Novel Pathways of Ponatinib Disposition Catalyzed By CYP1A1 Involving Generation of Potentially Toxic Metabolites

Dimethylmonothioarsinic acid (DMMTAV) differentially modulates the expression of AHR-regulated cytochrome P450 1A enzymes in vivo and in vitro

Dimethylmonothioarsinic acid (DMMTAV), a pentavalent thio-arsenic derivative, has been found in bodily fluids and tissues including urine, liver, kidney homogenates, plasma, and red blood cells. Although DMMTAV is a minor metabolite in humans and animals, its substantial toxicity raises concerns about potential carcinogenic effects. This toxicity could be attributed to arsenicals' ability to regulate cytochrome P450 1 A (CYP1A) enzymes, pivotal in procarcinogen activation or detoxification. The current study investigates DMMTAV's impact on CYP1A1/2 expression, individually and in conjunction with its inducer, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). C57BL/6 mice were intraperitoneally injected with 6 mg/kg DMMTAV, alone or with 15 μg/kg TCDD, for 6 and 24 h. Similarly, Hepa-1c1c7 cells were exposed to DMMTAV (0.5, 1, and 2 μM) with or without 1 nM TCDD for 6 and 24 h. DMMTAV hindered TCDD-induced elevation of Cyp1a1 mRNA, both in vivo (at 6 h) and in vitro, associated with reduced CYP1A regulatory element activation. Interestingly, in C57BL/6 mice, DMMTAV boosted TCDD-induced CYP1A1/2 protein and activity, unlike Hepa-1c1c7 cells where it suppressed both. DMMTAV co-exposure increased TCDD-induced Cyp1a2 mRNA. While Cyp1a1 mRNA stability remained unchanged, DMMTAV negatively affected protein stability, indicated by shortened half-life. Baseline levels of CYP1A1/2 mRNA, protein, and catalytic activities showed no significant alterations in DMMTAV-treated C57BL/6 mice and Hepa-1c1c7 cells. Taken together, these findings indicate, for the first time, that DMMTAV differentially modulates the TCDD-mediated induction of AHR-regulated enzymes in both liver of C57BL/6 mice and murine Hepa-1c1c7 cells suggesting that thio-arsenic pentavalent metabolites are extremely reactive and could play a role in the toxicity of arsenic.

Clinical pharmacokinetics and drug-drug interactions of tyrosine-kinase inhibitors in chronic myeloid leukemia: A clinical perspective

In the past decade, numerous tyrosine kinase inhibitors (TKIs) have been introduced in the treatment of chronic myeloid leukemia. Given the significant interpatient variability in TKIs pharmacokinetics, potential drug-drug interactions (DDIs) can greatly impact patient therapy. This review aims to discuss the pharmacokinetic characteristics of TKIs, specifically focusing on their absorption, distribution, metabolism, and excretion profiles. Additionally, it provides a comprehensive overview of the utilization of TKIs in special populations such as the elderly, children, and patients with liver or kidney dysfunction. We also highlight known or suspected DDIs between TKIs and other drugs, highlighting various clinically relevant interactions. Moreover, specific recommendations are provided to guide haemato-oncologists, oncologists, and clinical pharmacists in managing DDIs during TKI treatment in daily clinical practice.

Arsenic trioxide (ATO) up-regulates cytochrome P450 1A (CYP1A) enzymes in murine hepatoma Hepa-1c1c7 cell line

Arsenic trioxide (ATO) is a highly toxic arsenical which has been successfully exploited for treating acute promyelocytic leukemia (APL). Unfortunately, its therapeutic efficacy is accompanied by serious toxicities with undeciphered mechanisms. Cytochrome P450 1A (CYP1A) enzymes undergo modulation by arsenicals, with ensuing critical consequences regarding drug clearance or procarcinogen activation. Here, we investigated the potential of ATO to alter basal and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced CYP1A1/1A2 expressions. Mouse-derived hepatoma Hepa-1c1c7 cells were exposed to 0.63, 1.25, and 2.5μM ATO with or without 1nM TCDD. ATO increased TCDD-induced CYP1A1/1A2 mRNA, protein, and activity. Constitutively, ATO induced Cyp1a1/1a2 transcripts and CYP1A2 protein. ATO increased AHR nuclear accumulation and subsequently increased XRE-luciferase reporter activity. ATO enhanced CYP1A1 mRNA and protein stabilities. In conclusion, ATO up-regulates CYP1A in Hepa-1c1c7 cells transcriptionally, post-transcriptionally, and post-translationally. Therefore, ATO can be implicated in clearance-related interactions with CYP1A1/1A2 substrates, or in excessive activation of environmental procarcinogens.

