How to design PET experiments to study neurochemistry: application to alcoholism.

Positron Emission Tomography (PET) (and the related Single Photon Emission Computed Tomography) is a powerful imaging tool with a molecular specificity and sensitivity that are unique among imaging modalities. PET excels in the study of neurochemistry in three ways: 1) It can detect and quantify neuroreceptor molecules; 2) it can detect and quantify changes in neurotransmitters; and 3) it can detect and quantify exogenous drugs delivered to the brain. To carry out any of these applications, the user must harness the power of kinetic modeling. Further, the quality of the information gained is only as good as the soundness of the experimental design. This article reviews the concepts behind the three main uses of PET, the rationale behind kinetic modeling of PET data, and some of the key considerations when planning a PET experiment. Finally, some examples of PET imaging related to the study of alcoholism are discussed and critiqued.

A multi species evaluation of the radiation dosimetry of [11C]erlotinib, the radiolabeled analog of a clinically utilized tyrosine kinase inhibitor.

INTRODUCTION: Erlotinib is a tyrosine kinase inhibitor prescribed for non-small cell lung cancer (NSCLC) patients bearing epidermal growth factor receptor mutations in the kinase domain. The objectives of this study were to (1) establish a human dosimetry profile of [11C]erlotinib and (2) assess the consistency of calculated equivalent dose across species using the same dosimetry model. METHODS: Subjects examined in this multi-species study included: a stage IIIa NSCLC patient, 3 rhesus macaque monkeys, a landrace pig, and 4 athymic nude-Fox1nu mice. [11C]erlotinib PET data of the whole body were acquired dynamically for up to 120min. Regions of interest (ROIs) were manually drawn to extract PET time activity curves (TACs) from identifiable organs. TACs were used to calculate time-integrated activity coefficients (residence times) in each ROI, which were then used to calculate the equivalent dose in OLINDA. Subject data were used to predict the equivalent dose to the organs of a 73.7kg human male. RESULTS: In three of four species, the liver was identified as the organ receiving the highest equivalent dose (critical organ). The mean equivalent doses per unit of injected activity to the liver based on human, monkey, and mouse data were 29.4µSv/MBq, 17.4±6.0µSv/MBq, and 5.27±0.25µSv/MBq, respectively. The critical organ based on the pig data was the gallbladder wall (20.4µSv/MBq) but the liver received a nearly identical equivalent dose (19.5µSv/MBq). CONCLUSIONS: (1) When designing PET studies using [11C]erlotinib, the liver should be considered the critical organ. (2) In organs receiving the greatest equivalent dose, mouse data underestimated the dose in comparison to larger species. However, the effective dose of [11C]erlotinib to the whole body of a 73.7kg man was predicted with good consistency based on mice (3.14±0.05µSv/MBq) or the larger species (3.46±0.25µSv/MBq).

Quantitative analysis of [11C]-erlotinib PET demonstrates specific binding for activating mutations of the EGFR kinase domain.

Activating mutations of the epidermal growth factor receptor (EGFR) occur in multiple tumor types, including non-small cell lung cancer (NSCLC) and malignant glioma, and have become targets for therapeutic intervention. The determination of EGFR mutation status using a noninvasive, molecular imaging approach has the potential for clinical utility. In this study, we investigated [(11)C]-erlotinib positron emission tomography (PET) imaging as a tool to identify activating mutations of EGFR in both glioma and NSCLC xenografts. Radiotracer specific binding was determined for high and low specific activity (SA) [(11)C]-erlotinib PET scans in mice bearing synchronous human cancer xenografts with different EGFR expression profiles (PC9, HCC827, U87, U87 ΔEGFR, and SW620). Although xenograft immunohistochemistry demonstrated constitutive EGFR phosphorylation, PET scan analysis using the Simplified Reference Tissue Model showed that only kinase domain mutant NSCLC (HCC827 and PC9) had significantly greater binding potentials in high versus low SA scans. Xenografts with undetectable EGFR expression (SW620), possessing wild-type EGFR (U87), and expressing an activating extracellular domain mutation (U87 ΔEGFR) were indistinguishable under both high and low SA scan conditions. The results suggest that [(11)C]-erlotinib is a promising radiotracer that could provide a novel clinical methodology for assessing EGFR and erlotinib interactions in patients with tumors that harbor EGFR-activating kinase domain mutations.