Identification of Novel Pathways of Osimertinib Disposition and Potential Implications for the Outcome of Lung Cancer Therapy

Predictability of human exposure by human-CYP3A4-transgenic mouse models: A meta-analysis

First-in-human dose predictions are primarily based on no-observed-adverse-effect levels in animal studies. Predictions from these animal models are only as effective as their ability to predict human results. To narrow the gap between human and animals, researchers have, among other things, focused on the replacement of animal cytochrome P450 (CYP) enzymes with their human counterparts (called humanization), especially in mice. Whereas research in humanized mice is extensive, the emphasis has been particularly on qualitative rather than quantitative predictions. Because the CYP3A4 enzyme is most involved in the metabolism of clinically used drugs, most benefit was expected from CYP3A4 models. There are several applications of these mouse models regarding in vivo CYP3A4 functionality, one of which might be their capacity to help improve first-in-human (FIH) dose predictions for CYP3A4-metabolized drugs. To evaluate whether human-CYP3A4-transgenic mouse models are better predictors of human exposure compared to the wild-type mouse model, we performed a meta-analysis comparing both mouse models in their ability to accurately predict human exposure of small-molecule drugs metabolized by CYP3A4. Results showed that, in general, the human-CYP3A4-transgenic mouse model had similar accuracy in the prediction of human exposure compared to the wild-type mouse model, suggesting that there is limited added value in humanization of the mouse Cyp3a enzymes if the primary aim is to acquire more accurate FIH dose predictions. Despite the results of this meta-analysis, corrections for interspecies differences through extension of human-CYP3A4-transgenic mouse models with pharmacokinetic modeling approaches seems a promising contribution to more accurate quantitative predictions of human pharmacokinetics.

Insight into in silico prediction and chemical degradation study of osimertinib mesylate by LC-HRMS and NMR: Investigation of a typical case of alkaline pH-mediated oxidative degradation product

Osimertinib mesylate is a third-generation epidermal growth factor receptor tyrosine kinase inhibitor used to treat nonsmall-cell lung cancer. The objective was to understand in silico prediction and chemical-based stress testing of the osimertinib mesylate. A total of eight degradation products (DPs) were formed under chemical stress testing. An in silico tool viz., Zeneth predicted a higher percentage of DPs. The separation of all the DPs was achieved using reversed phase high-performance liquid chromatography, employing X-Bridge C18 column with ammonium acetate (pH adjusted to 7.50 with ammonia) and acetonitrile as mobile phase. The overall results showed it underwent significant degradation in acidic, alkaline, and oxidative conditions. In rest of the conditions, osimertinib mesylate was found to be stable or slight degradation was observed in photolytic condition. The structure of DPs was elucidated with a comparison of data generated from high-resolution mass spectrometry (HRMS) of osimertinib mesylate and its degradation products. To confirm the unambiguous regioisomers, one-dimensional (1D) and two-dimentional (2D) nuclear magnetic resonance studies were performed. Furthermore, the N-oxide position was assigned for the first time using the Meisenheimer rearrangement reaction in atmospheric pressure chemical ionization mode. Interestingly, an unusual reaction of DP2 formation was observed at alkaline conditions. In silico tools such as DEREK and Sarah predicted osimertinib mesylate and most of the DPs found to be structural alert for mutagenicity.

Effects of CYP3A4/5 and ABC transporter polymorphisms on osimertinib plasma concentrations in Japanese patients with non-small cell lung cancer

The effects of polymorphisms in CYP3A4 (20230G > A), CYP3A5 (6986A > G), ABCB1 (1236C > T, 2677G > T/A, 3435C > T), ABCG2 (421C > A), and ABCC2 (-24C > T) on the area under the concentration-time curve (AUC) of osimertinib in 23 patients with non-small cell lung cancer were investigated. Blood sampling was performed just prior to and at 1, 2, 4, 6, 8, 12, and 24 h after osimertinib administration at the steady-state on day 15 after beginning therapy. The osimertinib AUC_0-24 was significantly correlated with age (P = 0.038), serum albumin (P = 0.002), and serum creatinine (P = 0.012). Additionally, there were significant differences in the AUC_0-24 of osimertinib among the groups administered vonoprazan, histamine 2-receptor antagonists or esomeprazole, and no acid suppressants (P = 0.021). By contrast, there were no significant differences in the AUC_0-24 of osimertinib between genotypes of CYP3A4/5 or ABC transporters. Furthermore, there were no significant differences in the AUC_0-24 of osimertinib between patients with diarrhea, skin rash, or hepatotoxicity and those without these conditions. In multivariate analysis, only serum albumin value was an independent factor predicting the AUC_0-24 of osimertinib. Analysis of CYP3A4/5 and ABC transporter polymorphisms before osimertinib therapy may not predict the efficacy or side effects of osimertinib. The lower serum albumin values were associated with an increase in the AUC_0-24 of osimertinib; however, further studies are needed to assess the factors contributing to the interindividual variability of osimertinib pharmacokinetics.

