Prospective discovery of small molecule enhancers of an E3 ligase-substrate interaction

Protein-protein interactions (PPIs) governing the recognition of substrates by E3 ubiquitin ligases are critical to cellular function. There is significant therapeutic potential in the development of small molecules that modulate these interactions; however, rational design of small molecule enhancers of PPIs remains elusive. Herein, we report the prospective identification and rational design of potent small molecules that enhance the interaction between an oncogenic transcription factor, β-Catenin, and its cognate E3 ligase, SCF^β-TrCP. These enhancers potentiate the ubiquitylation of mutant β-Catenin by β-TrCP in vitro and induce the degradation of an engineered mutant β-Catenin in a cellular system. Distinct from PROTACs, these drug-like small molecules insert into a naturally occurring PPI interface, with contacts optimized for both the substrate and ligase within the same small molecule entity. The prospective discovery of 'molecular glue' presented here provides a paradigm for the development of small molecule degraders targeting hard-to-drug proteins.

Orally Absorbed Derivatives of the β-Lactamase Inhibitor Avibactam. Design of Novel Prodrugs of Sulfate Containing Drugs

Only one FDA-approved β-lactamase inhibitor has ever been orally available: clavulanic acid, approved in 1984. Avibactam, approved by FDA in 2015, is the first of a new class of BLIs called diazabicyclooctanes, or "DBOs". This class has much broader coverage than clavulanic acid but can only be administered by intravenous injection. Herein, we describe the synthesis and testing of the first approved BLI to be rendered orally bioavailable since clavulanic acid (1984).

A tele-otology course for primary care providers

The shortage of otolaryngologists and the high incidence of ear disease in remote areas are major problems in Australia. We have developed a multimedia course for primary care providers that incorporates material about ear anatomy and physiology, ear disease, video-otoscopy and telemedicine software. The computer-based course was followed by a practical one-day course. A multiple-choice test was given to participants before and at the end of the course and a form was used to record feedback. The course was conducted with 30 aboriginal health workers. The participants were able to obtain images of reasonable to good quality after a short period of training. There was an average improvement of about 25% in the test scores, and the feedback regarding the course was extremely positive. The CD-ROM and the Website provide a valuable resource to assist primary care providers in their care of patients with ear disorders.

Discovery of a novel potent GABA(B) receptor agonist

Structure-activity studies have led to a discovery of 3-(4-pyridyl)methyl ether derivative 9d that has 25- to 50-fold greater functional potency than R-baclofen at human and rodent GABA(B) receptors in vitro. Mouse hypothermia studies confirm that this compound crosses the blood-brain barrier and is approximately 50-fold more potent after systemic administration.

Arbaclofen placarbil, a novel R-baclofen prodrug: improved absorption, distribution, metabolism, and elimination properties compared with R-baclofen

Baclofen is a racemic GABA(B) receptor agonist that has a number of significant pharmacokinetic limitations, including a narrow window of absorption in the upper small intestine and rapid clearance from the blood. Arbaclofen placarbil is a novel transported prodrug of the pharmacologically active R-isomer of baclofen designed to be absorbed throughout the intestine by both passive and active mechanisms via the monocarboxylate type 1 transporter. Arbaclofen placarbil is rapidly converted to R-baclofen in human and animal tissues in vitro. This conversion seems to be primarily catalyzed in human tissues by human carboxylesterase-2, a major carboxylesterase expressed at high levels in various tissues including human intestinal cells. Arbaclofen placarbil was efficiently absorbed and rapidly converted to R-baclofen after oral dosing in rats, dogs, and monkeys. Exposure to R-baclofen was proportional to arbaclofen placarbil dose, whereas exposure to intact prodrug was low. Arbaclofen placarbil demonstrated enhanced colonic absorption, i.e., 5-fold higher R-baclofen exposure in rats and 12-fold higher in monkeys compared with intracolonic administration of R-baclofen. Sustained release formulations of arbaclofen placarbil demonstrated sustained R-baclofen exposure in dogs with bioavailability up to 68%. In clinical use, arbaclofen placarbil may improve the treatment of patients with gastroesophageal reflux disease, spasticity, and numerous other conditions by prolonging exposure and decreasing the fluctuations in plasma levels of R-baclofen.

