Selection of an Optimal In Vitro Model to Assess P-gp Inhibition: Comparison of Vesicular and Bidirectional Transcellular Transport Inhibition Assays.

The multidrug resistance protein 1 (MDR1) P-glycoprotein (P-gp) is a clinically important transporter. In vitro P-gp inhibition assays have been routinely conducted to predict the potential for clinical drug-drug interactions (DDIs) mediated by P-gp. However, high interlaboratory and intersystem variability of P-gp IC50 data limits accurate prediction of DDIs using static models and decision criteria recommended by regulatory agencies. In this study, we calibrated two in vitro P-gp inhibition models: vesicular uptake of N-methyl-quinidine (NMQ) in MDR1 vesicles and bidirectional transport (BDT) of digoxin in Lilly Laboratories Cell Porcine Kidney 1 cells overexpressing MDR1 (LLC-MDR1) using a total of 48 P-gp inhibitor and noninhibitor drugs and digoxin DDI data from 70 clinical studies. Refined thresholds were derived using receiver operating characteristic analysis, and their predictive performance was compared with the decision frameworks proposed by regulatory agencies and selected reference. Furthermore, the impact of various IC50 calculation methods and nonspecific binding of drugs on DDI prediction was evaluated. Our studies suggest that the concentration of inhibitor based on highest approved dose dissolved in 250 ml divided by IC50(I2/IC50) is sufficient to predict P-gp related intestinal DDIs. IC50 obtained from vesicular inhibition assay with a refined threshold of I2/IC50 ≥ 25.9 provides comparable predictive power over those measured by net secretory flux and efflux ratio in LLC-MDR1 cells. We therefore recommend vesicular P-gp inhibition as our preferred method given its simplicity, lower variability, higher assay throughput, and more direct estimation of in vitro kinetic parameters, rather than BDT assay. SIGNIFICANCE STATEMENT: This study has conducted comprehensive calibration of two in vitro P-gp inhibition models: uptake in MDR1 vesicles and bidirectional transport in LLC-MDR1 cell monolayers to predict DDIs. This study suggests that IC50s obtained from vesicular inhibition with a refined threshold of I2/IC50 ≥ 25.9 provide comparable predictive power over those in LLC-MDR1 cells. Therefore, vesicular P-gp inhibition is recommended as the preferred method given its simplicity, lower variability, higher assay throughput, and more direct estimation of in vitro kinetic parameters.

First Hard X-Ray Imaging Results by Solar Orbiter STIX.

The Spectrometer/Telescope for Imaging X-rays (STIX) is one of six remote sensing instruments on-board Solar Orbiter. The telescope applies an indirect imaging technique that uses the measurement of 30 visibilities, i.e., angular Fourier components of the solar flare X-ray source. Hence, the imaging problem for STIX consists of the Fourier inversion of the data measured by the instrument. In this work, we show that the visibility amplitude and phase calibration of 24 out of 30 STIX sub-collimators has reached a satisfactory level for scientific data exploitation and that a set of imaging methods is able to provide the first hard X-ray images of solar flares from Solar Orbiter. Four visibility-based image reconstruction methods and one count-based are applied to calibrated STIX observations of six events with GOES class between C4 and M4 that occurred in May 2021. The resulting reconstructions are compared to those provided by an optimization algorithm used for fitting the amplitudes of STIX visibilities. We show that the five imaging methods produce results morphologically consistent with the ones provided by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory (SDO/AIA) in UV wavelengths. The χ 2 values and the parameters of the reconstructed sources are comparable between methods, thus confirming their robustness.

Fluorinated Isoindolinone-Based Glucosylceramide Synthase Inhibitors with Low Human Dose Projections.

Inhibition of glucosylceramide synthase (GCS) has been proposed as a therapeutic strategy for the treatment of Parkinson's Disease (PD), particularly in patients where glycosphingolipid accumulation and lysosomal impairment are thought to be contributing to disease progression. Herein, we report the late-stage optimization of an orally bioavailable and CNS penetrant isoindolinone class of GCS inhibitors. Starting from advanced lead 1, we describe efforts to identify an improved compound with a lower human dose projection, minimal P-glycoprotein (P-gp) efflux, and acceptable pregnane X receptor (PXR) profile through fluorine substitution. Our strategy involved the use of predicted volume ligand efficiency to advance compounds with greater potential for low human doses down our screening funnel. We also applied minimized electrostatic potentials (Vmin) calculations for hydrogen bond acceptor sites to rationalize P-gp SAR. Together, our strategies enabled the alignment of a lower human dose with reduced P-gp efflux, and favorable PXR selectivity for the discovery of compound 12.

Pyrazole Ureas as Low Dose, CNS Penetrant Glucosylceramide Synthase Inhibitors for the Treatment of Parkinson's Disease.

Parkinson's disease is the second most prevalent progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra. Loss-of-function mutations in GBA, the gene that encodes for the lysosomal enzyme glucosylcerebrosidase, are a major genetic risk factor for the development of Parkinson's disease potentially through the accumulation of glucosylceramide and glucosylsphingosine in the CNS. A therapeutic strategy to reduce glycosphingolipid accumulation in the CNS would entail inhibition of the enzyme responsible for their synthesis, glucosylceramide synthase (GCS). Herein, we report the optimization of a bicyclic pyrazole amide GCS inhibitor discovered through HTS to low dose, oral, CNS penetrant, bicyclic pyrazole urea GCSi's with in vivo activity in mouse models and ex vivo activity in iPSC neuronal models of synucleinopathy and lysosomal dysfunction. This was accomplished through the judicious use of parallel medicinal chemistry, direct-to-biology screening, physics-based rationalization of transporter profiles, pharmacophore modeling, and use a novel metric: volume ligand efficiency.