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Panobinostat, a possible treatment for children with diffuse intrinsic pontine gliomas


Using brain tumor samples collected from children in the United States and Europe, a team of researchers found that the drug Panobinostat ( Farydak ) and similar gene regulating drugs may be effective at treating diffuse intrinsic pontine gliomas ( DIPG ), an aggressive and lethal form of pediatric cancer.
The study is published in Nature Medicine.

DIPG typically attacks children 4 to 9 years of age. Children progressively lose muscle control as the tumor rapidly attacks the pons, a region deep inside the brain that connects the brain to the spinal cord, and is difficult to reach and surgically remove. Despite radiation treatment, children usually survive for about nine months, and less than 1% survive longer than five years.

Six years ago, Michelle Monje at Stanford University ( California; USA ) started to create and share cell cultures of patients’ DIPG cells that could be studied in labs.
In this study, Monje and her colleagues used cell cultures collected from 16 patients in the United States and Europe to search for drugs that could kill or stop the growth of DIPG cells.
By performing experiments in petri dishes and with mice, they found that Panobinostat, a drug designed to change the way cells regulate genes, may be effective at inhibiting DIPG growth and extending survival rates.

Researchers tested 83 known or potential cancer drugs on each of the DIPG cell lines. They found that drugs called histone deacetylase ( HDAC ) inhibitors consistently slowed DIPG growth.
Several of these drugs block histone deacetylases, a group of enzymes that regulate genes by removing chemical tags, called acetyl groups, from histone proteins. The researchers saw similar results when they genetically blocked individual histone deacetylases in the DIPG cells.

They also analyzed the genes of each cell line. After reviewing the genetic and screening data they decided to focus on Panobinostat, a drug designed to block multiple types of histone deacetylases. In petri dishes, they showed that Panobinostat inhibited the growth of 12 out of 16 DIPG cell lines.
When researchers placed DIPG cells in the pons area of mice they found that systemic injections of Panobinostat inhibited DIPG growth and extended survival.

According to Monje, the results support the idea that histone modifications are the keys to understanding and treating DIPG.

Located in a cell’s nucleus, histones are protein complexes that act like genetic spools wound with genes on chromosomes. Enzymes, including histone deacetylases, influence how chromosomes wind around histones by adding or removing chemical tags. In turn, the tagging indirectly, or epigenetically, controls whether a gene on a chromosome will be used, or expressed, in that cell.

Researchers showed that Panobinostat may be effective at treating a variety of DIPG tumors. Approximately 80% of DIPG tumors have a specific mutation in a histone gene. This mutation, called H3K27M, blocks the ability of an enzyme called a methyltransferase from adding a chemical tag, called a methyl group, to the histone. Although the H3K27M mutation disrupts a different chemical tagging system, researchers showed that Panobinostat slowed the growth of a line of cells that had the mutation. Panobinostat also slowed the growth of DIPG cells that do not have that mutation.

Panobinostat may work in combination with other treatments. Studying H3K27M cells that developed resistance to Panobinostat over time, they showed that GSKJ4, a drug that blocks the removal of methyl groups from histones, slowed tumor growth. Combining Panobinostat and GSKJ4 appeared to slow growth further, suggesting the two compounds work synergistically. ( Xagena )

Source: National Institutes of Health, 2015

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