PI3-Kinase Inhibitors in Chronic Lymphocytic Leukemia

The phosphatidylinositol 3-kinase (PI3K) pathway is being explored as a target of inhibition for B-cell lymphoproliferative disorders, with agents specific for inhibition of the PI3K-delta subunit showing significant clinical activity in chronic lymphocytic leukemia (CLL). Idelalisib (CAL-101, GS-1101) and IPI-145 (INK-1147) are novel oral PI3K-delta inhibitors in development, with rates of objective response of 40-60 % and nodal responses exceeding 70 % in relapsed and refractory CLL. High rates of response have been seen in high-risk CLL (i.e., 17p and 11q deletions), and may allow for more effective therapy in inherently chemotherapy-resistant disease. Combination chemotherapy regimens with idelalisib have similarly demonstrated favorable tolerability and activity. Like other agents that target the B-cell receptor pathway, peripheral lymphocytosis, due to drug-induced changes in lymphocyte trafficking, is common. Noteworthy toxicities include transaminitis and pneumonia/pneumonitis. Multiple studies are evaluating PI3K-delta inhibitor combination regimens, and the rationale for these ongoing and planned studies is reviewed.