Modulation of cytochrome P450 1A (CYP1A) enzymes by monomethylmonothioarsonic acid (MMMTAV) in vivo and in vitro

Inorganic arsenic (iAs) is a natural toxicant which, upon entering the biosphere, undergoes extensive biotransformation and becomes a portal for generating various organic intermediates/products. The chemical diversity of iAs-derived organoarsenicals (oAs) is accompanied by varying degree of toxicity that can be held responsible, at least partly, for the overall health outcome of the originally encountered parent inorganic molecule. Such toxicity may originate from arsenicals ability to modulate cytochrome P450 1A (CYP1A) enzymes, whose activity is critical in activating/detoxifying procarcinogens. In this study, we evaluated the effect of monomethylmonothioarsonic acid (MMMTA^V) on CYP1A1 and CYP1A2 in absence and presence of their inducer; 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Therefore, C57BL/6 mice were intraperitoneally injected with 12.5 mg/kg MMMTA^V, with or without 15 μg/kg TCDD for 6 and 24 h. Moreover, murine Hepa-1c1c7 and human HepG2 cells were treated with MMMTA^V (1, 5, and 10 μM), with or without 1 nM TCDD for 6 and 24 h. MMMTA^V significantly inhibited TCDD-mediated induction of CYP1A1 mRNA, both in vivo and in vitro. This effect was attributed to decreased transcriptional activation of CYP1A regulatory element. Interestingly, MMMTA^V significantly increased TCDD-induced CYP1A1 protein and activity in C57BL/6 mice and Hepa-1c1c7 cells, while both were significantly inhibited by MMMTA^V treatment in HepG2 cells. CYP1A2 mRNA, protein and activity induced by TCDD were significantly increased by MMMTA^V co-exposure. MMMTA^V had no effect on CYP1A1 mRNA stability or protein stability and did not alter their half-lives. At basal level, only CYP1A1 mRNA was significantly decreased in MMMTA^V-treated Hepa-1c1c7 cells. Our findings show that MMMTA^V exposure potentiates procarcinogen-induced catalytic activity of both CYP1A1 and CYP1A2 in vivo. This effect entails excessive activation of such procarcinogens upon co-exposure, with potentially negative health-related outcomes.

Metabolic activation of tyrosine kinase inhibitors: recent advance and further clinical practice

At present, receptor tyrosine kinase signaling-related pathways have been successfully mediated to inhibit tumor proliferation and promote anti-angiogenesis effects for cancer therapy. Tyrosine kinase inhibitors (TKIs), a group of novel chemotherapeutic agents, have been applied to treat diverse malignant tumors effectively. However, the latent toxic and side effects of TKIs, such as hepatotoxicity and cardiotoxicity, limit their use in clinical practice. Metabolic activation has the potential to lead to toxic effects. Numerous TKIs have been demonstrated to be transformed into chemically reactive/potentially toxic metabolites following cytochrome P450-catalyzed activation, which causes severe adverse reactions, including hepatotoxicity, cardiotoxicity, skin toxicity, immune injury, mitochondria injury, and cytochrome P450 inactivation. However, the precise mechanisms of how these chemically reactive/potentially toxic species induce toxicity remain poorly understood. In addition, we present our viewpoints that regulating the production of reactive metabolites may decrease the toxicity of TKIs. Exploring this topic will improve understanding of metabolic activation and its underlying mechanisms, promoting the rational use of TKIs. This review summarizes the updated evidence concerning the reactive metabolites of TKIs and the associated toxicities. This paper provides novel insight into the safe use of TKIs and the prevention and treatment of multiple TKIs adverse effects in clinical practice.

