对125I-c（RGDyK）的半数抑制浓度（IC50）.采用无亚锡一步法制备99Tcm-HYNIC-Dimer和99Tcm-HYNIC-2PEG4-Dimer,评价＂TcmHYNIC-2PEG4-Dimer在荷U87MG瘤裸鼠的生物分布并进行γ显像.采用非配对t检验法对实验数据进行分析.结果 U87MG细胞和荷瘤裸鼠肿瘤组织中高表达整合素αvβ3.HYNIC-2PEG4-Dimer比c（RGDyK）和HYNIC-Dimer有更高的整合素αvβ3亲和力（IC50分别是0.8,27和2.4 nmol/L）.99Tcm-HYNIC-Dimer和99Tcm-HYNIC-2PEG4-Dimer的99Tcm标记率均＞95%,经Sep-Pek C18柱纯化后其放化纯＞99%.生物分布实验显示,2种标记物均主要经肾排泄,在注射后2h,肿瘤对99Tcm-HYNIC-2PEG4-Dimer的摄取为99Tcm-HYNIC-Dimer的2.7倍[（5.71±0.96）%ID/g和（2.10±0.50）%ID/g],t=4.80,P＜0.05,与体外受体竞争结合实验数据相一致.γ显像结果显示,注射99Tcm-HYNIC-2PEG4-Dimer后0.5 h肿瘤即清晰可见,随时间延长,体内放射性本底明显减低,显像对比度增高.结论 99Tcm-HYNIC-2PEG4-Dimer有希望用于整合素αvβ3阳性肿瘤显像.     

^99Tc^m标记RGD环肽在荷肺腺癌裸鼠中的显像研究

目的制备^99Tc^m标记的含RGD序列的^99Tc^m-联肼尼克酰胺（HYNIC）-c（RGDfK）环肽单体,评价其在整合素表达阳性的肺腺癌严重联合免疫缺陷（SCID）小鼠肿瘤模型中的生物学分布,并进行显像研究。方法（1）以HYNIC为双功能螯合剂,以三羟甲基甘氨酸（tricine）和乙二胺二乙酸为协同配体,采用二步法制备^99Tc^m标记HYNIC—c（RGDfK）,进行细胞结合实验,测定标记物生物学活性;（2）将荷A549肺腺癌模型小鼠分为7组[第7组作为竞争性抑制组,注射显像剂前0．5h先注射HYNIC-c（CRDGfk）100μg],每组5只,经尾静脉注射7．4MBq的^99Tc^m-HYNIC-c（RGDfK）,于注射后0．5,1,2,4,8,12h处死,计算荷A549肺腺癌小鼠模型各脏器％ID／g,同时采用ROI技术研究^99Tc^m-HYNIC—c（RGDfK）在小鼠体内的生物学分布,计算不同时间点的T／NT比值（NT选取肌肉）;（3）取6只荷瘤裸鼠,其中3只为竞争性抑制组,经尾静脉注射7．4MBq的^99Tc^m-HYNIC—c（RGDfK）,于注射后0．5,1,2,4,8,12h进行静态1显像。结果^99Tc^m-HYNIC—c（RGDfK）的标记率〉90％,放化纯〉95％。^99Tc^m-HYNIC—c（RGDfK）与A549肺腺癌细胞特异性结合率最高为36．14％,体内分布实验显示^99Tc^m-HYNIC—c（RGDfK）在肾的摄取率始终高于20％ID／g,注射后0．5h肿瘤％ID／g为10．52±1．48,8h为17．26±2．81,12h为8．93±0．90,竞争性抑制组注射后0．5h为2．29±0．85。通过ROI技术测得T／NT在8h达6．87。注射后1h肿瘤可显影,4～8h显影更清晰。结论^99Tc^m标记HYNIC—c（RGDfK）易于制备,具有良好的靶向性。     

