The application of rational drug design is proven to be more efficient than the traditional way of drug discovery since it aims to understand the molecular basis of a disease. The aim of this project is to deactivate the mutated cancerous PI3Kα protein with small molecule inhibitors. It was recently established that PIK3CA, the gene encoding the catalytic p110α subunit of PI3K, is frequently mutated in human malignancies. 80% of these mutations result in amino acid replacements located in either one of two hotspots: (a) in the helical domain the most common replacement is that of Glu by Lys in exon 9 (E545K), (b) in the kinase domain, a His is changed to Arg in exon 20 (H1047R). Both types of these mutations increase the kinase activity of the enzyme, upregulate the downstream AKT pathway and VEGF signaling, and thus stimulate tumorigensesis and angiogenesis. Several PI3Kα inhibitors have been reported in the literature; however, these non-selective antagonists target both the carcinogenic and wild-type PI3Kα proteins, causing undesirable side-effects. Selective inhibition of the mutated carcinogenic PI3Kα isoform is therefore a promising target in cancer research. In this joint computational and experimental study, we propose to selectively inhibit the mutated carcinogenic form of PI3Kα with small-molecule inhibitors through structure-based drug design, synthesis of potential leads, and in vitro/in vivo assaying. Following the assays, potent compounds will be iteratively optimized for both pharmacological and structural properties with computational methods and re-assayed for enhanced activity. Moreover, Molecular Dynamics simulations will be performed in order to gain insight into the dynamics of the mutated protein and the mechanism of oncogenesis. Overall, this study is expected to uncover new anti-cancer leads for further exploration through animal models, while improving our understanding of mechanistic relationships in the PI3Kα deregulated pathway.