Tyrosine kinase inhibitor-loaded biomimetic nanoparticles as a treatment for osteosarcoma

Small-molecule tyrosine kinase inhibitors (TKIs) represent a potentially powerful approach to the treatment of osteosarcoma (OS). However, dose-limiting toxicity, therapeutic efficacy, and targeting specificity are significant barriers to the use of TKIs in the clinic. Notably among TKIs, ponatinib demonstrated potent anti-tumor activity; however, it received an FDA black box warning for potential side effects. We propose ponatinib-loaded biomimetic nanoparticles (NPs) to repurpose ponatinib as an efficient therapeutic option for OS. In this study, we demonstrate enhanced targeting ability and maintain potent ponatinib nano-therapeutic activity, while also reducing toxicity. In in vitro two- and three-dimensional models, we demonstrate that ponatinib-loaded biomimetic NPs maintain the efficacy of the free drug, while in vivo we show that they can improve tumor targeting, slow tumor growth, and reduce evidence of systemic toxicities. Though there is limited Pon encapsulation within NPs, this platform may improve current therapeutic approaches and reduce dosage-related side effects to achieve better clinical outcomes in OS patients.

Graphical Abstract

Down-regulation of hepatic cytochromes P450 1A1 and 1A2 by arsenic trioxide (ATO) in vivo and in vitro: A role of heme oxygenase 1

Arsenic trioxide (ATO) has evolved from an environmental threat to a successful therapy for acute promyelocytic leukemia (APL) and probably for solid tumors in the future. However, its efficacy comes at a cost of multi-organ toxicity whose mechanism remains unresolved. Arsenicals have been reported to modulate cytochrome P450 1A (CYP1A) enzymes, thus modifying activation/detoxification of drugs/procarcinogens. Therefore, this study aimed to investigate the possible effects of ATO on CYP1A1 and CYP1A2, in absence and presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) using in vivo and in vitro models. For this purpose, C57BL/6 mice were intraperitoneally injected with 8 mg/kg ATO with or without 15 μg/kg TCDD for 6 and 24 h. Furthermore, HepG2 cells were treated with ATO (1, 5, and 10 μM) with or without 1 nM TCDD for 6 and 24 h. ATO significantly inhibited TCDD-mediated induction of CYP1A1/1A2 mRNA, protein, and activity in both models. ATO differentially modulated CYP1A1/1A2 basal levels in vivo. We also demonstrated that ATO downregulates CYP1A through inhibiting the transcriptional activation of its regulatory element at both basal and inducible levels. Additionally, ATO significantly induced mRNA and protein of heme oxygenase 1 (HMOX1) in vivo and in vitro. In HepG2 cells, inhibition of HMOX1 by tin (IV) mesoporphyrin (IX) (SnMP) resulted in a partial restoration of the TCDD-mediated induction of CYP1A1 activity that was inhibited by ATO co-exposure. Our findings show that ATO alters both constitutive and inducible CYP1A1/1A2 expressions through transcriptional and HMOX1-mediated post-translational mechanisms. This implies the possible involvement of ATO in clearance-related consequences for the substrates of these enzymes such as drug-drug interactions or suboptimal toxicant elimination.

Sex-related differential susceptibility to ponatinib cardiotoxicity and differential modulation of the Notch1 signalling pathway in a murine model

