3AcFNP-59 for Positron Emission Tomography Imaging of Cholesterol Trafficking and Utilization.

Cholesteryl ester analogues of [18F]FNP-59 have the ability to provide information on cholesterol trafficking and utilization at earlier time points than those of [18F]FNP-59 or [131I]NP-59. It is well-known that free cholesterol and cholesteryl esters have differing distribution profiles and that they can be interconverted enzymatically. Substitution of the ester influences the rate of cholesterol ester hydrolysis and the subsequent mixing of cholesterol esters with the lipid pool in the body. This can be utilized by preparing esters that are more readily taken up by lipoprotein, are quickly hydrolyzed and mixed with the endogenous lipid pool and delivered to tissues of interest more quickly than free cholesterol analogues that require esterification for lipoprotein association. The acetyl ester of FNP-59 demonstrated the preferred uptake properties and response to adrenal cortical manipulation, indicating its ability to image hormone production. Finally, dosimetry studies were conducted in preparation for the clinical translation of [18F]3AcFNP-59.

Automated Radiosynthesis of [18F]FluoFAPI and Its Dosimetry and Single Acute Dose Toxicological Evaluation.

BACKGROUND: Cancer-associated fibroblasts have become a new target for therapy. Fibroblasts present within malignancies express the fibroblast activation protein (FAP). Inhibitors to FAP (FAPI) are small molecules recently developed as a theranostic agents for imaging and radiotherapy. All currently used FAPI rely on a linker-chelator complex attached to the 'inhibitor'. We describe a new automated method of the direct attachment of the radioisotope to the inhibitor, resulting in a >50% MW reduction with the hope of an improved tumor-to-background ratio and tumor uptake. METHODS: [18F]FluroFAPI was developed from a Sn precursor. This allowed for subsequent automated radioflourination. We obtained the biodistribution of [18F]FluroFAPI in rats, performed estimated human radiation dosimetry, and performed a 100× expected single dose toxicology analysis for eventual first-in-human experiments. RESULTS: The synthesis of the Sn precursor for FluorFAPI and the automated synthesis of [18F]FluroFAPI was demonstrated. [18F]FluroFAPI had favorable estimated human radiation dosimetry, and demonstrated no adverse effects when injected at a dose of 100× that planned for [18F]FluroFAPI. CONCLUSIONS: With the successful development of an automated synthesis of [18F]FluroFAPI, first-in-human testing can be planned with the hope of an improved tumor-to-background performance compared to other FAPI agents.

Sestamibi as an alternative to mebrofenin for the diagnosis of acute cholecystitis: An alternative option during supply chain disruption.

Purpose: To determine the accuracy of Tc-99 m sestamibi for the diagnosis of acute cholecystitis during a supply chain disruption of mebrofenin. Material and methods: During a national shortage of Tc-99 m mebrofenin in 2019, our institution initiated sestamibi imaging for suspected cases of acute cholecystitis using a standard hepatobiliary imaging protocol. Forty-one patients underwent hepatobiliary imaging with sestamibi, 39 to assess for acute cholecystitis. The examinations were initially interpreted by one nuclear medicine physician and subsequently overread by 5 blinded nuclear medicine physicians (8-30 years' experience). SPECT/CT was obtained for 8 of these patients at the discretion of the primary interpreter. An additional 23 asymptomatic patients (6 with prior cholecystectomy) underwent abdominal scintigraphy as a negative control to determine the normal time to sestamibi accumulation in the gallbladder. A composite reference standard was used (chart review by 3 physicians). Sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were calculated with and without SPECT/CT (mean ± 95%CI). Results: Of 39 symptomatic patients, 17/39 had acute cholecystitis and 22 did not. The sensitivity, specificity, PPV and NPV for acute cholecystitis at planar imaging were 97.6 ± 4.6, 62.7 ± 5.2, 67.0 ± 3.6, and 97.3 ± 5.2 % (N = 39). The values changed to 95.7 ± 4.7, 77.9 ± 4.7, 72.1 ± 4.1, and 97.0 ± 3.3 % when control patients were included (N = 62). With SPECT/CT, these mildly improved to 98.8 ± 2.3 %, 69.1 ± 4.4 %, 71.3 ± 3.2 %, and 98.7 ± 2.6 % (N = 39), but not significantly different. On average, sestamibi activity was detected in the gallbladder in negative controls within 1 h. Conclusion: Tc-99 m sestamibi has excellent sensitivity and NPV for diagnosing acute cholecystitis and can serve as an alternative when mebrofenin is unavailable for evaluating cystic duct obstruction during shortages of standard agents.

