A phosphodiesterase 4B-dependent interplay between tumor cells and the microenvironment regulates angiogenesis in B-cell lymphoma

Abstract

Angiogenesis associates with poor outcome in diffuse large B-cell lymphoma (DLBCL), but the contribution of the lymphoma cells to this process remains unclear. Addressing this knowledge gap may uncover unsuspecting proangiogenic signaling nodes and highlight alternative antiangiogenic therapies. Here we identify the second messenger cyclic-AMP (cAMP) and the enzyme that terminates its activity, phosphodiesterase 4B (PDE4B), as regulators of B-cell lymphoma angiogenesis. We first show that cAMP, in a PDE4B-dependent manner, suppresses PI3K/AKT signals to down-modulate VEGF secretion and vessel formation in vitro. Next, we create a novel mouse model that combines the lymphomagenic Myc transgene with germline deletion of Pde4b. We show that lymphomas developing in a Pde4b-null background display significantly lower microvessel density in association with lower VEGF levels and PI3K/AKT activity. We recapitulate these observations by treating lymphoma-bearing mice with the FDA-approved PDE4 inhibitor Roflumilast. Lastly, we show that primary human DLBCLs with high PDE4B expression display significantly higher microvessel density. Here, we defined an unsuspected signaling circuitry in which the cAMP generated in lymphoma cells downmodulates PI3K/AKT and VEGF secretion to negatively influence vessel development in the microenvironment. These data identify PDE4 as an actionable antiangiogenic target in DLBCL.

Phosphodiesterase 4 inhibitors have wide-ranging activity in B-cell malignancies

“…Importantly, the findings from this genetically engineered mouse were recapitulated with the FDA-approved PDE4 inhibitor roflumilast. 9 These data suggest that PDE4 is as an actionable antiangiogenic target in B-cell lymphomas, which likely does not induce the cardiotoxicity found with the bevacizumab/ anthracyclines combination. 26,27 Remarkably, given their anti-inflammatory activity, PDE4 inhibitors have been independently shown to actually protect against doxorubicin-induced cardiomyopathy in rats.…”

“…In B-cell lymphomas with high PDE4B levels, cAMP is hydrolyzed to AMP, resulting in higher AKT-driven VEGFA expression in the tumor cell, excessive secretion in the tumor milieu, and enhanced angiogenesis. 9 cAMP, in a PDE4-dependent manner, also suppresses the survival and proliferation of endothelial cells, 28 downmodulates the secretion of various proinflammatory cytokines, and increases the number of Tregs. [51][52][53][54] The PDE4 inhibitor roflumilast abrogates cAMP hydrolysis, elevates the intracellular levels of this second messenger, and restores its suppressive effects in the lymphoma cell and the microenvironment.…”

“…However, notably absent from these efforts is a detailed examination of PDE inhibitors in cancer therapeutics. Here, we review a decade-long exploration of the contribution of cyclic-AMP and PDE4 to the pathogenesis of B-cell lymphoma, [5][6][7][8][9] culminating with the first-incancer clinical trial of a PDE4 inhibitor in advanced B-cell malignancies. 10 In particular, we highlight the interplay between cyclic-AMP/PDE4 and B-cell receptor (BCR) signals, discuss the antiangiogenic activity of PDE4 inhibitors, and, considering their anti-inflammatory/immunomodulatory activity, we suggest that adding these agents to rationally devised therapeutic combinations will prevent the development of inflammatory/ autoimmune toxicity that associates with the simultaneous use of multiple biological agents, the so-called biological doublets (eg, spleen tyrosine kinase [SYK] and phosphatidylinositol 3-kinase d [PI3Kd] inhibitors) and triplets (eg, anti-CD20, lenalidomide, and Bruton tyrosine kinase [BTK] or PI3Kd inhibitors).…”

“…[28][29][30][31] To address the contribution of PDE4B expression/ activity to lymphoma angiogenesis, a compound mouse combining Pde4b knockout with the Em-Myc allele was recently created. 9 In this model, lymphomas arising in a Pde4b-null background displayed significantly suppressed angiogenesis in association with decreased PI3K/AKT activity and VEGF expression in the tumor cells. PI3K/AKT signals are important hypoxia-inducible factor-independent regulators of VEGF expression/ angiogenesis in epithelial malignancies, 32-34 explaining the relationship between PDE4 levels, cyclic-AMP-modulated PI3K/AKT activity, VEGFA secretion, and lymphoma angiogenesis ( Figure 1).…”

“…26,27 Remarkably, given their anti-inflammatory activity, PDE4 inhibitors have been independently shown to actually protect against doxorubicin-induced cardiomyopathy in rats. 35 Although lenalidomide has also been suggested to inhibit lymphoma angiogenesis, 36 the proposed use of PDE4 inhibitors in this setting is grounded in a more robust mechanistic understanding of its effects on the tumor and endothelial cells, 9,[28][29][30][31] which may be leveraged for the development of successful antiangiogenesis initiatives.…”