Evaluation of a 188Re‐radiolabeled Arg‐Gly‐Asp peptide for tumor overexpressed αvβ3 receptors

To develop a peptide‐based radiopharmaceutical for the therapy of α_vβ₃ receptors overexpressed tumors, we have prepared a novel Arg‐Gly‐Asp (RGD) peptide (HCRGDCF(D)CRGDC, P12) radiolabeled with ¹⁸⁸Re. With His acid at the end of the peptide containing RGD, the label efficiency was more than 95% within 30 min. The peptide binds to human glioblastoma U87MG cells with high affinity [IC₅₀ = 86.3 nm]. The stability of ¹⁸⁸Re‐P12 in vitro was also investigated. More than 80% of radioactivity was kept in the peptide after 4 h incubation in phosphate buffer solution (pH = 7.4) or calf serum under physiological conditions. Biodistribution of this radiocompound was carried out in mice bearing S180 tumor. Fast clearance of ¹⁸⁸Re‐peptide from blood and specific uptakes by tumors realized higher tumor‐to‐blood ratio (1.80) 4 h post‐injection. Obvious difference was observed between the blocking and unblocking experiments in whole body autoradiography imaging. These results have demonstrated the potential of ¹⁸⁸Re‐labeling RGD as a radiotherapeutic agent.     

肺癌特异性靶向小分子多肽的核素分子探针的制备

目的:研究用NHS-MAG3作为双功能螯合剂进行99mTc标记针对肺癌特异性靶向小分子多肽的核素分子探针的制备方法.方法:利用组合化学肽库技术筛选得到与非小细胞肺癌(A549)发生特异性结合的小分子多肽cNGQGEQc,在合成多肽的过程中直接完成多肽与双功能螯合剂NHS-MAG3的偶联,然后采用氯化亚锡直接进行99mT...     

Fluorine‐18 radiolabeling of a nitrophenyl sulfoxide and its evaluation in an SK‐RC‐52 model of tumor hypoxia

The significance of imaging hypoxia with the positron emission tomography ligand [¹⁸F]FMISO has been demonstrated in a variety of cancers. However, the slow kinetics of [¹⁸F]FMISO require a 2‐h delay between tracer administration and patient scanning. Labeled chloroethyl sulfoxides have shown faster kinetics and higher contrast than [¹⁸F]FMISO in a rat model of ischemic stroke. However, these nitrogen mustard analogues are unsuitable for routine production and use in humans. Here, we report on the synthesis and in vitro and in vivo evaluation of a novel sulfoxide, which contains an ester moiety for hydrolysis and subsequent trapping in hypoxic cells. Non‐decay corrected yields of radioactivity were 1.18 ± 0.24% (n = 27, 2.5 ± 0.5% decay corrected radiochemical yield) based on K[¹⁸F]F. The radiotracer did not show any defluorination and did not undergo metabolism in an in vitro assay using S9 liver fractions. Imaging studies using an SK‐RC‐52 tumor model in BALB/c nude mice have revealed that [¹⁸F]1 is retained in hypoxic tumors and has similar hypoxia selectivity to [¹⁸F]FMISO. Because of a three times faster clearance rate than [¹⁸F]FMISO from normoxic tissue, [¹⁸F]1 has emerged as a promising new radiotracer for hypoxia imaging.     

Synthesis,Characterization, and Preclinical Evaluation of 99mTc‐Labeled Macrobicyclic and Tricyclic Chelators as Single Photon Emission Computed Tomography Tracer

The novel tetraaza macrobicyclic chelator 3,6,9,15‐tetraazabicyclo[9.3.1]pentadeca‐1(15),11,13‐triene‐2,10‐dione (TBPD) and pentaaza macrotricyclic chelator 9‐oxa‐3,6,12,15,21‐pentaazatricyclo[15,3,2,1]trieicos‐1(21),17,19‐triene‐2,7,11,16‐tetradione (OPTT) were synthesized, characterized, and radiolabeled with ^99mTc to produce ^99mTc‐TBPD and ^99mTc‐OPTT. These radiolabeled complexes were prepared with high radiolabeling yield, radiochemical purity, and good in vitro stability up to 24 h. The labeling efficiency of ^99mTc‐TBPD and ^99mTc‐OPTT was found 98% and 97%. In vitro serum stability of ^99mTc‐TBPD was found to be 95.2%, while that of ^99mTc‐OPTT 94.2% up to 24 h. Blood kinetics experiments of ^99mTc‐labeled complexes showed biphasic pattern of blood clearance. About 99.57 ± 0.89% activity of ^99mTc‐TBPD and 99.42 ± 0.88% activity of ^9mTc‐OPTT were cleared off blood stream at 24 h postadministration. The biological half‐life of ^99mTc‐TBPD was observed: t_1/2(F) 1 h 5 min and t_1/2(S) 12 h and biological half‐life of ^99mTc‐OPTT was observed: t_1/2(F) 1 h 10 min and t_1/2(S) 9 h 50 min, respectively. The biodistribution studies revealed that maximum uptake of ^99mTc‐TBPD was found in liver, concluded that excretory pathway is hepatobiliary, while that of ^99mTc‐OPTT was renal as well as hepatobiliary. The negligible activity observed in stomach confirming the stability of radiolabeled complex in biological milieu. In vitro cytotoxicity study of TBPD and OPTT did not show any considerable antiproliferative activity against cancer cells of human cervical SW756, HeLa, and glioblastoma U‐87, U373 cell lines.     

