The Role of Nf1 and Tp53 Deletions in Glioblastoma Pathogenesis and Drug Response (2016)

Undergraduates: Anne Whitacre, Robert S. McNeill Ryan E. Bash, Dr. Ralf Schmid

Faculty Advisor: Dr. C. Ryan Miller
Department: Biology

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Glioblastoma (GBM) is the most common and deadly type of malignant brain tumors. Two commonly mutated tumor suppressor genes in GBM are Nf1 and Tp53. To investigate the effects of homozygous deletions of Nf1 and Tp53 on gliomagenesis, we harvested astrocytes from neonatal mice and mutations were induced in vitro. We tested these cell lines with both Nf1 and Tp53 deletions and found that these mutations increased proliferation compared to normal murine astrocytes. We determined their response to temozolomide (TMZ), a DNA-damaging chemotherapeutic currently used in the standard-of-care of GBM. These astrocytes were highly resistant to TMZ, with [IC50] between 114-272.8 ¿¿M, which is beyond a physiological achievable dose. Next we tested two PI3K inhibitors. BEZ235 had a higher affinity for PI3K than BKM120. There is a very dramatic effect of BKM120, with an IC50 between 1.13-1.57 ¿¿M, whereas the IC50 range of BEZ235 was 22 to 62-fold lower IC50 concentration (0.01-0.06 ¿¿M). Both PI3K inhibitors inhibit growth by more than 90% at low to sub- ¿¿M doses. Next, we tested two MEK inhibitor drugs, AZD6244 and GSK212. AZD6244 had an IC50 between 2.32-13.29 ¿¿M and GSK212 has a greater than 100-fold lower IC50 concentration (0.001-0.04 ¿¿M). Both of the MEK inhibitor drugs have a more gradual change in effect than the PI3K inhibitors. For future work, we will characterize the effects of the Nf1 and Tp53 mutations on cell signaling and tumorigenesis in vivo.