靶向整合素αvβ3探针用于甲状腺乳头状癌显像的研究

目的 制备特异性整合素αvβ3探针[^18F]氟化铝-匹仑吉肽（^18F-Al-NOTA-PRGD2）,探讨其用于甲状腺乳头状癌（PTC） PET显像的可行性.方法 采用氟化铝新策略制备18F-Al-NOTA-PRGD2.取新鲜切除的人PTC肿瘤组织接种于裸鼠右腋下,制得荷人PTC裸鼠模型.再分别取人PTC标本及毗邻的正常组织、荷瘤裸鼠移植瘤行整合素αvβ3免疫组织化学染色.荷瘤裸鼠（n=5）尾静脉注射1.1 MBq ^18F-Al-NOTA-PRGD2后30、60和120 min分别行microPET显像,通过ROI技术计算肿瘤和主要脏器的放射性摄取值（％ ID/g）,并通过阻断实验验证其特异性.另取15只荷瘤裸鼠研究其注药后30、60及120 min生物分布,计算放射性摄取值（％ID/g）.用两样本t检验进行统计学处理.结果 成功制备^18F-Al-NOTA-PRGD2,标记率＞45％.免疫组织化学染色证实人PTC标本和裸鼠移植瘤组织整合素αvβ3染色均呈棕褐色阳性表达,人PTC毗邻正常组织不表达.荷瘤裸鼠注射^18 F-Al-NOTA-PRGD2后行microPET显像示,肿瘤清晰可见,且与周围组织对比度良好.注射后30、60、120 min肿瘤对显像剂的摄取值分别为（2.81±0.35）、（2.45±0.27）和（1.80±0.21） ％ID/g.PRGD2阻断后,注射^18F-Al-NOTA-PRGD2后60 min肿瘤对显像剂的摄取值降为（0.51±0.05） ％ID/g.荷瘤裸鼠生物分布实验示,注射显像剂后30、60、120 min肿瘤摄取值分别为（3.09±0.25）、（2.75±0.37）和（1.90±0.16） ％ID/g,与microPET显像基本一致（t=1.456、1.465和0.847,均P＞0.05）.^18F-Al-NOTA-PRGD2在血液和肌肉中清除快,注射后60 min肿瘤与血液和肌肉的摄取比值分别为6.15±0.45和7.86±0.56.结论 ^18F-Al-NOTA-PRGD2制备简单,放化纯高,可有效监测PTC中整合素αvβ3表达水平;其PET显像有望为研究PTC整合素αvβ3受体相关机制提供一种新方法.     

喉和鼻咽鳞状细胞癌整合素αvβ3放射性核素显像实验研究

目的 研究99Tcm标记的聚乙二醇(PEG)4修饰的环状RGD二聚体(99Tcm-3P-RGD2)显像用于检测人喉和鼻咽鳞状细胞癌(简称鳞癌)整合素αvβ3表达的可靠性.方法 对荷人HEP-2喉鳞癌、荷人CNE-1鼻咽鳞癌裸鼠各6只进行99Tcm-3P-RGD2平面显像,采用勾画ROI技术计算T/NT.显像结束后,测量99Tcm-3P-RGD2在荷瘤鼠体内的放射性分布,计算肿瘤与各组织器官的％ID/g.取肿瘤组织,行整合素αvβ3免疫组织化学染色,并参照Fromowitz法进行半定量分析.两组间比较采用独立样本t检验,相关性分析采用线性相关法.结果 荷HEP-2、CNE-1裸鼠2h显像时T/NT 分别为2.08±0.04与1.54±0.10.体内放射性分布示:HEP-2肿瘤2h放射性摄取值为(4.56±0.67)％ID/g,肿瘤与血液、肌肉的T/NT分别为6.37±0.68与4.44±0.42;CNE-1肿瘤2h放射性摄取值为(1.69 ±0.18) ％ID/g,肿瘤与血液、肌肉的T/NT分别为2.49±0.09与1.86±0.07.HEP-2、CNE-1肿瘤αvβ3免疫组织化学染色Fromowitz评分分别为4.97±0.37与2.60±0.36.荷HEP-2裸鼠2h显像时T/NT、％ID/g及免疫组织化学染色Fromowitz评分均显著高于荷CNE-1裸鼠(t值分别为11.83、7.17和11.31,P均＜0.05).2种荷瘤鼠2h显像时T/NT与免疫组织化学染色Fromowitz评分的相关性均较好(HEP-2:r2h =0.97,P＜0.05;CNE-1:r'2h =0.97,P＜0.05).结论 99Tcm-3P-RGD2显像有望成为检测喉和鼻咽鳞癌αvβ3表达的无创和有效方法.     