3-[18F]Fluoro-para-hydroxyphenethylguanidine (3-[18F]pHPG) PET-A Novel Imaging Modality for Paraganglioma.

Context: Functional positron emission tomography (PET) imaging for the characterization of pheochromocytoma and paraganglioma (PCC/PGL) and for detection of metastases in malignant disease, offers valuable clinical insights that can significantly guide patient treatment. Objective: This work aimed to evaluate a novel PET radiotracer, 3-[18F]fluoro-para-hydroxyphenethylguanidine (3-[18F]pHPG), a norepinephrine analogue, for its ability to localize PCC/PGL. Methods: 3-[18F]pHPG PET/CT whole-body scans were performed on 16 patients (8 male:8 female; mean age 47.6 ± 17.6 years; range, 19-74 years) with pathologically confirmed or clinically diagnosed PCC/PGL. After intravenous administration of 304 to 475 MBq (8.2-12.8 mCi) of 3-[18F]pHPG, whole-body PET scans were performed at 90 minutes in all patients. 3-[18F]pHPG PET was interpreted for abnormal findings consistent with primary tumor or metastasis, and biodistribution in normal organs recorded. Standardized uptake value (SUV) measurements were obtained for target lesions and physiological organ distributions. Results: 3-[18F]pHPG PET showed high radiotracer uptake and trapping in primary tumors, and metastatic tumor lesions that included bone, lymph nodes, and other solid organ sites. Physiological biodistribution was universally present in salivary glands (parotid, submandibular, sublingual), thyroid, heart, liver, adrenals, kidneys, and bladder. Comparison [68Ga]DOTATATE PET/CT was available in 10 patients and in all cases showed concordant distribution. Comparison [123I]meta-iodobenzylguanidine [123I]mIBG planar scintigraphy and SPECT/CT scans were available for 4 patients, with 3-[18F]pHPG showing a greater number of metastatic lesions. Conclusion: We found the kinetic profile of 3-[18F]pHPG PET affords high activity retention within benign and metastatic PCC/PGL. Therefore, 3-[18F]pHPG PET imaging provides a novel modality for functional imaging and staging of malignant paraganglioma with advantages of high lesion affinity, whole-body coregistered computed tomography, and rapid same-day imaging.

Evaluating immunotherapeutic outcomes in triple-negative breast cancer with a cholesterol radiotracer in mice.

Evaluating the response to immune checkpoint inhibitors (ICIs) remains an unmet challenge in triple-negative breast cancer (TNBC). The requirement for cholesterol in the activation and function of T cells led us to hypothesize that quantifying cellular accumulation of this molecule could distinguish successful from ineffective checkpoint immunotherapy. To analyze accumulation of cholesterol by T cells in the immune microenvironment of breast cancer, we leveraged the PET radiotracer, eFNP-59. eFNP-59 is an analog of cholesterol that our group validated as an imaging biomarker for cholesterol uptake in preclinical models and initial human studies. In immunocompetent mouse models of TNBC, we found that elevated uptake of exogenous labeled cholesterol analogs functions as a marker for T cell activation. When comparing ICI-responsive and -nonresponsive tumors directly, uptake of fluorescent cholesterol and eFNP-59 increased in T cells from ICI-responsive tumors. We discovered that accumulation of cholesterol by T cells increased in ICI-responding tumors that received anti-PD-1 checkpoint immunotherapy. In patients with TNBC, tumors containing cycling T cells had features of cholesterol uptake and trafficking within those populations. These results suggest that uptake of exogenous cholesterol analogs by tumor-infiltrating T cells allows detection of T cell activation and has potential to assess the success of ICI therapy.

