Torphy T J, DeWolf W E, Green D W, Livi G P
Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406.
Agents Actions Suppl. 1993;43:51-71. doi: 10.1007/978-3-0348-7324-6_5.
Considerable interest has been generated in the potential utility of phosphodiesterase (PDE) IV inhibitors as a novel class of anti-asthmatic agents. Because a detailed understanding of the molecular and biochemical characteristics of any molecular target of interest provides a key ingredient for rational drug design, we cloned a cDNA encoding a PDE IV (hPDE IV) from a human monocyte library and expressed, purified and characterized the recombinant gene product. Purified hPDE IV has kinetic characteristics consistent with native PDE IV isolated from tissue sources. In addition, it is inhibited by rolipram (Ki = 60 nM) and other archetypical PDE IV-selective inhibitors. Purified hPDE IV also contains a high affinity binding site for rolipram (Kd = 2 nM), although the precise relationship between this site and the cAMP catalytic site is not clear. In other studies in which the regulation of PDE IV expression was examined in U937 cells, a human monocytic cell line, prolonged treatment with salbutamol was shown to induce an increase in the activity of PDE IV. This up-regulation of PDE IV activity appears to be mediated by cAMP and occurs at the transcriptional or pretranscriptional level. As a consequence of PDE IV up-regulation, the sensitivity of U937 cells to the inhibitory effects of adenylyl cyclase activators on cell function is greatly diminished. If such regulation of PDE IV occurs in inflammatory cells in vivo, it could have implications for the therapeutic use of beta-adrenoceptor agonists. Specifically, induction of PDE IV activity in asthmatics being treated with beta-adrenoceptor agonists could result in a heterologous desensitization of inflammatory cells to endogenous anti-inflammatory agents (e.g., epinephrine, prostaglandin E2).
磷酸二酯酶（PDE）IV抑制剂作为一类新型抗哮喘药物的潜在效用已引起了广泛关注。由于深入了解任何感兴趣的分子靶点的分子和生化特性是合理药物设计的关键要素，我们从人单核细胞文库中克隆了编码PDE IV（hPDE IV）的cDNA，并对重组基因产物进行了表达、纯化和特性鉴定。纯化的hPDE IV具有与从组织来源分离的天然PDE IV一致的动力学特性。此外，它受到咯利普兰（Ki = 60 nM）和其他典型的PDE IV选择性抑制剂的抑制。纯化的hPDE IV还含有一个对咯利普兰的高亲和力结合位点（Kd = 2 nM），尽管该位点与cAMP催化位点之间的确切关系尚不清楚。在其他研究中，对人单核细胞系U937细胞中PDE IV表达的调节进行了检测，结果显示，用沙丁胺醇进行长时间处理可诱导PDE IV活性增加。PDE IV活性的这种上调似乎是由cAMP介导的，并且发生在转录或转录前水平。由于PDE IV上调，U937细胞对腺苷酸环化酶激活剂对细胞功能的抑制作用的敏感性大大降低。如果PDE IV在体内炎症细胞中发生这种调节，可能会对β-肾上腺素能受体激动剂的治疗应用产生影响。具体而言，在用β-肾上腺素能受体激动剂治疗的哮喘患者中，PDE IV活性的诱导可能导致炎症细胞对内源性抗炎剂（例如肾上腺素前列腺素E2）产生异源脱敏。