99Tcm-3P-RGD2用于肺癌整合素αv β3表达水平检测的实验研究

目的 采用99Tcm-3聚乙二醇4-RGD2(3P-RGD2)评估小细胞肺癌和肺腺癌细胞荷瘤鼠动物模型中整合素αvβ3表达水平.方法 按试剂盒说明书制备99Tcm-3P-RGD2.选取H446人小细胞肺癌细胞进行受体竞争抑制实验,检测3P-RGD2与整合素αvβ3的特异亲和性.通过细胞摄取实验检测H446和A549人肺腺癌细胞对99Tcm-3P-RGD2的摄取情况,以流式细胞术和免疫荧光染色测定2种细胞中整合素αvβ3的表达.观察99Tcm-3P-RGD2在H446和A549肺癌荷裸鼠模型(各6只)的microSPECT/CT显像情况.显像后断颈处死裸鼠,取部分肿瘤组织制备单细胞悬液,以流式细胞术检测细胞整合素αvβ3表达;部分组织制成切片,以免疫组织化学法检测肿瘤组织整合素αvβ3的表达.采用配对t检验对实验数据进行统计学分析.结果 99Tcm-3P-RGD2标记率为(97.0±2.0)％,4h时后放化纯仍高达95％.3P-RGD2与整合素αvβ3特异性结合的半数抑制浓度(IC5o)为8.759 nmol/L.H446细胞对99Tcm-3P-RGD2的亲和性高于A549细胞,摄取率均于120 min达峰值,分别为(5.75±0.50)％和(3.35±0.28)％(t=9.324,P＜0.05).H446和A549肺癌细胞均表达整合素αvβ3,且H446高于A549[(18.01±2.83)％和(5.77±0.64)％,t=7.488,P＜0.05].免疫荧光染色示H446细胞整合素信号明显高于A549细胞.MicroSPECT/CT显像示注射99Tcm-3P-RGD2后3 h T/NT达最大值,H446荷瘤鼠T/NT比值为6.39±1.29,高于A549荷瘤鼠(3.62±0.33,t=6.869,P＜0.05).H446和A549肿瘤组织经流式细胞术检测,整合素αvβ3表达水平分别为(22.89±3.63)％和(10.23±1.94)％(t=13.967,P＜0.05).免疫组织化学检测结果示H446和A549肿瘤组织和新生血管内皮细胞均有整合素αvβ3表达.结论 99Tcm-3P-RGD2可用于整合素αvβ3阳性肺癌的显像,并可无创评估不同肺癌组织整合素αvβ3的表达水平.     

^177Lu-EB-RGD分子探针的构建及其在非小细胞肺癌PDX模型中的显像与治疗研究

目的 构建靶向整合素αvβ3诊疗一体化放射性分子177 Lu-伊文思蓝(EB)-精氨酸-甘氨酸-天冬氨酸(RGD)并探讨其用于非小细胞肺癌(NSCLC)-患者来源异种移植瘤(PDX)模型显像及治疗的效果.方法 将RGD肽与白蛋白结合基团EB相连接,构建特异性靶向整合素αvβ3的EB-RGD,并经螯合剂1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸(DOTA)偶联完成靶向分子177 Lu标记.构建68只NSCLC-PDX模型鼠,取28只注射177 Lu-EB-RGD或177 Lu-RGD行microSPECT显像和生物分布研究;另行177 Lu-EB-RGD放射靶向治疗实验:取PDX模型鼠40只,分为生理盐水组(A组)、18.5 MBq ^177Lu-RGD组(B组)、18.5 MBq ^177Lu-EB-RGD组(C组)、29.6 MBq ^177Lu-EB-RGD组(D组),每组10只,观察治疗后50 d内模型鼠肿瘤体积变化情况.2组间比较采用两独立样本t检验.结果 ^177Lu-EB-RGD的标记率在95%以上,比活度为(55±14) GBq/μmol,其体外稳定性好,放化纯大于95%.注射^177Lu-EB-RGD后4~96 h,NSCLC-PDX模型鼠肿瘤清晰可见,注射后4、24、72、96 h的肿瘤/肌肉摄取比值(T/M)分别为7.34±0.67、14.63±3.82、15.69±3.58及15.99±5.42;生物分布结果示177 Lu-EB-RGD摄取[每克组织百分注射剂量率(%ID/g)]与SPECT显像结果一致,且4h时的^177Lu-EB-RGD在肿瘤中的摄取明显高于^177Lu-RGD[(10.15±1.17)与(3.30±1.47) %ID/g;t=18.60,P<0.05].^177Lu-EB-RGD治疗后,A组与B组模型鼠的肿瘤体积均快速增加;而C组与D组肿瘤体积呈持续降低趋势,在第28天时C组与D组肿瘤均已肉眼不可见,且在随后的监测时间内未见复发.结论 ^177Lu-EB-RGD能靶向αvβ3阳性的NSCLC-PDX模型,显像效果好,对肿瘤生长有明显抑制作用,有望为晚期靶向治疗耐药或无效的肺癌患者提供新的治疗策略.     

放射性核素标记RGD序列多肽与整合素αvβ3受体显像的研究进展

整合素主要介导细胞与细胞、细胞与细胞外基质(ECM)之间的相互黏附,对细胞的黏附、增殖、分化、转移、凋亡起到重要的调控作用,在肿瘤的侵袭转移中发挥重要作用.成熟血管内皮细胞和绝大多数正常器官系统中,整合素αvβ3受体表达缺乏或几乎不能被探及,但其在新生血管内皮细胞中有强烈表达,精氨酸-甘氨酸-天冬氨酸(RGD)肽是整合素αvβ3受体的特异性识别位点,因此,将放射性核素标记到含有RGD序列的肽类化合物上,用于整合素αvβ3受体显像,对于肿瘤早期和高特异性定位、定量诊断及治疗都具有重要意义.近年来国内外对RGD肽的标记方法和αvβ3受体显像进行了研究.     

