A new series of 3-ethynyl-1H-indazoles has been synthesized and evaluated in both biochemical and cell-based assays as potential kinase inhibitors. Interestingly, a selected group of compounds identified from this series exhibited low micromolar inhibition against critical components of the PI3K pathway, targeting PI3K, PDK1, and mTOR kinases. A combination of computational modeling and structure-activity relationship studies reveals a possible novel mode for PI3K inhibition, resulting in a PI3Kα isoform-specific compound. Hence, by targeting the most oncogenic mutant isoform of PI3K, the compound displays antiproliferative activity both in monolayer human cancer cell cultures and in three-dimensional tumor models. Because of its favorable physicochemical, in vitro ADME and drug-like properties, we propose that this novel ATP mimetic scaffold could prove useful in deriving novel selecting and multikinase inhibitors for clinical use.