Validation of tele-otology to diagnose ear disease in children

OBJECTIVE

To determine if digitised still eardrum images, with a clinical history, and audiometry and tympanometry data provide sufficient information to an ear specialist to make an assessment of a patient.

METHODS

66 children (9 months to 16 years) from remote communities were assessed by an ear specialist by standard otoscopy, using a clinical history, audiometry and tympanometry. Up to five images of each ear were digitised. At a later date, the ear specialist made observations, diagnoses and recommendations for management from the images and clinical data.

RESULTS

There was a significant correlation (p<0.01) between image quality and age of the subject. There were significant agreements for the clinically important observations of otorrhea, perforation, retracted tympanic membrane and atrophy of the tympanic membrane (p<0.05). There were significant agreements for the diagnoses of acute otitis media, chronic suppurative otitis media, otitis media with effusion and Eustachian tube dysfunction. The rate of recommendations for review or referral after a tele-otology assessment were between 4 and 16% higher than those in made in the field. The agreements between the various forms of advice or recommendations made in the field to those made by tele-otology were statistically significant (p<0.01).

CONCLUSIONS

A tele-otology system that incorporates good quality digitised images of the tympanic membrane, audiological and tympanometric data, and a comprehensive clinical history provides the ear specialist with sufficient information to make a confident diagnose of existing middle ear disease, and provide management advice to the patients' primary care provider.

Synthesis and biological evaluation of novel steroidal pyrazoles as substrates for bile acid transporters

A series of novel steroidal pyrazoles was synthesized as substrates for bile acid transporters to explore their potential as drug carriers. The selected pyrazole fused bile acids were further conjugated with drugs and drug surrogates. Their in vitro transport activities were evaluated in human ileal bile acid transporter (hIBAT) and human liver bile acid transporter (hLBAT) expressing Chinese hamster ovary (CHO)-cells and Xenopus laevis oocytes. The results of synthetic efforts and transporter assays studies are described herein.

XP13512 [(+/-)-1-([(alpha-isobutanoyloxyethoxy)carbonyl] aminomethyl)-1-cyclohexane acetic acid], a novel gabapentin prodrug: II. Improved oral bioavailability, dose proportionality, and colonic absorption compared with gabapentin in rats and monkeys

The absorption of gabapentin (Neurontin) is dose-dependent and variable between patients. Rapid clearance of the drug necessitates dosing three or more times per day to maintain therapeutic levels. These deficiencies appear to result from the low capacity, limited intestinal distribution, and variable expression of the solute transporter responsible for gabapentin absorption. Saturation of this transporter at doses used clinically leads to unpredictable drug exposure and potentially ineffective therapy in some patients. XP13512 [(+/-)-1-([(alpha-isobutanoyloxyethoxy)carbonyl]aminomethyl)-1-cyclohexane acetic acid] is a novel prodrug of gabapentin designed to be absorbed by high-capacity nutrient transporters located throughout the intestine. XP13512 was efficiently absorbed and rapidly converted to gabapentin after oral dosing in rats and monkeys. Exposure to gabapentin was proportional to prodrug dose, whereas exposure to intact XP13512 was low. In rats, >95% of an oral dose of (14)C-XP13512 was excreted in urine in 24 h as gabapentin. In monkeys, oral bioavailability of gabapentin from XP13512 capsules was 84.2% compared with 25.4% after a similar oral Neurontin dose. Compared with intracolonic gabapentin, intracolonic XP13512 gave a 17-fold higher gabapentin exposure in rats and 34-fold higher in monkeys. XP13512 may therefore be incorporated into a sustained release formulation to provide extended gabapentin exposure. XP13512 demonstrated improved gabapentin bioavailability, increased dose proportionality, and enhanced colonic absorption. In clinical use, XP13512 may improve the treatment of neuropathic pain, epilepsy, and numerous other conditions by increasing efficacy, reducing interpatient variability, and decreasing frequency of dosing.

