Molecular imaging, part 1: apertures into the landscape of genomic medicine

Engineering an enhanced, thermostable, monomeric bacterial luciferase gene as a reporter in plant protoplasts

The application of the luxCDABE operon of the bioluminescent bacterium Photorhabdus luminescens as a reporter has been published for bacteria, yeast and mammalian cells. We report here the optimization of fused luxAB (the bacterial luciferase heterodimeric enzyme) expression, quantum yield and its application as a reporter gene in plant protoplasts. The fused luxAB gene was mutated by error prone PCR or chemical mutagenesis and screened for enhanced luciferase activity utilizing decanal as substrate. Positive luxAB mutants with superior quantum yield were subsequently shuffled by DNase I digestion and PCR assembly for generation of recombinants with additional increases in luciferase activity in bacteria. The coding sequence of the best recombinant, called eluxAB, was then optimized further to conform to Arabidopsis (Arabidopsis thaliana) codon usage. A plant expression vector of the final, optimized eluxAB gene (opt-eluxAB) was constructed and transformed into protoplasts of Arabidopsis and maize (Zea mays). Luciferase activity was dramatically increased for opt-eluxAB compared to the original luxAB in Arabidopsis and maize cells. The opt-eluxAB driven by two copies of the 35S promoter expresses significantly higher than that driven by a single copy. These results indicate that the eluxAB gene can be used as a reporter in plant protoplasts. To our knowledge, this is the first report to engineer the bacterium Photorhabdus luminescens luciferase luxAB as a reporter by directed evolution which paved the way for further improving the luxAB reporter in the future.

Magnetic resonance tumor targeting imaging using gadolinium labeled human telomerase reverse transcriptase antisense probes

To develop a molecular probe for MRI detection of human tumor telomerase reverse transcriptase (hTERT) mRNA expression. Uniformly phosphorothioate-modified hTERT antisense oligonucleotide (ASON) homing hTERT mRNA was labeled with gadolinium (Gd) through the bifunctional chelator 1,4,7, 10-tetraazacyclododecane-N, N', N'', N'''-tetraacetic acid (DOTA) stirred within 45 minutes at 60 °C. The Gd labeled probes were characterized in vitro. The cellular uptake rate and biodistribution of (99m) Tc-DOTA-ASON was measured instead of that of Gd-DOTA-ASON. A549 lung adenocarcinoma model was established in BALB/c nude mice and Gd-DOTA-ASON was injected intraperitoneally and MR images were acquired using 7.0T Micro-MRI (Bruker Biospec, Ettlingen, Germany) at different time points. Immunohistochemical analysis of telomerase activity of each xenograft was operated two days after in vivo imaging. The binding efficiency of Gd-DOTA-ASON reached as high as 71.7 ± 4.5% (n = 6). Gd-DOTA-ASON displayed perfect stability in fresh human serum at 37 °C for 24 h. Compared with normal lung cells, A549 cells showed an obviously higher uptake of (99m) Tc-DOTA-ASON than that of lung cells (10.5 ± 2.7% vs. 4.8 ± 2.6%, P < 0.05). The signal intensity of A549 xenografts can be enhanced by Gd-DOTA-ASON and the signal to noise ratio (SNR) of tumor to muscle reached 2.37 and maintained a relatively high level within 6 h after injection. The activity of hTERT in A549 tumors can be suppressed by Gd-DOTA-ASON in pathological slices. The results of this study show that Gd-DOTA-ASON can be a promising intracellular MR contrast probe for targeting telomerase-positive carcinomas.

Imaging radiation-induced normal tissue injury

Technological developments in radiation therapy and other cancer therapies have led to a progressive increase in five-year survival rates over the last few decades. Although acute effects have been largely minimized by both technical advances and medical interventions, late effects remain a concern. Indeed, the need to identify those individuals who will develop radiation-induced late effects, and to develop interventions to prevent or ameliorate these late effects is a critical area of radiobiology research. In the last two decades, preclinical studies have clearly established that late radiation injury can be prevented/ameliorated by pharmacological therapies aimed at modulating the cascade of events leading to the clinical expression of radiation-induced late effects. These insights have been accompanied by significant technological advances in imaging that are moving radiation oncology and normal tissue radiobiology from disciplines driven by anatomy and macrostructure to ones in which important quantitative functional, microstructural, and metabolic data can be noninvasively and serially determined. In the current article, we review use of positron emission tomography (PET), single photon emission tomography (SPECT), magnetic resonance (MR) imaging and MR spectroscopy to generate pathophysiological and functional data in the central nervous system, lung, and heart that offer the promise of, (1) identifying individuals who are at risk of developing radiation-induced late effects, and (2) monitoring the efficacy of interventions to prevent/ameliorate them.

From atom to brain: applications of molecular imaging to neurosurgery

Molecular imaging is a field born out of the happy marriage of molecular biology and radiology. The first installment of this two-part series on molecular imaging demonstrated basic principles for practitioners in the field of the neurosciences. This installment seeks to provide some illustrative examples, insights, and specific applications to the neurosciences. The fields of functional neurosurgery including the treatment of neuropsychiatric disorders, novel treatments and imaging of tumors, neuroregenerative medicine, and nanotechnology in vascular disorders are covered. Finally, we give some parting thoughts on the future of molecular imaging, including advances in the imaging of neurodegenerative disorders.