Exposure-Response Analysis of Osimertinib in Patients with Advanced Non-Small-Cell Lung Cancer

High interindividual variability (IIV) of the clinical response to epidermal growth factor receptor (EGFR) inhibitors such as osimertinib in non-small-cell lung cancer (NSCLC) might be related to the IIV in plasma exposure. The aim of this study was to evaluate the exposure−response relationship for toxicity and efficacy of osimertinib in unselected patients with advanced EGFR-mutant NSCLC. This retrospective analysis included 87 patients treated with osimertinib. Exposure−toxicity analysis was performed in the entire cohort and survival analysis only in second-line patients (n = 45). No significant relationship between occurrence of dose-limiting toxicity and plasma exposure was observed in the entire cohort (p = 0.23, n = 86). The median overall survival (OS) was approximately two-fold shorter in the 4th quartile (Q4) of osimertinib trough plasma concentration (>235 ng/mL) than in the Q1−Q3 group (12.2 months [CI95% = 8.0−not reached (NR)] vs. 22.7 months [CI95% = 17.1−34.1]), but the difference was not statistically significant (p = 0.15). To refine this result, the exposure−survival relationship was explored in a cohort of 41 NSCLC patients treated with erlotinib. The Q4 erlotinib exposure group (>1728 ng/mL) exhibited a six-fold shorter median OS than the Q1−Q3 group (4.8 months [CI95% = 3.3-NR] vs. 22.8 months (CI95% = 10.6−37.4), p = 0.00011). These results suggest that high exposure to EGFR inhibitors might be related to worse survival in NSCLC patients.

Assessing cytochrome P450 function using genetically engineered mouse models

The ability to knock out and/or humanize different genes in experimental animals, globally or in cell- and tissue-specific patterns, has revolutionized scientific research in many areas. Genetically engineered mouse models, including knockout models, transgenic models, and humanized models, have played important roles in revealing the in vivo functions of various cytochrome P450 (CYP) enzymes. These functions are very diverse, ranging from the biotransformation of drugs and other xenobiotics, events that often dictate their pharmacokinetic or toxicokinetic properties and the associated therapeutic or adverse actions, to the metabolism of endogenous compounds, such as steroid hormones and other bioactive substances, that may determine susceptibility to many diseases, such as cancer and metabolic diseases. In this review, we provide a comprehensive list of Cyp-knockout, human CYP-transgenic, and CYP-humanized mouse models that target genes in the CYP1-4 gene families, and highlight their utility in assessing the in vivo metabolism, bioactivation, and toxicity of various xenobiotic compounds, including therapeutic agents and chemical carcinogens. We aim to showcase the advantages of utilizing these mouse models for in vivo drug metabolism and toxicology studies, and to encourage and facilitate greater utility of engineered mouse models to further improve our knowledge of the in vivo functions of various P450 enzymes, which is integral to our ability to develop safer and more effective therapeutics and to identify individuals predisposed to adverse drug reactions or environmental diseases.

Phase IB Study of Osimertinib in Combination with Navitoclax in EGFR-mutant NSCLC Following Resistance to Initial EGFR Therapy (ETCTN 9903)

PURPOSE

Osimertinib is an effective therapy in EGFR-mutant non-small cell lung cancer (NSCLC), but resistance invariably develops. Navitoclax is an oral inhibitor of BCL-2/BCL-xL that has exhibited synergy with osimertinib in preclinical models of EGFR-mutant NSCLC. In hematologic malignancies, BCL-2 family inhibitors in combination therapy effectively increase cellular apoptosis and decrease drug resistance.

PATIENTS AND METHODS

This single-arm phase Ib study evaluated safety, tolerability, and feasibility of osimertinib and navitoclax, including dose expansion in T790M-positive patients at the recommended phase II dose (RP2D). Eligible patients had advanced EGFR-mutant NSCLC with prior tyrosine kinase inhibitor exposure. Five dose levels were planned with osimertinib from 40 to 80 mg orally daily and navitoclax from 150 to 325 mg orally daily.

