A Clinical PET Imaging Tracer ([18F]DASA-23) to Monitor Pyruvate Kinase M2-Induced Glycolytic Reprogramming in Glioblastoma.

PURPOSE: Pyruvate kinase M2 (PKM2) catalyzes the final step in glycolysis, a key process of cancer metabolism. PKM2 is preferentially expressed by glioblastoma (GBM) cells with minimal expression in healthy brain. We describe the development, validation, and translation of a novel PET tracer to study PKM2 in GBM. We evaluated 1-((2-fluoro-6-[18F]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([18F]DASA-23) in cell culture, mouse models of GBM, healthy human volunteers, and patients with GBM. EXPERIMENTAL DESIGN: [18F]DASA-23 was synthesized with a molar activity of 100.47 ± 29.58 GBq/µmol and radiochemical purity >95%. We performed initial testing of [18F]DASA-23 in GBM cell culture and human GBM xenografts implanted orthotopically into mice. Next, we produced [18F]DASA-23 under FDA oversight, and evaluated it in healthy volunteers and a pilot cohort of patients with glioma. RESULTS: In mouse imaging studies, [18F]DASA-23 clearly delineated the U87 GBM from surrounding healthy brain tissue and had a tumor-to-brain ratio of 3.6 ± 0.5. In human volunteers, [18F]DASA-23 crossed the intact blood-brain barrier and was rapidly cleared. In patients with GBM, [18F]DASA-23 successfully outlined tumors visible on contrast-enhanced MRI. The uptake of [18F]DASA-23 was markedly elevated in GBMs compared with normal brain, and it identified a metabolic nonresponder within 1 week of treatment initiation. CONCLUSIONS: We developed and translated [18F]DASA-23 as a new tracer that demonstrated the visualization of aberrantly expressed PKM2 for the first time in human subjects. These results warrant further clinical evaluation of [18F]DASA-23 to assess its utility for imaging therapy-induced normalization of aberrant cancer metabolism.

[18F]-C-SNAT4: an improved caspase-3-sensitive nanoaggregation PET tracer for imaging of tumor responses to chemo- and immunotherapies.

Positron emission tomography (PET) imaging of apoptosis can noninvasively detect cell death in vivo and assist in monitoring tumor response to treatment in patients. While extensive efforts have been devoted to addressing this important need, no apoptosis PET imaging agents have yet been approved for clinical use. This study reports an improved 18F-labeled caspase-sensitive nanoaggregation tracer ([18F]-C-SNAT4) for PET imaging of tumor response to chemo- and immunotherapies in preclinical mouse models. METHODS: We rationally designed and synthesized a new PET tracer [18F]-C-SNAT4 to detect cell death both in vitro and in vivo. In vitro radiotracer uptake studies were performed on drug-sensitive and -resistant NSCLC cell lines (NCI-H460 and NCI-H1299, respectively) treated with cisplatin at different doses. In vivo therapy response monitoring by [18F]-C-SNAT4 PET imaging was evaluated with two treatment modalities-chemotherapy and immunotherapy in two tumor xenografts in mice. Radiotracer uptake in the tumors was validated ex vivo using γ-counting and cleaved caspase-3 immunofluorescence. RESULTS: This [18F]-C-SNAT4 PET tracer was facilely synthesized and displayed improved serum stability profiles. [18F]-C-SNAT4 cellular update was elevated in NCI-H460 cells in a time- and dose-dependent manner, which correlated well with cell death. A significant increase in [18F]-C-SNAT4 uptake was measured in NCI-H460 tumor xenografts in mice. In contrast, a rapid clearance of [18F]-C-SNAT4 was observed in drug-resistant NCI-H1299 in vitro and in tumor xenografts. Moreover, in BALB/C mice bearing murine colon cancer CT26 tumor xenografts receiving checkpoint inhibitors, [18F]-C-SNAT4 showed its ability for monitoring immunotherapy-induced apoptosis and reporting treatment-responding mice from non-responding. CONCLUSION: The uptake of [18F]-C-SNAT4 in tumors received chemotherapy and immunotherapy is positively correlated with the tumor apoptotic level and the treatment efficacy. [18F]-C-SNAT4 PET imaging can monitor tumor response to two different treatment modalities and predict the therapeutic efficacy in preclinical mouse models.

In Vivo Imaging of Methionine Aminopeptidase II for Prostate Cancer Risk Stratification.

