Abstract The novel boron-containing compound, AN2728, is being investigated in phase 3 trials for atopic dermatitis treatment. It exerts its anti-inflammatory effect by inhibiting phosphodiesterase-4 (PDE4), which catalyzes the breakdown of cAMP to AMP. AN2728 competes with cAMP to inhibit the PDE4B1-catalytic domain with Ki of 173±26 nM; thus AN2728 interacts at the enzyme-active site. The X-ray structure of PDE4B-catalytic domain with AN2728 and its structural relative AN2898 reveals that the boron atom interacts with the bimetal center and occupies a position in the catalytic site similar to that of the cAMP phosphate. AN2728 has good affinity across PDE4 gene products A-D. Its selective affinity for PDE4 is 4-10-fold greater than its affinity for PDE1, 2, 3A, 6, or 7B. It is inactive on PDE3B, 5, 7A1, and 8-11. AN2728 activity increases intracellular cAMP and activates PKA, followed by phosphorylation and negative regulation of various cytokine transcription factors. AN2728 inhibits production of specific cytokines with a pattern similar to that of other established PDE4 inhibitors and distinct from those of a glucocorticoid and calcineurin inhibitor. To investigate reactivity against other targets, AN2728 was tested against a set of 50 receptors and ligand-gated ion channels for inhibition at 10 µM. Inhibition was <25% for all receptors; thus, AN2728 is specific for PDE4 and appears to exert an anti-inflammatory effect through inhibition of inflammatory cytokine production.
Approximately one-third of the world's population carries Staphylococcus aureus. The recent emergence of extreme drug resistant strains that are resistant to the "antibiotic of last resort", vancomycin, has caused a further increase in the pressing need to discover new drugs against this organism. The S. aureus enoyl reductase, saFabI, is a validated target for drug discovery. To drive the development of potent and selective saFabI inhibitors, we have studied the mechanism of the enzyme and analyzed the interaction of saFabI with triclosan and two related diphenyl ether inhibitors. Results from kinetic assays reveal that saFabI is NADPH-dependent, and prefers acyl carrier protein substrates carrying fatty acids with long acyl chains. On the basis of product inhibition studies, we propose that the reaction proceeds via an ordered sequential ternary complex, with the ACP substrate binding first, followed by NADPH. The interaction of NADPH with the enzyme has been further explored by site-directed mutagenesis, and residues R40 and K41 have been shown to be involved in determining the specificity of the enzyme for NADPH compared to NADH. Finally, in preliminary inhibition studies, we have shown that triclosan, 5-ethyl-2-phenoxyphenol (EPP), and 5-chloro-2-phenoxyphenol (CPP) are all nanomolar slow-onset inhibitors of saFabI. These compounds inhibit the growth of S. aureus with MIC values of 0.03–0.06 µg/mL. Upon selection for resistance, three novel safabI mutations, A95V, I193S, and F204S, were identified. Strains containing these mutations had MIC values ∼100-fold larger than that of the wild-type strain, whereas the purified mutant enzymes had Ki values 5−3000-fold larger than that of wild-type saFabI. The increase in both MIC and Ki values caused by the mutations supports the proposal that saFabI is the intracellular target for the diphenyl ether-based inhibitors.
A synthetic chimeric IL-2/IL-6 gene was synthesized to engineer a bifunctional lymphokine which was overproduced in Escherichia coli. Following denaturation of the inclusion bodies in 6 M guanidine and refolding and reoxidation in the presence of a redox system, the fusion protein (rIL-2/IL-6) was purified to homogeneity and shown to react with both monospecific anti-IL-2 and anti-IL-6 antisera. A collagen-like spacer was introduced between the two cytokine moieties to generate IL-2 and IL-6 molecules upon collagenase digestion. After cleavage, the two subunits, purified in a single-step procedure, were found to be correctly reoxidized and functionally as active as their native counterparts. Circular dichroism studies of rIL-2/IL-6 revealed that both cytokine subunits refolded independently and exhibited the a-helical structures characteristic of the corresponding wild-type lymphokines. The chimera displayed full IL-2 activity in the CTLL-2 cell proliferation assay. It also retained the IL-6 property to enhance lgM synthesis in SKW6.4 cells, induce the proliferation of B-cell hybridomas and stimulate the production of fibrinogen in hepatocytes. Because IL-2 amplifies the cellular immune response and IL-6 up-regulates the humoral response, this bifunctional lyinphokine represents a potentially useful therapeutic adduct and may serve as an immunomodulator to enhance the host's response to vaccination.
