In this work, we have utilized in vitro1H- and phosphorus (31P)-NMR to monitor metabolic changes following PI3K pathway inhibition by PI-103 and pan–Class I PI3K inhibitor GDC-0941 which lacks significant mTOR activity and is entering Phase II clinical trials, using the pediatric glioblastoma cell lines SF188 and KNS42. Here, PIK3CA is linked to glioblastoma.