Role of human liver microsomal CYP3A4 and CYP2B6 in catalyzing N-dechloroethylation of cyclophosphamide and ifosfamide

Prodrugs in Oncology: Bioactivation and Impact on Therapeutic Efficacy and Toxicity

A prodrug is a molecule that lacks pharmacological activity, but upon enzymatic bioactivation, it can generate a therapeutically active molecule. The primary reason behind the design of a prodrug is to help circumvent challenges associated with the physicochemical properties of a drug molecule, such as solubility, absorption, distribution, and instability. Chemotherapy has been at the forefront of cancer treatment for over 70 years due to its ability to target rapidly proliferating tumor cells. However, a major concern with conventional chemotherapy is the lack of selectivity and its associated side toxicity, which can severely impact patients' quality of life. In oncology, prodrugs have been explored to enhance the bioavailability, improve efficacy, and minimize systemic toxicity of chemotherapeutic agents. Prodrugs activated by enzymes unique to a tumor microenvironment can significantly increase targeted delivery of chemotherapeutic drugs. This review aims to highlight commonly used chemotherapeutic prodrugs, including both alkylating and non-alkylating agents, and discuss their clinical relevance, mechanisms of bioactivation, and toxicity concerns.

Drug-drug interactions in HIV-infected patients receiving chemotherapy

INTRODUCTION

Coadministration of antiretrovirals and anti-cancer medications may present many complex clinical scenarios. This is characterized by the potential for drug-drug interactions (DDIs) and the challenges that arise in patient management. In this article, we investigate the potential for DDIs between antiretrovirals, including protease inhibitors (PIs), non-nucleoside reverse transcriptase inhibitors, nucleoside reverse transcriptase inhibitors (NRTIs), integrase strand transfer inhibitors (INSTIs), and anti-cancer medications.

AREAS COVERED

PubMed, Google Scholar, and Clinicaltrials.gov were searched for relevant articles in April 2024. Our review highlights PIs and NNRTIs as particularly prone to DDIs with anticancer agents, with implications for efficacy and toxicity of concomitant cancer therapy. We explain the mechanisms for interactions, emphasizing the significance of pharmacokinetic effects and enzyme induction or inhibition. We discuss clinical challenges encountered in the management of patients receiving combined ART and cancer therapy regimens.

EXPERT OPINION

Data are lacking for potential DDIs between antiretroviral and anti-cancer agents. While some interactions are documented, others are theoretical and based on the pharmacokinetic properties of the medications. Awareness of these interactions, inter-collaborative care between healthcare providers, and standardized treatment guidelines are all crucial for achieving optimal treatment outcomes and ensuring the well-being of patients with HIV/AIDS and cancer comorbidities.

Functional significance of CYP2B6 gene rare allelic variants identified in Japanese individuals

Cytochrome P450 2B6 (CYP2B6) catalyzes the metabolism of many drugs, including efavirenz and propofol. Genetic polymorphisms in CYP2B6 alter its enzymatic activity and substantially affect its pharmacokinetics. High-frequency variants, such as CYP2B6*6, are associated with the risk of developing side effects due to reduced CYP2B6 activity. However, the impact of rare alterations on enzyme function remains unknown, and some of these variants may significantly decrease the CYP2B6 activity. Therefore, in this study, we evaluated in vitro the functional alterations in 29 missense variants of the CYP2B6 gene identified in 8,380 Japanese individuals. Wild-type CYP2B6 and 29 rare CYP2B6 variants were transiently expressed in mammalian cells. The expression levels of variant CYP2B6 proteins in the microsomal fractions extracted from 293FT cells were assessed using western blotting and reduced-carbon monoxide difference spectroscopy, and a specific peak at 450 nm was detected in the wild-type and 19 variants. Furthermore, kinetic parameters were determined by assaying the reactions with efavirenz and propofol and quantifying the metabolite concentrations. We found that 12 variants had significantly lower or abolished enzymatic activity with both the substrates. In silico three-dimensional docking and molecular-dynamics simulations suggested that these functional changes were due to conformational changes in essential regions, such as the heme-binding site and ligand channels involved in transporting substrates to the active site. These findings have implications for predicting the plasma concentrations of CYP2B6 substrates and controlling their side effects.

Clinical Implications of Co-administering Apixaban with Key Interacting Medications

With many available data sources, clinicians need to consider the benefit-risk profile of individual anticoagulants when balancing the need for anticoagulation, including evaluating the risks in patients with comorbidities and potential drug-drug interactions. This narrative review presents clinical data across multiple phases of drug development for the use of apixaban, a selective factor Xa inhibitor, when taken concomitantly with other agents, and evaluates the benefit-risk profile of apixaban with these interacting medications. Key subgroup analyses from the phase 3 ARISTOTLE trial (NCT00412984) are presented using data from patients who received either concomitant inhibitors or inducers of cytochrome P450 3A4 and/or P‑glycoprotein. We also review the available evidence for the use of apixaban in patients with cancer-associated thromboembolism, as well as the use of apixaban in patients with COVID-19.

