Predicting the Intravenous Pharmacokinetics of Covalent Drugs in Animals and Humans

30 covalent drugs were used to assess clearance (CL) prediction reliability in animals and humans. In animals, marked CL underprediction was observed using cryopreserved hepatocytes or liver microsomes (LMs) supplemented for cytochrome P450 activity. Improved quantitative performance was observed by combining metabolic stability data from LMs and liver S9 fractions, the latter supplemented with reduced glutathione for glutathione transferase activity. While human LMs provided reliable human CL predictions, prediction statistics were improved further by incorporating S9 stability data. CL predictions with allometric scaling were less robust compared to in vitro drug metabolism methods; the best results were obtained using the fu-corrected intercept model. Human volume of distribution (Vd) was well predicted using allometric scaling of animal pharmacokinetic data; the most reliable results were achieved using simple allometric scaling of unbound Vd values. These results provide a quantitative framework to guide appropriate method selection for human PK prediction with covalent drugs.

Emerging and Re-emerging Warheads for Targeted Covalent Inhibitors: An Update

Covalent inhibitors and other types of covalent modalities have seen a revival in the past two decades, with a variety of new targeted covalent drugs having been approved in recent years. A key feature of such molecules is an intrinsically reactive group, typically a weak electrophile, which enables the irreversible or reversible formation of a covalent bond with a specific amino acid of the target protein. This reactive group, often called the "warhead", is a critical determinant of the ligand's activity, selectivity, and general biological properties. In 2019, we summarized emerging and re-emerging warhead chemistries to target cysteine and other amino acids (Gehringer, M.; Laufer, S. A. J. Med. Chem. 2019, 62, 5673-5724; DOI: 10.1021/acs.jmedchem.8b01153). Since then, the field has rapidly evolved. Here we discuss the progress on covalent warheads made since our last Perspective and their application in medicinal chemistry and chemical biology.

Virtual Bioequivalence Assessment of Ritlecitinib Capsules with Incorporation of Observed Clinical Variability Using a Physiologically Based Pharmacokinetic Model

Ritlecitinib, an orally available Janus kinase 3 and tyrosine kinase inhibitor being developed for the treatment of alopecia areata (AA), is highly soluble across the physiological pH range at the therapeutic dose. As such, it is expected to dissolve rapidly in any in vitro dissolution conditions. However, in vitro dissolution data showed slower dissolution for 100-mg capsules, used for the clinical bioequivalence (BE) study, compared with proposed commercial 50-mg capsules. Hence, a biowaiver for the lower 50-mg strength using comparable multimedia dissolution based on the f2 similarity factor was not possible. The in vivo relevance of this observed in vitro dissolution profile was evaluated with a physiologically based pharmacokinetic (PBPK) model. This report describes the development, verification, and application of the ritlecitinib PBPK model to translate observed in vitro dissolution data to an in vivo PK profile for ritlecitinib capsule formulations. Virtual BE (VBE) trials were conducted using the Simcyp VBE module, including the model-predicted within-subject variability or intra-subject coefficient of variation (ICV). The results showed the predicted ICV was predicted to be smaller than observed clinical ICV, resulting in a more optimistic BE risk assessment. Additional VBE assessment was conducted by incorporating clinically observed ICV. The VBE trial results including clinically observed ICV demonstrated that proposed commercial 50-mg capsules vs clinical 100-mg capsules were bioequivalent, with > 90% probability of success. This study demonstrates a PBPK model-based biowaiver for a clinical BE study while introducing a novel method to integrate clinically observed ICV into VBE trials with PBPK models. Trial registration: NCT02309827, NCT02684760, NCT04004663, NCT04390776, NCT05040295, NCT05128058.

