[Show abstract][Hide abstract] ABSTRACT: On the basis of the initial success of optimization of a novel series of imidazolopiperazines, a second generation of compounds involving changes in the core piperazine ring was synthesized to improve antimalarial properties. These changes were carried out to further improve the potency and metabolic stability of the compounds by leveraging the outcome of a set of in vitro metabolic identification studies. The optimized 8,8-dimethyl imidazolopiperazine analogues exhibited improved potency, in vitro metabolic stability profile and, as a result, enhanced oral exposure in vivo in mice. The optimized compounds were found to be more efficacious than the current antimalarials in a malaria mouse model. They exhibit moderate oral exposure in rat pharmacokinetic studies to achieve sufficient multiples of the oral exposure at the efficacious dose in toxicology studies.
Journal of Medicinal Chemistry 04/2012; 55(9):4244-73. · 5.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Starting from a hit series from a GNF compound library collection and based on a cell-based proliferation assay of Plasmodium falciparum, a novel imidazolopiperazine scaffold was optimized. SAR for this series of compounds is discussed, focusing on optimization of cellular potency against wild-type and drug resistant parasites and improvement of physiochemical and pharmacokinetic properties. The lead compounds in this series showed good potencies in vitro and decent oral exposure levels in vivo. In a Plasmodium berghei mouse infection model, one lead compound lowered the parasitemia level by 99.4% after administration of 100 mg/kg single oral dose and prolonged mice survival by an average of 17.0 days. The lead compounds were also well-tolerated in the preliminary in vitro toxicity studies and represents an interesting lead for drug development.
Journal of Medicinal Chemistry 06/2011; 54(14):5116-30. · 5.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Efflux transporters expressed in the apical membrane of intestinal enterocytes have been implicated in drug oral absorption. The current study presents a strategy and tools to quantitatively predict the impact of efflux on oral absorption for new chemical entities (NCEs) in early drug discovery. Sixty-three marketed drugs with human absorption data were evaluated in the Caco-2 bidirectional permeability assay and subjected to specific transporter inhibition. A four-zone graphical model was developed from apparent permeability and efflux ratios to quickly identify compounds whose efflux activity may distinctly influence human absorption. NCEs in "zone 4" will probably have efflux as a barrier for oral absorption and further mechanistic studies are required. To interpret mechanistic results, we introduced a new quantitative substrate classification parameter, transporter substrate index (TSI). TSI allowed more flexibility and considered both in vitro and in vivo outcomes. Its application ranged from addressing the challenge of overlapping substrate specificity to projecting the role of transporter(s) on exposure or potential drug-drug interaction risk. The potential impact of efflux transporters associated with physicochemical properties on drug absorption is discussed in the context of TSI and also the previously reported absorption quotient. In this way, the chemistry strategy may be differentially focused on passive permeability or efflux activity or both.
Drug metabolism and disposition: the biological fate of chemicals 11/2010; 39(2):265-74. · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We systematically validated a robust 96-well Caco-2 assay via an extended set of 93 marketed drugs with diverse transport mechanisms and quantified by LC/MS/MS, to investigate its predictive utility while dealing with challenging discovery compounds. Utilizing nonlinear fit, the validation led to a good correlation (R(2) = 0.76) between absorptive permeability, log P(app)(A-B), from in vitro Caco-2 assay and reported human fraction of dose absorbed. We observed that paracellular compounds could be flagged by log P(app)(A-B) (<-5.5 cm/s) and physicochemical property space (c log P < 1). Of 8000 Novartis discovery compounds examined 13% were subject to low recovery (<30%). Compound loss was investigated by comparing cell monolayer and artificial membrane, while 0.5% bovine serum albumin (in both donor and acceptor compartments) was utilized to improve recovery. The second focus of this study was to investigate the advantages and limitations of the current Caco-2 assay for predicting in vivo intestinal absorption. Caco-2 measurements for compounds with high aqueous solubility and low in vitro metabolic clearance were compared to 88 in vivo rat bioavailability studies. Despite the challenges posed by discovery compounds with suboptimal physicochemical properties, Caco-2 data successfully projected low intestinal absorption. This platform sets the stage for mechanistically evaluating compounds towards improving in vitro-in vivo correlations.
Journal of Pharmaceutical Sciences 02/2010; 99(7):3246-65. · 3.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It has been argued that selection of adequate ADME properties should be conducted in parallel with optimization of drug efficacy. To achieve this, highly efficient, accurate, as well as cost-effective assays are required. Permeability assays are fundamental in ADME profiling, as sufficient permeability through intestinal membranes can promote oral absorption, a highly desirable property for the majority of drug discovery programs. The Caco-2 cell-based permeability model is advantageous due to its human origin and expression of transporters prevalent in the human gastrointestinal tract. However, thus far, limited studies have described the adaptation of the Caco-2 assay from lower-throughput plate formats to 96-well filter plates with LC-MS/MS analysis. We describe a high throughput 96-well Caco-2 assay which has been correlated to experimental human fraction absorbed with nearly 100 validation standards and which has successfully measured thousands of new chemical entities (NCEs). Using validation standards reported to be actively transported, we establish an efflux “flag” for discovery compounds. Further, we present the reality of integrating permeability assessment with high throughput solubility and metabolic stability data for pharmacokinetic (PK) decision making and in vitro- in vivo correlations (IVIVC) in a discovery setting. In some instances, IVIVC may be improved with more in-depth mechanistic work, specifically efflux transporter inhibition (P-gp, MRP2, and BCRP) and dose-escalation studies. A case-study addresses how the use of the Caco-2 permeability assay and follow-up mechanistic assays made a significant impact in identifying potential development liabilities and integrating in vitro and PK results.
10th European Regional International society for the study of xenobiotics Meeting;