XP13512 [(+/-)-1-([(alpha-isobutanoyloxyethoxy)carbonyl] aminomethyl)-1-cyclohexane acetic acid], a novel gabapentin prodrug: I. Design, synthesis, enzymatic conversion to gabapentin, and transport by intestinal solute transporters

Gabapentin is thought to be absorbed from the intestine of humans and animals by a low-capacity solute transporter localized in the upper small intestine. Saturation of this transporter at doses used clinically leads to dose-dependent pharmacokinetics and high interpatient variability, potentially resulting in suboptimal drug exposure in some patients. XP13512 [(+/-)-1-([(alpha-isobutanoyloxyethoxy)carbonyl] aminomethyl)-1-cyclohexane acetic acid] is a novel prodrug of gabapentin designed to be absorbed throughout the intestine by high-capacity nutrient transporters. XP13512 was stable at physiological pH but rapidly converted to gabapentin in intestinal and liver tissue from rats, dogs, monkeys, and humans. XP13512 was not a substrate or inhibitor of major cytochrome P450 isoforms in transfected baculosomes or liver homogenates. The separated isomers of XP13512 showed similar cleavage in human tissues. The prodrug demonstrated active apical to basolateral transport across Caco-2 cell monolayers and pH-dependent passive permeability across artificial membranes. XP13512 inhibited uptake of (14)C-lactate by human embryonic kidney cells expressing monocarboxylate transporter type-1, and direct uptake of prodrug by these cells was confirmed using liquid chromatography-tandem mass spectrometry. XP13512 inhibited uptake of (3)H-biotin into Chinese hamster ovary cells overexpressing human sodium-dependent multivitamin transporter (SMVT). Specific transport by SMVT was confirmed by oocyte electrophysiology studies and direct uptake studies in human embryonic kidney cells after tetracycline-induced expression of SMVT. XP13512 is therefore a substrate for several high-capacity absorption pathways present throughout the intestine. Therefore, administration of the prodrug should result in improved gabapentin bioavailability, dose proportionality, and colonic absorption compared with administration of gabapentin.

Evaluation of video-otoscopes suitable for tele-otology

The objectives of this study were to assess the quality of digitized video-otoscopes as well as its ease of use and safety. Four video-otoscopes available in Australia were used to image 96 patients. At least 22 patients (age range 5-70 years) were imaged with each video-otoscope, and the images were stored in a JPEG format. Three experienced otolaryngologists assessed all images for quality, clarity, color accuracy, orientation of eardrum and therefore ability to make a definitive diagnosis. The grading was a five-level scale: poor, adequate, good, very good and excellent. Two telescope systems produced high quality images (>80% were adequate or better), essential for accurate diagnosis, but both were associated with increased risk for injury in unskilled hands. The MedRx video-otoscope produced high-quality images (87% were adequate or better), while the Welch Allyn Compact Video-otoscope produced poor image quality (only 40% were adequate or better). Both devices were seen to be safer to use than the telescope systems. The telescope systems and MedRx otoscope provided optimum quality images necessary for tele-otology. However, the telescope units were considered to be unsafe in unskilled hands. The MedRx can be recommended as a safe device producing high-quality images.