Comparative biodistribution studies of technetium‐99 m radiolabeled amphiphilic nanoparticles using three different reducing agents during the labeling procedure

Considering the confusing biodistribution data through the literature and few reported alerts as well as our preliminary biodistribution results, we decided to evaluate the interaction and interference of the commonly present ^99mTc (technetium‐99m)‐stannic oxide colloid during the direct stannous chloride ^99mTc‐labeling procedure and to assess its influence on the biodistribution pattern of amphiphilic poly(lactic‐co‐glycolic acid) nanoparticles. In order to confirm our thesis, beside stannous chloride, we employed two different reducing agents that don't form colloidal particles. The use of sodium borohydride was previously reported in the literature, whereas sodium dithionite was adapted for the first time in the ^99mTc direct labeling procedure for nanoparticles. The results in our paper clearly differentiate among samples with and without colloidal impurities originating from the labeling procedure with a logical follow up of the radiochemical, physicochemical evaluation, and biodistribution studies clarifying previously reported data on stannic oxide colloidal interference. ^99mTc‐nanoparticle complex labeled with sodium dithionite as reducing agent illustrated appropriate labeling efficacy, stability, and potential for further use in biodistribution studies thus providing solution for the problem of low‐complex stability when sodium borohydride is used and colloidal stannic oxide interference for stannous chloride procedure. Copyright © 2013 John Wiley & Sons, Ltd.     

Further Insights into Brevetoxin Metabolism by de Novo Radiolabeling

The toxic dinoflagellate Karenia brevis, responsible for early harmful algal blooms in the Gulf of Mexico, produces many secondary metabolites, including potent neurotoxins called brevetoxins (PbTx). These compounds have been identified as toxic agents for humans, and they are also responsible for the deaths of several marine organisms. The overall biosynthesis of these highly complex metabolites has not been fully ascertained, even if there is little doubt on a polyketide origin. In addition to gaining some insights into the metabolic events involved in the biosynthesis of these compounds, feeding studies with labeled precursors helps to discriminate between the de novo biosynthesis of toxins and conversion of stored intermediates into final toxic products in the response to environmental stresses. In this context, the use of radiolabeled precursors is well suited as it allows working with the highest sensitive techniques and consequently with a minor amount of cultured dinoflagellates. We were then able to incorporate [U-¹⁴C]-acetate, the renowned precursor of the polyketide pathway, in several PbTx produced by K. brevis. The specific activities of PbTx-1, -2, -3, and -7, identified by High-Resolution Electrospray Ionization Mass Spectrometer (HRESIMS), were assessed by HPLC-UV and highly sensitive Radio-TLC counting. We demonstrated that working at close to natural concentrations of acetate is a requirement for biosynthetic studies, highlighting the importance of highly sensitive radiolabeling feeding experiments. Quantification of the specific activity of the four, targeted toxins led us to propose that PbTx-1 and PbTx-2 aldehydes originate from oxidation of the primary alcohols of PbTx-7 and PbTx-3, respectively. This approach will open the way for a better comprehension of the metabolic pathways leading to PbTx but also to a better understanding of their regulation by environmental factors.     

荷乳腺癌小鼠c-myc mRNA反义寡核苷酸显像研究

目的 建立99mTc标记寡核苷酸的方法并用于荷乳腺癌小鼠反义寡核苷酸显像研究.方法 利用双功能螯合剂N-羟基琥珀酰亚胺-巯乙苷肽(S-Acetyl-NHS-MAG3)对一段15碱基c-myc mRNA反义寡核苷酸片段进行99mTc标记;对荷乳腺癌昆明种小鼠进行标记反义寡核苷酸生物学分布与显像研究.结果 生物学分布结果表明,相对于正义核酸而言,反义核酸在肿瘤组织中的摄取明显增高(P<0.05).在反义寡核苷酸显像组,肿瘤组织显像剂摄取活跃,肿瘤/肌肉比值最高可达5.5.在正义寡核苷酸显像组及阻断组,肿瘤组织均未出现明显的显像剂浓聚.结论 99mTc标记反义寡核苷酸有望成为一种新的显像剂,在分子水平上用于恶性肿瘤的早期、特异和无创性诊断.     

[18F]Fluoropropylsulfonyl chloride: a new reagent for radiolabeling primary and secondary amines for PET imaging

In vivo molecular imaging with positron emission tomography (PET) requires the preparation of an appropriate positron‐emitting radiotracer. New methods for the introduction of F‐18 into biologically interesting molecules could increase the availability of specific PET radiotracers and increase the application of PET to the study of human diseases. In this work, [¹⁸F]fluoropropylsulfonyl chloride was synthesized from 3‐toluenesulfonyloxypropyl thiocyanate in two steps and was successfully incorporated into molecules containing a reactive amino group. Both a primary amine, L‐phenylalanine ethyl ester hydrochloride, and a secondary amine, 1‐(2‐methoxyphenyl)‐piperazine, were successfully radiolabeled by this method. The entire radiochemical synthesis required 90 min. The products were obtained in 25.7±2.3% (n=3) and 22.8±9.1% (n=6) (EOB). This method provides a useful and easy way to make new F‐18 labeled radiopharmaceuticals for PET imaging. Copyright © 2008 John Wiley & Sons, Ltd.