Scientists "Reverse Engineer" Brain Cancer Cells to Find New Targets for Treatment

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Scientists "Reverse Engineer" Brain Cancer Cells to Find New Targets for Treatment

UoT/sickkids news
Genome-wide CRISPR-Cas9 screens expose vulnerabilities in patient-derived glioblastoma stem cells

Toronto, Canada – Glioblastoma is one of the most devastating forms of cancer, with few existing treatment options. It is also a leading cause of cancer-related death in children and young adults. Scientists have "reverse engineered" brain cancer stem cells gene by gene, uncovering multiple potential targets for this hard-to-treat cancer.

This work is a collaboration between the University of Toronto (UoT), The Hospital for Sick Children (SickKids), and the University of Calgary. Findings were published today in the journal Cell Reports, making this the first published study to systematically profile a large panel of patient-derived brain tumour cells that have stem cell properties.

"We think that, in one big experiment, we have uncovered many new targets for glioblastoma, some of which were surprising," says Dr. Peter Dirks, co-principal investigator of the study, Staff Neurosurgeon and Senior Scientist at SickKids. "These glioblastoma stem cells are also resistant to treatment, which is one reason that these tumours are so hard to cure. We need new ways to disrupt these cells specifically if we are going to give people a better chance of survival."

The research team also found that adult glioblastoma cells are actually dependent on the same genes that are important for brain development in infancy and early childhood. "This really emphasizes how much research needs to be done to understand the developing human brain," says Dr. Dirks, who, in 2003, was the first to discover the existence of cancer stem cells in brain tumours.

CRISPR: A Powerful New Tool
The emergence of the CRISPR-Cas9 technology provides a powerful new way to explore cancer biology through genome-wide screens. Dr. Stéphane Angers, co-principal investigator of the study and Professor at the Leslie Dan Faculty of Pharmacy, University of Toronto, specializes in the use of CRISPR-Cas9 in cancer. Taking 10 unique patient-derived glioblastoma stem cell cultures collected by the Dirks research team, the Angers lab used CRISPR "cell fitness screens" to determine which genes in the cancer stem cells were required for the cells to survive and to grow, therefore, important for tumour progression.

"Cancer stem cells fuel the growth of tumours and progression of the disease," says Dr. Angers. "In order to effectively target these cells, having a comprehensive view of the genes controlling the growth programs is critical. If you know which genes are necessary for these cells to survive and proliferate, you can then look at ways to attack or block these genes and stop tumour growth in its tracks."

By systematically knocking out each of the 20,000 genes, one at the time, from each of the 10 patient samples, the Angers team found multiple genetic vulnerabilities and revealed a wealth of data that can be further mined to identify possible drug targets for glioblastoma. "This is one of the first studies of its kind, where CRISPR screens are performed directly in multiple freshly isolated patient cells in parallel. This study has provided a massive amount of new information that the research community can now interrogate to help design new treatment strategies," says Dr. Angers.

One gene identified in the study, known as DOT1L, was found to be necessary for tumour persistence in seven of the 10 glioblastoma patient tumour cultures. In collaboration with Dr. Samuel Weiss at the Cumming School of Medicine, University of Calgary, the team used preclinical models to demonstrate the effectiveness of a drug currently used to treat leukemia to inhibit the DOT1L gene product in glioblastoma stem cells.

"We found that blocking this specific protein in this particular form of brain cancer reduced tumour growth and resulted in longer survival in the preclinical model," says Dr. Angers. "This is promising because it uncovered a biological process, not previously suspected to be implicated in glioblastoma, for which a small molecule drug already exists."

Moving Beyond a “Static Picture” of Cancer
In recent years, significant time, effort and funding dollars have been spent on the genomic sequencing of cancer tumours. While this has given us a clearer picture of the hundreds of genetic mutations present in glioblastoma and other cancers, for glioblastoma it has not led to any significant treatment advances, Dr. Angers says.

"This shows that just knowing about genetic mutations is not enough," says Graham MacLeod, a post-doctoral fellow with the Angers lab and co-first author of the study. "That is a static picture of cancer. We are learning that we need to better understand the blueprint of how this cancer functions and what specific genes fuel tumour growth in order to attack it."

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NOTES TO EDITORS
Full Study: Graham MacLeod, Danielle A. Bozek, Nishani Rajakulendran, Vernon Monteiro, Moloud Ahmadi, Zachary Steinhart, Michelle M. Kushida, Helen Yu, Fiona J. Coutinho, Florence M.G. Cavalli, Ian Restall, Xiaoguang Hao, Traver Hart, H. Artee Luchman, Samuel Weiss, Peter B. Dirks, and Stephane Angers (2019) "Genome-Wide CRISPR-Cas9 Screens Expose Genetic Vulnerabilities and Mechanisms of Temozolomide Sensitivity in Glioblastoma Stem Cells", Cell Reports, published online 16 Apr 2019 (DOI: 10.1016/j.celrep.2019.03.047).

This research was supported by Stand Up to Cancer Canada Cancer Stem Cell Dream Team funding provided by the Government of Canada through Genome Canada and the Canadian Institutes of Health Research, the Ontario Institute for Cancer Research, and SickKids Foundation.

About the Leslie Dan Faculty of Pharmacy, University of Toronto
The Leslie Dan Faculty of Pharmacy is Canada’s leading school of pharmacy, offering cutting-edge undergraduate and graduate programs. We are globally recognized for impactful research and fostering expert and innovative clinical practice. Our faculty members and graduates continually advance science and practice to improve health through pharmaceutical care. Our scientific research focuses on the role of pharmacists in the health care system, as well as drug discovery and delivery. We are committed to advancing education programs that develop leaders in clinical practice and to strengthening the link between research, education, and patient care.

About The Hospital for Sick Children
The Hospital for Sick Children (SickKids) is recognized as one of the world’s foremost paediatric health-care institutions and is Canada’s leading centre dedicated to advancing children’s health through the integration of patient care, research and education. Founded in 1875 and affiliated with the University of Toronto, SickKids is one of Canada’s most research-intensive hospitals and has generated discoveries that have helped children globally. Its mission is to provide the best in complex and specialized family-centred care; pioneer scientific and clinical advancements; share expertise; foster an academic environment that nurtures health-care professionals; and champion an accessible, comprehensive and sustainable child health system. SickKids is a founding member of Kids Health Alliance, a network of partners working to create a high quality, consistent and coordinated approach to paediatric health care that is centred around children, youth and their families. SickKids is proud of its vision for Healthier Children. A Better World.

Contact
Media contact: Kate Richards, University of Toronto (+1 416 978 7117, kate.richards@utoronto.cag).