Docetaxel, cyclophosphamide, and epirubicin: application of PBPK modeling to gain new insights for drug-drug interactions

The new adjuvant chemotherapy of docetaxel, epirubicin, and cyclophosphamide has been recommended for treating breast cancer. It is necessary to investigate the potential drug-drug Interactions (DDIs) since they have a narrow therapeutic window in which slight differences in exposure might result in significant differences in treatment efficacy and tolerability. To guide clinical rational drug use, this study aimed to evaluate the DDI potentials of docetaxel, cyclophosphamide, and epirubicin in cancer patients using physiologically based pharmacokinetic (PBPK) models. The GastroPlus™ was used to develop the PBPK models, which were refined and validated with observed data. The established PBPK models accurately described the pharmacokinetics (PKs) of three drugs in cancer patients, and the predicted-to-observed ratios of all the PK parameters met the acceptance criterion. The PBPK model predicted no significant changes in plasma concentrations of these drugs during co-administration, which was consistent with the observed clinical phenomenon. Besides, the verified PBPK models were then used to predict the effect of other Cytochrome P450 3A4 (CYP3A4) inhibitors/inducers on these drug exposures. In the DDI simulation, strong CYP3A4 modulators changed the exposure of three drugs by 0.71-1.61 fold. Therefore, patients receiving these drugs in combination with strong CYP3A4 inhibitors should be monitored regularly to prevent adverse reactions. Furthermore, co-administration of docetaxel, cyclophosphamide, or epirubicin with strong CYP3A4 inducers should be avoided. In conclusion, the PBPK models can be used to further investigate the DDI potential of each drug and to develop dosage recommendations for concurrent usage by additional perpetrators or victims.

Formation of potentially toxic metabolites of drugs in reactions catalyzed by human drug-metabolizing enzymes

Data are presented on the formation of potentially toxic metabolites of drugs that are substrates of human drug metabolizing enzymes. The tabular data lists the formation of potentially toxic/reactive products. The data were obtained from in vitro experiments and showed that the oxidative reactions predominate (with 96% of the total potential toxication reactions). Reductive reactions (e.g., reduction of nitro to amino group and reductive dehalogenation) participate to the extent of 4%. Of the enzymes, cytochrome P450 (P450, CYP) enzymes catalyzed 72% of the reactions, myeloperoxidase (MPO) 7%, flavin-containing monooxygenase (FMO) 3%, aldehyde oxidase (AOX) 4%, sulfotransferase (SULT) 5%, and a group of minor participating enzymes to the extent of 9%. Within the P450 Superfamily, P450 Subfamily 3A (P450 3A4 and 3A5) participates to the extent of 27% and the Subfamily 2C (P450 2C9 and P450 2C19) to the extent of 16%, together catalyzing 43% of the reactions, followed by P450 Subfamily 1A (P450 1A1 and P450 1A2) with 15%. The P450 2D6 enzyme participated in an extent of 8%, P450 2E1 in 10%, and P450 2B6 in 6% of the reactions. All other enzymes participate to the extent of 14%. The data show that, of the human enzymes analyzed, P450 enzymes were dominant in catalyzing potential toxication reactions of drugs and their metabolites, with the major role assigned to the P450 Subfamily 3A and significant participation of the P450 Subfamilies 2C and 1A, plus the 2D6, 2E1 and 2B6 enzymes contributing. Selected examples of drugs that are activated or proposed to form toxic species are discussed.

Designing cytochrome P450 enzymes for use in cancer gene therapy

Cancer is a significant global socioeconomic burden, as millions of new cases and deaths occur annually. In 2020, almost 10 million cancer deaths were recorded worldwide. Advancements in cancer gene therapy have revolutionized the landscape of cancer treatment. An approach with promising potential for cancer gene therapy is introducing genes to cancer cells that encode for chemotherapy prodrug metabolizing enzymes, such as Cytochrome P450 (CYP) enzymes, which can contribute to the effective elimination of cancer cells. This can be achieved through gene-directed enzyme prodrug therapy (GDEPT). CYP enzymes can be genetically engineered to improve anticancer prodrug conversion to its active metabolites and to minimize chemotherapy side effects by reducing the prodrug dosage. Rational design, directed evolution, and phylogenetic methods are some approaches to developing tailored CYP enzymes for cancer therapy. Here, we provide a compilation of genetic modifications performed on CYP enzymes aiming to build highly efficient therapeutic genes capable of bio-activating different chemotherapeutic prodrugs. Additionally, this review summarizes promising preclinical and clinical trials highlighting engineered CYP enzymes' potential in GDEPT. Finally, the challenges, limitations, and future directions of using CYP enzymes for GDEPT in cancer gene therapy are discussed.

