Here, we examined the mechanism by which the cyclic-AMP/PDE4 signaling axis suppresses PI3K, toward identifying a novel mechanism-based combinatorial strategy to attack BCR-dependency in mature B-cell malignancies.<b>Experimental Design:</b> We used <i>in vitro</i> and <i>in vivo</i> diffuse large B-cell lymphoma (DLBCL) cell lines and primary chronic lymphocytic leukemia (CLL) samples to preclinically evaluate the effects of the combination of the FDA-approved phosphodiesterase 4 (PDE4) inhibitor roflumilast and idelalisib on cell survival and tumor growth.
Taken together, our study showed that PIK3CD can promote proliferation of DLBCL cells both in vitro and in vivo, suggesting that PIK3CD could be druggable in the therapy of DLBCL.
Compared with follicular lymphoma, high PI3Kα expression was more prevalent in diffuse large B cell lymphoma (DLBCL), although both tumor types expressed substantial PI3Kδ.
PIK3CA mutations in exons 9 and 20 were investigated in 76 primary human DLBCLs, 3 DLBCL cell lines (LY1, LY8, and LY10), and 9 related samples using polymerase chain reaction-based sequence analysis to assess the possible relevance of PIK3CA mutations in DLBCL to the PI3K/AKT pathway activation.
We immunohistochemically evaluated the correlation between B-cell receptor (BCR)-phosphoinositide 3-kinase (PI3K) pathway activity and MYC level in 108 cases of de-novo DLBCL, 25 of which featured loss of BCR, and investigated the effects of BCR-PI3K signalling on MYC level and phosphorylation in DLBCL cell lines.
In DLBCL lines, TMD8 was the most sensitive to ibrutinib (GI<sub>50</sub> = 0.001); combinations with BCL-2 inhibitor ABT-199, and PI3K inhibitors IPI-145 and GDC-0941 showed the strongest synergistic activity.
Phosphatidylinositol-3 kinase (PI3K) signaling is a common feature of B-cell neoplasms, including chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL), and PI3K inhibitors have been introduced into the clinic.
Moreover, we detected a similarly functioning prosurvival pathway involving phosphorylated CD19 and PI3K-dependent Erk phosphorylation in human diffuse large B-cell lymphoma cell lines.
The phosphatidylinositol 3-kinase (PI3K)/RAC-α serine/threonine-protein kinase (AKT) pathway is constitutively activated in a number of lymphoid malignancy types, including diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma.
Phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling is frequently dysregulated in diffuse large B cell lymphoma (DLBCL) including the favorable germinal centre B-cell (GCB) and the unfavorable activated B-cell (ABC) subtypes. mTOR promotes cap-dependent translation of proteins, like Mcl-1, through inhibitory phosphorylation of the eukaryotic translation initiation factor 4E binding protein 1 (4EBP1).
This work suggests that multilevel inhibition of the PI3K/Akt/mTOR pathway and double-block of cell cycle progression are effective strategies for DLBCL therapy.