Prostate cancer is one of the most common malignancies worldwide, yet limited tools exist for prognostic risk stratification of the disease. Identification of new biomarkers representing intrinsic features of malignant transformation and development of prognostic imaging technologies are critical for improving treatment decisions and patient survival. In this study, we analyzed radical prostatectomy specimens from 422 patients with localized disease to define the expression pattern of methionine aminopeptidase II (MetAP2), a cytosolic metalloprotease that has been identified as a druggable target in cancer. MetAP2 was highly expressed in 54% of low-grade and 59% of high-grade cancers. Elevated levels of MetAP2 at diagnosis were associated with shorter time to recurrence. Controlled self-assembly of a synthetic small molecule enabled design of the first MetAP2-activated PET imaging tracer for monitoring MetAP2 activity in vivo. The nanoparticles assembled upon MetAP2 activation were imaged in single prostate cancer cells with post-click fluorescence labeling. The fluorine-18-labeled tracers successfully differentiated MetAP2 activity in both MetAP2-knockdown and inhibitor-treated human prostate cancer xenografts by micro-PET/CT scanning. This highly sensitive imaging technology may provide a new tool for noninvasive early-risk stratification of prostate cancer and monitoring the therapeutic effect of MetAP2 inhibitors as anticancer drugs. SIGNIFICANCE: This study defines MetAP2 as an early-risk stratifier for molecular imaging of aggressive prostate cancer and describes a MetAP2-activated self-assembly small-molecule PET tracer for imaging MetAP2 activity in vivo.

Sigma-1 Receptor Changes Observed in Chronic Pelvic Pain Patients: A Pilot PET/MRI Study.

Introduction: Chronic pelvic pain is a highly prevalent pain condition among women, but identifying the exact cause of pelvic pain remains a significant diagnostic challenge. In this study, we explored a new diagnostic approach with PET/MRI of the sigma-1 receptor, a chaperone protein modulating ion channels for activating nociceptive processes. Methods: Our approach is implemented by a simultaneous PET/MRI scan with a novel radioligand [18F]FTC-146, which is highly specific to the sigma-1 receptor. We recruited 5 chronic pelvic pain patients and 5 healthy volunteers and compared our PET/MRI findings between these two groups. Results: All five patients showed abnormally increased radioligand uptake on PET compared to healthy controls at various organs, including the uterus, vagina, pelvic bowel, gluteus maximus muscle, and liver. However, on MRI, only 2 patients showed abnormalities that could be potentially associated with the pain symptoms. For a subset of patients, the association of pain and the abnormally increased radioligand uptake was further validated by successful pain relief outcomes following surgery or trigger point injections to the identified abnormalities. Conclusion: In this preliminary study, sigma-1 receptor PET/MRI demonstrated potential for identifying abnormalities associated with chronic pelvic pain. Future studies will need to correlate samples with imaging findings to further validate the correlation between S1R distribution and pathologies of chronic pelvic pain. Trial Registration: The clinical trial registration date is June 2, 2018, and the registration number of the study is NCT03195270 (https://clinicaltrials.gov/ct2/show/NCT03556137).

The Characterization of 18F-hGTS13 for Molecular Imaging of xC- Transporter Activity with PET.

The aim of this study was development of an improved PET radiotracer for measuring xC- activity with increased tumor uptake and reduced uptake in inflammatory cells compared with (S)-4-(3-18F-fluoropropyl)-l-glutamate (18F-FSPG). Methods: A racemic glutamate derivative, 18F-hGTS13, was evaluated in cell culture and animal tumor models. 18F-hGTS13 was separated into C5 epimers, and the corresponding 18F-hGTS13-isomer1 and 18F-hGTS13-isomer2 were evaluated in H460 tumor-bearing rats. Preliminary studies investigated the cellular uptake of 18F-hGTS13-isomer2 in multiple immune cell populations and states. Results:18F-hGTS13 demonstrated excellent H460 tumor visualization with high tumor-to-background ratios, confirmed by ex vivo biodistribution studies. Tumor-associated radioactivity was significantly higher for 18F-hGTS13 (7.5 ± 0.9 percentage injected dose [%ID]/g, n = 3) than for 18F-FSPG (4.6 ± 0.7 %ID/g, n = 3, P = 0.01). 18F-hGTS13-isomer2 exhibited excellent H460 tumor visualization (6.3 ± 1.1 %ID/g, n = 3) and significantly reduced uptake in multiple immune cell populations relative to 18F-FSPG. 18F-hGTS13-isomer2 exhibited increased liver uptake relative to 18F-FSPG (4.6 ± 0.8 vs. 0.7 ± 0.01 %ID/g), limiting its application in hepatocellular carcinoma. Conclusion:18F-hGTS13-isomer2 is a new PET radiotracer for molecular imaging of xC- activity that may provide information on tumor oxidation states. 18F-hGTS13-isomer2 has potential for clinical translation for imaging cancers of the thorax because of the low background signal in healthy tissue.