99Tcm标记新型RGD环肽在神经胶质瘤动物模型的实验研究

Objective (1) To evaluate the effect of insertion of two 15-amino-4,7,10,13-tetraoxapentadecanoic (2 PEG4 ) linkers into cyclic Arg-Gly-Asp (RGD) Dimer E [c(RGDfK)]2 on receptor binding in vitro, (2) to assess its biodistribution in vivo and (3) to investigate the value of 99Tcm labeled 2PEG4-Dimer for integrin αvβ3-positive tumors imaging.Methods The expression of U87 human glioma cells and integrin αv β3 was determined by immunofluorescence staining.The half-inhibition concentrations (IC50) for 125 I-cyclo (Arg-Gly-Asp-D-Tyr-Lys) (c(RGDyK) ) of c ( RGDyK ), hydrazinonictinamide ( HYNIC )-Dimer and HYNIC-2PEG4-Dimer binding to integrin αvβ3 were measured.99Tcm-HYNIC-Dimer and 99Tcm-HYNIC-2PEG4-Dimer were synthesized using non-SnCl2 formulation.Biodistribution and imaging studies were performed in nude mice bearing human glioma xenografts.The unpaired t test was used for statistical analysis.Results The labeling yield of the two radiotracers was more than 95%, and the radiochemical purity was more than 99% through Sep-Pek C18 cartridge.HYNIC-2PEG4-Dimer had significantly higher binding affinity of integrin αvβ3 than c(RGDyK) and HYNIC-Dimer (IC50 = 0.8 nmol/L, 27 nmol/L and 2.4 nmol/L, respectively).Biodistribution study showed that 99Tcm-HYNIC-2PEG4-Dimer was mainly excreted via the kidney.The tumor uptake of 99Tcm-HYNIC-2PEG4-Dimer was higher than that of 99Tcm-HYNIC-Dimer at 2h post injection ((5.71 ±0.96) and (2.10 ±0.50) % ID/g, t =4.80, P＜0.05).The xenografted tumors were visible at 0.5 h post injection and the image contrast increased with time due to the tracer clearance of the background tissue.Conclusion 99 Tcm-HYNIC-2PEG4-Dimer is a promising radiotracer for integrin αvβ3-positive tumor imaging.     

microPET imaging of glioma integrin {alpha}v{beta}3 expression using (64)Cu-labeled tetrameric RGD peptide.

Integrin alpha(v)beta(3) plays a critical role in tumor-induced angiogenesis and metastasis and has become a promising diagnostic indicator and therapeutic target for various solid tumors. Radiolabeled RGD peptides that are integrin specific can be used for noninvasive imaging of integrin expression level as well as for integrin-targeted radionuclide therapy. METHODS: In this study we developed a tetrameric RGD peptide tracer (64)Cu-DOTA-E{E[c(RGDfK)](2)}(2) (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid) for PET imaging of integrin alpha(v)beta(3) expression in female athymic nude mice bearing the subcutaneous UG87MG glioma xenografts. RESULTS: The RGD tetramer showed significantly higher integrin binding affinity than the corresponding monomeric and dimeric RGD analogs, most likely due to a polyvalency effect. The radiolabeled peptide showed rapid blood clearance (0.61 +/- 0.01 %ID/g at 30 min and 0.21 +/- 0.01 %ID/g at 4 h after injection, respectively [%ID/g is percentage injected dose per gram]) and predominantly renal excretion. Tumor uptake was rapid and high, and the tumor washout was slow (9.93 +/- 1.05 %ID/g at 30 min after injection and 4.56 +/- 0.51 %ID/g at 24 h after injection). The metabolic stability of (64)Cu-DOTA-E{E[c(RGDfK)](2)}(2) was determined in mouse blood, urine, and liver and kidney homogenates at different times after tracer injection. The average fractions of intact tracer in these organs at 1 h were approximately 70%, 58%, 51%, and 26%, respectively. Noninvasive microPET studies showed significant tumor uptake and good contrast in the subcutaneous tumor-bearing mice, which agreed well with the biodistribution results. Integrin alpha(v)beta(3) specificity was demonstrated by successful blocking of tumor uptake of (64)Cu-DOTA-E{E[c(RGDfK)](2)}(2) in the presence of excess c(RGDyK) at 1 h after injection. The highest absorbed radiation doses determined for the human reference adult were received by the urinary bladder wall (0.262 mGy/MBq), kidneys (0.0296 mGy/MBq), and liver (0.0242 mGy/MBq). The average effective dose resulting from a single (64)Cu-DOTA-E{E[c(RGDfK)](2)}(2) injection was estimated to be 0.0164 mSv/MBq. CONCLUSION: The high integrin and avidity and favorable biokinetics make (64)Cu-DOTA-E{E[c(RGDfK)](2)}(2) a promising agent for peptide receptor radionuclide imaging and therapy of integrin-positive tumors.     

