The biochemical and pharmacological characteristics in human proinflammatory cells of BRL 50481 [3-(N,N-dimethylsulfonamido)-4-methyl-nitrobenzene], a novel and selective inhibitor of phosphodiesterase (PDE) 7, are described. BRL 50481 inhibited the activity of hrPDE7A1 expressed in baculovirus-infected Spodoptera frugiperda 9 cells in a competitive manner (K i value of 180 nM) and was 416 and 1884 times less potent against PDE3 and 38 and 238 times less potent against PDE4 at a substrate concentration of 1 M and 50 nM cAMP, respectively. Western blotting identified HSPDE7A1 but not HSPDE7A2 in three human cell types that are implicated in the pathogenesis of chronic obstructive lung disease, namely, CD8 ϩ T-lymphocytes, monocytes, and lung macrophages. BRL 50481 had no effect on the proliferation of CD8 ϩ Tlymphocytes and only marginally (ϳ2-11%) reduced the generation of tumor necrosis factor (TNF)␣ from blood monocytes and lung macrophages. However, in the presence of BRL 50481 the inhibitory effect of rolipram was enhanced on all three cell types. The expression of HSPDE7A1 was increased in a time-dependent manner in monocytes that were "aged" in culture medium. Under this condition, BRL 50481 now inhibited TNF␣ generation in a concentration-dependent manner. In aged monocytes, rolipram, Org 9935 (a PDE3 inhibitor), and prostaglandin E 2 inhibited TNF␣ generation in a concentrationdependent manner and interacted additively with BRL 50481. BRL 50481 is the first fully documented PDE7 inhibitor that has acceptable selectivity for in vitro studies. Furthermore, although BRL 50481 had only a modest inhibitory effect per se on the proinflammatory cells studied, it acted at least additively with other cAMP-elevating drugs, especially when HSPDE7A1 was up-regulated.

1 Of the four major phosphodiesterase 4 (PDE4) subtypes, PDE4A, PDE4B and PDE4D are widely expressed in human in¯ammatory cells, including monocytes and T lymphocytes. We explored the functional role of these subtypes using ten subtype-selective PDE4 inhibitors, each belonging to one of two classes: (i) dual PDE4A/PDE4B inhibitors or (ii) PDE4D inhibitors. 2 These compounds were evaluated for their ability to inhibit antigen-stimulated T-cell proliferation and bacterial lipopolysaccharide (LPS)-stimulated tumour necrosis factor a (TNFa) release from peripheral blood monocytes. 3 All compounds inhibited T-cell proliferation in a concentration-dependent manner; with IC 50 values distributed over an approximately 50 fold range. These compounds also inhibited TNFa release concentration-dependently, with a wider (*1000 fold) range of IC 50 values. 4 In both sets of experiments, mean IC 50 values were signi®cantly correlated with compound potency against the catalytic activity of recombinant human PDE4A or PDE4B when analysed by either linear regression of log IC 50 values or by Spearman's rank-order correlation. The correlation between inhibition of in¯ammatory cell function and inhibition of recombinant PDE4D catalytic activity was not signi®cant in either analysis. 5 These results suggest that PDE4A and/or PDE4B may play the major role in regulating these two in¯ammatory cell functions but do not rule out PDE4D as an important mediator of other activities in mononuclear leukocytes and other immune and in¯ammatory cells. Much more work is needed to establish the functional roles of the PDE4 subtypes across a broader range of cellular functions and cell types.

Therapies that mitigate the fibrotic process may be able to slow progressive loss of function in many lung diseases. Because cyclic adenosine monophosphate is known to regulate fibroblasts, the current study was designed to evaluate the activity of selective phosphodiesterase (PDE) inhibitors on two in vitro fibroblast responses: chemotaxis and contraction of three-dimensional collagen gels. Selective PDE4 inhibitors, rolipram and cilomilast, each inhibited the chemotaxis of human fetal lung fibroblasts (HFL-1) toward fibronectin in the blindwell assay system (control: 100% versus cilomilast [10 microM]: 40.5 +/- 7.3% versus rolipram: [10 microM] 32.1 +/- 2.7% cells/5 high-power fields; P < 0.05, both comparisons). These PDE4 inhibitors also inhibited contraction of three-dimensional collagen gels (control: 100% versus cilomilast: 167.7 +/- 6.9% versus rolipram: 129.9 +/- 1.9% of initial size; P < 0.05, both comparisons). Amrinone, a PDE3 inhibitor, and zaprinast, a PDE5 inhibitor, had no effect in either system. Prostaglandin E(2) (PGE(2)) inhibited both chemotaxis and gel contraction, and the PDE4 inhibitors shifted the PGE(2) concentration-dependence curve to the left in both systems. The inhibition of endogenous PGE(2) production by indomethacin diminished the effects of the PDE4 inhibitors in both chemotaxis and gel contraction, consistent with the concept that the PDE4 inhibitory effects on fibroblasts are related to the presence of cyclic adenosine monophosphate in the cells. In summary, these in vitro results suggest that PDE4 inhibitors may be able to suppress fibroblast activity and, thus, have the potential to block the development of progressive fibrosis.

We have isolated cDNA clones representing cyclic AMP (cAMP)-specific phosphodiesterases (PDEases) from a human monocyte cDNA library. One cDNA clone (hPDE-1) defines a large open reading frame of ca. 2.1 kilobases, predicting a 686-amino-acid, ca. 77-kilodalton protein which contains significant homology to both rat brain and Drosophila cAMP PDEases, especially within an internal conserved domain of ca. 270 residues. Amino acid sequence divergence exists at the NH2 terminus and also within a 40- to 100-residue domain near the COOH-terminal end. hPDE-1 hybridizes to a major 4.8-kilobase mRNA transcript from both human monocytes and placenta. The coding region of hPDE-1 was engineered for expression in COS-1 cells, resulting in the overproduction of cAMP PDEase activity. The hPDE-1 recombinant gene product was identified as a low-Km cAMP phosphodiesterase on the basis of several biochemical properties including selective inhibition by the antidepressant drug rolipram. Known inhibitors of other PDEases (cGMP-specific PDEase, cGMP-inhibited PDEase) had little or no effect on the hPDE-1 recombinant gene product. Human genomic Southern blot analysis suggests that this enzyme is likely to be encoded by a single gene. The presence of the enzyme in monocytes may be important for cell function in inflammation. Rolipram sensitivity, coupled with homology to the Drosophila cAMP PDEase, which is required for learning and memory in flies, suggests an additional function for this enzyme in neurobiochemistry.

We have cloned a Candida albicans gene, which encodes a cyclic nucleotide phosphodiesterase (PDEase), by complementation in a Saccharomyces cerevisiae PDEase-def icient mutant. The deduced amino acid sequence is similar to that of the low-affinity PDEase of 5. cerevisiae (PDEI) and the cyclic nucleotide PDEase (PD) of Dictyostelium discoideum. Biochemical analysis of recombinant protein produced in 5. cerevisiae indicated that the enzyme behaves as a PDEl homologue: it hydrolyses both cAMP (Km = 0.49 mM) and cGMP (K, = 0.25 mM), does not require divalent cations for maximal activity and is only moderately inhibited by millimolar concentrations of standard PDEase inhibitors. Based on these data, we designate the C. albicans we have cloned, PDEl . Low-stringency genomic Southern blots showed crosshybridization between C. albicans PDEl and DNA from Candida stellatoidea, but not with DNA from 5. cerevisiae or several closely related Candida species. 19406, USA