Recent advances in the development of inhibitors targeting KRAS-G12C and its related pathways

The RAS gene, also known as the mouse sarcoma virus, includes three genes (KRAS, HRAS, and NRAS) that are associated with human tumors. Among them, KRAS has the highest incidence of mutations in cancer, accounting for around 80% of cases. At the molecular level, the RAS gene plays a regulatory role in transcription and translation, while at the cellular level, it affects cell proliferation and migration, making it crucial for cancer development. In 2021, the FDA approved AMG510, the first direct inhibitor targeting the KRAS-G12C mutation, which has shown tumor regression, prolonged survival, and low off-target activity. However, with the increase of drug resistance, a single inhibitor is no longer sufficient to achieve the desired effect on tumors. Therefore, a large number of other highly efficient inhibitors are being developed at different stages. This article provides an overview of the mechanism of action targeting KRAS-G12C in the KRASGTP-KRASGDP cycle pathway, as well as the structure-activity relationship, structure optimization, and biological activity effects of inhibitors that target the upstream and downstream pathways, or combination therapy.

Covalent drug discovery using sulfur(VI) fluoride exchange warheads

INTRODUCTION

Covalent drug discovery has traditionally focused on targeting cysteine, but the amino acid is often absent in protein binding sites. This review makes the case to move beyond cysteine labeling using sulfur (VI) fluoride exchange (SuFEx) chemistry to expand the druggable proteome.

AREAS COVERED

Recent advances in SuFEx medicinal chemistry and chemical biology are described, which have enabled the development of covalent chemical probes that site-selectively engage amino acid residues (including tyrosine, lysine, histidine, serine, and threonine) in binding pockets. Areas covered include chemoproteomic mapping of the targetable proteome, structure-based design of covalent inhibitors and molecular glues, metabolic stability profiling, and synthetic methodologies that have expedited the delivery of SuFEx modulators.

EXPERT OPINION

Despite recent innovations in SuFEx medicinal chemistry, focused preclinical research is required to ensure the field moves from early chemical probe discovery to the delivery of transformational covalent drug candidates. The authors believe that covalent drug candidates designed to engage residues beyond cysteine using sulfonyl exchange warheads will likely enter clinical trials in the coming years.

The war on hTG2: warhead optimization in small molecule human tissue transglutaminase inhibitors

Human tissue transglutaminase (hTG2) is a multifunctional enzyme with protein cross-linking and G-protein activity, both of which have been implicated in the progression of diseases such as fibrosis and cancer stem cell propagation when dysregulated, prompting the development of small molecule targeted covalent inhibitors (TCIs) possessing a crucial electrophilic 'warhead'. In recent years there have been significant advances in the library of warheads available for the design of TCIs; however, the exploration of warhead functionality in hTG2 inhibitors has remained relatively stagnant. Herein, we describe a structure-activity relationship study entailing rational design and synthesis for systematic variation of the warhead on a previously reported small molecule inhibitor scaffold, and rigorous kinetic evaluation of inhibitory efficiency, selectivity, and pharmacokinetic stability. This study reveals a strong influence on the kinetic parameters k inact and K I with even subtle variation in warhead structure, suggesting that the warhead plays a significant role in not only reactivity, but also binding affinity, which consequently extends to isozyme selectivity. Warhead structure also influences in vivo stability, which we model by measuring intrinsic reactivity with glutathione, as well as stability in hepatocytes and in whole blood, giving insight into degradation pathways and relative therapeutic potential of different functional groups. This work provides fundamental structural and reactivity information highlighting the importance of strategic warhead design for the development of potent hTG2 inhibitors.