Predicting efficacy of immunotherapy in mice with triple negative breast cancer using a cholesterol PET radiotracer.

Predicting the response to cancer immunotherapy remains an unmet challenge in triple-negative breast cancer (TNBC) and other malignancies. T cells, the major target of current checkpoint inhibitor immunotherapies, accumulate cholesterol during activation to support proliferation and signaling. The requirement of cholesterol for anti-tumor functions of T cells led us to hypothesize that quantifying cellular accumulation of this molecule could distinguish successful from ineffective checkpoint immunotherapy. To analyze accumulation of cholesterol by T cells in the immune microenvironment of breast cancer, we leveraged a novel positron emission tomography (PET) radiotracer, FNP-59. FNP-59 is an analog of cholesterol that our group has validated as an imaging biomarker for cholesterol uptake in pre-clinical models and initial human studies. In immunocompetent mouse models of TNBC, we found that elevated uptake of exogenous labeled cholesterol analogs functions as a marker for T cell activation. When comparing immune checkpoint inhibitor (ICI)-responsive EO771 tumors to non-responsive AT-3 tumors, we found significantly higher uptake of a fluorescent cholesterol analog in T cells of the ICI-responsive tumors both in vitro and in vivo. Using the FNP-59 radiotracer, we discovered that accumulation of cholesterol by T cells increased further in ICI-responding tumors that received ant-PD-1 checkpoint immunotherapy. We verified these data by mining single cell sequencing data from patients with TNBC. Patients with tumors containing cycling T cells showed gene expression signatures of cholesterol uptake and trafficking. These results suggest that uptake of exogenous cholesterol analogs by tumor-infiltrating T cells predict T cell activation and success of ICI therapy.

Incidental Uptake in a Subacute Stroke on 18 F-Piflufolastat PSMA PET/CT.

ABSTRACT: Prostate-specific membrane antigen (PSMA) PET/CT has proven to be effective in the evaluation of prostate cancer and has become increasingly used clinically as multiple radiopharmaceuticals have become commercially available. With increasing use, incidental uptake from a variety of nononcologic processes will be encountered and considered interpretive pitfalls. We outline a case of a 71-year-old man who underwent imaging with PSMA PET/CT, which demonstrated uptake in the left parietal-temporal junction that was shown to be a subacute stroke. This case demonstrates a reported cause of uptake on PSMA PET for which the underlying mechanism is not yet well understood.

Development of Fluorinated NP-59: A Revival of Cholesterol Use Imaging with PET.

Imaging of cholesterol use is possible with the 131I scintiscanning/SPECT agent NP-59. This agent provided a noninvasive measure of adrenal function and steroid synthesis. However, iodine isotopes resulted in poor resolution, manufacturing challenges, and high radiation dosimetry to patients that have limited their use and clinical impact. A 18F analog would address these shortcomings while retaining the ability to image cholesterol use. The goal of this study was to prepare and evaluate a 18F analog of NP-59 to serve as a PET imaging agent for functional imaging of the adrenal glands based on cholesterol use. Previous attempts to prepare such an analog of NP-59 have proven elusive. Preclinical and clinical evaluation could be performed once the new fluorine analog of NP-59 production was established. Methods: The recent development of a new reagent for fluorination along with an improved route to the NP-59 precursor allowed for the preparation of a fluorine analog of NP-59, FNP-59. The radiochemistry for the 18F-radiolabeled 18F-FNP-59 is described, and rodent radiation dosimetry studies and in vivo imaging in New Zealand rabbits was performed. After in vivo toxicity studies, an investigational new drug approval was obtained, and the first-in-humans images with dosimetry using the agent were acquired. Results: In vivo toxicity studies demonstrated that FNP-59 is safe for use at the intended dose. Biodistribution studies with 18F-FNP-59 demonstrated a pharmacokinetic profile similar to that of NP-59 but with decreased radiation exposure. In vivo animal images demonstrated expected uptake in tissues that use cholesterol: gallbladder, liver, and adrenal glands. In this first-in-humans study, subjects had no adverse events and images demonstrated accumulation in target tissues (liver and adrenal glands). Manipulation of uptake was also demonstrated with patients who received cosyntropin, resulting in improved uptake. Conclusion: 18F-FNP-59 provided higher resolution images, with lower radiation dose to the subjects. It has the potential to provide a noninvasive test for patients with adrenocortical diseases.