RESULTS

A total of 27 patients were enrolled (18 in the dose-escalation cohort and nine in the dose-expansion cohort): median age 65, 67% female, 48% exon 19 del, and 37% L858R, median one prior line of therapy. The most common adverse events were lymphopenia (37%), fatigue (22%), nausea (22%), and thrombocytopenia (37%). No dose-limiting toxicities were seen in dose-escalation cohort; osimertinib 80 mg, navitoclax 150 mg was chosen as the RP2D. Most patients (78%) received >95% of planned doses through three cycles. In expansion cohort, objective response rate was 100% and median progression-free survival was 16.8 months. A proapoptotic effect from navitoclax was demonstrated by early-onset thrombocytopenia.

CONCLUSIONS

Oral combination therapy with navitoclax and osimertinib was safe and feasible at RP2D with clinical efficacy. Early thrombocytopenia was common, supporting an target engagement by navitoclax. Further study of BCL-2/BCL-xL inhibition to enhance osimertinib activity is warranted.

Chromatographic bioanalytical assays for targeted covalent kinase inhibitors and their metabolites

Deriving from targeted kinase inhibitors (TKIs), targeted covalent kinase inhibitors (TCKIs) are a new class of TKIs that are covalently bound to their target residue of kinase receptors. Currently, there are many new TCKIs under clinical development besides afatinib, ibrutinib, osimertinib, neratinib, acalabrutinib, dacomitinib, and zanubrutinib that are already approved by the FDA. Subsequently, there is an increasing demand for bioanalytical methods to qualitatively and quantitively investigate those compounds, leading to a number of papers reporting the development, validation, and use of bioanalytical methods for TCKIs. Most publications describe the technological set up of analytical methods that allow quantification of TCKIs in various biomatrices such as plasma, cerebrospinal fluid, urine, tissue, and liver microsomes. In addition, the identification of metabolites and biotransformation pathways of new TCKIs has gained more interest in recent years. We provide an overview of bioanalytical methods of this new class of TCKIs. The included issues are sample pretreatment, chromatographic separation, detection, and method validation. In the scope of bioanalysis of TCKIs, protein precipitation is mostly applied to treat the biological matrices sample. Liquid chromatographic in reversed-phase mode (RPLC) and mass detection with triple quadrupole (QqQ) are the most often utilized separation and quantitative detection modes, respectively. There may be a possibility of increased use of the high-resolution mass spectrometry (HRMS) for qualitative investigation purposes in the future. We also found that US FDA and EMA guidelines are the most common guidelines employed as validation framework for the bioanalytical methods of TCKIs.

Metabolite Profiling in Anticancer Drug Development: A Systematic Review

Drug metabolism is one of the most important pharmacokinetic processes and plays an important role during the stage of drug development. The metabolite profile investigation is important as the metabolites generated could be beneficial for therapy or leading to serious toxicity. This systematic review aims to summarize the research articles relating to the metabolite profile investigation of conventional drugs and herb-derived compounds for cancer chemotherapy, to examine factors influencing metabolite profiling of these drugs/compounds, and to determine the relationship between therapeutic efficacy and toxicity of their metabolites. The literature search was performed through PubMed and ScienceDirect databases up to January 2019. Out of 830 published articles, 78 articles were included in the analysis based on pre-defined inclusion and exclusion criteria. Both phase I and II enzymes metabolize the anticancer agents/herb-derived compounds . The major phase I reactions include oxidation/hydroxylation and hydrolysis, while the major phase II reactions are glucuronidation, methylation, and sulfation. Four main factors were found to influence metabolite formation, including species, gender, and route and dose of drug administration. Some metabolites were identified as active or toxic metabolites. This information is critical for cancer chemotherapy and anticancer drug development.

Decreased Disposition of Anticancer Drugs Predominantly Eliminated via the Liver in Patients with Renal Failure

Background:

Evidence has revealed that renal impairment can affect the systemic exposure of drugs which are predominantly eliminated via the liver. The modulation of drug-metabolizing enzymes and transporters expressed in the liver and/or small intestine by diverse entities, including uremic toxins, in systemic circulation of patients with severe renal failure is considered as the cause of atypical pharmacokinetics, which sometimes induce undesirable adverse events that are especially critical for drugs with narrow therapeutic window such as anticancer drugs. A dosing strategy for anticancer drugs in these patients needs to be established.

Methods:

The effects of renal impairment on the systemic exposure and safety of anticancer drugs were summarized. The proposed mechanisms for the alterations in the pharmacokinetics of these anticancer drugs were also discussed.

Results:

Changes in pharmacokinetics and clinical response were reported in 9 out of 10 cytotoxic anticancer drugs investigated, although available information was limited and sometimes controversial. Systemic exposure of 3 out of 16 tyrosine kinase inhibitors was higher in patients with severe renal failure than that in patients with normal kidney function. An increase in systemic exposure of anticancer drugs in patients with renal impairment is likely to be observed for substrates of OATP1B1, despite the limited evidence.

