In a new study published in the April 2008 print issue of The FASEB Journal (fasebj), Harvard researchers describe the development of gene probe eye drops that - for the first time - make it possible to monitor and detect tissue repair in the brain of living organisms using MRI. Current methods involve a risky, invasive, and relatively slow process of penetrating the skull to extract tissue samples and then examining those samples in a laboratory.

We hope our study provides a tool for better treatments of neurological diseases, diagnosis, prognosis during therapy, and improved delivery of therapeutic agents to the brain, said Philip Liu of Harvard, one of the researchers involved in the study. Liu also said that more research is necessary to determine exactly how these gene probes reach brain tissue.

In this report, Harvard researchers describe how they link a relatively common MRI probe (superparamagnetic iron oxide nanoparticles) to a short DNA sequence that binds to proteins in cells responsible for brain tissue repair (glia and astrocytes). Then, researchers used the eye drops on mice with conditions that cause leaks in the blood-brain barrier. When the animals' brains were scanned using MRI, brain repair activity was visible. Glia and astrocytes help repair brain and nerve tissue, and have a role in numerous diseases and disorders that cause at least microscopic breaches in the blood-brain barrier, including traumatic brain injury, multiple sclerosis, stroke, cardiac arrest, and glioma, among others. Furthermore, the researchers believe that the probes may also help diagnose thinning of vascular walls in brains, which occurs as Alzheimer's disease progresses.

When people are sick, the last thing you want to do is puncture their skulls for a biopsy, said Gerald Weissmann, MD, Editor-in-Chief of The FASEB Journal, but sometimes this is unavoidable. These probes of genes in action go a long way toward ushering in an age where extracting brain tissue to identify a disease will seem as crude as when doctors measured skulls to diagnose a mental disease.

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The authors found that miR-200 microRNAs helped regulate EMT transition. They bind directly to non-coding regions in the RNA of ZEB1 and ZEB2, known blockers of E-cadherin transcription. Both ZEB proteins have previously been implicated in human malignancies, ZEB1 in aggressive colorectal and uterine cancers, and ZEB2 in advanced stages of ovarian, gastric and pancreatic tumors.

By inhibiting miR-200, Peter and his coworkers could induce EMT. More important, by introducing miR-200, they managed to activate production of E-cadherin protein and reverse tumors from a more-invasive mesenchymal into a less-invasive epithelial form.

"In a previous paper we found that another micro RNA, let-7, drives tumor progression at an earlier stage," Peter said. "Let-7 appears to be a key player in preventing a cancer from becoming more aggressive. Now we want to figure out how these two micro RNAs work together to regulate carcinogenesis."

Once they understand this process, they want to use these microRNAs to treat cancer. Both microRNA families have the connection to drug resistance as well as to cancer stem cells, sub-population of cancer cells that have self-renewal properties and the ability to give rise to new tumors that are more resistant to current therapy.

"Our aim is not only to make tumors less invasive by reintroducing let-7 and miR-200," explained Peter. "We hope that we'll make tumors more sensitive to drugs and be able to target the stem cell population, which gives tumors their renewal capacity."

"The idea is a two-hit strategy," Peter said, "hit them first with the microRNA and make those drug-resistant cells sensitive again, then hit them again with low levels of conventional chemotherapy."

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