PSMA PET Validates Higher Rates of Metastatic Disease for European Association of Urology Biochemical Recurrence Risk Groups: An International Multicenter Study.

The European Association of Urology (EAU) prostate cancer guidelines panel recommends risk groups for biochemical recurrence (BCR) of prostate cancer to identify men at high risk of progression or metastatic disease. The rapidly growing availability of PSMA-directed PET imaging will impact prostate cancer staging. We determined the rates of local and metastatic disease in BCR and biochemical persistence (BCP) of prostate cancer stratified by EAU BCR risk groups and BCP. Methods: Patients with BCR or BCP were enrolled under the same prospective clinical trial protocol conducted at 3 sites (n = 1,777 [91%]: UCLA, n = 662 [NCT02940262]; University of California San Francisco, n = 508 [NCT03353740]; University of Michigan, n = 607 [NCT03396874]); 183 patients with BCP from the Universities of Essen, Bologna, and Munich were included retrospectively. Patients with BCR had to have sufficient data to determine the EAU risk score. Multivariate, binomial logistic regression models were applied to assess independent predictors of M1 disease. Results: In total, 1,960 patients were included. Post-radical prostatectomy EAU BCR low-risk, EAU BCR high-risk, and BCP groups yielded distant metastatic (M1) detection in 43 of 176 (24%), 342 of 931 (37%), and 154 of 386 (40%) patients. For postradiotherapy EAU BCR low-risk and EAU BCR high-risk groups, the M1 detection rate was 113 of 309 (37%) and 110 of 158 (70%), respectively. BCP, high-risk BCR, and higher levels of serum prostate-specific antigen were significantly associated with PSMA PET M1 disease in multivariate regression analysis. PSMA PET revealed no disease in 25% and locoregional-only disease in 33% of patients with post-radical prostatectomy or postradiotherapy EAU BCR high risk. Conclusion: Our findings support the new EAU classification; EAU BCR high-risk groups have higher rates of metastatic disease on PSMA PET than do the low-risk groups. Discordant subgroups, including metastatic disease in low-risk patients and no disease in high-risk patients, warrant inclusion of PSMA PET stage to refine risk assessment.

Investigating the SPECT Dose-Function Metrics Associated With Radiation-Induced Lung Toxicity Risk in Patients With Non-small Cell Lung Cancer Undergoing Radiation Therapy.

PURPOSE: Dose to normal lung has commonly been linked with radiation-induced lung toxicity (RILT) risk, but incorporating functional lung metrics in treatment planning may help further optimize dose delivery and reduce RILT incidence. The purpose of this study was to investigate the impact of the dose delivered to functional lung regions by analyzing perfusion (Q), ventilation (V), and combined V/Q single-photon-emission computed tomography (SPECT) dose-function metrics with regard to RILT risk in patients with non-small cell lung cancer (NSCLC) patients who received radiation therapy (RT). METHODS AND MATERIALS: SPECT images acquired from 88 patients with locally advanced NSCLC before undergoing conventionally fractionated RT were retrospectively analyzed. Dose was converted to the nominal dose equivalent per 2 Gy fraction, and SPECT intensities were normalized. Regional lung segments were defined, and the average dose delivered to each lung region was quantified. Three functional categorizations were defined to represent low-, normal-, and high-functioning lungs. The percent of functional lung category receiving ≥20 Gy and mean functional intensity receiving ≥20 Gy (iV20) were calculated. RILT was defined as grade 2+ radiation pneumonitis and/or clinical radiation fibrosis. A logistic regression was used to evaluate the association between dose-function metrics and risk of RILT. RESULTS: By analyzing V/Q normalized intensities and functional distributions across the population, a wide range in functional capability (especially in the ipsilateral lung) was observed in patients with NSCLC before RT. Through multivariable regression models, global lung average dose to the lower lung was found to be significantly associated with RILT, and Q and V iV20 were correlated with RILT when using ipsilateral lung metrics. Through a receiver operating characteristic analysis, combined V/Q low-function receiving ≥20 Gy (low-functioning V/Q20) in the ipsilateral lung was found to be the best predictor (area under the curce: 0.79) of RILT risk. CONCLUSIONS: Irradiation of the inferior lung appears to be a locational sensitivity for RILT risk. The multivariable correlation between ipsilateral lung iV20 and RILT, as well as the association of low-functioning V/Q20 and RILT, suggest that irradiating low-functioning regions in the lung may lead to higher toxicity rates.