Background Reliance on just one drug to treat the prevalent tropical disease, schistosomiasis, spurs the search for new drugs and drug targets. Inhibitors of human cyclic nucleotide phosphodiesterases (huPDEs), including PDE4, are under development as novel drugs to treat a range of chronic indications including asthma, chronic obstructive pulmonary disease and Alzheimer's disease. One class of huPDE4 inhibitors that has yielded marketed drugs is the benzoxaboroles (Anacor Pharmaceuticals). Methodology/Principal findings A phenotypic screen involving Schistosoma mansoni and 1,085 benzoxaboroles identified a subset of huPDE4 inhibitors that induced parasite hypermotility and degeneration. To uncover the putative schistosome PDE4 target, we characterized four PDE4 sequences (SmPDE4A-D) in the parasite's genome and transcriptome, and cloned and recombinantly expressed the catalytic domain of SmPDE4A. Among a set of benzoxaboroles and catechol inhibitors that differentially inhibit huPDE4, a relationship between the inhibition of SmPDE4A, and parasite hypermotility and degeneration, was measured. To validate SmPDE4A as the benzoxaborole molecular target, we first generated Caenorhabditis elegans lines that express a cDNA for smpde4a on a pde4(ce268) mutant (hypermotile) background: the smpde4a transgene restored mutant worm motility to that of the wild type. We then showed that benzoxaborole inhibitors of SmPDE4A that induce hypermotility in the schistosome also elicit a hypermotile response in the C. elegans lines that express the smpde4a transgene, thereby confirming SmPDE4A as the relevant target. Conclusions/Significance The orthogonal chemical, biological and genetic strategies employed identify SmPDE4A's contribution to parasite motility and degeneration, and its potential as a drug target. Transgenic C. elegans is highlighted as a potential screening tool to optimize small molecule chemistries to flatworm molecular drug targets.
Psoriasis and atopic dermatitis are skin diseases affecting millions of patients. Here, we characterize benzoxaborole phosphodiesterase (PDE)-4 inhibitors, a new topical class that has demonstrated therapeutic benefit for psoriasis and atopic dermatitis in phase 2 or phase 3 studies. Crisaborole [AN2728, 4-((1-hydroxy-1,3-dihydrobenzo[c][1,2]oxaborol-5-yl)oxy)benzonitrile], compd2 [2-ethoxy-6-((1-hydroxy-1,3-dihydrobenzo[c][1,2]oxaborol-5-yl)oxy)nicotinonitrile], compd3 [6-((1-hydroxy-1,3-dihydrobenzo[c][1,2]oxaborol-5-yl)oxy)-2-(2-isopropoxyethoxy)nicotinonitrile], and compd4 [5-chloro-6-((1-hydroxy-1,3-dihydrobenzo[c][1,2]oxaborol-5-yl)oxy)-2-((4-oxopentyl)oxy)nicotinonitrile] are potent PDE4 inhibitors with similar affinity for PDE4 isoforms and equivalent inhibition on the catalytic domain and the full-length enzyme. These benzoxaboroles are less active on other PDE isozymes. Compd4 binds to the catalytic domain of PDE4B2 with the oxaborole group chelating the catalytic bimetal and overlapping with the phosphate in cAMP during substrate hydrolysis, and the interaction extends into the adenine pocket. In cell culture, benzoxaborole PDE4 inhibitors suppress the release of tumor necrosis factor-α, interleukin (IL)-23, IL-17, interferon-γ, IL-4, IL-5, IL-13, and IL-22, and these cytokines contribute to the pathologic changes in skin structure and barrier functions as well as immune dysregulation in atopic dermatitis and psoriasis. Treatment with compd3 or N6,2′-O-dibutyryladenosine 3′,5′-cyclic monophosphate increases cAMP response element binding protein phosphorylation in human monocytes and decreases extracellular signal-regulated kinase phosphorylation in human T cells; these changes lead to reduced cytokine production and are among the mechanisms by which compd3 blocks cytokine release. Topical compd3 penetrates the skin and suppresses phorbol myristate acetate–induced IL-13, IL-22, IL-17F, and IL-23 transcription and calcipotriol-induced thymic stromal lymphopoietin expression in mouse skin. Skin thinning is a major dose-limiting side effect of glucocorticoids. By contrast, repeated application of compd3 did not thin mouse skin. These findings show the potential benefits and safety of benzoxaborole PDE4 inhibitors for the treatment of psoriasis and atopic dermatitis.
Across several cancer types, activated transforming growth factor-β (TGFb) helps support an immuno-suppressive microenvironment that contributes to immune checkpoint blockade (ICB) resistance and treatment failure. Alpha-V integrins, specifically αVβ8, αVβ6 and αVβ1, are the primary activators of TGFb from the latent complex. These integrins have a limited cell-expression profile that make them potential targets to safely and potently inhibit the activation of TGFb in cancer. Targeting αVβ8 has recently emerged as a promising approach to realizing the potential of anti-TGFb therapies to address ICB resistance. In the stroma, integrin αVβ1 is the major source of activated TGFb. Here, we describe the development of PLN-1095, a dual small molecule inhibitor of αVβ8 and αVβ1 and characterize this approach in ICB-resistant mouse tumor models.
