The group found that the cell lines that were more resistant to radiation treatment also had higher levels of purines biological compounds that are known as the building blocks of DNA and RNA, and that can also activate signaling pathways.

This was very exciting because lots of different genetic mutations that occur in glioblastoma lead to this purine pathway being activated, Wahl says.

This suggested that they might be able to target the downstream effect of multiple genetic mutations.

We hypothesized that targeting this metabolic activity might work across tumor cells with different types of mutations instead of just whatever fraction of cells has that one particular genetic aberration you might go after with a mutation-targeting therapy.

Once the researchers discovered the correlation between high levels of purines and radiation resistance, they set out to demonstrate whether the metabolic changes actually caused the radiation to be less effective.

We gave cells more purines. It made them more resistant, Wahl says. We took away purines. It made them more sensitive to radiation. And we found it was doing this by affecting the cells ability to repair radiation-induced DNA damage.

To better understand whether targeting purine metabolism might help overcome resistance to radiation therapy in patients, the team used mouse models of glioblastoma with tumors grown from human patients cells.

They gave the mice a drug called mycophenolate mofetil, or MMF, which blocks purine biosynthesis and which has been approved for the treatment of organ transplant rejection since 2000.

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Tumor growth was moderately slowed down in mice who received radiation therapy alone or MMF alone, but almost totally halted in the mice who received both, Wahl explains. The benefits of MMF were similar whether animal tumors were grown in the brains of the mice or elsewhere in their bodies, demonstrating the drugs ability to effectively penetrate the blood-brain barrier which is critical for treating brain cancer patients.

Since the FDA has already found the drug to be safe enough to use in patients for one purpose, it makes it easier to set up a clinical trial aimed at a second disease, he says.

Ultimately, Wahl adds, the research was made possible by the collaborative, multidisciplinary environment at U-M where clinicians and researchers with expertise in glioblastoma can team up with others who specialize in cancer metabolism, data modeling and launching new clinical trials.

None of this happens without all these different teams sharing knowledge, models, methods and enthusiasm for making a difference in the lives of patients, he says.

Additional authors include Weihua Zhou, Andrew J. Scott, Kari Wilder-Romans,Joseph J. Dresser, Christian K. Werner, Hanshi Sun, Drew Pratt, Peter Sajjakulnukit, Shuang G. Zhao, Mary Davis, Meredith A. Morgan, Alnawaz Rehemtualla, Barbara S. Nelson, Christopher J. Halbrook, Li Zhang, Angela K. Walker, Maureen Kachman, Jianping Xiong, Maria G. Castro, Pedro Lowenstein, Sriram Chandrasekaran, Theodore S. Lawrence and Costas A. Lyssiotis of U-M; Yangyang Yao of U-M and First Affiliated Hospital of Nanchang University, China; Francesco Gatto of Chalmers University of Technology, Gteborg, Sweden; and Jann N. Sarkaria of the Mayo Clinic.

The research was supported by grants from the American Cancer Society, the Forbes Institute for Cancer Discovery, the National Cancer Institute (K08CA234416), the Jones Family Foundation Fund within the Chad Carr Pediatric Brain Tumor Center and U-M Taubman Emerging Scholars Program, as well as grants from the National Institutes of Health, the Michigan Institute for Clinical & Health Research, Rogel Cancer Center, an AACR NextGen Grant for Transformative Cancer Research (17-747 20-01-LYSS) and an American Cancer Society Research Scholar Grant (RSG-18-186-01).

Paper cited: Purine metabolism regulates DNA repair and therapy resistance in glioblastoma, Nature Communications. DOI: 10.1038/s41467-020-17512-x

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Study Suggests New Approach to Improve Radiation Therapy Resistance in Glioblastoma - Michigan Medicine