Laura Lane has worked as a health and science journalist since 1997. She received her master's degree in biology from Stanford University. Since then, she has written for the Dallas Morning News, the Contra Costa Times, Shape magazine, WebMD, Yoga Journal, Diagnostic Imaging, the International Medical News Group, The Scientist, Bio IT World and Biocompare.
Molecular diagnostic tests are enabling physicians to pinpoint killers: cancer, Alzheimer’s Disease, cardiovascular disease, bacterial and viral infections and other conditions. By analyzing nucleic acids, proteins and other molecules, diagnostic tests can raise the red flag before disease develops or progresses. Molecular information also allows for specific diagnoses and targeted treatments.
“Diagnostic signatures inform of underlying biology and inform of druggable targets,” says Lorenzo Sempere, research assistant professor of medicine at Dartmouth-Hitchcock Medical Center.
We’re not talking about cholesterol here. Nor has the time come for protein isoforms and metabolite profiles. In the clinic, physicians and patients increasingly discuss genetic markers and transcript profiles. In the lab, researchers are fine-tuning the transcript profiles that correlate with disease. Physicians now have a reason to consider the stuff of DNA and RNA: The selection of biologically targeted therapies is rapidly expanding. At the same time, technological advances have reached a stage where detection platforms are efficient and robust enough for clinical labs.
RNA takes the stage
With the Human Genome Project making headlines, DNA has long stood in the spotlight. RNA now shares the star status. In addition to plumbing the depths of the nucleus with its genetic markers and susceptibilities, researchers are giving more time to understanding how expression of genes affects health.
Most recently, researchers have turned to microRNA, denoted as miRNA, as another diagnostic option. Biologically, miRNA controls gene expression by binding to mRNA and preventing translation. Because miRNA fulfills its function without further processing, its expression levels correlate with its biological activity, Sempere says.
“The idea with [studying] microRNA is that the expression levels that you detect correlate with the activity of the microRNA,” he says. “Whereas with messenger RNA, they get translated into proteins and undergo other processing before there’s activity.
And, with only a finite number of miRNAs, about 1,000, researchers can more easily characterize the expression patterns of each, Sempere says. On the other hand, mRNA brings so much more complexity with all the alternative splicing and other processing.
Using miRNAs as diagnostic markers could also be more convenient. With the size of a mere 22 to 24 nucleotides, miRNA is an unlikely target for degradation. The molecules survive intact in the bloodstream and don’t require invasive procedures for sampling.
Three diagnostic tests that assess miRNA profiles to help with cancer treatment are already on the market (miRview® mets and mets2, miRview squamous, and miRview meso—all from Rosetta Genomics; and miRInform™ Pancreas from Asuragen).
Better...stronger...faster
Still, researchers consider blood, saliva and other bodily fluids as good samples for profiling RNA as well as DNA. The increasing sensitivity of assays, in part, allows for such convenience. Automation and high-throughput technology speed up the process. Multiplexing further quickens diagnosis. It’s one of the most significant advances in nucleic acid diagnostics, says Alina Deshpande, senior scientist in R&D at Los Alamos National Laboratory.
“That’s where the promise is for the future,” Deshpande says. “Multiplex PCR has been around forever, but what's more cutting edge now is the detection platform.”
She suggests microsphere arrays as ideal platforms for carrying out multiplexed diagnostics or for simultaneous probing for more than one marker. Currently, these arrays beads are encoded using fluorophores to distinguish beads carrying different probes. In the future, multiplexing could take advantage of anistropic particles made of polymeric, oxide and metallic materials, which lead to encoding based on the bead’s size, shape and density. This would increase the possibilities for differentiation between microspheres and enable higher levels of multiplexing.
High speed, high confidence
Speed can be critical in the case of infection. The sooner physicians identify the pathogen, the sooner they can dispense appropriate treatments—and the sooner public-health officials can move to prevent others from being infected.
In determining the pathogen’s nucleic acid profile, the multiplexing approach would probe for all possibilities. Not only would the correct diagnosis be made more quickly but also more confidently, which naturally comes with the greater amounts of data from multiplexing, Deshpande says. The same goes for genotyping cancer and characterizing other diseases.
The applications of molecular diagnostics continue to grow. The life sciences will continue to discover new targets. Physicians will continue to learn about new directions for treatment. And patients can look forward to more promising and healthier futures.