Cell-permeable. A highly potent, pan phosphoinositide 3-kinase (PI 3-K) family kinase inhibitor with biochemical Ki’s of 0.019 nM (PI 3-K⍺), 0.13 nM (PI 3-Kβ), 0.024 nM (PI 3-Kδ), 0.06 nM (PI 3-Kɣ), 0.18 nM (mTORC1), and 0.3 nM (mTORC2). In vivo, GSK2126458 displays anti-tumor activity in both pharmacodynamic and tumor growth efficacy models.