68Ga-DOTATATE PET/CT Imaging of Refractory Pituitary Macroadenoma Invading the Orbit.

ABSTRACT: In addition to gastroenteropancreatic neuroendocrine neoplasms, a wide variety of tumors express somatostatin receptors. Somatostatin receptor imaging, heavily utilized in neuroendocrine oncology, may also have utility in the diagnosis of other neoplasms and raises the possibility of potential therapeutic options. We describe the case of a 60-year-old man who underwent 68Ga-DOTATATE PET/CT, demonstrating an avid invasive pituitary macroadenoma. This mass was persistent and refractory despite traditional treatment options. Because of the avidity, 177Lu-DOTATATE therapy was offered, although not ultimately performed, demonstrating a potential treatment for challenging cases utilizing the principles of theranostics.

Advanced CKD Among Adults With Cerebral Palsy: Incidence and Risk Factors.

RATIONALE & OBJECTIVE: Recent evidence suggests that adults with cerebral palsy have an elevated risk for developing advanced chronic kidney disease (CKD). To develop effective interventions, the objective was to identify whether demographics and preexisting medical conditions are risk factors for advanced CKD among adults with cerebral palsy. STUDY DESIGN: Retrospective cohort study. SETTING & PARTICIPANTS: Data were from the Optum Clinformatics Data Mart. Adults 18 years or older with cerebral palsy and without advanced CKD (CKD stage 4 or later) were identified from 2013 and subsequently followed up from January 1, 2014, to the development of advanced CKD, death, loss to follow-up, or end of the study period (December 31, 2017), whichever came first. Diagnostic, procedure, and diagnosis-related group codes were used to identify cerebral palsy, incident cases of advanced CKD, comorbid intellectual disability, and 10 preexisting medical conditions. EXPOSURES: Demographic variables and 10 preexisting medical conditions: CKD stages 1-3, hypertension, diabetes, heart and cerebrovascular disease, non-CKD urologic conditions, bowel conditions, respiratory disease, skeletal fragility, arthritis, and dysphagia. OUTCOME: Incidence of advanced CKD. ANALYTIC APPROACH: Crude incidence rate (IR) of advanced CKD and IR ratios with 95% CIs were estimated. Cox proportional hazards regression models that were adjusted for demographics, intellectual disability, and preexisting medical conditions were used to evaluate the adjusted independent effect of predictor variables. RESULTS: 237 of the 8,011 adults with cerebral palsy developed advanced CKD during follow-up (IR, 10.16/1,000 person years; 95% CI, 8.87-11.46). In the crude analysis, all preexisting medical conditions were associated with an elevated IR and IR ratio of advanced CKD. In the fully adjusted Cox proportional hazards regression model, the HR was elevated for older age, CKD stages 1-3 (HR, 3.32; 95% CI, 2.39-4.61), diabetes (HR, 2.69; 95% CI, 2.03-3.57), hypertension (HR, 1.54; 95% CI, .10-2.16), heart and cerebrovascular disease (HR, 1.53; 95% CI, 1.12-2.07), and non-CKD urologic conditions (HR, 1.39; 95% CI, 1.05-1.84). LIMITATIONS: Private insurance database, short follow-up period, and lack of laboratory values, such as albuminuria/proteinuria. CONCLUSIONS: Advanced CKD was common among adults with cerebral palsy and its development was associated with both traditional and nontraditional urologic risk factors.

