[en] With the wide use of positron emission tomography (PET) imaging for the detection of cancer, neurological diseases, and cardiovascular diseases, peptides labeled with positron-emitting radionuclide (¹⁸F) as the promising PET tracers have been made rapid development in recent years. There are many methods for ¹⁸F-labeled peptides. According to the characteristics of the labeling reactions, this review summarized the methods of ¹⁸F-labeled peptide as follows: 1) ¹⁸F-labeled prosthetic group method; 2) solid-phase labeling method; 3) ¹⁸F-AlF labeling method; 4) click reaction; 5) ¹⁸F-¹⁹F isotope exchange method; 6) aromatic electrophilic or nucleophilic labeling method; 7) the other labeling methods. Furthermore, these methods' advantage and disadvantage were analyzed. (authors)

[en] In this work,we investigated the feasibility of automated synthesis of (S-[¹¹C]-methyl)-D-cysteine(¹¹C-D-MCYS) as positron emission tomography tracer for tumor imaging. ¹¹CH₃I was prepared by substitution reaction of HI with ¹¹CH₃OH, which was obtained from the reaction of LiAlH₄ with ¹¹CO₂. ¹¹C-D-MCYS was produced by ¹¹C-methylation of the precursor D-cysteine with ¹¹CH₃I and purification on commercial Sep Pak C18 cartridges. The uncorrected radiochemical yield of ¹¹C-D-MCYS from ¹¹CH₃I was over (51±4)%, the radiochemical purity of ¹¹C-D-MCYS was more than 99%, and the total synthesis time was about 12 min. PET imaging studies showed that ¹¹C-D-MCYS had high uptake in the S180 sarcoma-bearing tissues,but low uptake in inflammatory tissues. It seems that ¹¹C-D-MCYS is a potential PET tracer for tumor imaging. (authors)

[en] Maintenance of acid-base homeostasis is critical in human tissues. Many pathological processes, such as ischemia, renal failure, inflammation, cancer, and chronic obstructive pulmonary disease, involve in acid-base imbalance (pH alteration). Acidic tumor pH can be used as a target and universal biomarker for cancer imaging and therapy. Magnetic resonance molecular imaging (MRMI), nuclear medicine imaging, and optical imaging have been used in preclinical imaging of acidic tumor pH and also used in clinical investigation. However, currently non-invasive molecular imaging was unavailable in routine clinic imaging of tumor pH. The molecular imaging of acidic tumor pH was summarized in this review. (authors)

[en] [Background] Gonadotropin releasing hormone (GnRH) receptor is overexpressed in many human tumors and is currently used as a target for molecular imaging. [Purpose] This study aims to design and synthesize a new ¹⁸F-labeled GnRH peptide by automatic radiosynthesis for preliminary Micro-PET/CT imaging. [Methods] [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH was automated radiolabeled with ¹⁸F by using Al¹⁸F complex on the modified PET-MF-2V-IT-I synthesis module. The stability of [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH was incubated in phosphate buffer saline (PBS) at 37℃ and the octanol/water partition coefficient was studied. The dynamic Micro-positron emission tomography (PET) study of [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH in nude mice bearing PC-3 cancer was carried out. [Results] The total radiochemical synthesis and purification of [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH was completed in 35 min with a decay-corrected yield of (25 ± 6)% and a specific activity of 8 ∼ 30 GBq · μmol^-1 (n = 6). The logP value of [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH was-2.70 ± 0.06 and the tracer was stable in phosphate-buffered saline for 2 h. Dynamic PET imaging analysis revealed that [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH was clearly delineated in PC-3 xenografted tumor with high tumor-to-muscle ratios and excreted mainly through the kidneys. [Conclusion] [¹⁸F] AlF-NOTA-P-L-Lys⁶-GnRH was an efficient automated production of commercially available synthetic modules that could be used as a potential PET tracer for the imaging PC-3 prostate tumors. (authors)