Recent advances in the translation of drug metabolism and pharmacokinetics science for drug discovery and development

Drug metabolism and pharmacokinetics (DMPK) is an important branch of pharmaceutical sciences. The nature of ADME (absorption, distribution, metabolism, excretion) and PK (pharmacokinetics) inquiries during drug discovery and development has evolved in recent years from being largely descriptive to seeking a more quantitative and mechanistic understanding of the fate of drug candidates in biological systems. Tremendous progress has been made in the past decade, not only in the characterization of physiochemical properties of drugs that influence their ADME, target organ exposure, and toxicity, but also in the identification of design principles that can minimize drug-drug interaction (DDI) potentials and reduce the attritions. The importance of membrane transporters in drug disposition, efficacy, and safety, as well as the interplay with metabolic processes, has been increasingly recognized. Dramatic increases in investments on new modalities beyond traditional small and large molecule drugs, such as peptides, oligonucleotides, and antibody-drug conjugates, necessitated further innovations in bioanalytical and experimental tools for the characterization of their ADME properties. In this review, we highlight some of the most notable advances in the last decade, and provide future perspectives on potential major breakthroughs and innovations in the translation of DMPK science in various stages of drug discovery and development.

Analysis of lorlatinib analogs reveals a roadmap for targeting diverse compound resistance mutations in ALK-positive lung cancer

Lorlatinib is currently the most advanced, potent and selective anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitor for the treatment of ALK-positive non-small cell lung cancer in the clinic; however, diverse compound ALK mutations driving therapy resistance emerge. Here, we determine the spectrum of lorlatinib-resistant compound ALK mutations in patients, following treatment with lorlatinib, the majority of which involve ALK G1202R or I1171N/S/T. We further identify structurally diverse lorlatinib analogs that harbor differential selective profiles against G1202R versus I1171N/S/T compound ALK mutations. Structural analysis revealed increased potency against compound mutations through improved inhibition of either G1202R or I1171N/S/T mutant kinases. Overall, we propose a classification of heterogenous ALK compound mutations enabling the development of distinct therapeutic strategies for precision targeting following sequential tyrosine kinase inhibitors.

IVIVE: Facilitating the Use of In Vitro Toxicity Data in Risk Assessment and Decision Making

During the past few decades, the science of toxicology has been undergoing a transformation from observational to predictive science. New approach methodologies (NAMs), including in vitro assays, in silico models, read-across, and in vitro to in vivo extrapolation (IVIVE), are being developed to reduce, refine, or replace whole animal testing, encouraging the judicious use of time and resources. Some of these methods have advanced past the exploratory research stage and are beginning to gain acceptance for the risk assessment of chemicals. A review of the recent literature reveals a burst of IVIVE publications over the past decade. In this review, we propose operational definitions for IVIVE, present literature examples for several common toxicity endpoints, and highlight their implications in decision-making processes across various federal agencies, as well as international organizations, including those in the European Union (EU). The current challenges and future needs are also summarized for IVIVE. In addition to refining and reducing the number of animals in traditional toxicity testing protocols and being used for prioritizing chemical testing, the goal to use IVIVE to facilitate the replacement of animal models can be achieved through their continued evolution and development, including a strategic plan to qualify IVIVE methods for regulatory acceptance.

Discovery of AZD4625, a Covalent Allosteric Inhibitor of the Mutant GTPase KRASG12C

KRAS is an archetypal high-value intractable oncology drug target. The glycine to cysteine mutation at codon 12 represents an Achilles heel that has now rendered this important GTPase druggable. Herein, we report our structure-based drug design approach that led to the identification of 21, AZD4625, a clinical development candidate for the treatment of KRAS^G12C positive tumors. Highlights include a quinazoline tethering strategy to lock out a bio-relevant binding conformation and an optimization strategy focused on the reduction of extrahepatic clearance mechanisms seen in preclinical species. Crystallographic analysis was also key in helping to rationalize unusual structure-activity relationship in terms of ring size and enantio-preference. AZD4625 is a highly potent and selective inhibitor of KRAS^G12C with an anticipated low clearance and high oral bioavailability profile in humans.