Synthesis and Evaluation of 11C- and 18F-Labeled SOAT1 Inhibitors as Macrophage Foam Cell Imaging Agents.

PD-132301, an inhibitor of sterol O-acyltransferase 1 (SOAT1; also known as acyl-coenzyme A:cholesterol acyltransferase-1, ACAT1), is under clinical investigation for numerous adrenal disorders. Radiolabeled SOAT1 inhibitors could support drug discovery and help diagnose SOAT1-related disorders, such as atherosclerosis. We synthesized two radiolabeled SOAT1 inhibitors, [11C]PD-132301 and fluorine analogue [18F]1. Rat biodistribution studies were conducted with both agents and, as the most selective tracer, [11C]PD-132301 was advanced to preclinical positron emission tomography studies in (atherosclerotic) ApoE-/- mice. The uptake of [11C]PD-132301 in SOAT1-rich tissue warrants further investigation into the compound as an atherosclerosis and adrenal imaging agent.

Predicting late radiation-induced xerostomia with parotid gland PET biomarkers and dose metrics.

PURPOSE: To assess associations between parotid gland PET biomarkers and late radiation-induced xerostomia, and to validate improvement of xerostomia predictive models by adding pre-treatment PET features to models based on dose and pre-treatment xerostomia. MATERIALS AND METHODS: Intensity PET features from 47 patients treated on institutional prospective clinical trials for HPV-associated oropharyngeal squamous cell carcinoma with uniform chemoRT were analyzed. Associations between 90th percentile of the parotid gland standardized uptake values (P90) from pre-treatment and post-treatment PET scans, mean parotid gland doses, and late xerostomia defined by the Xerostomia Questionnaire (XQ) and salivary flow rates were quantified. Multivariable analysis was applied for dose and PET features using penalized logistic regression for feature selection and generation of predictive models using the LASSO technique, and optimism bias was estimated by bootstrap resampling. RESULTS: Significant associations between late xerostomia and both mean parotid gland dose and P90 were demonstrated, and were generally stronger for post-treatment PET scans. The addition of P90 from pre-treatment PET scans improved the prediction model for late moderate or severe xerostomia compared to the base model, from AUC = 0.74 to 0.78 (p-value <0.001) for XQ summary score and from 0.77 to 0.84 (p-value <0.001) for the single eating-related XQ item with the largest inter-patient variability; however, only the latter remained significant on cross validation (AUC = 0.69 to 0.70 and 0.73 to 0.80, respectively). CONCLUSIONS: The addition of pre-treatment parotid gland PET biomarkers improved a predictive model for late patient-reported xerostomia over dose and pre-treatment xerostomia.

The impact of infection and inflammation in oncologic 18F-FDG PET/CT imaging.

Sites of infection and inflammation can be misleading in oncology PET/CT imaging because these areas commonly show 18F-FDG activity. Caution in the interpretation must be taken to avoid the misdiagnosis of malignancy. Utilization of both CT findings as well as patient history can help differentiate benign infectious and inflammatory processes from malignancy, although occasionally additional work-up may be required. This article discusses the mechanism of 18F-FDG uptake in infection and inflammation with illustrative examples.

Ring opening of epoxides with [18F]FeF species to produce [18F]fluorohydrin PET imaging agents.

A simple technique for the preparation of [18F]HF has been developed and applied to the generation of an [18F]FeF species for opening sterically hindered epoxides. This method has been successfully employed to prepare four drug-like molecules, including 5-[18F]fluoro-6-hydroxy-cholesterol, a potential adrenal/endocrine PET imaging agent. This easily automated one-pot procedure produces sterically hindered fluorohydrin PET imaging agents in good yields and high molar activities.