Targeted inhibition of PIK3CA mutations in glioma cell models

Abstract

Gliomas are the most common and lethal brain tumors in adults, with efficient therapies non-existent. PIK3CA mutations are potential therapeutic targets, described as early constitutive events in glioblastomas (GBM). The goal of this project was to assess the impact of PIK3CA mutations on glioma aggressiveness and evaluate the inhibition of PI3Kα in glioma cell models harboring PIK3CA mutations. Additionally, we intended to characterize the IPOLFG cohort with IDH2 mutational analysis, previously classified according to IDH1 and PIK3CA mutational status and 1p19q co-deletion. Thus, IDH2 mutations were evaluated by Sanger sequencing, and immune cell infiltrates were estimated using the TIMER platform. Functional studies were performed using a GBM cell line – U87MG, transfected to contain E545K and H1047R mutations. The effects of temozolomide and alpelisib treatment on cell viability, death, and PI3K/AKT pathway activation were assessed. Only one out of 279 sequenced samples harbored an IDH2 mutation. PIK3CA mutation frequencies remained unaltered in glioma molecular subgroups. Using TIMER analysis, we observed increased CD8+ T cell infiltration in PIK3CA mutant low-grade gliomas, whilst PIK3CA and STAT5B expressions were positively correlated. Regarding PIK3CA mutations on glioma aggressiveness, no differences were observed in U87MG colony formation, migration, or invasion, regardless of PIK3CA mutational status. Moreover, PIK3CA mutations did not change U87MG cells’ sensitivity to either alpelisib or temozolomide, with alpelisib potentiating PI3K/AKT signaling. Here, we achieved a more refined characterization of the IPOLFG glioma cohort and uncovered a possible, novel link between tumor microenvironment and the prevalence of PIK3CA mutations during glioma progression. Our data shows that PIK3CA mutations neither significantly impact GBM cell aggressiveness nor confer added sensitivity to PI3Kα targeted inhibition. Nevertheless, we found that GBM cells seem to trigger complex, not yet described compensatory mechanisms, which could pave the way for future studies relating pan-PI3K inhibitors and the targeting of other pathways.