Quaternary Ammonium Compounds: Bioaccumulation Potentials in Humans and Levels in Blood before and during the Covid-19 Pandemic

Quaternary ammonium compounds (QACs) are commonly used in a variety of consumer, pharmaceutical, and medical products. In this study, bioaccumulation potentials of 18 QACs with alkyl chain lengths of C8-C18 were determined in the in vitro-in vivo extrapolation (IVIVE) model using the results of human hepatic metabolism and serum protein binding experiments. The slowest in vivo clearance rates were estimated for C12-QACs, suggesting that these compounds may preferentially build up in blood. The bioaccumulation of QACs was further confirmed by the analysis of human blood (sera) samples (n = 222). Fifteen out of the 18 targeted QACs were detected in blood with the ΣQAC concentrations reaching up to 68.6 ng/mL. The blood samples were collected during two distinct time periods: before the outbreak of the COVID-19 pandemic (2019; n = 111) and during the pandemic (2020, n = 111). The ΣQAC concentrations were significantly higher in samples collected during the pandemic (median 6.04 ng/mL) than in those collected before (median 3.41 ng/mL). This is the first comprehensive study on the bioaccumulation and biomonitoring of the three major QAC groups and our results provide valuable information for future epidemiological, toxicological, and risk assessment studies targeting these chemicals.

Role of epoxide hydrolases and cytochrome P450s on metabolism of KZR-616, a first-in-class selective inhibitor of the immunoproteasome

KZR-616 is an irreversible tripeptide epoxyketone-based selective inhibitor of the human immunoproteasome. Inhibition of the immunoproteasome results in anti-inflammatory activity in vitro and, based on promising therapeutic activity in animal models of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), KZR-616 is being developed for potential treatment of multiple autoimmune and inflammatory diseases. The presence of a ketoepoxide pharmacophore presents unique challenges in the study of drug metabolism during lead optimization and clinical candidate profiling. This study presents a thorough and systematic in vitro and cell-based enzymatic metabolism and kinetic investigation to identify the major enzymes involved in the metabolism and elimination of KZR-616. Upon exposure to liver microsomes in the absence of NADPH, KZR-616 and its analogs were converted to their inactive diol derivatives with varying degrees of stability. Diol formation was also shown to be the major metabolite in pharmacokinetic studies in monkeys and correlated with in vitro stability results for individual compounds. Further study in intact hepatocytes and a hepatocellular carcinoma cell line revealed that KZR-616 metabolism was sensitive to an inhibitor of microsomal epoxide hydrolase (mEH) but not inhibitors of cytochrome P450 (CYP) or soluble epoxide hydrolase (sEH). Primary human hepatocytes were determined to be the most robust source of mEH activity for study in vitro These findings also suggest that the exposure of KZR-616 in vivo is unlikely to be affected by co-administration of inhibitors or inducers of CYP and sEH. Significance Statement This work presents a thorough and systematic investigation of metabolism and kinetic of KZR-616 and other peptide epoxyketones in in vitro and cell-based enzymatic systems. Gained information could be useful in assessing novel covalent proteasome inhibitors during lead compound optimization. The study also demonstrates a robust source of in vitro metabolism identification that correlated very well with in vivo PK metabolism for peptide epoxyketones.

Recent developments in predicting CYP-independent metabolism

As lead optimization efforts have successfully reduced metabolic liabilities due to cytochrome P450 (CYP)-mediated metabolism, there has been an increase in the frequency of involvement of non-CYP enzymes in the metabolism of investigational compounds. Although there have been numerous notable advancements in the characterization of non-CYP enzymes with respect to their localization, reaction mechanisms, species differences and identification of typical substrates, accurate prediction of non-CYP-mediated clearance, with a particular emphasis with the difficulties in accounting for any extrahepatic contributions, remains a challenge. The current manuscript comprehensively summarizes the recent advancements in the prediction of drug metabolism and the in vitro to in vitro extrapolation of clearance for substrates of non-CYP drug metabolizing enzymes.