Agonists of the Follicle Stimulating Hormone Receptor from an Encoded Thiazolidinone Library

The design, synthesis, characterization, and screening of a large, encoded thiazolidinone library are described. Three sets of 35 building blocks were combined by encoded split-pool synthesis to give a library containing more than 42 000 members. Building block selection was based in part on a novel small molecule follicle stimulating hormone receptor agonist hit and in part for diversity. HPLC/MS techniques were applied at the single-bead level to build confidence in the reliability of library construction. Application of two distinct screening strategies resulted in the identification of compounds with significantly improved potency over the initial hit. This work demonstrates the versatility of encoded libraries for preparing a large number of analogues of a given hit while simultaneously generating a large collection of compounds for screening against other targets.

Synthetic Compound Libraries Displayed on the Surface of Encoded Bacteriophage

We describe a technology for attaching libraries of synthetic compounds to coat proteins of bacteriophage particles such that the identity of the chemical structure is encoded in the genome of the phage, analogous to peptides displayed on phage surfaces by conventional phage-display techniques. This format allows a library of synthetic compounds to be screened very efficiently as a single pool. Encoded phage serve as extremely robust reporters of the presence of each compound, providing exquisite sensitivity for identification of active compounds engaged in complex biological processes such as receptor-mediated endocytosis and transcytosis. To evaluate this approach, we constructed a library of 980 analogs of folic acid displayed on T7 phage, and demonstrated rapid identification of compounds that bind to folate receptor and direct endocytosis of associated phage particles into cells that express the targeted receptor.

Stereoselective Solid-Phase Synthesis of a Triaza Tricyclic Ring System: A New Chemotype for Lead Discovery

Sequential pyrrolidine and hydantoin ring-forming reactions have been applied in the stereoselective solid-phase synthesis of a conformationally constrained, tricyclic triazacyclopenta[c]pentalene scaffold. These novel compounds share the structural complexity characteristic of certain alkaloid natural products and represent a source of chemical diversity that complements more traditional classes of heterocyclic compounds of interest as potential pharmaceutical agents. They are assembled in a 12-step reaction sequence from 4 variable building blocks by combining an intramolecular azomethine ylide cycloaddition reaction with a final cyclative cleavage from resin.

Exploring structure-activity relationships around the phosphomannose isomerase inhibitor AF14049 via combinatorial synthesis

Phosphomannose Isomerase (PMI) has been shown by genetic methods to be an essential enzyme in fungal cell wall biosynthesis. The PMI inhibitor AF14049 was discovered as an unanticipated side product from high-throughput library screening against the enzyme from C, albicans. Solid-phase synthetic methods were developed and a series of libraries and discrete analogs synthesized to explore SAR around AF14049.

New methods for analyzing compounds on polymeric supports

Beyond specialized applications in peptide and oligonucleotide synthesis, widespread utilization of solid-phase methods in organic chemistry has been hampered by a lack of powerful analytical methods for characterization of polymer-supported compounds. The advent of combinatorial organic synthesis has recently spawned efforts to develop spectroscopic techniques such as infrared spectrometry, mass spectrometry and nuclear magnetic resonance as routine tools for structure elucidation in solid-phase synthesis.

Encoded combinatorial chemistry: synthesis and screening of a library of highly functionalized pyrrolidines

The application of a new encoding technology for drug discovery is described. A combinatorial library of mercaptoacyl pyrrolidines has been prepared on a beaded polymeric support. Each polymer bead carries one library constituent in association with an oligomeric "tag," the structure of which is a record of the specific reagents from which that library member was prepared. After the ligands were solubilized, an array of such beads was screened for angiotensin-converting enzyme inhibitory activity, and the structures of active pyrrolidines were deduced by analysis of the associated tags at sub-picomole levels. Several extremely potent enzyme inhibitors were identified, many from multiple beads. The most potent inhibitor was found to have a Ki of 160 pM, approximately 3-fold more active than captopril in the same assay. Direct comparison with iterative deconvolution shows that the encoded screening strategy is a much more efficient means for extracting information from such compound collections, producing more data on a larger number of active structures.