Role of Cytochrome P450 3A4 in Cancer Drug Resistance: Challenges and Opportunities

One of the biggest obstacles to the treatment of diseases, particularly serious conditions like cancer, is therapeutic resistance. The process of drug resistance is influenced by a number of important variables, including MDR genes, drug efflux, low-quality medications, inadequate dosage, etc. Drug resistance must be addressed, and new combinations based on the pharmacokinetics/pharmacodynamics (PK-PD) characteristics of the partner pharmaceuticals must be developed in order to extend the half-lives of already available medications. The primary mechanism of drug elimination is hepatic biotransformation of medicines by cytochrome P450 (CYP) enzymes; of these CYPs, CYP3A4 makes up 30-40% of all known cytochromes that metabolize medications. Induction or inhibition of CYP3A4-mediated metabolism affects the pharmacokinetics of most anticancer drugs, but these details are not fully understood and highlighted because of the complexity of tumor microenvironments and various influencing patient related factors. The involvement of CYPs, particularly CYP3A4 and other drug-metabolizing enzymes, in cancer medication resistance will be covered in the current review.

Pharmacogenetic Variation in Neanderthals and Denisovans and Implications for Human Health and Response to Medications

Modern humans carry both Neanderthal and Denisovan (archaic) genome elements that are part of the human gene pool and affect the life and health of living individuals. The impact of archaic DNA may be particularly evident in pharmacogenes-genes responsible for the processing of exogenous substances such as food, pollutants, and medications-as these can relate to changing environmental effects, and beneficial variants may have been retained as modern humans encountered new environments. However, the health implications and contribution of archaic ancestry in pharmacogenes of modern humans remain understudied. Here, we explore 11 key cytochrome P450 genes (CYP450) involved in 75% of all drug metabolizing reactions in three Neanderthal and one Denisovan individuals and examine archaic introgression in modern human populations. We infer the metabolizing efficiency of these 11 CYP450 genes in archaic individuals and find important predicted phenotypic differences relative to modern human variants. We identify several single nucleotide variants shared between archaic and modern humans in each gene, including some potentially function-altering mutations in archaic CYP450 genes, which may result in altered metabolism in living people carrying these variants. We also identified several variants in the archaic CYP450 genes that are novel and unique to archaic humans as well as one gene, CYP2B6, that shows evidence for a gene duplication found only in Neanderthals and modern Africans. Finally, we highlight CYP2A6, CYP2C9, and CYP2J2, genes which show evidence for archaic introgression into modern humans and posit evolutionary hypotheses that explain their allele frequencies in modern populations.

Activation/Inactivation of Anticancer Drugs by CYP3A4: Influencing Factors for Personalized Cancer Therapy

Cytochrome P450 3A4 (CYP3A4), one of the most important members of the cytochrome P450 subfamily, is a crucial catalyst in the metabolism of numerous drugs. As it catalyzes numerous processes for drug activation or inactivation, the pharmacological activities and clinical outcomes of anticancer drugs metabolized by CYP3A4 are highly dependent on the enzyme's activity and expression. Due to the complexity of tumor microenvironments and various influencing factors observed in human in vitro models and clinical studies, the pharmacokinetics of most anticancer drugs are influenced by the extent of induction or inhibition of CYP3A4-mediated metabolism, and these details are not fully recognized and highlighted. Therefore, this interindividual variability due to genetic and nongenetic factors, together with the narrow therapeutic index of most anticancer drugs, contributes to their unique set of exposures and responses, which have important implications for achieving the expected efficacy and minimizing adverse events of chemotherapy for cancer in individuals. To elucidate the mechanisms of CYP3A4-mediated activation/inactivation of anticancer drugs associated with personalized therapy, this review focuses on the underlying determinants that contribute to differences in CYP3A4 metabolic activity and provides a comprehensive and valuable overview of the significance of these factors, which differs from current considerations for dosing regimens in cancer therapy. We also discuss knowledge gaps, challenges, and opportunities to explore optimal dosing regimens for drug metabolic activation/inactivation in individual patients, with particular emphasis on pooling and analyzing clinical information that affects CYP3A4 activity. SIGNIFICANCE STATEMENT: This review focuses on anticancer drugs that are activated/deactivated by CYP3A4 and highlights outstanding factors affecting the interindividual variability of CYP3A4 activity in order to gain a detailed understanding of CYP3A4-mediated drug metabolism mechanisms. A systematic analysis of available information on the underlying genetic and nongenetic determinants leading to variation in CYP3A4 metabolic activity to predict therapeutic response to drug exposure, maximize efficacy, and avoid unpredictable adverse events has clinical implications for the identification and development of CYP3A4-targeted cancer therapeutics.

