Copper-mediated nucleophilic radiofluorination of [18 F]ß-CFT for positron emission tomography imaging of dopamine transporter.

[18 F]ß-CFT is a positron emission tomography (PET) ligand for imaging of dopamine transporter. It was proved to be a sensitive PET marker to detect presynaptic dopaminergic hypofunction in Parkinson's disease. In recent years, copper-mediated 18 F-fluorination of aryl boronic esters has been successful in some molecules containing aromatic groups. In this study, we describe the novel synthetic strategy of [18 F]ß-CFT by copper-mediated nucleophilic radiofluorination with pinacol-derived aryl boronic esters upon reaction with [18 F]KF/K222 and Cu (OTf)2 (py)4 . The radiolabeling protocol was optimized with [18 F]fluoride elution method and amount of copper catalyst used. [18 F]ß-CFT is obtained from boronic ester precursors in 2.2% to 10.6% non-isolated radiochemical yield (RCY). Purified [18 F]ß-CFT with >99% radiochemical purity (RCP) and high molar activity was obtained in validation runs. The radiolabeling procedure is straightforward and can easily be adapted for clinical use.

Use of 111In-Hexavalent Lactoside for Liver Reserve Estimation in Rodents with Thioacetamide-Induced Hepatic Fibrosis.

Many biochemical tests detecting the presence of liver disease are not liver-specific and may be abnormal in nonhepatic conditions. The asialoglycoprotein receptor (ASGPR) is a hepatocyte-specific receptor for Gal/GalNAc-terminated glycopeptide or glycoprotein. The number of these receptors decreases in patients with chronic liver diseases. Here, we aimed to evaluate the use of 111In-hexavalent lactoside, a known ASGPR imaging biomarker, as a more sensitive probe to detect small changes in liver reserve in animal models of chronic liver injury. Thioacetamide (TAA) treatment via intraperitoneal injection every 2 days in BALB/c mice continued for 1, 2, 3, or 4 months. The liver fibrosis stages were determined by Sirius Red staining and were based on the METAVIR classification method. Serum transaminase enzymes (alanine transaminase (ALT) and aspartate transaminase (AST)), alkaline phosphatase, albumin, and bilirubin were measured using a FUJI FDC3500 i/s analyzer. The ASGPR staining was performed by immunohistocytochemical stain. The percentages of fibrosis and ASGPR were calculated using ImageJ software after collagen staining and anti-ASGPR staining, respectively. A nanoSPECT/CT was used for molecular imaging and liver uptake measurement. We observed fibrosis grades of F0-F1 in mice treated with TAA for 1 month, F2 in mice treated for 2 months, F3-F4 in mice treated for 3 months, and F4 in mice treated for 4 months. The levels of ALT and albumin were not significantly different in the TAA groups from those in the controls. Although the average levels of AST, alkaline phosphatase, and bilirubin in the TAA groups were different from those in the control group, there was little difference between TAA groups. More sensitive distinctions among TAA groups were detected in 111In-hexavalent lactoside uptake of ASGPR, ASGPR staining, and fibrosis % than when using the conventional AST, ALT, albumin, alkaline phosphatase, and bilirubin tests. The absorption and distribution of 111In-hexavalent lactoside were lower in the chronic hepatitis models than the normal controls. The liver reserves measured by 111In-hexavalent lactoside uptake were 71.7 ± 7.5% and 50.9 ± 5.6% after 1 and 2 months, respectively, of TAA treatment. As an ASGPR biomarker, 111In-hexavalent lactoside has higher sensitivity than traditional liver function tests and collagen stain to provide more objective data for evaluating compensated cirrhosis or changes in liver damage. ASGPR staining can reflect the regenerated hepatocytes, but the need for a biopsy limits its use. 111In-hexavalent lactoside measurement is comparable with ASGPR staining, which suggests that 111In-hexavalent lactoside measurement will be more useful as a practical, noninvasive test of chronic liver injury.

Development of single vial kits for preparation of 68 Ga-labelled hexavalent lactoside for PET imaging of asialoglycoprotein receptor.

