A highly selective, potent, and orally bioavailable small molecule inhibitor of the delta isoform of the 110 kDa catalytic subunit of class IA phosphoinositide-3 kinases (PI3K) with potential immunomodulating and antineoplastic activities. PI3K-delta inhibitor AMG 319 prevents the activation of the PI3K signaling pathway through inhibition of the production of the second messenger phosphatidylinositol-3,4,5-trisphosphate (PIP3), thus decreasing proliferation and inducing cell death. Unlike other isoforms of PI3K, PI3K-delta is expressed primarily in hematopoietic lineages. The targeted inhibition of PI3K-delta is designed to preserve PI3K signaling in normal, non-neoplastic cells.