Low Meox2 Expression Is A Feature Of Stem-Like Rat Btuc Glioma Cell Line And Contributes To Its Profound Resistance To Oncolytic Herpes Virus Infection

Herpes Simplex Virus 1 (HSV1) is an oncolytic virus that is often engineered with viral gene manipulations to selectively destroy cancer cells through its lytic replication cycle. The engineered HSV1 features effective tumor cell killing and low toxicity in clinical applications, making it an ideal therapeutic option for gliomas and other cancers. However, there are many examples where HSV1 demonstrates poor killing efficacy in highly malignant rat glioblastoma multiforme (GBM) models as well as in clinical samples of high grade human GBM. Further vitro evidence revealed the problem may not be simply physical obstacles in the tumor mass, but rather the resistance of glioma cells themselves to HSV1 infection. A good example is the stem-like BTUC (BTUCsph) rat glioma cell line, which we find to be completely resistant to HSV1 entry. Unlike other glioma cell lines, the BTUCsph cells are derived from an aggressive rat GBM model that strongly mimics the histological features of a malignant and highly infiltrative form of human GBM known as gliosarcoma. BTUCsph shares many features with brain tumor initiating cells including: 1) the expression of neural stem cell markers such as CD133 and nestin; 2) their ability to grow as self-renewing spheres; and 3) their remarkable tumor initiating abilities, where as few as 100 cells are sufficient to generate a tumor in vivo. Further molecular characterization of the BTUCsph cell line revealed that it expresses very low levels of the MEOX2, a tumor suppressor that not only inhibits cell proliferation, but also suppresses epithelial-mesenchymal transition (EMT) - a hallmark of malignant progression in GBMs. Interestingly, we find that many HSV1-permissive glioma cell lines (U87, SF188, 9L) express significantly higher MEOX2 compared to the HSV1-resistant BTUCsph cell line. Hypothesis and Rationale: Based on our characterization of BTUCsph, we suggest that low MEOX2 is a feature of the HSV1-resistant BTUCsph cell line that sets it apart from HSV1-permissive glioma cell lines. We further suggest that low MEOX2 expression profile may contribute to their resistance to HSV1 entry. Experiments and Key Findings: Using a defective HSV1 virus UL53-RTK-UL54 (ICP27 deleted virus expressing GFP reporter) to infect a panel of glioma cell lines (BTUCsph, 9L, U87, SF188) and BTUCsph derived tumors in vivo, we find that cells permissive to HSV1 infection strongly correlates with MEOX2 positivity. In our functional studies, we further revealed that MEOX2 knockdown in the HSV1-permissive 9L glioma cell line resulted in marked decline in HSV1 entry, while MEOX2 overexpression in the HSV1-resistant BTUCsph glioma cell line resulted in significant increase in HSV1 entry. Conclusion: Low MEOX2 expression is a feature of the highly malignant BTUCsph glioma cells that contributes to their resistance to HSV1 entry. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5648. doi:1538-7445.AM2012-5648