Idelalisib is a potent PI 3-Kinase δ inhibitor (IC50 = 2.5 nM for p110δ); it exhibits >40-fold selectivity for the δ isoform over other PI 3-K class I enzymes (IC50s = 89, 565, and 820 nM for p110γ, p110β, and p110α respectively). Idelalisib blocks constitutive PI 3-K signaling in malignant B-cell lines and primary patient tumor cells. Idelalisib inhibits chronic lymphocytic leukemia cell chemotaxis and downregulates chemokine secretion triggered by B-cell receptor signaling in stromal cocultures. Idelalisib lacks significant cytotoxicity toward natural killer (NK) cells. Idelalisib also decreases production of inflammatory cytokines, including TNF-γ, CD40L, and IL-6 by T cells and IFN-γ by NK cells. Idelalisib is cell-permeable and orally bioavailable.
