Nature Biotechnology pp 856 - 860

Prostate cancer is currently the most prevalent form of cancer in men and the second leading cause of male cancer death in the United States. Prostate specific antigen (PSA), which is detectable in serum, has proven to be an extremely useful marker for early detection of prostate cancer as well as for monitoring disease progression and the effectiveness of treatment. Because current tests are complicated, requiring several steps and some form of labeling (enzymatic or fluorescent) to detect PSA, there is a pressing need for the development of cost-effective diagnostics that can carry out high-throughput and sensitive tests for PSA. Now, Arun Majumdar and colleagues have developed a specific test that uses micron-scale beams or microcantilevers to detect PSA.

The researchers attached PSA antibodies on the surface of microcantilevers, and then applied a sample containing PSA to the microcantilevers. Binding of PSA and the antibodies causes a change in the surface stress on the microcantilever that makes it bend enough to be detected using a laser beam. Majumdar and colleagues were able to detect clinically relevant concentrations of PSA in a background of other proteins. The technique is simpler and potentially more cost effective than other diagnostic tests because it does not require labeling and can be performed in a single reaction. The authors showed their system was less prone to false positives commonly caused by non specific binding of other proteins to the microcantilever.

Devices comprising many cantilevers, each coated with a different antibody, could be used to test a sample rapidly for the presence of several disease-related proteins simultaneously.

Nature Biotechnology pp 833 - 837 and pp 823 - 824

Soon it may be possible for doctors to listen, quite literally, for viral infections. In this issue, David Klenerman and colleagues from the University of Cambridge explain how they used quartz crystals as acoustic detectors of viruses.

Quartz crystals vibrate when placed in an electric field—the stronger the electric field, the greater the vibration. Add an additional mass to the crystals, and the vibrations grow stronger. Klenerman and his team reasoned that if they loosely attached a mass to a quartz crystal, then at a certain frequency, the mass might be thrown off with the force of vibration. Here, the researchers use herpes simplex virus as the "mass," which was attached to an antibody coating a disk of quartz crystal. When the virus particles break lose, the "rupturing event" is detected by the quartz, which doubles up as a miniature microphone.

The rupture-event scanning method is sensitive enough to detect just one virus in a drop of fluid. However, it is also robust enough to measure the millions of viral particles created as infections worsen. This simple and cost-effective test for viruses could be valuable for detecting viral infections in their early stages, and for monitoring the effectiveness of antiviral drugs—such as those to treat HIV and influenza.

Nature Biotechnology pp 870 - 875 and pp 826 - 827

Medicinal fruits produced through genetic engineering could facilitate administration of medicines and lower their cost as well, especially in developing countries. But there are concerns as to the environmental hazards resulting from transgene transfer from GM crops to weeds. Now, a team of plant scientists in Germany and Brazil are closer to the goal of a safer GM crop that could be used to produce medicinals. Rather than transforming the chromosomes of the plant cell nucleus, they have targeted the circular DNA genome of tomato chloroplasts, the structures that generate energy from sunlight in plant cells.

Plants engineered by nuclear transformation often express only low amounts of a foreign protein and suffer the drawback that windborne pollen can spread the transgene to neighboring plants, raising containment concerns. For these and other reasons, several research groups have focused on subcellular structures called plastids (e.g., chloroplasts and chromoplasts), tiny granules that inhabit every cell of higher plants. Each cell can contain thousands of copies of each plastid genome, meaning that transformation leads to hyperexpression of the desired protein. Yet plastid DNA is generally not transmitted in pollen, lessening the chance of unwanted spread. Until now, though, chloroplast transformation has been achieved routine only in tobacco; other plants have been sterile and/or shown disappointing expression levels in nonleafy tissues.

By especially refining the circle of foreign DNA used for chloroplast transformation and making a few changes in tissue culture technique, Ralph Bock and colleagues cultivated fertile transplastomic tomatoes loaded with the desired protein. This system could potentially facilitate the delivery of vaccines, drugs, and antibodies in edible tomatoes.