(64)Cu-labeled tetrameric and octameric RGD peptides for small-animal PET of tumor alpha(v)beta(3) integrin expression.

Integrin alpha(v)beta(3) plays a critical role in tumor angiogenesis and metastasis. Suitably radiolabeled cyclic arginine-glycine-aspartic (RGD) peptides can be used for noninvasive imaging of alpha(v)beta(3) expression and targeted radionuclide therapy. In this study, we developed (64)Cu-labeled multimeric RGD peptides, E{E[c(RGDyK)](2)}(2) (RGD tetramer) and E(E{E[c(RGDyK)](2)}(2))(2) (RGD octamer), for PET imaging of tumor integrin alpha(v)beta(3) expression. METHODS: Both RGD tetramer and RGD octamer were synthesized with glutamate as the linker. After conjugation with 1,4,7,10-tetra-azacyclododecane-N,N',N',N'-tetraacetic acid (DOTA), the peptides were labeled with (64)Cu for biodistribution and small-animal PET imaging studies (U87MG human glioblastoma xenograft model and c-neu oncomouse model). A cell adhesion assay, a cell-binding assay, receptor blocking experiments, and immunohistochemistry were also performed to evaluate the alpha(v)beta(3)-binding affinity/specificity of the RGD peptide-based conjugates in vitro and in vivo. RESULTS: RGD octamer had significantly higher integrin alpha(v)beta(3)-binding affinity and specificity than RGD tetramer analog (inhibitory concentration of 50% was 10 nM for octamer vs. 35 nM for tetramer). (64)Cu-DOTA-RGD octamer had higher tumor uptake and longer tumor retention than (64)Cu-DOTA-RGD tetramer in both tumor models tested. The integrin alpha(v)beta(3) specificity of both tracers was confirmed by successful receptor-blocking experiments. The high uptake and slow clearance of (64)Cu-DOTA-RGD octamer in the kidneys was attributed mainly to the integrin positivity of the kidneys, significantly higher integrin alpha(v)beta(3)-binding affinity, and the larger molecular size of the octamer, as compared with the other RGD analogs. CONCLUSION: Polyvalency has a profound effect on the receptor-binding affinity and in vivo kinetics of radiolabeled RGD multimers. The information obtained here may guide the future development of RGD peptide-based imaging and internal radiotherapeutic agents targeting integrin alpha(v)beta(3).     

<Superscript>68</Superscript>Ga-labeled multimeric RGD peptides for microPET imaging of integrin α<Subscript>v</Subscript>β<Subscript>3</Subscript> expression

PURPOSE: We and others have reported that (18)F- and (64)Cu-labeled arginine-glycine-aspartate (RGD) peptides allow positron emission tomography (PET) quantification of integrin alpha(v)beta(3) expression in vivo. However, clinical translation of these radiotracers is partially hindered by the necessity of cyclotron facility to produce the PET isotopes. Generator-based PET isotope (68)Ga, with a half-life of 68 min and 89% positron emission, deserves special attention because of its independence of an onsite cyclotron. The goal of this study was to investigate the feasibility of (68)Ga-labeled RGD peptides for tumor imaging. METHODS: Three cyclic RGD peptides, c(RGDyK) (RGD1), E[c(RGDyK)](2) (RGD2), and E{E[c(RGDyK)](2)}(2) (RGD4), were conjugated with macrocyclic chelator 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and labeled with (68)Ga. Integrin affinity and specificity of the peptide conjugates were assessed by cell-based receptor binding assay, and the tumor targeting efficacy of (68)Ga-labeled RGD peptides was evaluated in a subcutaneous U87MG glioblastoma xenograft model. RESULTS: U87MG cell-based receptor binding assay using (125)I-echistatin as radioligand showed that integrin affinity followed the order of NOTA-RGD4 > NOTA-RGD2 > NOTA-RGD1. All three NOTA conjugates allowed nearly quantitative (68)Ga-labeling within 10 min (12-17 MBq/nmol). Quantitative microPET imaging studies showed that (68)Ga-NOTA-RGD4 had the highest tumor uptake but also prominent activity accumulation in the kidneys. (68)Ga-NOTA-RGD2 had higher tumor uptake (e.g., 2.8 +/- 0.1%ID/g at 1 h postinjection) and similar pharmacokinetics (4.4 +/- 0.4 tumor/muscle ratio, 2.0 +/- 0.1 tumor/liver ratio, and 1.1 +/- 0.1 tumor/kidney ratio) compared with (68)Ga-NOTA-RGD1. CONCLUSIONS: The dimeric RGD peptide tracer (68)Ga-NOTA-RGD2 with good tumor uptake and favorable pharmacokinetics warrants further investigation for potential clinical translation to image integrin alpha(v)beta(3).     