The aim of this study was to formulate and evaluate the freeze-dried kit of NOTA-hexavalent lactoside (NOTA-HL) for the preparation of 68 Ga-labeled glycoligand for PET imaging of the asialoglycoprotein receptor (ASGPR). 68 GaCl3 was obtained from a commercial 68 Ge/68 Ga generator. Single-vial kits of HL were formulated. Optimization of radiolabeling with 68 Ga, various evaluations of NOTA-HL kits, and in vitro stability study of 68 Ga-HL were carried out. PET/CT imaging of normal mice injected with 68 Ga-NOTA-HL was performed. NOTA-HL kit was successfully formulated. High radiochemical yields (>95%) were obtained by 68 Ga radiolabeling. The NOTA-HL kits were stable for at least 12 months, and 68 Ga-NOTA-HL exhibited good in vitro stability. PET studies in normal mice revealed high specific accumulation of activity in the liver. The NOTA-HL kit was developed for fast 68 Ga labeling. 68 Ga-NOTA-HL showed high specific uptake in liver. The availability of ready-to-use NOTA-HL kits combined with 68 Ge/68 Ga generators would provide an efficient approach for PET imaging of ASGPR.

The specificity and accuracy of (111)In-hexavalent lactoside in estimating liver reserve and its threshold value for mortality in mice.

BACKGROUND & AIMS: The asialoglycoprotein receptor on hepatocyte membranes recognizes the galactose residues of glycoproteins. We investigated the specificity, accuracy and threshold value of asialoglycoprotein receptor imaging for estimating liver reserve via scintigraphy using (111)In-hexavalent lactoside in mouse models. METHODS: (111)In-hexavalent lactoside scintigraphy for asialoglycoprotein receptor imaging was performed on groups of normal mice, orthotopic SK-HEP-1-bearing mice, subcutaneous HepG2-bearing mice, mice with 20-80% partial hepatectomy and mice with acute hepatitis induced by acetaminophen. Liver reserve was measured by relative liver uptake and compared with normal mice. Asialoglycoprotein receptor blockade was performed via an in vivo asialofetuin competitive binding assay. RESULTS: A total of 73.64±7.11% of the injection dose accumulated in the normal liver tissue region, and radioactivity was barely detected in the hepatoma region. When asialoglycoprotein receptor was blocked using asialofetuin, less than 0.41±0.04% of the injection dose was detected as background in the liver. Asialoglycoprotein receptor imaging data revealed a linear correlation between (111)In-hexavalent lactoside binding and residual liver mass (R(2)=0.8548) in 20-80% of partially hepatectomized mice, demonstrating the accuracy of (111)In-hexavalent lactoside imaging for measuring the functional liver mass. Asialoglycoprotein receptor imaging data in mice with liver failure induced using 600mg/kg acetaminophen revealed 19-45% liver reserve relative to normal mice and a fatal threshold value of 25% liver reserve. CONCLUSION: The (111)In-hexavalent lactoside imaging method appears to be a good, specific, visual and quantitative predictor of functional liver reserve. The diagnostic threshold for survival was at 25% liver reserve in mice.

Synthesis of (68)Ga-labeled NOTA-RGD-GE11 heterodimeric peptide for dual integrin and epidermal growth factor receptor-targeted tumor imaging.

Radiolabeled Arg-Gly-Asp (RGD) peptide analogs have been extensively studied for αvß3 integrin-targeted angiogenesis imaging. According to recently presented evidence, the dodecapeptide GE11 has high affinity to the epidermal growth factor receptor (EGFR), which is overexpressed in many types of cancer. Dual-receptor molecular imaging probes with two different heterodimeric peptides exhibit improved cancer targeting efficacy. In the present study, the design and synthesis of a new RGD-GE11 peptide heterodimer for dual αvß3 integrin/EGFR-targeted cancer imaging are described. The RGD-GE11 heterodimer was linked with 6-aminohexanoic acid (6-Ahx) and cysteine and conjugated with 1,4,7-triazacyclononane-N,N',N″-triacetic acid (NOTA) to form NOTA-RGD-cys-6-Ahx-GE11. The monomeric peptides, NOTA-cys-6-Ahx-GE11 and c(RGDyK), were formed by a peptide synthesizer. The peptide heterodimer NOTA-RGD-GE11 was obtained by NOTA-cys-6-Ahx-GE11 and maleimidopropyl-c(RGDyK) conjugation with a thioether linkage. The NOTA peptide conjugate was labeled with freshly eluted (68)Ga and purified using reversed-phase high-performance liquid chromatography. The (68)Ga-NOTA-RGD-cys-6-Ahx-GE11 was successfully prepared, in this study, with a radiochemical yield of 85% and a radiochemical purity of >98%. These results warrant further investigation of this heterodimeric peptide's binding affinity to the receptors.

Synthesis, Radiolabeling, and Preliminary in vivo Evaluation of [68Ga] IPCAT-NOTA as an Imaging Agent for Dopamine Transporter.

