Dual-modality gene reporter for in vivo imaging.

The ability to track cells and their patterns of gene expression in living organisms can increase our understanding of tissue development and disease. Gene reporters for bioluminescence, fluorescence, radionuclide, and magnetic resonance imaging (MRI) have been described but these suffer variously from limited depth penetration, spatial resolution, and sensitivity. We describe here a gene reporter, based on the organic anion transporting protein Oatp1a1, which mediates uptake of a clinically approved, Gd(3+)-based, hepatotrophic contrast agent (gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid). Cells expressing the reporter showed readily reversible, intense, and positive contrast (up to 7.8-fold signal enhancement) in T1-weighted magnetic resonance images acquired in vivo. The maximum signal enhancement obtained so far is more than double that produced by MRI gene reporters described previously. Exchanging the Gd(3+) ion for the radionuclide, (111)In, also allowed detection by single-photon emission computed tomography, thus combining the spatial resolution of MRI with the sensitivity of radionuclide imaging.

A comparison between radiolabeled fluorodeoxyglucose uptake and hyperpolarized (13)C-labeled pyruvate utilization as methods for detecting tumor response to treatment.

Detection of early tumor responses to treatment can give an indication of clinical outcome. Positron emission tomography measurements of the uptake of the glucose analog, [(18)F] 2-fluoro-2-deoxy-D-glucose (FDG), have demonstrated their potential for detecting early treatment response in the clinic. We have shown recently that (13)C magnetic resonance spectroscopy and spectroscopic imaging measurements of the uptake and conversion of hyperpolarized [1-(13)C]pyruvate into [1-(13)C]lactate can be used to detect treatment response in a murine lymphoma model. The present study compares these magnetic resonance measurements with changes in FDG uptake after chemotherapy. A decrease in FDG uptake was found to precede the decrease in flux of hyperpolarized (13)C label between pyruvate and lactate, both in tumor cells in vitro and in tumors in vivo. However, the magnitude of the decrease in FDG uptake and the decrease in pyruvate to lactate flux was comparable at 24 hours after drug treatment. In cells, the decrease in FDG uptake was shown to correlate with changes in plasma membrane expression of the facilitative glucose transporters, whereas the decrease in pyruvate to lactate flux could be explained by an increase in poly(ADP-ribose) polymerase activity and subsequent depletion of the NAD(H) pool. These results show that measurement of flux between pyruvate and lactate may be an alternative to FDG-positron emission tomography for imaging tumor treatment response in the clinic.