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Background and Objective: The overexpression of gelatinases, that is, matrix metalloproteinase MMP2 and MMP9, has been associated with tumor progression, invasion, and metastasis. To image MMP2 in tumors, we developed a novel ligand termed [18F]AlF-NOTA-C6, with consideration that: c(KAHWGFTLD)NH2 (herein, C6) is a selective gelatinase inhibitor; Cy5.5-C6 has been visualized in many in vivo tumor models; positron emission tomography (PET) has a higher detection sensitivity and a wider field of view than optical imaging; fluorine-18 (18F) is the optimal PET radioisotope, and the creation of a [18F]AlF-peptide complex is a simple procedure. Methods: C6 was conjugated to the bifunctional chelator NOTA (1, 4, 7-triazacyclononanetriacetic acid) for radiolabeling [18F]AlF conjugation. The MMP2-binding characteristics and tumor-targeting efficacy of [18F]AlF-NOTA-C6 were tested in vitro and in vivo. Results: The non-decay corrected yield of [18F]AlF-NOTA-C6 was 46.2–64.2%, and the radiochemical purity exceeded 95%. [18F]AlF-NOTA-C6 was favorably retained in SKOV3 and PC3 cells, determined by cell uptake. Using NOTA-C6 as a competitive ligand, the uptake of [18F]AlF-NOTA-C6 in SKOV3 cells decreased in a dose-dependent manner. In biodistribution and PET imaging studies, higher radioactivity concentrations were observed in tumors. Pre-injection of C6 caused a marked reduction in tumor tissue uptake. Immunohistochemistry showed MMP2 in tumor tissues. Conclusions: [18F]AlF-NOTA-C6 was easy to synthesize and has substantial potential as an imaging agent that targets MMP2 in tumors. [ABSTRACT FROM AUTHOR]

To realize the diagnosis of HER2-positive gastric cancer via PET imaging, herein, a new kind of 18 F-labeled HER2 affibody probe was created; the bifunctional maleimide derivative 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA-MAL) was first coupled to a polypeptide, and the resulting compound was subsequently labeled with the 18 FAl complex. The binding characteristics of the probe were assessed using both in vitro studies and in vivo microPET imaging and biodistribution experiments. Immunohistochemical staining was performed to confirm the expression level of HER2 in the studied cell lines and tumors. The probe was successfully produced with the radiochemical purity of more than 95%. The NCI N87 cell-associated radioactivity was 19.31 ± 1.01% AD, and it decreased to 0.83 ± 0.04% AD per 10 6 cells after blocking HER2 as early as 15 minutes post-incubation ( p < 0.05). A competition binding assay between radiolabeled and non-radioactive affibody molecules with NCI N87 indicated that the IC 50 was 8.10 nM. The microPET imaging and biodistribution of human gastric cancer xenografts demonstrated that the probe could specifically accumulate in tumors at early time points. Protein detection confirmed a strong HER2 expression in NCIN87 and a weak HER2 expression in SGC7901. In conclusion, 18 FAl-NOTA-MAL-Cys-GGGRDN(M 0 )-Z HER2:342 was successfully prepared via a one-step method. The favorable preclinical data showed specific and effective tumor targeting capacity of the proposed probe; this revealed that the probe proposed herein might have potential application in gastric cancer imaging., Competing Interests: None., (This journal is © The Royal Society of Chemistry.)

FSHR is an appealing target for cancer theranostics. Radiolabeled FSH1 and its derivatives have shown potential to in vivo detect FSHR expression. However, moderate labeling yields (~50% nondecay-corrected) may partially limit their wide use. 68 Ga is an excellent PET nuclide due to availability, nearly quantitative reaction, and short physical half-life. In this study, 68 Ga labeled FSH1 peptide was developed for imaging of FSHR in cancers. In vitro studies and MicroPET imaging were performed in PC-3 prostate tumor model. [ 68 Ga] Ga-NOTA-MAL-FSH1 can be produced within 20 min with 93.2 ± 2.1% yield and the radiochemical purity was greater than 95%. It showed that [ 68 Ga] Ga-NOTA-MAL-FSH1 possessed FSHR binding affinities. The tracer was stable in PBS and human serum for at least 2 hours. MicroPET imaging revealed that the PC-3 xenografts were clearly visualized and the tumor uptakes were 1.87 ± 0.10, 1.26 ± 0.06, and 0.71 ± 0.10% ID/g at 0.5, 1 h, and 2 h postinjection. The corresponding tumor to blood and tumor to muscle ratios were 1.77 ± 0.70, 7.94 ± 1.35, and 10.37 ± 1.16 and 7.42 ± 0.46, 26.13 ± 2.99, and 36.40 ± 2.54, respectively. FSHR binding specificity was also demonstrated by reduced tumor uptake of [ 68 Ga] Ga-NOTA-MAL-FSH1 after coinjecting excess unlabeled FSH1 peptide. The favorable characters of [ 68 Ga] Ga-NOTA-MAL-FSH1 such as convenient synthesis and specific tumor uptake warrant its further investigation for FSHR expression imaging.

Background: Human epidermal growth factor receptor type 2 (HER2) is abundant in a wide variety of tumors and associated with the poor prognosis. Radiolabeled affibodies are potential candidates for detecting HER2-positive lesions. However, laborious multiple-step synthetic procedure and high abdomen background may hinder the widespread use. Herein, cysteinylated ZHER 2:342 modified with a new hydrophilic linker (denoted as MZHER 2:342 ) was designed and labeled using 18 FAl-NOTA strategies. The biologic efficacy of the novel tracer and its feasibilities for in vivo monitoring HER2 levels were also investigated in xenograft models with different HER2 expressions. Method: MZHER 2:342 was conjugated with MAL-NOTA under standard reaction conditions. The affibody molecule was then radiolabeled with 18 FAl complex. The binding specificity of the tracer, 18 FAl-NOTA-MAL-MZHER 2:342 , with HER2 was primarily characterized via in vitro studies. MicroPET imaging were performed in nude mice bearing tumors (SKOV-3, JIMT-1 and MCF-7) after injection. The HER2 levels of xenografts were determined using Western blotting analysis. Results: 18 FAl-NOTA-MAL-MZHER 2:342 can be efficiently produced within 30 min with a non-decaycorrected yield of about 10% and a radiochemical purity of more than 95%. In vitro experiments revealed that the modified affibody retained the specific affinity to HER2. PET imaging showed that SKOV-3 and JIMT-1 xenografts were clearly visualized with excellent contrast and low abdomen backgrounds. On the contrary, the signals of MCF-7 tumor were difficult to visualize. The ROI values ranged from16.54±2.69% ID/g for SKOV-3 to 8.42±1.20 %ID/g for JIMT-1 tumors at 1h postinjection respectively. Poor uptake was observed from MCF-7 tumors with 1.71±0.34% ID/g at the same time point. Besides, a significant linear correlation between % ID/g values and relative HER2 expression levels was also found. Conclusions: 18 FAl-NOTA-MAL-MZHER 2:342 is a promising tracer for in vivo detecting HER2 status with the advantages of facile synthesis and favorable pharmacokinetics. It may be useful in differential diagnosis, molecularly targeted therapy and prognosis of the cancers., Competing Interests: Competing Interests: The authors have declared that no competing interest exists.