INTRODUCTION: Novel radiotracer development for imaging dopamine transporters is a subject of interest because although [99mTc]TRODAT-1, [123I]ß-CIT, and [123I]FP-CIT are commercially available; 99Mo/99mTc generator is in short supply and 123I production is highly dependent on compact cyclotron. Therefore, we designed a novel positron emission tomography (PET) tracer based on a tropane derivative through C-2 modification to conjugate NOTA for chelating 68Ga, a radioisotope derived from a 68Ge/68Ga generator. METHODS: IPCAT-NOTA 22 was synthesized and labeled with [68Ga]GaCl4 - at room temperature. Biological studies on serum stability, LogP, and in vitro autoradiography (binding assay and competitive assay) were performed. Furthermore, ex vivo autoradiography, biodistribution, and dynamic PET imaging studies were performed in Sprague Dawley rats. RESULTS: [68Ga]IPCAT-NOTA 24 obtained had a radiochemical yield of ≥90% and a specific activity of 4.25 MBq/nmol. [68Ga]IPCAT-NOTA 24 of 85% radiochemical purity (RCP%) was stable at 37°C for up to 60 minutes in serum with a lipophilicity of 0.88. The specific binding ratio (SBR%) reached 15.8 ± 6.7 at 60 minutes, and the 85% specific uptake could be blocked through co-injection at 100- and 1000-fold of the cold precursor in in vitro binding studies. Tissue regional distribution studies in rats with [68Ga]IPCAT-NOTA 24 showed striatal uptake (0.02% at 5 minutes and 0.007% at 60 minutes) with SBR% of 6%, 25%, and 62% at 5-15, 30-40, and 60-70 minutes, respectively, in NanoPET studies. The RCP% of [68Ga]IPCAT-NOTA 24 at 30 minutes in vivo remained 67.65%. CONCLUSION: Data described here provide new information on the design of PET probe of conjugate/pendent approach for DAT imaging. Another chelator or another direct method of intracranial injection must be used to prove the relation between [68Ga]IPCAT-NOTA 24 uptake and transporter localization.

Hexavalent lactoside labeled with [18F]AlF for PET imaging of asialoglycoprotein receptor.

Several methods have been developed to label compounds with 18F. However, in general these are laborious and require a multistep synthesis. A method based on the chelation of 18F-aluminum fluoride ([18F]AlF) by 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) was developed recently. The present work was aimed to radiolabel hexavalent lactoside (NOTA-HL) by [18F]AlF method for PET imaging of asialoglycoprotein receptor (ASGPR). METHODS: hexavalent lactoside was conjugated with the NOTA chelate and labeled with 18F in a one-pot method. The labeling procedure was investigated with different amounts of NOTA-HL and aluminum concentration. Radiochemical yield and radiochemical purity were determined by radio-TLC and radio-HPLC respectively. In vitro stability study of [18F]AlF-HL were carried out. PET/CT imaging of normal mice injected with [18F]AlF-NOTA-HL was performed. RESULTS: The Radiochemical yield of [18F]AlF-NOTA-HL was higher with more precursor and optimal Al+ concentration. The radiochemical purity of labeled product was >95% after purified by Sep-Pak cartridge to remove unbound [18F]AlF. The radiolabeling, including purification, was performed in 30 min [18F]AlF-NOTA-HL exhibited good in vitro stability. PET studies in normal mice revealed high specific accumulation of activity in the liver. CONCLUSION: NOTA-HL could be labeled rapidly and efficiently with aqueous 18F using AlF method. [18F]AlF-NOTA-HL would provide another efficient approach for PET imaging of ASGPR.

Evaluation of 5-[18F]fluoro-2'-deoxycytidine as a tumor imaging agent: A comparison of [18F]FdUrd, [18F]FLT and [18F]FDG.

One of the hallmarks of cancer is increased cell proliferation. Measurements of cell proliferation by estimation of DNA synthesis with several radiolabeled nucleosides have been tested to assess tumor growth. Deoxycytidine can be phosphorylated by deoxycytidine kinase (dCK) and is incorporated into DNA. This study evaluated a radiofluorinated deoxycytidine analog, 5-[18F]fluoro-2'-deoxycytidine ([18F]FdCyd), as a proliferation probe and compared it with 5-[18F]fluoro-2'-deoxyuridine ([18F]FdUrd), 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT), and [18F]fluorodeoxyglucose ([18F]FDG) in a tumor-bearing mouse model. [18F]FdCyd was synthesized from two precursors by direct electrophilic substitution. The serum stability and partition coefficient of [18F]FdCyd were evaluated in vitro. Positron emission topography (PET) imaging of Lewis lung carcinoma (LLC)-bearing mice with [18F]FdCyd, [18F]FdUrd, [18F]FLT, and [18F]FDG were evaluated. [18F]FdCyd was stable in mouse serum and normal saline for up to 4 h. With all radiotracers except [18F]FLT, PET can clearly delineate the tumor lesion. [18F]FdCyd and [18F]FdUrd showed high accumulation in the liver and kidney. The SUV and tumor-to-muscle (T/M) ratios derived from PET imaging of the radiotracers were [18F]FDG > [18F]FdCyd > [18F]FdUrd > [18F]FLT. Selective retention in tumors with a favorable tumor/muscle ratio makes [18F]FdCyd a protential candidate for further investigation as a proliferation imaging agent.