Ponatinib (PON), a tyrosine kinase inhibitor approved in chronic myeloid leukaemia, has proven cardiovascular toxicity. We assessed mechanisms of sex‐related PON‐induced cardiotoxicity and identified rescue strategies in a murine model. PON+scrambled siRNA‐treated male mice had a higher number of TUNEL‐positive cells (%TdT+6.12 ± 0.17), higher percentage of SA‐β‐gal‐positive senescent cardiac area (%SA‐β‐gal 1.41 ± 0.59) and a lower reactivity degree (RD) for the survival marker Bmi1 [Abs (OD) 5000 ± 703] compared to female (%TdT+3.75 ± 0.35; %SA‐β‐gal 0.77 ± 0.02; Bmi1 [Abs (OD) 8567 ± 2173]. Proteomics analysis of cardiac tissue showed downstream activation of cell death in PON+siRNA scrambled compared to vehicle or PON+siRNA‐Notch1‐treated male mice. Upstream analysis showed beta‐oestradiol activation, and downstream analysis showed activation of cell survival and inhibition of cell death in PON+scrambled siRNA compared to vehicle or PON+siRNA‐Notch1‐treated female mice. PON+scrambled siRNA‐treated mice also had a downregulation of cardiac actin—more marked in males—and vessel density—more marked in females. Female hearts showed greater cardiac fibrosis than their male counterparts at baseline, with no significant change after PON treatment. PON+siRNA‐scrambled mice had less fibrosis than vehicle or PON+siRNA‐Notch1‐treated mice. The left ventricular systolic dysfunction showed by PON+scrambled siRNA‐treated mice (male %EF 28 ± 9; female %EF 36 ± 7) was reversed in both PON+siRNA‐Notch1‐treated male (%EF 53 ± 9) and female mice (%EF 52 ± 8). We report sex‐related differential susceptibility and Notch1 modulation in PON‐induced cardiotoxicity. This can help to identify biomarkers and potential mechanisms underlying sex‐related differences in PON‐induced cardiotoxicity.

Hepatotoxicity of FDA-approved small molecule kinase inhibitors

Introduction: Given their importance in cellular processes and association with numerous diseases, protein kinases have emerged as promising targets for drugs. The FDA has approved greater than fifty small molecule kinase inhibitors (SMKIs) since 2001. Nevertheless, severe hepatotoxicity and related fatal cases have grown as a potential challenge in the advancement of these drugs, and the identification and diagnosis of drug-induced liver injury (DILI) are thorny problems for clinicians.Areas covered: This article summarizes the progression and analyzes the significant features in the study of SMKI hepatotoxicity, including clinical observations and investigations of the underlying mechanisms.Expert opinion: The understanding of SMKI-associated hepatotoxicity relies on the development of preclinical models and improvement of clinical assessment. With a full understanding of the role of inflammation in DILI and the mediating role of cytokines in inflammation, cytokines are promising candidates as sensitive and specific biomarkers for DILI. The emergence of three-dimensional spheroid models demonstrates potential use in providing clinically relevant data and predicting hepatotoxicity of SMKIs.

Inhibition and induction of CYP enzymes in humans: an update

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug–drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug–drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Advances in the study of drug metabolism - symposium report of the 12th Meeting of the International Society for the Study of Xenobiotics (ISSX)

The 12th International Society for the Study of Xenobiotics (ISSX) meeting, held in Portland, OR, USA from July 28 to 31, 2019, was attended by diverse members of the pharmaceutical sciences community. The ISSX New Investigators Group provides learning and professional growth opportunities for student and early career members of ISSX. To share meeting content with those who were unable to attend, the ISSX New Investigators herein elected to highlight the "Advances in the Study of Drug Metabolism" symposium, as it engaged attendees with diverse backgrounds. This session covered a wide range of current topics in drug metabolism research including predicting sites and routes of metabolism, metabolite identification, ligand docking, and medicinal and natural products chemistry, and highlighted approaches complemented by computational modeling. In silico tools have been increasingly applied in both academic and industrial settings, alongside traditional and evolving in vitro techniques, to strengthen and streamline pharmaceutical research. Approaches such as quantum mechanics simulations facilitate understanding of reaction energetics toward prediction of routes and sites of drug metabolism. Furthermore, in tandem with crystallographic and orthogonal wet lab techniques for structural validation of drug metabolizing enzymes, in silico models can aid understanding of substrate recognition by particular enzymes, identify metabolic soft spots and predict toxic metabolites for improved molecular design. Of note, integration of chemical synthesis and biosynthesis using natural products remains an important approach for identifying new chemical scaffolds in drug discovery. These subjects, compiled by the symposium organizers, presenters, and the ISSX New Investigators Group, are discussed in this review.

