Incurable astrocytomas, including the particularly malignant glioblastomas, diffusively grow like mycelium into healthy brain tissue. Therefore, these tumors cannot be completely removed by surgery and invariably start growing again at some point despite intensive treatment. They appear to have effective resistance mechanisms.
In their latest publication, scientists co-working with Frank Winkler from the Clinical Cooperation Unit (CCU) "Neurooncology" of the DKFZ and Heidelberg University Hospital, describe a striking feature of astrocytoma cells: They form extremely thin and long extensions of their cellular membrane, which they use to constantly scan the healthy brain, thus invading and colonizing it. As the tumor grows, the cancer cells use these extensions to interconnect to a large network where they communicate intensively and via long distances, making astrocytomas appear like highly complex, organ-like entities. "Our first thought was: this looks like the formation of a new brain within the existing one," Winkler said. "The tumor cells were interconnected in a network that resembles the ones we know of neurons and other cell types in the brain."
For up to one year, the researchers observed the growth of human glioblastoma cells that they had transferred to mice. They used a special microscopy technique that facilitates insights into the brain's deep zones. In this way, they discovered that the cancer cells exchanged molecules via their membrane microtubes which they also used as communication channels.
The investigators also found this network of tumor microtubes in tissue samples from brain cancer patients. The more the cancer cells were interconnected, the more malignant and resistant the tumor subtype was.
The scientists therefore hypothesized that the tumor microtube networks must be linked to therapy resistance. They observed that the tumors in fact recognize damage to the network and repair it immediately. Radiation therapy - the standard treatment in glioblastoma - fails to kill mainly the tumor cells that are part of the network, whereas cancer cells outside the network die.
How do the tumor cells form these extraordinary membrane extensions? An analysis of the gene activities in tumor tissue from 250 brain cancer patients provided a clue. For building their network, the cancer cells make use of specific molecular signaling pathways that are normally active during early development of the nervous system. Experiments in which the scientists blocked these pathways in mice showed that the animals subsequently developed smaller tumors with fewer interconnections that responded very sensitively to radiotherapy.
"The resistance of astrocytomas, particularly glioblastomas, against all types of therapy is an enormous problem," says Wolfgang Wick, who heads the CCU as well as the Neurology Department of Heidelberg University Hospital. "For the first time, our results show a long sought-after new approach toward breaking this resistance and thus enabling us eventually to enhance the treatment efficacies of these tumors. The results also explain why a specific subtype of brain cancer responds much better to therapy. Their capability of building networks seems to be limited." Matthias Osswald, the article's first author, adds: "Even though this discovery does not immediately enable us to offer a new treatment to our brain tumor patients, it does show the direction that therapy development should take: we have to destroy the malignant network."
Matthias Osswald, Erik Jung, Felix Sahm, Gergely Solecki, Varun Venkataramani, Jonas Blaes, Sophie Weil, Heinz Horstmann, Benedikt Wiestler, Mustafa Syed, Lulu Huang, Miriam Ratliff, Kianush Karimian Jazi, Felix T. Kurz, Torsten Schmenger, Dieter Lemke, Miriam Gömmel, Martin Pauli, Yunxiang Liao, Peter Häring, Stefan Pusch, Verena Herl, Christian Steinhäuser, Damir Krunic, Mostafa Jarahian, Hrvoje Miletic, Anna S. Berghoff, Oliver Griesbeck, Georgios Kalamakis, Olga Garaschuk, Matthias Preusser, Samuel Weiss, Haikun Liu, Sabine Heiland, Michael Platten, Peter E. Huber, Thomas Kuner, Andreas von Deimling, Wolfgang Wick und Frank Winkler: Brain tumor cells interconnect to a functional and resistant network. Nature 2015, DOI: 10.1038/nature16071
Link to Nature "News and Views": http://www.
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Caption: 3D-Illustration of a glioblastoma: Interconnected tumor cells (blue) with the connecting microtubes (pink). Tumor cells and microtubes outside the network are grey (Source: Nature).
The German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ) with its more than 3,000 employees is the largest biomedical research institute in Germany. At DKFZ, more than 1,000 scientists investigate how cancer develops, identify cancer risk factors and endeavor to find new strategies to prevent people from getting cancer. They develop novel approaches to make tumor diagnosis more precise and treatment of cancer patients more successful. The staff of the Cancer Information Service (KID) offers information about the widespread disease of cancer for patients, their families, and the general public. Jointly with Heidelberg University Hospital, DKFZ has established the National Center for Tumor Diseases (NCT) Heidelberg, where promising approaches from cancer research are translated into the clinic. In the German Consortium for Translational Cancer Research (DKTK), one of six German Centers for Health Research, DKFZ maintains translational centers at seven university partnering sites. Combining excellent university hospitals with high-profile research at a Helmholtz Center is an important contribution to improving the chances of cancer patients. DKFZ is a member of the Helmholtz Association of National Research Centers, with ninety percent of its funding coming from the German Federal Ministry of Education and Research and the remaining ten percent from the State of Baden-Württemberg.