The stem cell-determining transcription factor Sox2 is required for the maintenance of normal neural stem cells. In this study, we investigated the requirement for Sox2 in neural cancer stem-like cells using a conditional genetic deletion mutant in a mouse model of platelet-derived growth factor-induced malignant oligodendroglioma. Transplanting wild-type oligodendroglioma cells into the brain generated lethal tumors, but mice transplanted with Sox2-deleted cells remained free of tumors. Loss of the tumor-initiating ability of Sox2-deleted cells was reversed by lentiviral-mediated expression of Sox2. In cell culture, Sox2-deleted tumor cells were highly sensitive to differentiation stimuli, displaying impaired proliferation, increased cell death, and aberrant differentiation. Gene expression analysis revealed an early transcriptional response to Sox2 loss. The observed requirement of oligodendroglioma stem cells for Sox2 suggested its relevance as a target for therapy. In support of this possibility, an immunotherapeutic approach based on immunization of mice with SOX2 peptides delayed tumor development and prolonged survival. Taken together, our results showed that Sox2 is essential for tumor initiation by mouse oligodendroglioma cells, and they illustrated a Sox2-directed strategy of immunotherapy to eradicate tumor-initiating cells. Cancer Res; 74(6); 1833-44. Ó2014 AACR.

Oncolytic herpes simplex viruses (HSVs) represent a novel frontier against tumors resistant to standard therapies, like glioblastoma (GBM). The oncolytic HSVs that entered clinical trials so far showed encouraging results; however, they are marred by the fact that they are highly attenuated. We engineered HSVs that maintain unimpaired lytic efficacy and specifically target cells that express tumor-specific receptors, thus limiting the cytotoxicity only to cancer cells, and leaving unharmed the neighboring tissues. We report on the safety and efficacy in a high-grade glioma (HGG) model of R-LM113, an HSV recombinant retargeted to human epidermal growth factor receptor 2 (HER2), frequently expressed in GBMs. We demonstrated that R-LM113 is safe in vivo as it does not cause encephalitis when intracranially injected in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, extremely sensitive to wild-type HSV. The efficacy of R-LM113 was assessed in a platelet-derived growth factor (PDGF)-induced infiltrative glioma model engineered to express HER2 and transplanted intracranially in adult NOD/SCID mice. Mice injected with HER2-engineered glioma cells infected with R-LM113 showed a doubled survival time compared with mice injected with uninfected cells. A doubling in survival time from the beginning of treatment was obtained also when R-LM113 was administered into already established tumors. These data demonstrate the efficacy of R-LM113 in thwarting tumor growth.

Although the infiltrative behavior of malignant gliomas is one of their most critical aspects, the mechanisms underlying it have not yet been elucidated. To migrate in the brain parenchyma, malignant glioma cells need to bypass the cell-cell contact inhibitory signals. Here we propose that the blinding of cell-cell contact sensing in gliomas is caused by an unusual mechanism of cadherin switch, involving the replacement of N-cadherin with R-cadherin (Rcad) at the cell-cell junctions and the activation of ERK and p27. In our model of malignant glioma, we found that Rcad expression is necessary and sufficient to release cells from contact inhibition of proliferation, and is necessary, although not sufficient, for overriding contact inhibition of migration and for tumorigenicity. Altogether, these observations suggest that Rcad is a potential target for malignant glioma therapies.