Optimization of an Imidazo[1,2-a]pyridine Series to Afford Highly Selective Type I1/2 Dual Mer/Axl Kinase Inhibitors with In Vivo Efficacy

Inhibition of Mer and Axl kinases has been implicated as a potential way to improve the efficacy of current immuno-oncology therapeutics by restoring the innate immune response in the tumor microenvironment. Highly selective dual Mer/Axl kinase inhibitors are required to validate this hypothesis. Starting from hits from a DNA-encoded library screen, we optimized an imidazo[1,2-a]pyridine series using structure-based compound design to improve potency and reduce lipophilicity, resulting in a highly selective in vivo probe compound 32. We demonstrated dose-dependent in vivo efficacy and target engagement in Mer- and Axl-dependent efficacy models using two structurally differentiated and selective dual Mer/Axl inhibitors. Additionally, in vivo efficacy was observed in a preclinical MC38 immuno-oncology model in combination with anti-PD1 antibodies and ionizing radiation.

Impact of Interindividual Differences in Plasma Fraction Unbound on the Pharmacokinetics of a Novel Syk Kinase Inhibitor in Beagle Dogs

Inconsistencies in pharmacokinetic parameters between individual animals in preclinical studies are a common occurrence. Often such differences between animals are simply accepted as experimental variability rather than as indications of specific differences in animal phenotype that could lead to a different interpretation of the data. The fraction unbound in plasma is one factor influencing pharmacokinetic parameters and is typically determined using pooled plasma from multiple animals, making the assumption that there is limited population variance. However, this assumption is not often tested and may not hold true if there are polymorphisms affecting binding or variation in the concentrations of individual plasma proteins that could give rise to different fraction unbound phenotypes in individual animals. During profiling of a novel Syk inhibitor, AZ8399, striking interindividual differences in total plasma clearance and volume of distribution were observed between dogs consistent with differences in fraction unbound between animals. Determination of the fraction unbound showed a ∼5-fold difference in fraction unbound between the animals in the study. Broader analysis of individual dogs across a colony demonstrated a correlation between individual animal fraction unbound with total plasma clearance and volume of distribution. The concentrations of the common drug-binding proteins albumin and α1-acid glycoprotein in plasma were determined, and α1-acid glycoprotein levels were found to correlate with fraction unbound. Finally, single-nucleotide polymorphisms were identified at c.502 and c.522 of exon 5 of the dog α1-acid glycoprotein gene that may be correlated to the α1-acid glycoprotein concentration phenotype observed. SIGNIFICANCE STATEMENT: The current work demonstrates the potential for significant interindividual differences in plasma fraction unbound in beagle dogs and goes on to examine the underlying cause for the compound described. The findings suggest that the application of a population mean value of fraction unbound generated from a pooled sample may not always be appropriate and could introduce significant errors in scaling of in vitro clearance values, PBPK understanding, and interpretation of PKPD or toxicokinetic data in the context of unbound concentrations.

Abstract 1042: Preclinical pharmacokinetic and metabolic characterization of the next generation oral SERD AZD9833

AZD9833 is a potent, orally delivered, non-steroidal selective estrogen receptor degrader (SERD) that both antagonizes and degrades ERα. It is currently in clinical testing for the treatment of ER+ metastatic breast cancer (SERENA-1; NCT03616587). While ER is a clinically validated target, sustained inhibition of the target via oral delivery has proven an elusive goal. Despite intensive research, no oral SERD options are currently approved. Poor pharmacokinetic (PK) properties and/or short half-life (t ½) are often underlying features that limit oral SERD candidates from once or twice daily dose regimens. AZD9833 is a clinical stage next generation oral SERD that may overcome these challenges.

The pre-clinical PK properties of AZD9833 are consistent with once daily oral dosing in patients and are reported herein. AZD9833 is a low molecular weight (<500 Da), low lipophilicity (logD <3) base with good permeability characteristics. High volume of distribution (6-13 L/kg) and high bioavailability were observed in preclinical species. The in vitro hepatic metabolic clearance (CLint) for AZD9833 varied across species and were found to be nonlinear as a function of concentration. This nonlinear behaviour most strongly manifested in dog where in vivo bioavailability was <2 or 95 %F depending on dose. To explain these observations, detailed in vitro mechanistic studies were conducted and physiologically based PK (PBPK) models were created. Cytochrome P450 phenotyping studies suggest dog clearance is mediated by CYP2D15 whereas CYP3A is the dominant P450 isoform responsible for clearance in human. In vitro CLint vs. concentration studies exhibited a low Km in dog (0.2 μM) relative to human (2 μM) and other species. To further our understanding, we constructed PBPK models which demonstrated that the dose dependent exposures in dog were predictable. The human model suggests that nonlinear behaviour will manifest well above predicted efficacious doses. Modeling also allowed us to assess the potential for drug-drug interactions with likely co-medications such as CDK 4/6 inhibitors. The PBPK predictions of good human exposure and long t ½ are being explored in the ongoing clinical trial.

Citation Format: Eric T. Gangl, Roshini Markandu, Pradeep Sharma, Andy Sykes, Petar Pop-Damkov, Pablo Morentin Gutierrez, James S. Scott, Dermot F. McGinnity, Adrian J. Fretland, Teresa Klinowska. Preclinical pharmacokinetic and metabolic characterization of the next generation oral SERD AZD9833 [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1042.

Drug metabolite identification using ultrahigh-performance liquid chromatography-ultraviolet spectroscopy and parallelized scans on a tribrid Orbitrap mass spectrometer

RATIONALE

To capture all metabolites in metabolite identification studies, MS/MS information is required in both positive and negative ionization mode, usually involving several sample injections to gain all information about samples. A high-resolution and high mass accuracy quadrupole/linear trap/Orbitrap tribrid instrument was used to gain this information in a novel single injection 'capture-all' approach to metabolite identification.

METHODS

Diclofenac, a model compound, was incubated in human and rat hepatocytes. These incubated samples were run using an ultrahigh-performance liquid chromatography/ultraviolet (UHPLC-UV) system coupled to a Thermo Fusion tribrid mass spectrometer. Five parallel scans were used: positive and negative ion full scan, data-dependent MS/MS, both high energy dissociation and collision-induced dissociation, and data-independent all ion fragmentation (AIF) spectra were collected in positive and negative ion mode.

RESULTS

Nine metabolites were identified; a metabolite observed in the UV trace, but not positive ion full scan MS, was detected in the same sample injection by negative ion full scan MS. This was identified as a sulphate metabolite, and the corresponding negative ion AIF allowed for some structural elucidation. The use of a photo-diode array (PDA) detector allowed for spectral assessment in case of changes in absorbance spectra, and the subsequent semi-quantification of metabolites.

CONCLUSIONS

This method provided good-quality MS/MS data across the m/z range in both positive and negative ion mode. The addition of both negative ion full scan MS and negative ion MS/MS allowed for the detection and structural elucidation of metabolites not observed in positive ion mode. The use of the PDA detector allowed for the semi-quantification of metabolites.