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

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.

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.

Clinical utility of nuclear imaging in the evaluation of pediatric adrenal neoplasms

Adrenal neoplasms rarely occur in children. They can be diagnosed in the presence of endocrine, metabolic or neurological problems, an abdominal mass, more rarely an adrenal incidentaloma, or in the context of an adrenal mass discovered in the evaluation of childhood cancer including hematologic malignancy. According to standard medical practice, pediatric malignancies are almost always evaluated by ¹⁸F-fluorodeoxyglucose positron emission tomography with computed tomography ([¹⁸F]FDG PET/CT). Nuclear imaging using specific radiotracers is also an important tool for diagnosing and staging neuroblastoma, pheochromocytoma, hormone hypersecretion, or indeterminate adrenal masses. The Hippocratic oath "primum non nocere" encourages limitation of radiation in children per the ALARA concept (as low as reasonably achievable) but should not lead to the under-use of nuclear imaging because of the potential risk of inaccurate diagnosis or underestimation of the extent of disease. As in adults, nuclear imaging in children should be performed in conjunction with hormone evaluation and morphological imaging.