Michael E. Phelps

Direct correlation between positron emission tomographic images of two reporter genes delivered by two distinct adenoviral vectors.

Biodistribution, magnitude and duration of a therapeutic transgenes expression may be assessed by linking it to the expression of a positron emission tomography (PET) reporter gene (PRG) and then imaging the PRGs expression by a PET reporter probe (PRP) in living animals. We validate the simple approach of co-administering two distinct but otherwise identical adenoviruses, one expressing a therapeutic transgene and the other expressing the PRG, to track the therapeutic genes expression. Two PET reporter genes, a mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) and dopamine-2 receptor (D2R), each regulated by the same cytomegalovirus (CMV) promoter, have been inserted into separate adenoviral vectors (Ad). We demonstrate that cells co-infected with equivalent titers of Ad-CMV-HSV1-sr39tk and Ad-CMV-D2R express both reporter genes with good correlation (r2 = 0.93). Similarly, a high correlation (r2 = 0.97) was observed between the expression of both PRGs in the livers of mice co-infected via tail-vein injection with equivalent titers of these two adenoviruses. Finally, microPET imaging of HSV1-sr39tk and D2R expression with 9-(4-[18F]fluoro-3-hydroxymethylbutyl) guanine ([18F]FHBG) and 3-(2-[18F]fluoroethyl)spiperone ([18F]FESP), utilizing several adenovirus-mediated delivery routes, illustrates the feasibility of evaluating relative levels of transgene expression in living animals, using this approach.

Quantitative imaging of gene induction in living animals

Methods to repeatedly, non-invasively, and quantitatively image gene expression in living animals are rapidly emerging and should fundamentally change studies of gene expression in vivo. We previously developed assays utilizing positron emission tomography (PET) to image reporter gene expression. In this paper we: (1) describe a new bi-directional, tetracycline-inducible system that can be used to pharmacologically induce target gene expression and to quantitatively image induced expression by using a PET reporter gene; (2) demonstrate the potential of this system in transient and stable cell transfection assays; and (3) demonstrate the ability to repetitively and quantitatively image tetracycline and tetracycline analog induction of gene expression in living animals. We utilize the dopamine type-2 receptor (D2R) and the mutant herpes-simplex virus type 1 thymidine kinase (HSV1-sr39tk) reporter genes to validate this system. We utilize microPET technology to show that quantitative tomographic imaging of gene induction is possible. We find a high correlation (r2 = 0.98) between ‘target’ and reporter gene expression. This work establishes a new technique for imaging time-dependent variation of gene expression both from vectors with inducible promoters and in transgenic animals in which pharmacologic induction of gene expression must be monitored. These techniques may be applied both in gene therapy and for the study of gene expression in transgenic animals.

A study on the cost effectiveness of sestamibi scintimammography for screening women with dense breasts for breast cancer.

The potential impact of Sestamibi scintimammography (SSMM) on the cost effective management of women with dense breasts is not known. This study addresses this issue quantitatively by examining the impact of SSMM based screening strategies on the ∼3,000,000 women over 40 with very dense breasts (DY patterns) without palpable masses and who have had one or more prior mammograms, who undergo routine screening each year. Quantitative decision tree sensitivity analysis was used to compare the conventional mammography (MM) strategy (strategy A), which does not subject patients with negative mammograms to any further examination until their next screening, with two decision strategies for screening with SSMM SSMM after a negative mammogram (strategy B) or SSMM as the only screening test for women already identified as having dense breasts by a previous mammogram (strategy C). Cost effectiveness was measured by calculating the incremental cost effectiveness ratio (ICER) of strategies B and C, which is the cost of achieving an additional year of life in the screening population by choosing a SSMM based decision strategy rather than the conventional strategy. Strategies B and C reduced the number of false negative diagnoses by 62% and 8%, respectively. The ICER was

Molecular imaging of biological processes from microPET in mice to PET in patients

632,000 and

Imaging gene expression: principles and assays.

3.18M per life year for strategy B and C, respectively. To be cost effective, the pre‐test probability of cancer in the study population must be greater than 3% for strategy B or the cost of SSMM must be less than

Regional abnormality of oxygen consumption in reperfused myocardium assessed with [1-11C] acetate and positron emission tomography

50 for strategy C. These results show the ICER of an SSMM based breast cancer screening strategy in the management of patients with dense breasts is not currently within the range (∼

chapter 14 – The Gamma Camera: Performance Characteristics

50,000 per year life saved) of other commonly performed medical interventions that are considered cost effective.

chapter 10 – Pulse-Height Spectrometry

This article focuses on bringing together mice to patients with microPET to PET and molecular imaging probes and drugs for molecular diagnostics and molecular therapeutics. In the latter there is a common disease target in which near massless amounts of a molecular imaging probe is used to image the presence and function of the target and then to use the same molecule, or analogs of it, in mass amounts to modify the function of the target therapeutically. The biological world has gone molecular from the revolutionary paradigm shift from the genome, proteome and systems biology to molecular biology, molecular pharmacology, molecular therapeutics, molecular diagnostics, molecular medicine and molecular imaging. The heart of this movement is the molecular basis of instructions, communication, regulation and function of the cellular make up of the body. Classical nomenclature and descriptions of disease are giving way to molecular descriptions of disease to define the diagnostic and disease information required to select and evaluate molecular therapies. As the basis of disease and its therapeutic management shifts to the molecular basis of the biology of disease, imaging diagnostics must shift to this basis also. Many advances in various molecular and anatomical techniques are occurring to meet this challenge from research to clinical practice.