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Archive - Nov 13, 2012

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Origins Matter for Brain Tumors

Cancers arise when a normal cell acquires a mutation in a gene that regulates cellular growth or survival. But the particular cell this mutation happens in—the cell of origin—can have an enormous impact on the behavior of the tumor, and on the strategies used to treat it. Robert Wechsler-Reya, Ph.D., professor and director of the Tumor Development Program in Sanford-Burnham’s NCI-designated Cancer Center, and his team study medulloblastoma, the most common malignant brain cancer in children. A few years ago, they made an important discovery: medulloblastoma can originate from one of two cell types: 1) stem cells, which can make all the different cell types in the brain or 2) neuronal progenitor cells, which can only make neurons. Stem cells and progenitor cells are regulated by different growth factors. So, Dr. Wechsler-Reya thought, maybe the tumors arising from these cells respond differently to different therapies. In a study published October 8, 2012 in the journal Oncogene, he and his team show that this is indeed the case. They looked at one growth factor in particular—basic fibroblast growth factor (bFGF)—and found that while it induces stem cell growth, it also inhibits neuronal progenitor cell growth. What’s more, the researchers discovered that bFGF also blocks the growth of tumors that originate from progenitors. When they treated a mouse model of medulloblastoma with bFGF, it dramatically inhibited tumor growth. Although bFGF itself can’t be used as a drug (it would cause too many off-target effects), this study suggests that molecules like it might be used to treat medulloblastoma—but only for tumors that have the appropriate origins. “Medulloblastomas are not all alike, and the same is true for cancers of the breast, prostate, and other tissues.

Sequencing ID’s Abnormal Gene That Launches Rare Childhood Leukemia

Research led by the St. Jude Children's Research Hospital – Washington University Pediatric Cancer Genome Project has identified a fusion gene responsible for almost 30 percent of a rare subtype of childhood leukemia with an extremely poor prognosis. The finding offers the first evidence of a mistake that gives rise to a significant percentage of acute megakaryoblastic leukemia (AMKL) cases in children. AMKL accounts for about 10 percent of pediatric acute myeloid leukemia (AML). The discovery paves the way for desperately needed treatment advances. Investigators traced the genetic misstep to the rearrangement of chromosome 16, which brings together pieces of two genes and sets the stage for production of an abnormal protein. The fusion protein features the front end of CBFA2T3, a blood protein, and the back of GLIS2, a protein that is normally produced only in the kidney. Work that appears in the November 13, 2012 edition of the journal Cancer Cell reports that in a variety of laboratory models the CBFA2T3-GLIS2 protein switched on genes that drive immature blood cells to keep dividing long after normal cells had died. This alteration directly contributes to leukemia. AMKL patients with the fusion gene were also found to be at high risk of failing therapy. Researchers checked long-term survival of 40 AMKL patients treated at multiple medical centers around the world and found about 28 percent of patients with the fusion gene became long-term survivors, compared to 42 percent for patients without CBFA2T3-GLIS2. Overall long-term survival for pediatric AML patients in the U.S. is now 71 percent.

New Cause of Thyroid Hormone Deficiency Discovered

International researchers, including a team at McGill University, have discovered a new cause for thyroid hormone deficiency, or hypothyroidism. This common endocrine disorder is typically caused by problems of the thyroid gland, and more rarely, by defects in the brain or the pituitary gland (hypophysis). However, a new cause of the disease has been discovered from an unsuspected source and was reported online on November 11, 2012 in the journal Nature Genetics. The scientists, led by McGill Professor Daniel Bernard, Department of Pharmacology and Therapeutics in the Faculty of Medicine, identified a new hereditary form of hypothyroidism that is more prevalent in males than in females. This sex bias shone a light on where to look for the underlying cause. "Our collaborators in the Netherlands had been following a family in which two cousins had an unusual syndrome of hypothyroidisim and enlarged testicles," said Professor Bernard. "Using state-of-the-art DNA sequencing technologies, we identified a mutation in a gene called immunoglobulin superfamily, member 1 (IGSF1), in both boys and their maternal grandfather. As one of few labs in the world studying this gene, we initiated a collaboration to determine whether the observed mutation might cause the disorder. At the time, the IGSF1 gene was known to be active in the pituitary gland, but its function was a mystery.