The DMPK group was established within the Therapeutic Development Branch in the Division of Preclinical Innovation (DPI) to address issues related to drug absorption, biodistribution and elimination via metabolism or excretion. The DMPK group has supported diverse projects across DPI, contributing significantly to all stages of translational research at NCATS, from early probe development in drug discovery to Phase II clinical trials. Our major capabilities include: 1. In vitro ADME high-throughput screening (Tier I HTS assays) on solubility, permeability and microsomal stability for all small molecule compounds registered at NCATS ( 3000 compounds/year). 2. Customized in vitro ADME assays (Tier II assays) as required by each projects specific needs. The common Tier II assays include metabolic stability in different species, metabolite identification (MetID), aldehyde oxidase stability in cytosol fraction, plasma stability for prodrugs and biologics, blood/plasma partition, CYP inhibition, and transporter assessments in Caco-2 and MDKC cells. 3. PK studies in lab animals and bioanalytical measurements of drug concentrations in different biological fluids (e.g., blood, plasma, urine, bile) and tissue extracts. 4. UPLC-MS/MS and high-resolution accurate mass spectrometry for quantitation of small molecules and peptides, and structure identification of metabolites. 5. Bioanalytical method development for therapeutic macromolecules, such as recombinant human proteins and engineered proteins. 6. Pharmacokinetic parameter calculation and simulation. Examples of the DMPK group contributions to recent projects within the Therapeutic Development Branch include: In Silico ADME Modeling: Characterization of in vitro ADME properties of a novel compound is very important in drug discovery research as it will guide structure optimization and lead selection. We have developed high-throughput assays for key ADME properties, such as aqueous solubility, membrane permeability and hepatic metabolic stability in microsomes. Over the years, we have collected data for 20,000 compounds synthesized or registered at DPI/NCATS. To ensure the quality of the datasets, we use controls in each plate and monitor the performance of these controls for all plates. We calculate Minimum Significant Ratio (MSR) for controls, a statistical parameter that characterizes the reproducibility of an assay, in order to evaluate assay performance. With high quality datasets in hand, we start to develop in silico models for these ADME properties (PMID: 3117656). These in silico models are useful tools for medicinal chemists to design new drug-like molecules, which will potentially reduce the number of compounds to be synthesized during drug discovery, save valuable resources and minimize chemical wastes. Ultimately it could help to accelerate the drug discovery process. Applying Metabolite Identification (MetID) to Guide Structure Optimization: To develop a novel therapy for fibrodysplasia ossificans progressiva (FOP), a lead compound (LDN-189) was proposed as a development candidate by our collaborator. However, based on our past experience with similar chemical structures, we immediately realized that this molecule could have metabolic issues associated with toxicity. To confirm this, we conducted extensive MetID experiments, and several metabolic liable spots (red flags) were identified. The formation of a major metabolite, NIH-Q55, was mediated by aldehyde oxidase (AO), an enzyme known to be species-dependent. AO enzyme activity (greatest to least) could be ranked in the order of monkey > human > rodents. Dog, a common non-rodent species used for drug safety evaluation, totally lacks AO activity. The AO-mediated metabolism could also contribute to a large variability in exposures observed among different human subjects. In addition to the AO-mediated metabolism, the piperazinyl moiety was the target of NADPH-dependent metabolism, resulting in reactive iminium intermediates as confirmed through chemical trapping experiments. Two aniline metabolites were also detected, which brought up concerns about drug safety. These findings provided valuable information to the chemists, guiding subsequent structure modifications to generate safer drug candidates. By blocking the AO-mediated metabolic site and changing the piperazinyl moiety, the chemists were able to develop new lead compounds with better metabolic stability and less toxicity, while retaining pharmacological activity. Our work was recently published in Frontiers in Pharmacology (PMID: 31068801). Currently, the lead compound is in a clinical Phase I trial in Australia. Optimization of Dosing Regimen for Fungal Infection Treatment: VT-1129 is a potent antifungal agent with a slow absorption phase followed by a slow elimination phase in the PK profile after oral administration. In order to deliver a high initial drug concentration for a quick kill on fungus while avoiding significant drug accumulation in tissues (especially liver) after multiple-dose treatment, we proposed a dosing regimen with a high loading dose, followed by low daily maintenance doses. A series of simulations were conducted with different dosage combinations. The predicted drug concentrations based on simulations were confirmed by in vivo measured concentrations in mice. The optimized dosing regimen was successfully used in subsequent mouse efficacy studies, supporting a successful IND application to the FDA. Two recent manuscripts were published on our work for VT-1129 (PMID: 30104280; PMID: 29987152).
Showing the most recent 10 out of 14 publications
