Mouse models of human
cancers afford unique opportunities to evaluate novel
therapies in preclinical trials. For this purpose, we analyzed three genetically engineered mouse (GEM) models of low-grade
glioma resulting from either inactivation of the neurofibromatosis-1 (Nf1) tumor suppressor gene or constitutive activation of KRas in glial cells. Based on
tumor proliferation, location, and penetrance, we selected one of these Nf1 GEM models for preclinical
drug evaluation. After detection of an
optic glioma by
manganese-enhanced magnetic resonance imaging, we randomized mice to either treatment or control groups. We first validated the Nf1
optic glioma model using conventional single-agent
chemotherapy (
temozolomide) currently used for children with low-grade
glioma and showed that treatment resulted in decreased proliferation and increased apoptosis of
tumor cells in vivo as well as reduced
tumor volume. Because
neurofibromin negatively regulates
mammalian target of rapamycin (mTOR) signaling, we showed that pharmacologic mTOR inhibition in vivo led to decreased
tumor cell proliferation in a dose-dependent fashion associated with a decrease in
tumor volume. Interestingly, no additive effect of combined
rapamycin and
temozolomide treatment was observed. Lastly, to determine the effect of these
therapies on the normal brain, we showed that treatments that affect
tumor cell proliferation or apoptosis did not have a significant effect on the proliferation of progenitor cells within brain germinal zones. Collectively, these findings suggest that this Nf1
optic glioma model may be a potential preclinical benchmark for identifying novel
therapies that have a high likelihood of success in human clinical trials.