Prediction of Drug Clearance from Enzyme and Transporter Kinetics

Accurate estimation of in vivo clearance in human is pivotal to determine the dose and dosing regimen for drug development. In vitro-in vivo extrapolation (IVIVE) has been performed to predict drug clearance using empirical and physiological scalars. Multiple in vitro systems and mathematical modeling techniques have been employed to estimate in vivo clearance. The models for predicting clearance have significantly improved and have evolved to become more complex by integrating multiple processes such as drug metabolism and transport as well as passive diffusion. This chapter covers the use of conventional as well as recently developed methods to predict metabolic and transporter-mediated clearance along with the advantages and disadvantages of using these methods and the associated experimental considerations. The general approaches to improve IVIVE by use of appropriate scalars, incorporation of extrahepatic metabolism and transport and application of physiologically based pharmacokinetic (PBPK) models with proteomics data are also discussed. The chapter also provides an overview of the advantages of using such dynamic mechanistic models over static models for clearance predictions to improve IVIVE.

Predicting Chemotherapy-Induced Neutropenia and Granulocyte Colony-Stimulating Factor Response Using Model-Based In Vitro to Clinical Translation

The ability to predict the incidence of chemotherapy-induced neutropenia in early drug development can inform risk monitoring and mitigation strategies, as well as decisions on advancing compounds to clinical trials. In this report, a physiological model of granulopoiesis that incorporates the drug's mechanism of action on cell cycle proliferation of bone marrow progenitor cells was extended to include the action of the cytotoxic agents paclitaxel, carboplatin, doxorubicin, and gemcitabine. In vitro bone marrow studies were conducted with each compound, and results were used to determine the model's drug effect parameters. Population simulations were performed to predict the absolute neutrophil count (ANC) and incidence of neutropenia for each compound, which were compared to results reported in the literature. In addition, using the single agent in vitro study results, the model was able to predict ANC time course in response to paclitaxel plus carboplatin in combination, which compared favorably to the results reported in a phase 1 clinical trial of 46 patients (r2 = 0.70). Model simulations were used to compare the relative risk (RR) of neutropenia in patients with high baseline ANCs for five chemotherapeutic regimens: doxorubicin (RR = 0.59), paclitaxel plus carboplatin combination (RR = 0.079), carboplatin (RR = 0.047), paclitaxel (RR = 0.031), and gemcitabine (RR = 0.013). Finally, the model was applied to quantify the reduced incidence of neutropenia with coadministration of pegfilgrastim or filgrastim, for both paclitaxel and the combination of paclitaxel plus carboplatin. The model provides a framework for predicting clinical neutropenia using in vitro bone marrow studies of anticancer agents that may guide drug development decisions.

Metabolic disposition of [14 C]-abivertinib, an epidermal growth factor receptor tyrosine kinase inhibitor: Role of glutathione conjugation

AIMS

To determine the absorption, distribution, metabolism and excretion of abivertinib, a third-generation epidermal growth factor receptor tyrosine kinase inhibitor, in patients with advanced non-small cell lung cancer (NSCLC).

METHODS

Seven patients with advanced NSCLC were given a single 200 mg/83 μCi oral suspension of [¹⁴ C]-abivertinib. Blood, urine and faeces were collected. Mass balance of radioactivity, the pharmacokinetics of abivertinib, and the total radioactivity were determined. Metabolite profiling and characterisation were performed.

RESULTS

The mean recovery was 82.16%, with 2.38 and 79.78% of the radioactive dose excreted in urine and faeces, respectively. The unchanged abivertinib was the major radioactive component detected in plasma within the first 24 hours after dosing, accounting for 59.17% of the total drug-related radioactivity. Abivertinib in urine accounted for only 0.96% of the administered dose, whereas in faeces it accounted for 33.36%. Eight metabolites were detected and characterised in plasma, among which MII-7, a product of cysteine glycine conjugate, was the only circulating metabolite, accounting for approximate 10.6% of the total drug-related exposure. MII-2 (an abivertinib cysteine-glycine adduct) and M7 (a reduced product of abivertinib) were the 2 major metabolites in the excreta, accounting for 20.0 and 12.4%, respectively, of the drug-related radioactivity in faeces.