[en] [${}^{18}$F]FAPI-42 is a new fibroblast activation protein (FAP)-specific tracer used for cancer imaging. Here, we describe the optimal acquisition time and in vivo evaluation of [${}^{18}$F]FAPI-42 and compared intra-individual biodistribution, tumor uptake, and detection ability to [${}^{68}$Ga]Ga-FAPI-04. A total of 22 patients with various types of cancer received [${}^{18}$F]FAPI-42 whole-body positron emission tomography/computed tomography (PET/CT). Among them, 4 patients underwent PET/CT scans, including an early dynamic 20-min, static 1-h, and static 2-h scans. The in vivo biodistribution in normal organs and tumor uptake were semiquantitatively evaluated using the standardized uptake value (SUV) and tumor-to-background ratio (TBR). Furthermore, both [${}^{18}$F]FAPI-42 and [${}^{68}$Ga]Ga-FAPI-04 PET/CT were performed in 12 patients to compare biodistribution, tumor uptake, and tumor detection ability. [${}^{18}$F]FAPI-42 uptake in the tumors was rapid and reached a high level with an average SUVmax of 15.8 at 18 min, which stayed at a similarly high level to 2 h. The optimal image acquisition time for [${}^{18}$F]FAPI-42 was determined to be 1 h postinjection. For tumor detection, [${}^{18}$F]FAPI-42 had a high uptake and could be clearly visualized in the lesions. Compared to [${}^{68}$Ga]Ga-FAPI-04, [${}^{18}$F]FAPI-42 had the same detectability for 144 positive lesions. In addition, [${}^{18}$F]FAPI-42 showed a higher SUVmax in liver and bone lesions (P < 0.05) and higher TBRs in liver, bone, lymph node, pleura, and peritoneal lesions (all P < 0.05). The present study demonstrates that the optimal image acquisition time of [${}^{18}$F]FAPI-42 is 1 h postinjection and that [${}^{18}$F]FAPI-42 exhibits comparable lesion detectability to [${}^{68}$Ga]Ga-FAPI-04.

[en] Objective: To prepare ¹⁸F-2-fluoropropionyl(FP)-Lladtthhrpwt(¹⁸F-FP-ZS-6) by a multifunctional ¹⁸F radiolabeling module and investigate its in vivo distribution in human lung cancer cell (NCI-H1299)-bearing nude mice by microPET. Methods: Using a phage display peptide library to screen and identify Lladtthhrpwt (ZS-6) which has an affinity for human lung cancer. PET-MF-2V-IT-I synthesizer was used for the synthesis and purification of ¹⁸F-FP-ZS-6. MicroPET studies were carried out in NCI-H1299-bearing nude mice after injection of ¹⁸F-FP-ZS-6. Results: 4-nitrophenyl 2-[¹⁸F] fluoropropionate (¹⁸F-NFP) was prepared by 'one-pot' radiochemical procedure. The radiochemical yield of ¹⁸F-FP-ZS-6 was (5 ± 2) % (n = 3, decay-corrected) from ¹⁸F and the radiochemical purity was more than 95%. MicroPET studies showed that the uptake of ¹⁸F-FP-ZS-6 was high in the tumor and stomach of NCI-H1299-bearing nude mice model. The tumor uptake of ¹⁸F-FP-ZS-6 was 0.329, 0.350, 0.405, 0.433, 0.420, 0.415, 0.402 , 0.403, 0.390 %ID/g at 5, 15, 25, 35, 45, 55, 65, 75, 85 min post-injection, respectively. The tumor uptake peak was at 35 min post-injection and then ¹⁸F-FP-ZS-6 was cleared slowly. Conclusions: ¹⁸F-FP-ZS-6 could be successfully prepared. It might be a potential tracer for imaging human lung cancer. (authors)

[en] To study a simple and rapid automated synthetic technology of "1"1C-acetate ("1"1C- AC), automated synthesis of "1"1C-AC was performed by carboxylation of MeMgBr/tetrahydrofuran (THF) on a polyethylene loop with "1"1C-CO_2, followed by hydrolysis and purification on solid-phase extraction cartridges using a "1"1C-Choline/Methionine synthesizer made in China. A high and reproducible radiochemical yield of above 40% (decay corrected) was obtained within the whole synthesis time about 8 min from "1"1C-CO_2. The radiochemical purity of "1"1C-AC was over 95%. The novel, simple and rapid on-column hydrolysis-purification procedure should adaptable to the fully automated synthesis of "1"1C-AC at several commercial synthesis module. "1"1C-AC injection produced by the automated procedure is safe and effective, and can be used for PET imaging of animals and humans. (authors)