Methods
In vivo efficacy and activities of a dual αVβ8 and αVβ1 integrin inhibitor, PLN-1095, in combination with anti-programmed death receptor-1 antibody (anti mPD-1) was evaluated in EMT6, Pan02, and CT26 cancer syngeneic mouse models by monitoring animal survival, tumor growth, gene expression, and infiltrating CD8+ lymphocytes. In addition, PLN-1095 single agent proinflammatory and antifibrotic activities was assessed using mouse EMT6 tumors in vivo and human breast tumor tissues ex vivo.
Results
PLN-1095 showed selective inhibition of integrins αVβ8 and αVβ1 at nanomolar concentrations. Treatment of mice bearing EMT6 tumors with PLN-1095 alone and in combination with anti-mPD-1 significantly reduced tumor growth. Anti-mPD-1 treatment showed a peripherally restricted CD8+ and CD4+ pattern, whereas PLN-1095 treatment significantly increased intra-tumoral CD8+ T cell infiltration. PLN-1095 treatment, both alone and in combination with anti-mPD-1 was associated with elevated gene expression of CXCL9 and other pro-inflammatory cytokines, enhanced expression of genes involved in antigen presentation, reduced TGFβ signaling, diminished expression of pro-fibrogenic and angiogenic transcripts across the models tested. A significant increase in granzyme B positive T cells was observed in human breast cancer tissues treated with PLN-1095 ex vivo.
Conclusions
PLN-1095 sensitized immunologically cold murine tumors to anti mPD-1 ICB. PLN-1095-mediated inhibition of integrins αVβ8 and αVβ1 effectively reduced the immunosuppressive effects of TGFβ by activating the immune system thereby promoting CD8+ cytotoxic T cell infiltration in the tumors. Based on these results, a first-in-human clinical trial investigating the effects of PLN-1095 is being planned.
Ethics Approval
All the animal Studies were approved by Pliant IACUC protocol # PLI-010-2019. Fresh breast tumor samples were collected from the Biological Resource Center of the Centre Léon Bérard by Marie's laboratory, according to the institutional review board and ethics committee and with fully informed patient consent (French Ministry of Research agreement number: AC-2013-1871 and AC-2019-3426).
Gram-negative bacteria cause approximately 70% of the infections in intensive care units. A growing number of bacterial isolates responsible for these infections are resistant to currently available antibiotics and to many in development. Most agents under development are modifications of existing drug classes, which only partially overcome existing resistance mechanisms. Therefore, new classes of Gram-negative antibacterials with truly novel modes of action are needed to circumvent these existing resistance mechanisms. We have previously identified a new a way to inhibit an aminoacyl-tRNA synthetase, leucyl-tRNA synthetase (LeuRS), in fungi via the oxaborole tRNA trapping (OBORT) mechanism. Herein, we show how we have modified the OBORT mechanism using a structure-guided approach to develop a new boron-based antibiotic class, the aminomethylbenzoxaboroles, which inhibit bacterial leucyl-tRNA synthetase and have activity against Gram-negative bacteria by largely evading the main efflux mechanisms in Escherichia coli and Pseudomonas aeruginosa. The lead analogue, AN3365, is active against Gram-negative bacteria, including Enterobacteriaceae bearing NDM-1 and KPC carbapenemases, as well as P. aeruginosa. This novel boron-based antibacterial, AN3365, has good mouse pharmacokinetics and was efficacious against E. coli and P. aeruginosa in murine thigh infection models, which suggest that this novel class of antibacterials has the potential to address this unmet medical need.
African trypanosomiasis, caused by the proto zoal pathogen Trypanosoma brucei (T. brucei), is one of the most neglected tropical diseases that are in great need of new drugs. We report the design and synthesis of T. brucei leucyl-tRNA synthetase (TbLeuRS) inhibitors and their structure−activity relationship. Benzoxaborole was used as the core structure and C(6) was modified to achieve improved affinity based on docking results that showed further binding space at this position. Indeed, compounds with C(7) substitutions showed diminished activity due to clash with the eukaryote specific I4ae helix while substitutions at C(6) gave enhanced affinity. TbLeuRS inhibitors with IC50 as low as 1.6 μM were discovered, and the structure−activity relationship was discussed. The most potent enzyme inhibitors also showed excellent T. brucei parasite growth inhibition activity. This is the first time that TbLeuRS inhibitors are reported, and this study suggests that leucyl-tRNA synthetase (LeuRS) could be a potential target for antiparasitic drug development.
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