Metabolism and disposition of the SGLT2 inhibitor bexagliflozin in rats, monkeys and humans.

Bexagliflozin is a C-aryl glucoside inhibitor of human sodium-glucose linked transporter 2 (SGLT2) that undergoes oxidation and glucuronidation to form six principal metabolites in humans.In vitro metabolism by human liver microsomes and recombinant enzymes is primarily mediated by CYP3A4 and UGT1A9. Three major oxidation products and three major glucuronides have been identified in vivo. Metabolism by rats is mostly by oxidation whereas metabolism by monkeys and humans is mostly by glucuronidation. Metabolism by monkeys closely resembles metabolism by humans and all metabolites found in humans are also found in monkeys. A greater diversity of metabolites has been identified among human in vivo specimens than among in vitro reaction products.Following oral dosing of humans with 14C-bexagliflozin, the 3'-O-glucuronide contributed 32% of the parent AUC and all other metabolites contributed <10%. Of the 91.6% of input radioactivity recovered, 51.1% was in faeces, predominantly as bexagliflozin, and 40.5% was in urine, largely as the 3'-O-glucuronide. Unidentified metabolites contributed 0.27% of the input radiolabel.A quantitative accounting for the metabolism and disposition of bexagliflozin in vivo has been developed.

A spinosyn-sensitive Drosophila melanogaster nicotinic acetylcholine receptor identified through chemically induced target site resistance, resistance gene identification, and heterologous expression.

Strains of Drosophila melanogaster with resistance to the insecticides spinosyn A, spinosad, and spinetoram were produced by chemical mutagenesis. These spinosyn-resistant strains were not cross-resistant to other insecticides. The two strains that were initially characterized were subsequently found to have mutations in the gene encoding the nicotinic acetylcholine receptor (nAChR) subunit Dalpha6. Subsequently, additional spinosyn-resistant alleles were generated by chemical mutagenesis and were also found to have mutations in the gene encoding Dalpha6, providing convincing evidence that Dalpha6 is a target site for the spinosyns in D. melanogaster. Although a spinosyn-sensitive receptor could not be generated in Xenopus laevis oocytes simply by expressing Dalpha6 alone, co-expression of Dalpha6 with an additional nAChR subunit, Dalpha5, and the chaperone protein ric-3 resulted in an acetylcholine- and spinosyn-sensitive receptor with the pharmacological properties anticipated for a native nAChR.

Invertebrate and fungal model organisms: emerging platforms for drug discovery.

Early-stage translational research programs have increasingly exploited yeast, worms and flies to model human disease. These genetically tractable organisms represent flexible platforms for small molecule and drug target discovery. This review highlights recent examples of how model organisms are integrated into chemical genomic approaches to drug discovery with an emphasis on fungal yeast, nematode Caenorhabditis elegans and fruit fly Drosophila melanogaster. The roles of these organisms are expanding as novel models of human disease are developed and novel high-throughput screening technologies are created and adapted for drug discovery.

Development of a Drosophila seizure model for in vivo high-throughput drug screening.

An important application of model organisms in neurological research has been to identify and characterise therapeutic approaches for epilepsy, a recurrent seizure disorder that affects > 1% of the human population. Proconvulsant-treated rodent models have been widely used for antiepileptic drug discovery and development, but are not suitable for high-throughput screening. To generate a genetically tractable model that would be suitable for large-scale, high-throughput screening for antiepileptic drug candidates, we characterized a Drosophila chemical treatment model using the GABA(A) receptor antagonist picrotoxin. This proconvulsant, delivered to Drosophila larvae via simple feeding methods suitable for automated screening, generated robust generalised seizures with lethality occurring at doses between 0.3 and 0.5 mg/mL. Electrophysiological analysis of CNS motor neuron output in picrotoxin-treated larvae revealed generalised seizures within minutes of drug exposure. At subthreshold doses for seizure induction, picrotoxin produced an increased frequency of motor neuron action potential bursting, indicating that CNS GABAergic transmission regulates patterned activity. Mutants in the Drosophila Rdl GABA(A) receptor are resistant to picrotoxin, confirming that seizure induction occurs via a conserved GABA(A) receptor pathway. To validate the usefulness of this model for in vivo drug screening, we identified several classes of neuroactive antiepileptic compounds in a pilot screen, including phenytoin and nifedipine, which can rescue the seizures and lethal neurotoxicity induced by picrotoxin. The well-defined actions of picrotoxin in Drosophila and the ease with which compounds can be assayed for antiseizure activity makes this genetically tractable model attractive for high-throughput in vivo screens to identify novel anticonvulsants and seizure susceptibility loci.