TPT sulfonate, a single, oral dose schistosomicidal prodrug: In vivo efficacy, disposition and metabolic profiling.

Treatment of schistosomiasis relies precariously on just one drug, praziquantel (PZQ). In the search for alternatives, 15 S-[2-(alkylamino)alkane] thiosulfuric acids were obtained from a previous research program and profiled in mice for efficacy against both mature (>42-day-old) and juvenile (21-day-old) Schistosoma mansoni using a screening dose of 100 mg/kg PO QDx4. One compound, S-[2-(tert-butylamino)-1-phenylethane] thiosulfuric acid (TPT sulfonate), was the most effective by decreasing female and male worm burdens by ≥ 90% and ≥46% (mature), and ≥89% and ≥79% (juvenile), respectively. In contrast, PZQ decreased mature female and male worm burdens by 95% and 94%, respectively, but was ineffective against juvenile stages. Against 7-day-old lung-stage worms, TPT sulfonate was only effective at twice the dose decreasing female and male burdens by 95 and 80%, respectively. Single oral doses at 400 and/or 600 mg/kg across various developmental time-points (1-, 7-, 15-, 21- and/or 42 day-old) were consistent with the QD x4 data; efficacy was strongest once the parasites had completed lung migration, and female and male burdens were decreased by at least 90% and 80%, respectively. In vitro, TPT sulfonate is inactive against the parasite suggesting a pro-drug mechanism of action. In mice, TPT sulfonate is fully absorbed and subject to rapid, non-CYP-mediated, first-pass metabolism that is initiated by desulfation and yields a series of metabolites. The initially-formed free thiol-containing metabolite, termed TP thiol, was chemically synthesized; it dose-dependently decreased S. mansoni and Schistosoma haematobium motility in vitro. Also, when administered as a single 50 mg/kg IP dose, TP thiol decreased 33-day-old S. mansoni female and male burdens by 35% and 44%, with less severe organomegaly. Overall, TPT sulfonate's efficacy profile is competitive with that of PZQ. Also, the characterization of a parasiticidal metabolite facilitates an understanding and improvement of the chemistry, and identification of the mechanism of action and/or target.

Identification and Optimization of Thienopyridine Carboxamides as Inhibitors of HIV Regulatory Complexes.

Viral regulatory complexes perform critical functions during virus replication and are important targets for therapeutic intervention. In HIV, the Tat and Rev proteins form complexes with multiple viral and cellular factors to direct transcription and export of the viral RNA. These complexes are composed of many proteins and are dynamic, making them difficult to fully recapitulate in vitro Therefore, we developed a cell-based reporter assay to monitor the assembly of viral complexes for inhibitor screening. We screened a small-molecule library and identified multiple hits that inhibit the activity of the viral complexes. A subsequent chemistry effort was focused on a thieno[2,3-b]pyridine scaffold, examples of which inhibited HIV replication and the emergence from viral latency. Notable aspects of the effort to determine the structure-activity relationship (SAR) include migration to the regioisomeric thieno[2,3-c]pyridine ring system and the identification of analogs with single-digit nanomolar activity in both reporter and HIV infectivity assays, an improvement of >100-fold in potency over the original hits. These results validate the screening strategy employed and reveal a promising lead series for the development of a new class of HIV therapeutics.

Capture of micrococcin biosynthetic intermediates reveals C-terminal processing as an obligatory step for in vivo maturation.

Thiopeptides, including micrococcins, are a growing family of bioactive natural products that are ribosomally synthesized and heavily modified. Here we use a refactored, modular in vivo system containing the micrococcin P1 (MP1) biosynthetic genes (TclIJKLMNPS) from Macrococcus caseolyticus str 115 in a genetically tractable Bacillus subtilis strain to parse the processing steps of this pathway. By fusing the micrococcin precursor peptide to an affinity tag and coupling it with catalytically defective enzymes, biosynthetic intermediates were easily captured for analysis. We found that two major phases of molecular maturation are separated by a key C-terminal processing step. Phase-I conversion of six Cys residues to thiazoles (TclIJN) is followed by C-terminal oxidative decarboxylation (TclP). This TclP-mediated oxidative decarboxylation is a required step for the peptide to progress to phase II. In phase II, Ser/Thr dehydration (TclKL) and peptide macrocycle formation (TclM) occurs. A C-terminal reductase, TclS, can optionally act on the substrate peptide, yielding MP1, and is shown to act late in the pathway. This comprehensive characterization of the MP1 pathway prepares the way for future engineering efforts.

Reconstitution and Minimization of a Micrococcin Biosynthetic Pathway in Bacillus subtilis.