Utilizing Stimulated Raman Scattering Microscopy To Study Intracellular Distribution of Label-Free Ponatinib in Live Cells

Stimulated Raman scattering (SRS) microscopy represents a powerful method for imaging label-free drug distribution with high resolution. SRS was applied to image label-free ponatinib with high sensitivity and specificity in live human chronic myeloid leukemia (CML) cell lines. This was achieved at biologically relevant, nanomolar concentrations, allowing determination of ponatinib uptake and sequestration into lysosomes during the development of acquired drug resistance and an improved understanding of target engagement.

In vitro metabolites characterization of ponatinib in human liver microsomes using ultra-high performance liquid chromatography combined with Q-Exactive-Orbitrap tandem mass spectrometry

Ponatinib is an oral drug for the treatment of chronic myeloid leukemia and acute lymphoblastic leukemia, which has been reported to increase the risk of hepatotoxicity. The aim of this study was to characterize the metabolites of ponatinib in human liver microsomes as well as its reactive metabolites. Ponatinib was incubated with human liver microsomes in the presence of NADPH and trapping agents (glutathione or potassium cyanide). The metabolites were characterized by liquid chromatography in combination with Q-Exactive-Orbitrap-MS. Under the current conditions, six metabolites were detected and structurally identified on the basis of their accurate masses, fragmentation patterns, and retention times. M3 (N-demethylation) was unambiguously identified by matching its retention time and fragment ions with those of its reference standard. N-demethylation and oxygenation were proved to be the predominant metabolic pathways of ponatinib. In addition, two reactive metabolites (cyano adducts) were detected in human liver microsomes in the presence of potassium cyanide and NADPH, suggesting that ponatinib underwent CYP450-mediated metabolic activation, which could be one of the causative mechanisms for its hepatotoxicity. The current study provides new information regarding the metabolic profiles of ponatinib and would be helpful in understanding the effectiveness and toxicity of ponatinib, especially the mechanism of hepatotoxicity.

Human Cytochrome P450 1A1 Adapts Active Site for Atypical Nonplanar Substrate

The human cytochrome P450 1A1 (CYP1A1) is well known for chemical activation of procarcinogens and often has a substrate scope of small and highly planar compounds. Substrates deviating from these characteristics are certainly known, but how these larger and nonplanar substrates are accommodated and oriented within the CYP1A1 active site is not understood. Herein a new X-ray structure of CYP1A1 bound to the pan-Pim kinase inhibitor GDC-0339 reveals how the CYP1A1 active site cavity is reconfigured to bind larger and nonplanar compounds. The shape and size of the cavity are controlled by structural elements in the active site roof, with major changes in the conformation of the F helix break and relocation of Phe224 from the active site to the protein surface. This altered CYP1A1 active site architecture is consistent with the proposed mechanism for CYP1A1 generation of an unusual aminoazepane-rearranged metabolite for this substrate. SIGNIFICANCE STATEMENT: Cytochrome P450 1A1 metabolizes drugs, procarcinogens, and toxins and although previous structures have revealed how its stereotypical planar, aromatic compounds are accommodated in the CYP1A1 active site, this is not the case for flexible and nonplanar compounds. The current work determines the X-ray structure of CYP1A1 with such a flexible, nonplanar Pim kinase inhibitor, revealing significant modification of the CYP1A1 roof that accommodate this preclinical candidate and support an unusual intramolecular rearrangement reaction.

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.

Netarsudil Ophthalmic Solution 0.02%: First Global Approval

Netarsudil ophthalmic solution 0.02% (hereafter referred to as netarsudil 0.02%) [Rhopressa^®] is a Rho-associated protein kinase inhibitor that is thought to lower intraocular pressure (IOP) by increasing aqueous humour outflow through the trabecular meshwork. It has been developed by Aerie Pharmaceuticals and was recently approved in the USA for the reduction of elevated IOP in patients with open-angle glaucoma or ocular hypertension. The recommended dosage is one drop in the affected eye(s) once daily in the evening. Phase III development in the EU and phase II development in Japan are underway for this indication. This article summarizes the milestones in the development of netarsudil 0.02% leading to this first approval for the reduction of elevated IOP in patients with open-angle glaucoma or ocular hypertension.

