P04.03 Different role of integrin a6 in glioblastoma proneural and mesenchymal stem-like cells

BACKGROUND

The plasticity of tumoral cells and the presence of cells displaying stem-like features are two interrelated traits of Glioblastoma (GBM) lesions and both concur in defining its heterogeneity. Particularly, GBM stem-like cells (GSC) can be classified according to trascriptional data in different subgroups, being the Proneural (PN-GSC) and the Mesenchymal (MES-GSC) the most consolidated clusters. GSC are responsible of most of the malignant characteristics of GBM, including therapeutic resistance and tumor recurrence. Therefore, a better understanding of the mechanisms regulating GSC responsiveness to therapy taking into account GSC molecular heterogeneity may help to improve patient’s outcome. Integrin a6 is a commonly used marker for GSC capable to enrich for GSC population and sustain stemness. We investigate the role of integrin a6 in both PN and MES GSC on stemness and radioresistance.

MATERIAL AND METHODS

The expression of integrin a6 was analyzed in GSC cultures obtained from post-surgical specimens either displaying PN or MES trascriptional traits. Using cell sorting to enrich for integrin a6 expression (integrin a6-high and a6-low) and gene silencing with lentiviral-based shRNA, integrin a6 impact on both GSC cultures was tested. Also, silenced MES-GSC were analysed by means of RNA-seq. The major pathways found altered by integrin a6 silencing were validated at functional level using gliomasphere-based clonogenic assay, extreme limiting dilution assay and gamma-H2AX to monitor DNA damage repair kinetics.

RESULTS

After sorting GSC cultures by integrin a6 expression, PN-GSC a6-low showed a significant reduction in clonogenic capability and gliomasphere size when compared to a6-high (p<0.0001). On the contrary, sorted MES-GSC did not display any differences. Similar results were obtained following integrin a6 lentiviral silencing. However, RNAseq on silenced MES-GSC revealed a significant impact on cell cycle regulation and DNA damage repair pathways. Indeed, Integrin a6 trascriptional inhibition in MES-GSCs impaired the capacity to clear gamma-H2AX foci after ionizing radiation (p<0.001) and significantly alters MES-GSC capacity to recover from radiation treatment in gliomasphere formation assay (p<0.01). According to the interpretation of the curves with the linear quadratic model, integrin a6 silenced cells displayed higher alpha- and beta- values and lower alpha/beta ratio. The obtained values demonstrate increased radiosensitivity and impaired capacity to repair sublethal DNA damage, in addition to an enhanced sensitivity to fractionated doses.

CONCLUSION

The data obtained showed that Integrin a6 regulates proliferation and stemness-related features in PN-GSC while supports radioresistance of MES-GSCs. Altogether, we reveal that integrin a6 controls different stem-associated features in GSCs depending on the molecular subtype.

OS12.4 In vivo dynamics and targeting of vessel co-option in glioma

BACKGROUND

Gliomas comprise heterogeneous malignant glial and stromal cells. While blood vessel co-option is a potential mechanism to escape anti-angiogenic therapy, the relevance of glial phenotype in this process is unclear.

MATERIAL AND METHODS

Here, we intravitally study preclinical syngenetic models of glioma as well as patient-derived cells transplanted orthotopically. Moreover, we profoundly confirm our preclinical results with histological studies on patient specimens.

RESULTS

We show that Olig2+ oligodendrocyte precursor-like glioma cells invade by single-cell vessel co-option and preserve the blood-brain barrier (BBB). Conversely, Olig2-negative glioma cells form dense perivascular collections and promote angiogenesis and BBB breakdown, leading to innate immune cell activation. Experimentally, Olig2 promotes Wnt7b expression, a finding that correlates in human glioma profiling. Targeted Wnt7a/7b deletion or pharmacologic Wnt inhibition blocks Olig2+ glioma single-cell vessel co-option and enhances responses to temozolomide. Finally, Olig2 and Wnt7 become upregulated after anti-VEGF treatment in preclinical models and patients.

CONCLUSION

Here, we show that glioma is able to employ vessel co-option, i.e. the movement of tumor cells towards and along the pre-existing vasculature.

Glioma oligodendrocyte-like (OPCL) cells express Wnt7 that is necessary for vessel co-option and Wnt inhibitors significantly improve survival with temozolomide. Moreover, we demonstrated that anti-VEGF-treatment of glioma selects for Olig2/Wnt7+ cells