Versatile approach to encoding combinatorial organic syntheses using chemically robust secondary amine tags

Encoded combinatorial organic synthesis has recently emerged as a powerful tool for the discovery of biologically active compounds from complex chemical libraries. This report describes a new encoding methodology that uses chemically robust secondary amines as tags. These amines are incorporated into an N-[(dialkylcarbamoyl)methyl]glycine-coding oligomer through simple chemistry that is compatible with a wide range of polymer-supported transformations useful in combinatorial synthesis. In the decoding process acidic hydrolysis of the tagging polymer regenerates the secondary amines, which after dansylation are resolved and detected at sub-picomole levels by reversed-phase HPLC. The versatility of this strategy is demonstrated here by encoded syntheses of members of several representative heterocyclic compound classes, including beta-lactams, 4-thiazolidinones, and pyrrolidines.

Strategies for the synthesis and screening of glycoconjugates. 2. Covalent immobilization for flow cytometry

Glycosylamines are readily available carbohydrate derivatives that undergo acylation reactions with homobifunctional N-hydroxysuccinimidyl esters. The product glycosylamides carry a spacer group equipped with one active ester functionality. This route provides well-defined glycoconjugates, which may be cross-linked to various amino-functionalized resins. Carbohydrate recognition of the resulting sugar-bead conjugates is probed by lectin immunostaining or flow cytometry using a fluorescently labeled lectin.

Strategies for the synthesis and screening of glycoconjugates. 1. A library of glycosylamines

A simple one-step procedure is found to be highly effective for the "functionalization" of glycodiversity. This study encompasses 50 unprotected mono- and oligosaccharides, which are subjected to Kochetkov aminations in saturated aqueous ammonium carbonate. The reaction allows for the stereo- and regioselective introduction of an amino group into all oligosaccharides tested, as well as into a great variety of monosaccharides including charged species. The resulting unprotected glycosylamines are stable compounds, and the inherent amino group provides a convenient site for chemoselective conjugation and modification as described in the following paper in this issue.

Generation and screening of an oligonucleotide-encoded synthetic peptide library

We have prepared a library of approximately 10(6) different peptide sequences on small, spherical (10-microns diameter) beads by the combinatorial chemical coupling of both L- and D-amino acid building blocks. To each bead is covalently attached many copies of a single peptide sequence and, additionally, copies of a unique single-stranded oligonucleotide that codes for that peptide sequence. The oligonucleotide tags are synthesized through a parallel combinatorial procedure that effectively records the process by which the encoded peptide sequence is assembled. The collection of beads was screened for binding to a fluorescently labeled anti-peptide antibody using a fluorescence-activated cell sorting instrument. Those beads to which the antibody bound tightly were isolated by fluorescence-activated sorting, and the oligonucleotide identifiers attached to individual sorted beads were amplified by the PCR. Sequences of the amplified DNAs were determined to reveal the identity of peptide sequences that bound to the antibody with high affinity. By combining the capacity for information storage in an oligonucleotide code with the tremendous level of amplification possible through the PCR, we have devised a means for specifying the identity of each member of a vast library of molecules synthesized from both natural and unnatural chemical building blocks. In addition, we have shown that the use of flow cytometry instrumentation permits facile isolation of individual beads that bear high-affinity ligands for biological receptors.

Peptide ligands for a sugar-binding protein isolated from a random peptide library

Peptide ligands for the carbohydrate-binding protein concanavalin A (Con A) have been identified by screening a large, diverse peptide library expressed on the surface of filamentous phage. A dodecapeptide containing the consensus sequence Tyr-Pro-Tyr was found to bind Con A with an affinity (dissociation constant, Kd) of 46 microM, comparable to that of a known carbohydrate ligand, methyl alpha-D-mannopyranoside (Kd of 89 microM). In addition the peptide inhibited precipitation of the alpha-glucan dextran 1355 by Con A. Given the complexity of oligosaccharide synthesis, the prospect of finding peptides that competitively inhibit carbohydrate-specific receptors may simplify the development of new therapeutic agents.