CONCLUSION

Following a single oral administration, the unchanged abivertinib was the predominant drug-related material in plasma, urine and faeces. The drug-related materials were primarily eliminated via the faecal route. Direct glutathione conjugation of abivertinib played a significant role in the metabolic clearance and metabolite exposure of abivertinib.

Approaches to mitigate the risk of serious adverse reactions in covalent drug design

INTRODUCTION

Covalent inhibition of target proteins using high affinity ligands bearing weakly electrophilic warheads is being adopted increasingly as design strategy in the discovery of novel therapeutics, and several covalent drugs have now received regulatory approval for indications in oncology. Experience to date with targeted covalent inhibitors has led to a number of design principles that underlie the safety and efficacy of this increasingly important class of molecules.

AREAS COVERED

A review is provided of the current status of the covalent drug approach, emphasizing the unique benefits and attendant risks associated with reversible and irreversible binders. Areas of application beyond inhibition of tyrosine kinases are presented, and design considerations to de-risk covalent inhibitors with respect to undesirable off-target effects are discussed.

EXPERT OPINION

High selectivity for the intended protein target has emerged as a key consideration in mitigating safety risks associated with widespread proteome reactivity. Powerful chemical proteomics-based techniques are now available to assess selectivity in a drug discovery setting. Optimizing pharmacokinetics to capitalize on the intrinsically high potency of covalent drugs should lead to low daily doses and greater safety margins, while minimizing susceptibility to metabolic activation likewise will attenuate the risk of covalent drug toxicity.

Estimating renal and hepatic clearance rates of organophosphate esters in humans: Impacts of intrinsic metabolism and binding affinity with plasma proteins

The renal and hepatic clearance rates of organophosphate esters (OPEs) in humans were estimated. Six OPEs and their corresponding diester metabolites (mOPEs) were quantified respectively in 30 paired human plasma and urine samples collected in Hengshui, Hebei province, China. The renal clearance rate (CL_renal) of triphenyl phosphate (TPHP), tris(chloroethyl) phosphate (TCEP) and tris(1,3-dichloro-isopropyl) phosphate (TDCIPP) was estimated to be 68.9, 50.9 and 33.3 mL/kg/day, respectively, while it was not calculated for other three OPEs due to the low detection frequencies in human samples. To estimate the clearance rates of the target OPEs, hepatic clearance rates (CL_h) of OPEs were extrapolated from their in vitro intrinsic clearance data in human liver microsomes (CL_HLM). The calculated CL_h values of TCEP and TDCIPP were comparable to their CL_renal, indicating that the in vitro extrapolation method was suitable for estimating the clearance rates of OPEs. The higher binding affinity of TDCIPP with plasma proteins could reduce its renal clearance. The estimated half-lives of Cl-OPEs in human were longer than those of the aryl- and alkyl-OPEs. This study provided a feasible in vitro method to predict the clearance and half-lives of OPEs in human, which is significant for their accurate health risk assessment.

Current Status in the Discovery of Covalent Janus Kinase 3 (JAK3) Inhibitors

The search for inhibitors of the Janus kinase family (JAK1, JAK2, JAK3 and TYK2) has been ongoing for several decades and has resulted in a number of JAK inhibitors being approved for use in patients, such as tofacitinib for the treatment of autoimmune diseases such as Rheumatoid Arthritis (RA). Although initially thought to be a JAK3 selective inhibitor, tofacitinib was subsequently found to possess significant activity to inhibit JAK1 and JAK2 which has contributed to some adverse side effects. A selective JAK3 inhibitor should only have an effect within the immune system since JAK3 is solely expressed in lymphoid tissue; this makes JAK3 a target of interest in the search for treatments of autoimmune diseases. A method to obtain selectivity for JAK3 over the other JAK family members, which has attracted more scientific attention recently, is the targeting of the active site cysteine residue, unique in JAK3 within the JAK family, with compounds containing electrophilic warheads which can form a covalent bond with the nucleophilic thiol of the cysteine residue. This review encompasses the historical search for a covalent JAK3 inhibitor and the most recently published research which hasn't been reviewed to date. The most important compounds from the publications reviewed the activity and selectivity of these compounds together with some of the more important biological results are condensed in to an easily digested form that should prove useful for those interested in the field.