UNLABELLED: Thiopeptides represent one of several families of highly modified peptide antibiotics that hold great promise for natural product engineering. These macrocyclic peptides are produced by a combination of ribosomal synthesis and extensive posttranslational modification by dedicated processing enzymes. We previously identified a compact, plasmid-borne gene cluster for the biosynthesis of micrococcin P1 (MP1), an archetypal thiopeptide antibiotic. In an effort to genetically dissect this pathway, we have reconstituted it in Bacillus subtilis Successful MP1 production required promoter engineering and the reassembly of essential biosynthetic genes in a modular plasmid. The resulting system allows for rapid pathway manipulation, including protein tagging and gene deletion. We find that 8 processing proteins are sufficient for the production of MP1 and that the tailoring enzyme TclS catalyzes a C-terminal reduction step that distinguishes MP1 from its sister compound micrococcin P2. IMPORTANCE: The emergence of antibiotic resistance is one of the most urgent human health concerns of our day. A crucial component in an integrated strategy for countering antibiotic resistance is the ability to engineer pathways for the biosynthesis of natural and derivatized antimicrobial compounds. In this study, the model organism B. subtilis was employed to reconstitute and genetically modularize a 9-gene system for the biosynthesis of micrococcin, the founding member of a growing family of thiopeptide antibiotics.

Intervention to decrease glyburide use in elderly patients with renal insufficiency.

OBJECTIVES: The objectives of this study were to describe changes in glyburide prescribing in cohorts that were and were not targeted by a risk reduction project, assess factors associated with glyburide discontinuation, and evaluate changes in glycated hemoglobin (ie, HbA(1c)) levels and rates of serious hypoglycemia. METHODS: This historical cohort study included a targeted cohort of 4368 outpatient veterans aged ≥65 years with active prescriptions for glyburide between April 1, 2007 and June 30, 2007 and serum creatinine (SCr) ≥2 mg/dL and a nontargeted cohort of 1886 outpatients meeting these same criteria between July 1, 2007 and September 3, 2007. The intervention in the risk reduction project took place on September 4, 2007 and entailed giving regional pharmacy leaders information about the increased risk of hypoglycemia with glyburide and the list of targeted patients for follow up with providers. For each patient, the study period was the time between the date they first met the eligibility criteria and March 31, 2008. All data were obtained from Veterans Affairs (VA) administrative databases. The primary outcome was the discontinuation of glyburide. Secondary outcomes were the change in HbA(1c) after stopping glyburide and the rate of serious hypoglycemia after intervention. RESULTS: Incidence rate ratios (IRRs) for glyburide discontinuation in targeted versus nontargeted cohorts were statistically significantly elevated in September (IRR 2.1; 95% CI 1.7-2.5), October (IRR 1.3; 95% CI 1.1-1.6), and November 2007 (IRR 1.4; 95% CI 1.1-1.7). The intervention, black race, SCr, Charlson comorbidity score, new glyburide use, and VA region were independently associated with discontinuation. Among patients in the targeted cohort who discontinued glyburide, mean (SD) HbA(1c) at baseline and after discontinuation were 7.17% (1.35%), and 7.22% (1.34%), respectively (P = 0.36). The hypoglycemia rates/1000 person-days were 0.093 before the intervention and 0.070 afterwards (P = 0.10). CONCLUSION: A one-time intervention in a risk reduction project decreased glyburide use over a 3-month period in elderly outpatients with renal insufficiency without compromising glucose control.

Simple one-pot synthesis of disulfide fragments for use in disulfide-exchange screening.

Disulfide exchange screening is a method for evaluating the binding of small molecule fragments to proteins that have at least one accessible cysteine. While operationally simple, it does require a large library of small fragment molecules bearing disulfide-containing side chains. These specialized fragments are not available commercially and this has limited the adoption of the method. We report here a convenient one-pot procedure that enables facile preparation of disulfide screening fragments while also producing less of an environmental impact. The new synthetic method involves the initial formation of symmetric disulfides, followed by a disulfide exchange reaction in which the symmetrical dimer is converted into the final screening fragment by introduction of a solubilizing 'cap'. The method is amenable to parallel synthetic methods and can be carried out in air without the need for the specialized equipment typically required for performing organic synthesis.

Turning a protein kinase on or off from a single allosteric site via disulfide trapping.

There is significant interest in identifying and characterizing allosteric sites in enzymes such as protein kinases both for understanding allosteric mechanisms as well as for drug discovery. Here, we apply a site-directed technology, disulfide trapping, to interrogate structurally and functionally how an allosteric site on the Ser/Thr kinase, 3-phosphoinositide-dependent kinase 1 (PDK1)--the PDK1-interacting-fragment (PIF) pocket--is engaged by an activating peptide motif on downstream substrate kinases (PIFtides) and by small molecule fragments. By monitoring pairwise disulfide conjugation between PIFtide and PDK1 cysteine mutants, we defined the PIFtide binding orientation in the PIF pocket of PDK1 and assessed subtle relationships between PIFtide positioning and kinase activation. We also discovered a variety of small molecule fragment disulfides (< 300 Da) that could either activate or inhibit PDK1 by conjugation to the PIF pocket, thus displaying greater functional diversity than is displayed by PIFtides conjugated to the same sites. Biochemical data and three crystal structures provided insight into the mechanism of action of the best fragment activators and inhibitors. These studies show that disulfide trapping is useful for characterizing allosteric sites on kinases and that a single allosteric site on a protein kinase can be exploited for both activation and inhibition by small molecules.