64Cu Labeled AmBaSar-RGD2 for micro-PET Imaging of Integrin αvβ3 Expression

Integrin αvβ3 plays a critical role in tumor-induced angiogenesis and metastasis. Previously, a 64Cu-AmBaSar- RGD monomer with high in vivo stability compared with 64Cu-DOTA-RGD was developed for integrin αvβ3 PET imaging. It has been established that dimeric RGD peptides have higher receptor-binding affinity and superior in vivo kinetics compared with monomeric RGD peptides due to the polyvalency effect. In this context, we synthesized and evaluated 64Cu-labeled AmBaSar dimeric RGD conjugates (64Cu-AmBaSar-RGD2) for PET imaging of integrin αvβ3 expression. The dimeric RGD peptide was conjugated with a cage-like chelator AmBaSar and labeled with 64Cu. Cell binding, microPET imaging, receptor blocking, and biodistribution studies of 64Cu-AmBaSar-RGD2 were conducted in the U87MG human glioblastoma xenograft model. AmBaSar-RGD2 conjugate was obtained in reasonable yield (45.0 ± 2.5%, n= 4) and the identity was confirmed by HPLC and MS (found 1779.8, calculated m/z for [M+H]+ M: C81H125N27O19 1779.9). 64Cu-AmBaSar-RGD2 was obtained with high radiochemical yield (92.0 ± 1.3%) and purity (≥ 98.0%) under mild conditions (pH 5.0~5.5, 23~37 °C) in 30 min. The specific activity of 64Cu-AmBaSar-RGD2 was estimated to be 15-22 GBq/μmol at the end of synthesis. Based on microPET imaging and biodistribution studies, 64Cu-AmBaSar-RGD2 has demonstrated higher tumor uptake at selected time points than 64Cu-AmBaSar-RGD. At 20 h p.i., the tumor uptake reached 0.65 ± 0.05 %ID/g for 64Cu-AmBaSar-RGD and 1.76 ± 0.38 %ID/g for 64Cu-AmBaSar-RGD2, respectively. The integrin αvβ3 targeting specificity was confirmed by blocking experiments. Therefore, the new tracer 64Cu-AmBaSar- RGD2 exhibited better tumor-targeting efficacy and more favorable in vivo pharmacokinetics than the 64Cu labeled RGD monomer due to the polyvalency effect.     

Favorable biokinetic and tumor-targeting properties of 99mTc-labeled glucosamino RGD and effect of paclitaxel therapy.

Compared with the recent advancements in radiohalogenated Arg-Gly-Asp (RGD) peptides for alpha(v)beta(3)-targeted imaging, there has been limited success with (99m)Tc-labeled RGD compounds. In this article, we describe the favorable in vivo kinetics and tumor-imaging properties of a novel (99m)Tc-RGD compound that contains a glucosamine moiety. METHODS: Glucosamino (99m)Tc-d-c(RGDfK) was prepared by incorporating (99m)Tc(CO)(3) to the glucosamino peptide precursor in high radiochemical yield. Cell-binding characteristics were tested on human endothelial cells. Mice bearing RR1022 fibrosarcoma and Lewis lung carcinoma (LLC) tumors were used for in vivo biodistribution and blocking experiments and for imaging studies. Separate LLC-bearing mice underwent antiangiogenic therapy with 0, 20, or 40 mg of paclitaxel per kilogram of body weight every 2 d. Tumor volume was serially monitored, and tumor glucosamino (99m)Tc-d-c(RGDfK) uptake and Western blots of alpha(v) integrin expression were analyzed at day 14. RESULTS: Glucosamino (99m)Tc-d-c(RGDfK) binding to endothelial cells was dose-dependently inhibited by excess RGD. Biodistribution in mice showed rapid blood clearance of glucosamino (99m)Tc-d-c(RGDfK), with substantially lower liver uptake and higher tumor uptake compared with (125)I-c(RGD(I)yV). Tumor uptake was 1.03 +/- 0.21 and 1.18 +/- 0.26 %ID/g at 1 h and 0.85 +/- 0.05 and 0.89 +/- 0.28 %ID/g at 4 h for sarcomas and carcinomas, respectively. Excess RGD blocked uptake by 76.5% and 70.2% for the respective tumors. gamma-Camera imaging allowed clear tumor visualization, with an increase of sarcoma-to-thigh count ratios from 5.5 +/- 0.7 at 1 h to 10.1 +/- 2.2 at 4 h and sustained carcinoma-to-thigh count ratios from 4 to 17 h. Pretreatment with excess cRGDyV significantly reduced tumor contrast on images. Paclitaxel therapy in LLC tumor-bearing mice significantly retarded tumor growth. This was accompanied by a corresponding reduction of tumor glucosamino (99m)Tc-d-c(RGDfK) uptake, which correlated significantly with tumor alpha(v) integrin expression levels. CONCLUSION: Glucosamino (99m)Tc-d-c(RGDfK) has favorable in vivo biokinetics and tumor-imaging properties and may be useful for noninvasive evaluation of tumor integrin expression and response to antiangiogenic therapeutics. Because of the wide accessibility of gamma-cameras and high availability and excellent imaging characteristics of (99m)Tc, glucosamino (99m)Tc-d-c(RGDfK) may be an attractive alternative to radiohalogenated RGD peptides for angiogenesis-imaging research.     

microPET of tumor integrin alphavbeta3 expression using 18F-labeled PEGylated tetrameric RGD peptide (18F-FPRGD4).