Bioavailability, Biotransformation, and Excretion of the Covalent Bruton Tyrosine Kinase Inhibitor Acalabrutinib in Rats, Dogs, and Humans

Acalabrutinib is a targeted, covalent inhibitor of Bruton tyrosine kinase (BTK) with a unique 2-butynamide warhead that has relatively lower reactivity than other marketed acrylamide covalent inhibitors. A human [¹⁴C] microtracer bioavailability study in healthy subjects revealed moderate intravenous clearance (39.4 l/h) and an absolute bioavailability of 25.3% ± 14.3% (n = 8). Absorption and elimination of acalabrutinib after a 100 mg [¹⁴C] microtracer acalabrutinib oral dose was rapid, with the maximum concentration reached in <1 hour and elimination half-life values of <2 hours. Low concentrations of radioactivity persisted longer in the blood cell fraction and a peripheral blood mononuclear cell subfraction (enriched in target BTK) relative to plasma. [¹⁴C]Acalabrutinib was metabolized to more than three dozen metabolites detectable by liquid chromatography-tandem mass spectrometry, with primary metabolism by CYP3A-mediated oxidation of the pyrrolidine ring, thiol conjugation of the butynamide warhead, and amide hydrolysis. A major active, circulating, pyrrolidine ring-opened metabolite, ACP-5862 (4-[8-amino-3-[4-(but-2-ynoylamino)butanoyl]imidazo[1,5-a]pyrazin-1-yl]-N-(2-pyridyl)benzamide), was produced by CYP3A oxidation.Novel enol thioethers from the 2-butynamide warhead arose from glutathione and/or cysteine Michael additions and were subject to hydrolysis to a β-ketoamide. Total radioactivity recovery was 95.7% ± 4.6% (n = 6), with 12.0% of dose in urine and 83.5% in feces. Excretion and metabolism characteristics were generally similar in rats and dogs. Acalabrutinib's highly selective, covalent mechanism of action, coupled with rapid absorption and elimination, enables high and sustained BTK target occupancy after twice-daily administration.

Discovery of a JAK3-Selective Inhibitor: Functional Differentiation of JAK3-Selective Inhibition over pan-JAK or JAK1-Selective Inhibition

PF-06651600, a newly discovered potent JAK3-selective inhibitor, is highly efficacious at inhibiting γc cytokine signaling, which is dependent on both JAK1 and JAK3. PF-06651600 allowed the comparison of JAK3-selective inhibition to pan-JAK or JAK1-selective inhibition, in relevant immune cells to a level that could not be achieved previously without such potency and selectivity. In vitro, PF-06651600 inhibits Th1 and Th17 cell differentiation and function, and in vivo it reduces disease pathology in rat adjuvant-induced arthritis as well as in mouse experimental autoimmune encephalomyelitis models. Importantly, by sparing JAK1 function, PF-06651600 selectively targets γc cytokine pathways while preserving JAK1-dependent anti-inflammatory signaling such as the IL-10 suppressive functions following LPS treatment in macrophages and the suppression of TNFα and IL-1β production in IL-27-primed macrophages. Thus, JAK3-selective inhibition differentiates from pan-JAK or JAK1 inhibition in various immune cellular responses, which could potentially translate to advantageous clinical outcomes in inflammatory and autoimmune diseases.