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The phosphoinositide 3'-kinase delta inhibitor, CAL-101, inhibits B-cell receptor signaling and chemokine networks in chronic lymphocytic leukemia

In lymphocytes, the phosphoinositide 3'-kinase (PI3K) isoform p110δ (PI3Kδ) transmits signals from surface receptors, including the B-cell receptor (BCR). CAL-101, a selective inhibitor of PI3Kδ, displays clinical activity in CLL, causing rapid lymph node shrinkage and a transient lymphocytosis. Inhibition of pro-survival pathways, the presumed mechanism of CAL-101, does not explain this characteristic pattern of activity. Therefore, we tested CAL-101 in assays that model CLL-microenvironment interactions in vitro. We found that CAL-101 inhibits CLL cell chemotaxis toward CXCL12 and CXCL13 and migration beneath stromal cells (pseudoemperipolesis). CAL-101 also down-regulates secretion of chemokines in stromal cocultures and after BCR triggering. CAL-101 reduces survival signals derived from the BCR or from nurse-like cells, and inhibits BCR- and chemokine-receptor-induced AKT and MAP kinase (ERK) activation. In stromal cocultures, CAL-101sensitizes CLL cells toward bendamustine, fludarabine, and dexamethasone. These results are corroborated by clinical data showing marked reductions in circulating CCL3, CCL4, and CXCL13 levels, and a surge in lymphocytosis during CAL-101 treatment. Thus, CAL-101 displays a dual mechanism of action, directly decreasing cell survival while reducing interactions that retain CLL cells in protective tissue microenvironments. These data provide an explanation for the clinical activity of CAL-101, and a roadmap for future therapeutic development.

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Cat.No. Product Name Information
S2226 Idelalisib (CAL-101) Idelalisib (CAL-101) is a selective p110δ inhibitor with IC50 of 2.5 nM in cell-free assays; shown to have 40- to 300-fold greater selectivity for p110δ than p110α/β/γ, and 400- to 4000-fold more selectivity to p110δ than C2β, hVPS34, DNA-PK and mTOR. Idelalisib also stimulates autophagy.

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