The cyclic AMP/phosphodiesterase4 axis regulates proximal B cell receptor signaling and offers a new therapeutic strategy for B cell lymphomas

 描述(由申请人提供)：B细胞受体(BCR)的异常激活是成熟B细胞肿瘤的一个新的标志。BcR启动信号转导通路，激活多种信号通路，包括SYK、BTK和PI3Kδ，导致NF-κB、PI3K/AKT、RAS和MAPK通路的激活，从而促进B细胞的增殖和存活。考虑到这种促进生长的结果，恶性B细胞为了自己的利益劫持这个信号模块也就不足为奇了。因此，开发抑制BCR的治疗方法已成为当务之急，初步结果表明这是一种合理的方法。然而，这些新的治疗方法主要依赖于一次靶向一种激酶，很少能引起完全反应。此外，最近有报道称，在接受btk抑制剂伊布鲁替尼治疗的患者中，bcr途径(btk/plcγ2)内的获得性突变和随后的临床反应丧失。此外，人们对诱导BCR活性终止的信号分子知之甚少。早期我们发现磷酸二酯酶4B(PDE4B)基因在致死性弥漫性大B细胞淋巴瘤(DLBCL)中高表达。随后，我们证明了PDE4B抑制导致环腺苷酸(CAMP)介导的SYK、BTK和PI3K的抑制，这与淋巴瘤的生长抑制有关。这些观察表明，cAMP/PDE4和BCR之间存在相互作用，当完全理解这一观察结果时，可以发展为临床倡议。在这里，我们将验证一种假设，即抑制PDE4通过提高cAMP水平来抑制bcr的活性，从而抑制bcr依赖的激酶SYK、BTK和PI3Kδ的活性。在我们初步数据的基础上，我们还计划测试cAMP/PDE4轴通过激活脂质磷酸酶SHIP1来调节BCR，从而终止PI3K活性的想法。通过延伸，我们建议将PDE4抑制剂与专门针对这些bcr相关激酶的药物相结合将带来临床益处。我们认为，这种垂直靶向方法将是协同的，并可能阻止源自单一药物策略的补偿机制，从而限制耐药性的出现。为了测试这些概念，我们将使用转基因的DLBCL细胞系，一只Pdeb4基因敲除的小鼠，一种由我们小组创建的新的复合小鼠模型，该模型结合了PDE4B纯合缺失和致淋巴瘤的Myc转基因等位基因，以及临床级别的PDE4、BTK和PI3Kδ的抑制剂。我们的具体目标是：1.在体外和体内确定cAMP/PDE4轴在调节正常成熟B淋巴细胞和B细胞淋巴瘤bcr活性中的作用；2.在体外和体内确定联合靶向PDE4和bcr依赖的激酶在人和小鼠B细胞淋巴瘤中的作用。这项研究完成后，可能确定cAMP是bcr信号终止的媒介，而抑制PDE4可能是针对异常的bcr信号通路的一种新方法。如果是阳性的，我们的数据将满足当代合理治疗设计的原则之一，即以关键途径BCR为靶点，使用不同的药物类别、磷酸二酯酶和激酶抑制剂。

 DESCRIPTION (provided by applicant): Aberrant activation of the B cell receptor (BCR) is an emerging hallmark of mature B cell tumors. The BCR initiates a signaling cascade that activates multiple kinases, including SYK, BTK and PI3Kδ, leading to engagement of the NF-κB, PI3K/AKT, RAS and MAPK pathways, thus promoting proliferation/survival of B cells. Considering this pro-growth outcome, it is not surprising that malignant B cells hijack this signaling module for their benefit. Consequently, the development of therapies to inhibit the BCR has become a high priority and preliminary results suggest that this is a sound approach. However, these novel therapeutic approaches rely primarily on the targeting of one kinase at a time and only rarely induce complete responses. Moreover, acquired mutations within the BCR pathway (BTK/PLCγ2) and subsequent loss of clinical response have recently been reported in patients treated with the BTK inhibitor Ibrutinib. Moreover, little is known about the signaling molecules that induce the termination of BCR activity. Earlier we identified phosphodiesterase 4B (PDE4B) as a highly expressed gene in fatal diffuse large B cell lymphoma (DLBCL). Subsequently, we demonstrated that PDE4B inhibition leads to a cyclic-AMP (cAMP) mediated suppression of SYK, BTK and PI3K, which associates with growth inhibition in lymphoma. These observations suggested a cross-talk between cAMP/PDE4 and the BCR, an observation that when fully understood can be developed into clinical initiatives. Here, we will test the hypothesis that PDE4 inhibition, by elevating cAMP levels, suppresses the activity of the BCR and consequently that of BCR-dependent kinases SYK, BTK and PI3Kδ. Building on our preliminary data, we also plan to test the idea that the cAMP/PDE4 axis modulates the BCR via activation of of the lipid phosphatase SHIP1, thus terminating PI3K activity. By extension, we propose that combining PDE4 inhibitors with agents that specifically target these BCR-related kinases will impart clinical benefit. We suggest that this vertical targeting approach will be synergistic and may block compensatory mechanisms derived from single agent strategies, thus limiting the emergence of resistance. To test these concepts, we will use genetically modified DLBCL cell lines, a Pdeb4 knock-out mouse, a new composite mouse model generated in our group that combines homozygous loss of Pde4b with a lymphomagenic Myc transgenic allele, and clinical grade inhibitors of PDE4, BTK and PI3Kδ. Our specific aims are: 1. Define in vitro and in vivo the role of the cAMP/PDE4 axis in modulating BCR activity in normal mature B lymphocytes and B cell lymphomas; 2. Determine in vitro and vivo the effects of the combinatorial targeting of PDE4 and BCR-dependent kinases in human and murine B cell lymphoma. Upon completion, this study may identify cAMP as mediator of BCR signal termination, and PDE4 inhibition as a novel approach to target the aberrant BCR signaling pathway. If positive, our data will fulfill one of the tenets of contemporary rational therapeutic design, the targeting of a critical pathway, the BCR, with distinct drug classes, phosphodiesterase and kinase inhibitors.