Conclusion:

The molecular basis for the effect of uremia on non-renal drug elimination still needed to be clarified with further studies to generate generalizable concepts, which may provide insights into establishing better clinical usage of anticancer drugs, i.e. identifying patients at risk and dose adjustment.

Defining the Contribution of CYP1A1 and CYP1A2 to Drug Metabolism Using Humanized CYP1A1/1A2 and Cyp1a1/Cyp1a2 Knockout Mice

Cytochrome P450s CYP1A1 and CYP1A2 can metabolize a broad range of foreign compounds and drugs. However, these enzymes have significantly overlapping substrate specificities. To establish their relative contribution to drug metabolism in vivo, we used a combination of mice humanized for CYP1A1 and CYP1A2 together with mice nulled at the Cyp1a1 and Cyp1a2 gene loci. CYP1A2 was constitutively expressed in the liver, and both proteins were highly inducible by 2,3,7,8-tetrachlorodibenzodioxin (TCDD) in a number of tissues, including the liver, lung, kidney, and small intestine. Using the differential inhibition of the human enzymes by quinidine, we developed a method to distinguish the relative contribution of CYP1A1 or CYP1A2 in the metabolism of drugs and foreign compounds. Both enzymes made a significant contribution to the hepatic metabolism of the probe compounds 7-methoxy and 7-ehthoxyresorufin in microsomal fractions from animals treated with TCDD. This enzyme kinetic approach allows modeling of the CYP1A1, CYP1A2, and non-CYP1A contribution to the metabolism of any substrate at any substrate, inhibitor, or enzyme concentration and, as a consequence, can be integrated into a physiologically based pharmacokinetics model. The validity of the model can then be tested in humanized mice in vivo. SIGNIFICANCE STATEMENT: Human CYP1A1 and CYP1A2 are important in defining the efficacy and toxicity/carcinogenicity of drugs and foreign compounds. In light of differences in substrate specificity and sensitivity to inhibitors, it is of central importance to understand their relative role in foreign compound metabolism. To address this issue, we have generated mice humanized or nulled at the Cyp1a gene locus and, through the use of these mouse lines and selective inhibitors, developed an enzyme kinetic-based model to enable more accurate prediction of the fate of new chemicals in humans and which can be validated in vivo using mice humanized for cytochrome P450-mediated metabolism.

Brain accumulation of osimertinib and its active metabolite AZ5104 is restricted by ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein)

Osimertinib is an irreversible EGFR inhibitor registered for advanced NSCLC patients whose tumors harbor recurrent somatic activating mutations in EGFR (EGFRm⁺) or the frequently occurring EGFR-T790M resistance mutation. Using in vitro transport assays and appropriate knockout and transgenic mouse models, we investigated whether the multidrug efflux transporters ABCB1 and ABCG2 transport osimertinib and whether they influence the oral availability and brain accumulation of osimertinib and its most active metabolite, AZ5104. In vitro, human ABCB1 and mouse Abcg2 modestly transported osimertinib. In mice, Abcb1a/1b, with a minor contribution of Abcg2, markedly limited the brain accumulation of osimertinib and AZ5104. However, no effect of the ABC transporters was seen on osimertinib oral availability. In spite of up to 6-fold higher brain accumulation, we observed no acute toxicity signs of oral osimertinib in Abcb1a/1b;Abcg2 knockout mice. Interestingly, even in wild-type mice the intrinsic brain penetration of osimertinib was already relatively high, which may help to explain the documented partial efficacy of this drug against brain metastases. No substantial effects of mouse Cyp3a knockout or transgenic human CYP3A4 overexpression on oral osimertinib pharmacokinetics were observed, presumably due to a dominant role of mouse Cyp2d enzymes in osimertinib metabolism. Our results suggest that pharmacological inhibition of ABCB1 and ABCG2 during osimertinib therapy might potentially be considered to further benefit patients with brain (micro-)metastases positioned behind an intact blood-brain barrier, or with substantial expression of these transporters in the tumor cells, without invoking a high toxicity risk.