[en] Research on fibroblast activating protein (FAP)-targeting inhibitor (FAPI) has become an important focus for cancer imaging and radiotherapy. Quinoline-based tracers [${}^{68}$Ga]FAPI-04 and [${}^{18}$F]FAPI-42 have been widely used for positron emission tomography (PET) imaging of most tumors. However, there exist some limitations of these tracers with high uptake in biliary duct system and unstable uptake in pancreas, unsuitable for abdominal tumors PET imaging. Here we developed a [${}^{18}$F]-labeled glycopeptide-containing FAPI tracer (named [${}^{18}$F]FAPT) for PET imaging of FAP in cancers. [${}^{18}$F]FAPT was synthesized manually and automatically. The competitive binding to FAP, cellular internalization, and efflux characteristics were examined in vitro using A549-FAP cells. Dynamic MicroPET and biodistribution studies of [${}^{18}$F]FAPT were then conducted in A549-FAP and U87MG xenograft tumor mouse models compared with [${}^{18}$F]FAPI-42. Five healthy volunteers and three patients with cancer underwent [${}^{18}$F]FAPT PET/CT. Preclinical and clinical studies showed specific binding of [${}^{18}$F]FAPT to FAP and favorable pharmacokinetic properties with better hydrophilicity, lower uptake in biliary duct system, higher tumor uptake and longer tumor retention compared with [${}^{18}$F]FAPI-42. The biodistribution of [${}^{18}$F]FAPT in healthy volunteers and patients with cancer displayed low uptake in most normal tissues except for pancreas, thyroid and salivary gland, which could contribute to high tumor-to-background ratios in most cancers. [${}^{18}$F]FAPT is better PET tracer than [${}^{18}$F]FAPI-42 for imaging of biliary duct system cancer, potentially providing a tool to examine FAP expression in most cancers with high tumor-to-background ratios.

[en] Background: The noninvasive imaging of cell death plays an important role in the evaluation of degenerative diseases and detection of tumor treatments. Duramycin, a peptide with 19-amino acid, is produced by Streptoverticillium cinnamoneus. It binds specifically to phosphatidylethanolamine (PE), a novel molecular target for cell death. Purpose: The aim is to develop a synthetic method to label duramycin using "1"8F ion. The automated synthesis was carried out by multi-step procedure on the modified PET-MF-2V-IT-I synthesizer. Methods: Firstly, the prosthetic group of 4-nitrophenyl 2-["1"8F]fluoropropionate ("1"8F-NFP) was automatically synthesized by a convenient three-step procedure. Secondly, "1"8F-FPDuramycin was synthesized by conjunction of "1"8F-_NFP with duramycin, which was purified by a solid-phase extraction cartridge. Orthogonal test was performed to confirm the suitable reaction conditions (solvent, base and temperature). Results: The radiochemical yields of "1"8F-NFP were (25±5)% (n=10, decay-uncorrected) based on["1"8F]fluoride in 80 min. "1"8F-FPDuramycin was obtained with yield of (70±3)% (n=8, decay-uncorrected) based on "1"8F-NFP within 20 min. The radiochemical purity of "1"8F-FPDuramycin was greater than 99% and the specific activity was greater than (23.7±13.7) GBq·μmol"-"1 (n=10). Conclusion: "1"8F-FPDuramycin injection is easy to be prepared with 'two-pot reaction' and is a promising radiotracer used for the clinical and scientific study on positron emission tomography (PET) imaging. (authors)

[en] Alzheimer's disease (AD) is unknown cause progressive degenerative diseases of central nervous system. It is a serious threat to the health of the elderly people. The diagnosis is mainly based on pathological examination after death. With the wide application of positron emission tomography (PET) imaging in clinic, in vivo noninvasive imaging diagnosis of AD at the early stage become possible. PET imaging mainly depends on the positron-labeled imaging agents. The PET imaging agents can be used in the early diagnosis and differential diagnosis on AD include several kinds: PET traces for glucose metabolic, PET traces combined with amyloid protein plaques, tau protein, neurotransmitter and receptor, activation of microglia and PET traces for cell apoptosis. The research progress of various PET tracers were reviewed that can be used in the early diagnosis and differential diagnosis on AD in recent years. (authors)