68Ga-labelled NOTA-RGD-GE11 peptide for dual integrin and EGFR-targeted tumour imaging.

INTRODUCTION: Multiple peptide receptors are co-expressed in many types of cancers. Arg-Gly-Asp (RGD) and GE11 peptides specifically target integrin αVß3 and EGFR, respectively. Recently, we designed and synthesized a heterodimer peptide NOTA-c(RGDyK)-GE11 (NOTA-RGD-GE11). The aim of this study was to investigate the characteristics of NOTA-RGD-GE11 for dual receptor imaging. METHODS: NOTA-RGD-GE11 heterodimer was labelled with 68Ga. The dual receptor binding affinity was investigated by antibody competition binding assay. The in vitro and in vivo characteristics of [68Ga]Ga-NOTA-RGD-GE11 were investigated and compared with that of monomeric peptides [68Ga]Ga-NOTA-RGD and [68Ga]Ga-NOTA-GE11. RESULTS: NOTA-RGD-GE11 had binding affinities with both integrin αVß3 and EGFR. The dual receptor targeting property of [68Ga]Ga-NOTA-RGD-GE11 was validated by blocking studies in a NCI-H292 tumour model. [68Ga]Ga-NOTA-RGD-GE11 showed higher tumour uptake than [68Ga]Ga-NOTA-RGD and [68Ga]Ga-NOTA-GE11 in biodistribution and PET/CT imaging studies. CONCLUSION: The dual receptor targeting and enhanced tumour uptake of [68Ga]Ga-NOTA-RGD-GE11 warrant its further investigation for dual integrin αVß3 and EGFR-targeted tumour imaging.

Molecular imaging with 123I-FIAU, 18F-FUdR, 18F-FET, and 18F-FDG for monitoring herpes simplex virus type 1 thymidine kinase and ganciclovir prodrug activation gene therapy of cancer.

UNLABELLED: The ability to monitor tumor responses during prodrug activation gene therapy and other anticancer gene therapies is critical for their translation into clinical practice. Previously, we demonstrated the feasibility of noninvasive in vivo imaging with 131I-5-iodo-2'-fluoro-1-beta-D-arabinofuranosyluracil (131I-FIAU) for monitoring herpes simplex virus type 1 thymidine kinase (HSV1-tk) cancer gene expression in an experimental animal model. Here we tested the efficacy of SPECT with 123I-FIAU and PET with 5-18F-fluoro-2'-deoxyuridine (18F-FUdR), 2-18F-fluoroethyl-L-tyrosine (18F-FET), and 18F-FDG for monitoring tumor responses during prodrug activation gene therapy with HSV1-tk and ganciclovir (GCV). METHODS: In the flanks of FVB/N female mice, 4 tumors per animal were established by subcutaneous injection of 1 x 10(5) cells of NG4TL4 sarcoma cells, HSV1-tk-transduced NG4TL4-STK cells, or a mixture of these cells in different proportions to model different efficacies of transfection and HSV1-tk gene expression levels in tumors. Ten days later, the animals were treated with GCV (10 mg/kg/d intraperitoneally) for 7 d. Gamma-Imaging with 123I-FIAU and PET with 18F-FUdR, 18F-FET, and 18F-FDG were performed before and after initiation of therapy with GCV in the same animal. RESULTS: Before GCV treatment, no significant difference in weight and size was found in tumors that expressed different HSV1-tk levels, suggesting similar in vivo proliferation rates for NG4TL4 and NG4TL4-STK sarcomas. The accumulation of 123I-FIAU at 24 h after injection was directly proportional to the percentage of NG4TL4-STK cells in the tumors. The 123I-FIAU accumulation at 4 and 7 d of GCV therapy decreased significantly compared with pretreatment levels and was proportional to the percentage of HSV1-tk-positive tumor cells. Tumor uptake of 18F-FUdR in all HSV1-tk-expressing tumors also decreased significantly compared with pretreatment levels and was proportional to the percentage of HSV1-tk-positive tumor cells. The accumulation of 18F-FET decreased minimally (about 1.5-fold) and 18F-FDG decreased only 2-fold after 7 d of GCV therapy, and the degree of reduction was proportional to the percentage of HSV1-tk-positive tumor cells. CONCLUSION: We have shown that gamma-camera imaging with 123I-FIAU was the most reliable method for prediction of tumor response to GCV therapy, which was proportional to the magnitude of HSV1-tk expression in tumor tissue. 123I-FIAU imaging can be used to verify the efficacy of elimination of HSV1-tk-expressing cells by therapy with GCV. PET with 18F-FUdR reliably visualizes proliferating tumor tissue and is most suitable for the assessment of responses in tumors undergoing HSV1-tk plus GCV prodrug activation gene therapy. PET with 18F-FDG or 18F-FET can be used as additional "surrogate" biomarkers of the treatment response, although these radiotracers are less sensitive than 18F-FUdR for monitoring tumor responses to prodrug activation gene therapy with HSV1-tk and GCV in this sarcoma model.