In vivo imaging of alpha(v)beta(3) expression has important diagnostic and therapeutic applications. Multimeric cyclic RGD peptides are capable of improving the integrin alpha(v)beta(3)-binding affinity due to the polyvalency effect. Here we report an example of (18)F-labeled tetrameric RGD peptide for PET of alpha(v)beta(3) expression in both xenograft and spontaneous tumor models. METHODS: The tetrameric RGD peptide E{E[c(RGDyK)](2)}(2) was derived with amino-3,6,9-trioxaundecanoic acid (mini-PEG; PEG is poly(ethylene glycol)) linker through the glutamate alpha-amino group. NH(2)-mini-PEG-E{E[c(RGDyK)](2)}(2) (PRGD4) was labeled with (18)F via the N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) prosthetic group. The receptor-binding characteristics of the tetrameric RGD peptide tracer (18)F-FPRGD4 were evaluated in vitro by a cell-binding assay and in vivo by quantitative microPET imaging studies. RESULTS: The decay-corrected radiochemical yield for (18)F-FPRGD4 was about 15%, with a total reaction time of 180 min starting from (18)F-F(-). The PEGylation had minimal effect on integrin-binding affinity of the RGD peptide. (18)F-FPRGD4 has significantly higher tumor uptake compared with monomeric and dimeric RGD peptide tracer analogs. The receptor specificity of (18)F-FPRGD4 in vivo was confirmed by effective blocking of the uptake in both tumors and normal organs or tissues with excess c(RGDyK). CONCLUSION: The tetrameric RGD peptide tracer (18)F-FPRGD4 possessing high integrin-binding affinity and favorable biokinetics is a promising tracer for PET of integrin alpha(v)beta(3) expression in cancer and other angiogenesis related diseases.     

Improved targeting of the α<Subscript>v</Subscript>β<Subscript>3</Subscript> integrin by multimerisation of RGD peptides

Purpose The integrin α_vβ₃ is expressed on sprouting endothelial cells and on various tumour cell types. Due to the restricted expression of α_vβ₃ in tumours, α_vβ₃ is considered a suitable receptor for tumour targeting. In this study the α_vβ₃ binding characteristics of an ¹¹¹In-labelled monomeric, dimeric and tetrameric RGD analogue were compared. Methods A monomeric (E-c(RGDfK)), dimeric (E-[c(RGDfK)]₂), and tetrameric (E{E[c(RGDfK)]₂}₂) RGD peptide were synthesised, conjugated with DOTA and radiolabelled with ¹¹¹In. In vitro α_vβ₃ binding characteristics were determined in a competitive binding assay. In vivo α_vβ₃ targeting characteristics of the compounds were assessed in mice with SK-RC-52 xenografts. Results The IC₅₀ values for DOTA-E-c(RGDfK), DOTA-E-[c(RGDfK)]₂, and DOTA-E{E[c(RGDfK)]₂}₂were 120 nM, 69.9 nM and 19.6 nM, respectively. At all time points, the tumour uptake of the dimer was significantly higher as compared to that of the monomer. At 8 h p.i., tumour uptake of the tetramer (7.40±1.12%ID/g) was significantly higher than that of the monomer (2.30±0.34%ID/g), p<0.001, and the dimer (5.17±1.22%ID/g), p<0.05. At 24 h p.i., the tumour uptake was significantly higher for the tetramer (6.82±1.41%ID/g) than for the dimer (4.22±0.96%ID/g), p<0.01, and the monomer (1.90±0.29%ID/g), p<0.001. Conclusion Multimerisation of c(RGDfK) resulted in enhanced affinity for α_vβ₃ as determined in vitro. Tumour uptake of a tetrameric RGD peptide was significantly higher than that of the monomeric and dimeric analogues, presumably owing to the enhanced statistical likelihood for rebinding to α_vβ₃.     