Structures of human cytochrome P450 1A1 with bergamottin and erlotinib reveal active-site modifications for binding of diverse ligands

Human cytochrome P450 1A1 (CYP1A1) is an extrahepatic enzyme involved in the monooxygenation of structurally diverse compounds ranging from natural products to drugs and protoxins. Because CYP1A1 has a role in human carcinogenesis, inhibiting its activity may potentially aid in cancer chemoprevention, whereas utilizing CYP1A1's oxidative activity could help selectively activate anticancer prodrugs. Such potential therapeutic purposes require detailed knowledge of CYP1A1's interactions with potential ligands. Known CYP1A1 ligands also vary substantially in size, and it has not been apparent from a single existing CYP1A1 structure how larger, structurally diverse ligands are accommodated within the enclosed active site. Here, two new X-ray structures with the natural product furanocoumarin bergamottin (at 2.85 Å resolution) and the lung cancer drug erlotinib (3.0 Å) revealed binding orientations consistent with the formation of innocuous metabolites and of toxic metabolites, respectively. They also disclosed local changes in the roof of the active site that enlarge the active site and ultimately form a channel to the protein exterior. Although further structural modifications would be required to accommodate the largest CYP1A1 ligands, knowing which components of the active site are malleable provides powerful information for those attempting to use computational approaches to predict compound binding and substrate metabolism by this clinically relevant monooxygenase.

Role of Cytochrome P450 Enzymes in the Metabolic Activation of Tyrosine Kinase Inhibitors

Tyrosine kinase inhibitors are a rapidly expanding class of molecular targeted therapies for the treatment of various types of cancer and other diseases. An increasing number of clinically important small molecule tyrosine kinase inhibitors have been shown to undergo cytochrome P450-mediated bioactivation to form chemically reactive, potentially toxic products. Metabolic activation of tyrosine kinase inhibitors is proposed to contribute to the development of serious adverse reactions, including idiosyncratic hepatotoxicity. This article will review recent findings and ongoing studies to elucidate the link between drug metabolism and tyrosine kinase inhibitor-associated hepatotoxicity.

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.

The role of hepatic cytochrome P450s in the cytotoxicity of dronedarone

Dronedarone is used to treat patients with cardiac arrhythmias and has been reported to be associated with liver injury. Our previous mechanistic work demonstrated that DNA damage-induced apoptosis contributes to the cytotoxicity of dronedarone. In this study, we examined further the underlying mechanisms and found that after a 24-h treatment of HepG2 cells, dronedarone caused cytotoxicity, G1-phase cell cycle arrest, suppression of topoisomerase II, and DNA damage in a concentration-dependent manner. We also investigated the role of cytochrome P450s (CYPs)-mediated metabolism in the dronedarone-induced toxicity using our previously established HepG2 cell lines expressing individually 14 human CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). We demonstrated that CYP3A4, 3A5, and 2D6 were the major enzymes that metabolize dronedarone, and that CYP3A7, 2E1, 2C19, 2C18, 1A1, and 2B6 also metabolize dronedarone, but to a lesser extent. Our data showed that the cytotoxicity of dronedarone was decreased in CYP3A4-, 3A5-, or 2D6-overexpressing cells compared to the control HepG2 cells, indicating that the parent dronedarone has higher potency than the metabolites to induce cytotoxicity in these cells. In contrast, cytotoxicity was increased in CYP1A1-overexpressing cells, demonstrating that CYP1A1 exerts an opposite effect in dronedarone's toxicity, comparing to CYP3A4, 3A5, or 2D6. We also studied the involvement of topoisomerase II in dronedarone-induced toxicity, and demonstrated that the overexpression of topoisomerase II caused an increase in cell viability and a decrease in γ-H2A.X induction, suggesting that suppression of topoisomerase II may be one of the mechanisms involved in dronedarone-induced liver toxicity.