Juvenile myelomonocytic leukaemia (JMML) is the most common chronic cancer of the blood in children and tends to have a poor response to chemotherapy. Prof. Dr. Christian Flotho and his team from the Centre of Paediatric and Adolescent Medicine in Freiburg have shown that epigenetic mechanisms play a key role in the pathogenesis of JMML. As part of a German Research Foundation priority programme, the researchers from Freiburg are working on improving stem cell transplantation, which to date is the only JMML treatment that offers long-term cure. The researchers have come up with a map of epigenetic changes present in JMML patients from which they have extrapolated that the presence of hypermethylation might be predictive of disease outcome.
Human blood cells are constantly being renewed day in, day out; bone marrow stem cells are constantly dividing and producing red and white blood cells in a highly regulated process. Mutations in bone marrow-derived stem cells may give rise to abnormal progenitors, whose unregulated self-renewal can lead to blood cancer. In juvenile myelomonocytic leukaemia (JMML), abnormal blood cells multiply and fewer normal blood cells are produced; infants and children with JMML exhibit pallor, a poor general condition and a bulging belly, the latter caused by the massive enlargement of liver and spleen. The disease can also affect other organs. “This type of leukaemia is insensitive to chemotherapy,” said Prof. Dr. Christian Flotho, doctor and researcher at the Centre of Paediatric and Adolescent Medicine at the University of Freiburg Medical Centre. “And even stem cell transplantation, which is currently the only treatment that offers long-term cure, leads to the recurrence of the disease in around one third of all children affected.”
This is a frighteningly high rate. Flotho and his colleagues from the Department of Paediatric Oncology and Haematology (medical director: Prof. Dr. Charlotte Niemeyer) at the Centre of Paediatric and Adolescent Medicine are therefore determined to do all they can to improve the treatment of JMML. However, they first have a largely practical problem to overcome: although JMML is the most common chronic type of leukaemia in children, it only occurs in one to two children in a million per year. JMML is therefore classified as a rare (orphan) disease. The treatment and diagnosis of orphan diseases is still an unsolved issue in modern medicine. “A normal clinical paediatrician is unlikely to come across more than two or three children with so-called rare diseases in the course of his or her career,” said Flotho. Due to their low incidence it is difficult to systematically investigate rare diseases. Professor Niemeyer has therefore been involved in a multicentre study for the past two decades or so that seeks to collect evidence from all JMML cases across Europe during which time she, Flotho and their team have collected blood samples and information from around 400 patients.
As stem cell therapy, which involves the transplantation of normal blood stem cells to replace abnormal ones, is ineffective in around one third of all cases, Flotho and his team of researchers started focussing on the causes of the varying courses of the disease around seven years ago. Back then, it was becoming evident that epigenetic changes played a role in many other cancers. Epigenetic changes are DNA modifications involving the addition of methyl groups. Although this does not lead to any alterations in the underlying DNA sequence, methylation nevertheless disturbs the packaging of the DNA and prevents it from being transcribed. Entire genes might be turned off, which in turn has a dramatic effect on key biological processes such as cell growth and cell division. This can then lead to malignant tumours. As they do not change the underlying DNA sequence, epigenetic changes therefore represent a higher level of control of DNA transcription. Flotho and his team of researchers have analysed the distribution of methyl groups in the DNA of healthy and JMML children, concentrating specifically on the DNA regions that were previously found to be of major relevance for the pathogenesis of other cancers.
Of fifteen DNA regions studied, the researchers identified four regions in JMML with frequent hypermethylation. However, this was not the most significant discovery. Of even greater significance was the fact that these areas were only found in one third of all JMML patients studied. And it was these patients that suffered from a rather aggressive biological variant of JMML and were at much higher risk of relapse following stem cell transplantation. In addition, the researchers found that extensively methylated DNA regions were also associated with a higher mortality rate. “Our data suggest that the methylation pattern of the four DNA regions is an important predictor of JMML outcome,” said Flotho highlighting the huge importance of these regions in diagnosing the disease. “If the alterations on the epigenetic level play such a major role as they seem to, this might also have implications for the treatment of the disease,” said Flotho. Can the methyl residues be removed with drugs? Other types of cancer are already being treated with azacytidine, a drug which has been shown to interfere with DNA methylation.
The treatment of JMML with drugs that interfere with DNA methylation is still a pipe dream. For the time being, the researchers need to broaden the basis of their knowledge. They have plans to study the epigenetic changes in the DNA of the JMML children whose data and blood samples are stored in their database. The investigations might eventually lead to a map of epigenetically altered regions in the DNA of JMML patients that can be used to make founded predictions about disease progression. This research is part of the German Research Foundation’s (DFG) priority programme 1463 (Epigenetic regulation of normal haematopoesis and its dysregulation in myeloid neoplasia). “We are quite fortunate that the DFG launched this programme. It’s almost like it was custom built for us,” said Flotho. The state of technology is much better than it was seven years ago, and the Freiburg researchers now have access to improved methods that make the genome-wide screening of the DNA of JMML patients for the presence of conspicuous methylation patterns a lot easier. Their objective to develop an epigenetic map does not seem quite so unrealistic.
Prof. Dr. Christian Flotho
University of Freiburg Medical Centre
Centre of Paediatric and Adolescent Medicine
Tel.: +49 (0)761/ 27 04 628
Fax: +49 (0)761/ 27 04 518