Structure-activity relationships of 9-substituted-9-dihydroerythromycin-based motilin agonists: optimizing for potency and safety.

A series of 9-dihydro-9-acetamido-N-desmethyl-N-isopropyl erythromycin A analogues and related derivatives was generated as motilin agonists. The compounds were optimized for potency while showing both minimal antibacterial activity and hERG inhibition. As the substituent on the amide was increased in lipophilicity the potency and hERG inhibition increased, while polar groups lowered potency, without significantly impacting hERG inhibition. The N-methyl acetamide 7a showed the optimal in vitro profile and was probed further by varying the chain length to the macrocycle as well as changing the macrocycle scaffold. 7a remained the compound with the best in vitro properties.

Preparation of erythromycin analogs having functional groups at C-15.

Chemobiosynthesis has been used to prepare analogs of erythromycins having unique functional groups at the 15-position. Using diketide thioester feeding to genetically engineered Streptomyces coelicolor, analogs of 6-deoxyerythronolide B were prepared having 15-fluoro, 15-chloro, and 15-azido groups. Bioconversion using a genetically engineered mutant of Saccharopolyspora erythraea was used to produce 15-fluoroerythromycin A and 15-azidoerythromycin A. These new erythromycin analogs provide antibacterial macrolides with unique physicochemical properties and functional groups that allow for selective derivatization.

A series of 23,24-dihydrodiscodermolide analogues with simplified lactone regions.

A collection of seven new 23,24-dihydrodiscodermolide analogues have been synthesized with modifications to the lactone ring, some of which show antiproliferative activities similar to discodermolide.

Toward understanding how the lactone moiety of discodermolide affects activity.

A series of simplified discodermolide analogues have been designed and synthesized in an attempt to understand the role of the lactone ring. These synthetic efforts have led to an unsubstituted butyrolactone 9 being generated, which shows improved activity over the natural product.

Design, synthesis, and evaluation of analogues of (+)-14-normethyldiscodermolide.

[Structure: see text] The design, syntheses, and biological evaluation of nine totally synthetic analogues of the microtubule-stabilizing agent (+)-14-normethyldiscodermolide (2) are reported. Simplification at the C(21)-C(24) terminal diene and at the C(1)-C(5) lactone moieties reveals significant structure-activity relationships.

Design, synthesis, and evaluation of carbamate-substituted analogues of (+)-discodermolide.

[Structure: see text] The design, syntheses, and biological evaluation of 22 totally synthetic analogues of the potent microtubule-stabilizing agent (+)-discodermolide (1) have been achieved. Structure-activity relationships of the C(19) carbamate were defined, exploiting two synthetically simplified scaffolds, as well as the parent (+)-discodermolide framework.

Design, synthesis and cytotoxicity of 7-deoxy aryl discodermolide analogues.

A series of 7-deoxy discodermolide analogues in which the lactone fragment 'C' was replaced by aryl substituents were designed, synthesized, and evaluated for cytotoxicity.

Saccharopolyspora erythraea-catalyzed bioconversion of 6-deoxyerythronolide B analogs for production of novel erythromycins.

A method was developed for the large-scale bioconversion of novel 6-deoxyerythronolide B (6-dEB) analogs into erythromycin analogs. Erythromycin biosynthesis in Saccharopolyspora erythraea proceeds via the formation of a polyketide aglycone, 6-dEB, which is subsequently glycosylated, hydroxylated and methylated to yield the antibiotic erythromycin A. A modular polyketide synthase (PKS) directs 6-dEB synthesis using a dedicated set of active sites for the condensation of each of seven propionate units. Strategies based on genetic manipulation and precursor feeding are available for the efficient generation of novel 6-dEB analogs using a plasmid-based system in Streptomyces coelicolor. 6-dEB and 13-substituted 6-dEB analogs produced in this manner were fed to S. erythraea mutants which could not produce 6-dEB, yet retained their 6-dEB modification systems, and resulted in the generation of erythromycin A and 13-substituted erythromycin A analogs. Erythromycin B, C and D analogs were observed as intermediates of the process. Dissolved oxygen, temperature, the specific aglycone feed concentration, and pH were found to be important for obtaining a high yield of erythromycin A analogs. Cultivation conditions were identified which resulted in the efficient bioconversion of 6-dEB analogs into erythromycin A analogs, which this process demonstrated at the 100 l scale.