An Extensively Humanized Mouse Model to Predict Pathways of Drug Disposition and Drug/Drug Interactions, and to Facilitate Design of Clinical Trials

Species differences in drug metabolism and disposition can confound the extrapolation of in vivo PK data to man and also profoundly compromise drug efficacy studies owing to differences in pharmacokinetics, in metabolites produced (which are often pharmacologically active), and in differential activation of the transcription factors constitutive androstane receptor (CAR) and pregnane X receptor (PXR), which regulate the expression of such enzymes as P450s and drug transporters. These differences have gained additional importance as a consequence of the use of genetically modified mouse models for drug-efficacy testing and also patient-derived xenografts to predict individual patient responses to anticancer drugs. A number of humanized mouse models for cytochrome P450s, CAR, and PXR have been reported. However, the utility of these models has been compromised by the redundancy in P450 reactions across gene families, whereby the remaining murine P450s can metabolize the compounds being tested. To remove this confounding factor and create a mouse model that more closely reflects human pathways of drug disposition, we substituted 33 murine P450s from the major gene families involved in drug disposition, together with Car and Pxr, for human CAR, PXR, CYP1A1, CYP1A2, CYP2C9, CYP2D6, CYP3A4, and CYP3A7. We also created a mouse line in which 34 P450s were deleted from the mouse genome. Using model compounds and anticancer drugs, we demonstrated how these mouse lines can be applied to predict drug-drug interactions in patients and discuss here their potential application in the more informed design of clinical trials and the personalized treatment of cancer.

Modulation of Fexofenadine Pharmacokinetics by Osimertinib in Patients With Advanced EGFR-Mutated Non-Small Cell Lung Cancer

Osimertinib is a potent, third-generation, irreversible, central nervous system active epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) that selectively inhibits EGFR-TKI sensitizing and EGFR T790M resistance mutations. It is approved for first-line treatment of patients with advanced non-small cell lung cancer (NSCLC) whose tumors have EGFR exon 19 deletions or exon 21 L858R mutations, and for patients with T790M-positive advanced NSCLC whose disease has progressed on or after EGFR-TKI therapy. This study investigated the pharmacokinetics (PK) of fexofenadine (P-glycoprotein substrate) following single- and multiple-dose osimertinib in patients with advanced NSCLC who have progressed on prior EGFR-TKI therapy. This open-label, phase 1 study (NCT02908750) comprised the PK phase and continued access phase. The former comprised 2 distinct periods with a 3- to 7-day washout: treatment period 1 (n = 24, fexofenadine 120 mg, day 1) and treatment period 2 (fexofenadine 120 mg + osimertinib 80 mg single dose on days 1 and 39 and osimertinib 80 mg once daily from days 4 to 41). Patients could continue osimertinib 80 mg once daily based on investigator's discretion in the continued access phase. Fexofenadine area under the plasma concentration-time curve and maximum concentration increased by 56% (90% confidence interval [CI], 35.4-78.6) and 76% (90%CI, 49.3-108.3) following coadministration with osimertinib single dose, and by 27% (90%CI, 11.2-45.8) and 25% (90%CI, 5.6-48.1) when given with osimertinib at steady state, respectively. Following osimertinib coadministration, median fexofenadine time to maximum concentration increased by approximately 30 minutes compared with time to maximum concentration following fexofenadine alone. No new osimertinib safety findings were observed. The increase in fexofenadine exposure following osimertinib coadministration shows osimertinib as a weak P-glycoprotein inhibitor.

Biomarker Testing for Patients With Advanced Non-Small Cell Lung Cancer: Real-World Issues and Tough Choices

Over the last decade, the treatment of patients with advanced non-small cell lung cancer (NSCLC) has become reliant on tissue and/or blood biomarkers to help guide treatment decisions. There are now multiple biomarker-defined patient subgroups, with evidence showing that treatment with targeted therapies has superior clinical outcomes when compared with traditional cytotoxic chemotherapy. However, rapid change in the field of precision oncology brings with it the challenge of translating recommendations into clinical practice. In this review, we discuss the major guidelines recommending biomarker testing in NSCLC, as well the logistical challenges to applying these guidelines to patients with NSCLC both in the United States and worldwide. The techniques commonly used for biomarker testing will be discussed, both for tissue- and blood-based biomarkers. Finally, we discuss the challenge of interpreting the results of biomarker testing and using these results to guide treatment decisions.

P450-Humanized and Human Liver Chimeric Mouse Models for Studying Xenobiotic Metabolism and Toxicity

Preclinical evaluation of drug candidates in experimental animal models is an essential step in drug development. Humanized mouse models have emerged as a promising alternative to traditional animal models. The purpose of this mini-review is to provide a brief survey of currently available mouse models for studying human xenobiotic metabolism. Here, we describe both genetic humanization and human liver chimeric mouse models, focusing on the advantages and limitations while outlining their key features and applications. Although this field of biomedical science is relatively young, these humanized mouse models have the potential to transform preclinical drug testing and eventually lead to a more cost-effective and rapid development of new therapies.