Effects of linker variation on the in vitro and in vivo characteristics of an 111In-labeled RGD peptide

INTRODUCTION: Due to the selective expression of the alpha(v)beta3 integrin in tumors, radiolabeled arginine-glycine-aspartic acid (RGD) peptides are attractive candidates for tumor targeting. Minor modifications of these peptides could have a major impact on in vivo characteristics. In this study, we systematically investigated the effects of linker modification between two cyclic RGD sequences and DOTA (1,4,7,10-tetraazadodecane-N,N',N",N'-tetraacetic acid) on the in vitro and in vivo characteristics of the tracer. METHODS: A dimeric RGD peptide was synthesized and conjugated either directly with DOTA or via different linkers: PEG4 (polyethylene glycol), glutamic acid or lysine. The RGD peptides were radiolabeled with 111In, and their in vitro and in vivo alpha(v)beta3-binding characteristics were determined. RESULTS: LogP values varied between -2.82+/-0.06 and -3.95+/-0.33. The IC50 values for DOTA-E-[c(RGDfK)]2, DOTA-PEG4-E-[c(RGDfK)]2, DOTA-E-E-[c(RGDfK)]2 and DOTA-K-E-[c(RGDfK)]2 were comparable. Two hours after injection, the tumor uptakes of the 111In-labeled compounds were not significantly different. The kidney accumulation of [111In]-DOTA-K-E-[c(RGDfK)]2 [4.05+/-0.20% of the injected dose per gram (ID/g)] was significantly higher as compared with that of [111In]-DOTA-E-[c(RGDfK)]2 (2.63+/-0.19% ID/g; P<.05) as well as that of [111In]-DOTA-E-E-[c(RGDfK)]2 (2.16+/-0.21% ID/g; P<.01). The liver uptake of [111In]-DOTA-E-E-[c(RGDfK)]2 (2.12+/-0.09% ID/g) was significantly higher as compared with that of [111In]-DOTA-E-[c(RGDfK)]2 (1.64+/-0.1% ID/g; P<.05) as well as that of [111In]-DOTA-K-E-[c(RGDfK)]2 (1.52+/-0.04% ID/g; P<.01). CONCLUSIONS: Linker variation did not affect affinity for alpha(v)beta3 and tumor uptake. Insertion of lysine caused enhanced kidney retention; that of glutamic acid also resulted in enhanced retention in the kidneys. PEG4 appeared to be the most suitable linker as compared with glutamic acid and lysine because it has the highest tumor-to-blood ratio and the lowest uptake in the kidney and liver.     

Design and biological evaluation of 99mTc-N2S2-Tat(49–57)-c(RGDyK): A hybrid radiopharmaceutical for tumors expressing α(v)β(3) integrins

The α(ν)β(3) integrin is over-expressed in the tumor neovasculature and the tumor cells of glioblastomas. The HIV Tat-derived peptide has been used to deliver various cargos into cells. The aim of this research was to synthesize and assess the in vitro and in vivo uptake of ^99mTc-N₂S₂-Tat(49–57)-c(RGDyK) (^99mTc-Tat-RGD) in α(ν)β(3) integrin positive cancer cells and compare it to that of a conventional ^99mTc-RGD peptide (^99mTc-EDDA/HYNIC-E-[c(RGDfK)]₂). Methods: The c(RGDyK) peptide was conjugated to a maleimidopropionyl (MP) moiety through Lys, and the MP group was used as the branch position to form a thioether with the Cys¹² side chain of the Tat(49–57)-spacer-N₂S₂ peptide. ^99mTc-Tat-RGD was prepared, and stability studies were carried out by size exclusion HPLC analyses in human serum. The in vitro affinity for α(v)β(3) integrin was determined by a competitive binding assay. In vitro internalization was determined using glioblastoma C6 cells. Biodistribution studies were accomplished in athymic mice with C6 induced tumors that had blocked and unblocked receptors. Images were obtained using a micro-SPECT/CT. Results: ^99mTc-Tat-RGD was obtained with a radiochemical purity higher than 95%, as determined by radio-HPLC and ITLC-SG analyses. Protein binding was 15.7% for ^99mTc-Tat-RGD and 5.6% for ^99mTc-RGD. The IC₅₀ values were 6.7 nM (^99mTc-Tat-RGD) and 4.6 nM (^99mTc-RGD). Internalization in C6 cells was higher in ^99mTc-Tat-RGD (37.5%) than in ^99mTc-RGD (10%). Biodistribution studies and in vivo micro-SPECT/CT images in mice showed higher tumor uptake for ^99mTc-Tat-RGD (6.98% ± 1.34% ID/g at 3 h) than that of ^99mTc-RGD (3.72% ± 0.52% ID/g at 3 h) with specific recognition for α(v)β(3) integrins. Conclusions: Because of the significant cell internalization (Auger and internal conversion electrons) and specific recognition for α(v)β(3) integrins, the hybrid ^99mTc-N₂S₂-Tat(49–57)-c(RGDyK) radiopharmaceutical is potentially useful for the imaging and possible therapy of tumors expressing α(v)β(3) integrins.