Modulation of 5-fluorouracil cytotoxicity through thymidylate synthase and NF-kappaB down-regulation and its application on the radiolabelled iododeoxyuridine therapy on human hepatoma cell.

The inhibition of thymidylate synthase (TS) by 5-fluorouracil (5-FU) was known to increase the incorporation of radiolabelled iododeoxyuridine (IdUrd) into DNA. The relatively non-toxic compounds such as thiol-containing antioxidant pyrrolidinodithiocarbamte (PDTC) or aromatic fatty acid phenylbutyrate (PB) had been reported to enhance the cytotoxic efficacy of 5-FU. We designed a novel strategy through triplet combination of PB, PDTC and 5-FU to increase the radiolabelled IdUrd uptake and investigated the underlying mechanisms. The growth inhibition and [(125)I]IdUrd-DNA incorporation by PB, PDTC, 5-FU in different combinations were tested on parent or p21(Waf1) transfected Hep3B cells. The combination of PB and PDTC was more effective in enhancing 5-FU cytotoxicity than either drug alone. The combination of PB/PDTC and 5-FU blocked cells in S-phase and resulted in 8.5-fold increase of radiolabelled IdUrd-DNA incorporation. The transfection of p21(Waf1) did not change the general pattern of enhancement. Intriguingly, the combination of PB and PDTC effectively down-regulated NF-kappaB and TS and prevented their up-regulation from 5-FU treatment than either drug alone through a p21(Waf1)-independent mechanism. Based on this strategy, the 3-drug combination offered potential for improved radiolabelled IdUrd molecular radiotherapy for hepatoma treatment.

Antisense thymidylate synthase electrogene transfer to increase uptake of radiolabeled iododeoxyuridine in a murine model.

UNLABELLED: In vitro and in vivo experiments from our laboratory and others have suggested that the combination of thymidylate synthase (TS) inhibitor and radiolabeled iododeoxyuridine (IdUrd) is synergistic. Efficacy is limited by drug resistance, which is often mediated by TS overexpression. We designed an in vivo electrogene transfer (EGT) model for delivering antisense TS plasmid (ATS) into tumor to increase the subsequent efficacy of (131)I-IdUrd therapy. METHODS: Plasmid complementary to nucleotide 531-710 in the coding region of the mouse TS (mTS) mRNA was constructed. TS activity and (131)I-IdUrd DNA incorporation were determined 48 h after in vitro EGT of ATS to CT26 cells. In vivo therapeutic effect and radioactivity retained in tumor after various combinations of EGT ATS, 5-fluorouracil (5-FU), and continuous infusion of (131)I-IdUrd by osmotic minipump were determined. RESULTS: A reduction of TS activity was achieved after in vitro EGT ATS. Flow cytometry analysis indicated that ATS-treated cells were arrested at S phase. In the in vivo tumor model, the combination of EGT ATS and 5-FU was able to partially overcome 5-FU drug resistance. Sixty percent of tumors can be eradicated by the combination of EGT ATS, 5-FU, and infusion of (131)I-IdUrd. The tumors treated by EGT ATS had higher radioactivity retained 1 wk after (131)I-IdUrd therapy than after EGT of control plasmid. CONCLUSION: In situ EGT ATS can downregulate TS and increase the therapeutic effect of radiolabeled IdUrd therapy. The combination of EGT ATS, 5-FU, and (131)I-IdUrd may result in tumor eradication.