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Defensa de Tesis Doctoral: Andrea Álvarez Vázquez

Glioblastomas (GBM) are the most malignant primary brain tumors, and they remain incurable. Despite the current standard of care, which involves surgical resection of the tumor and adjuvant administration of chemotherapy and radiotherapy, some GBM stem cells (GSCs) stay in the brain parenchyma becoming one of the primary causes of tumor recurrence. Importantly, the Src-inhibitory peptide TAT-Cx43266-283 has shown promising antitumor results in GBM preclinical models, reducing GSC viability and increasing survival in GBM-bearing mice. However, being aware of the many obstacles to overcome when translating preclinical results into a clinical setting, we have investigated some of these main gaps in order to promote the progress of TAT-Cx43266-283 as a new clinical therapy to fight GBM.

First, we investigated biomarkers of treatment response in order to design a more targeted therapeutic approach in potential clinical applications. For that purpose, we assessed cell viability after treatment with TAT-Cx43266-283, in a set of 13 patient-derived GSC lines. Interestingly, we found a stronger treatment response in those patient GSCs that had alterations in the Epidermal Growth Factor Receptor (EGFR) (EGFR amplification or EGFRvIII mutation). Additionally, analyzing GBM patient databases, we found a correlation between EGFR alterations and a higher Src activity, as well as worse survival outcomes. The role of EGFR as a treatment-response biomarker were confirmed in 6 murine GBM lines with and without EGFR alterations. Importantly, we found that treatment with TAT-Cx43266-283 was more effective than the standard-of-care chemotherapeutic temozolomide (TMZ) or the classical EGFR inhibitor, erlotinib, in our murine and human GSC models. Moreover, we identified EGFR as an additional participant in TAT-Cx43266-283 response together with Src, as shown by the decrease in EGFR and EGFRvIII activity observed in some GSCs and the increased survival upon TAT-Cx43266-283-administration in a mouse model in which tumors were generated by neural stem cells (NSCs) with EGFR and other glioma-driver mutations (NPE-IE cells).

Next, we studied the effect of TAT-Cx43266-283 in a clinical context by administering the treatment in a murine model of tumor resection. We additionally analyzed the histopathology of this GBM model, uncovering histological features typical of human GBM, such as necrosis, invasive borders, and the presence of multiple proliferative spread foci outside the primary tumor mass. We found that resection alone improved, although not significantly, GBM-bearing mice survival. However, tumors that regrew after resection exhibited more aggressive features. Importantly, the combination of tumor resection and TAT-Cx43266-283 achieved better survival outcomes and showed reduced invasive features.

Altogether, these results serve as a base for future clinical investigations and, together with previous studies, support the therapeutic potential of TAT-Cx43266-283 as a treatment for GBM.