Population pharmacokinetic analysis reveals no impact of aprepitant on the pharmacokinetics of ifosfamide, 2-dechloroifosfamide, and 3-dechloroifosfamide

PURPOSE

Several case reports and retrospective series have clearly pointed to the role of aprepitant, an antiemetic drug, in the development of encephalopathy when used with ifosfamide. Described as an inhibitor of several CYP metabolic pathways, aprepitant is suspected of drug-drug-interaction on ifosfamide pharmacokinetics. The pharmacokinetics of ifosfamide and two of its metabolites (2-dechloroifosfamide and 3-dechloroifosfamide) was studied in patients with soft tissue sarcomas to evaluate the impact of aprepitant administration.

METHODS

A population pharmacokinetic approach was applied to analyze data obtained in 42 patients at cycle 1 (without aprepitant) and cycle 2 (with aprepitant for 34 of them).

RESULTS

A previously published pharmacokinetic model including a time-dependency process well fit the data. Aprepitant had no impact on ifosfamide or its two metabolite pharmacokinetic parameters.

CONCLUSION

This study suggests that aprepitant does not lead to a significant modification of ifosfamide metabolization, even though other metabolites such as 4 hydroxyifosfamide and chloroacetaldehyde were not monitored in this study.

Evaluation of Genotoxic Effect and Antigenotoxic Potential against DNA Damage of the Aqueous and Ethanolic Leaf Extracts of Annona muricata Using an In Vivo Erythrocyte Rodent Micronucleus Assay

Annona muricata have been extensively used in traditional medicine to treat multiple diseases, including cancers. This study evaluated the genotoxic potential and antigenotoxic activities of A. muricata aqueous and ethanolic leaf extracts by employing an in vivo erythrocyte rodent micronucleus assay. Different doses (187.5, 375, and 750 mg/kg) of both extracts were administered orally for 5 days alone and combined with cyclophosphamide (CP, 60 mg/kg) to BALB/c mice. Also, it was administered orally to Wistar rats for 5 days through the final stage of gestation. No genotoxic or cytotoxic effects were observed in the two adult rodent models when A. muricata was administered orally nor in newborn rats transplacentally exposed to the extracts. Moreover, A. muricata aqueous and ethanolic leaf extracts demonstrated a protective effect against CP-induced DNA damage. Due to its lack of genotoxic effect and its capacity to decrease DNA damage, A. muricata is likely to open an interest field regarding its potential safe use in clinical applications.

Adenosine N6-methylation upregulates the expression of human CYP2B6 by altering the chromatin status

N⁶-Methyladenosine (m⁶A) modification is the most prevalent RNA modification in mammals. We have recently demonstrated that inhibition of m⁶A modification by 3-deazaadenosine results in an increase in the expression of the cytochrome P450 (CYP) isoforms CYP1A2, CYP2B6, and CYP2C8 in human liver-derived cells. In the present study, we aimed to clarify the mechanism of m⁶A-mediated regulation of CYP2B6 expression. RNA immunoprecipitation using an anti-m⁶A antibody revealed that CYP2B6 mRNA in human liver and hepatocarcinoma-derived HepaRG cells was m⁶A-modified around the stop codon. In contrast to the treatment with 3-deazaadenosine, double knockdown of methyltransferase like (METTL) 3 and METTL14 (METTL3/14) resulted in a decrease in the levels of CYP2B6 mRNA in Huh-7 and HepaRG cells and a decrease in bupropion hydroxylase activity, a marker activity of CYP2B6, in HepaRG cells. The stability of CYP2B6 mRNA was not influenced by siMETTL3/14. Reporter assays using the plasmids containing the last exon or 5'-flanking region of CYP2B6 indicated that reporter activities were not influenced by knockdown of METTL3/14. The expression levels of the constitutive androstane receptor, pregnane X receptor, and retinoid X receptor, which are the nuclear receptors regulating the transcription of CYP2B6, were not influenced by siMETTL3/14. The chromatin immunoprecipitation and formaldehyde-assisted enrichment of regulatory elements assays revealed that H3K9me2, a repressive histone marker, was enriched in the vicinity of the upstream region of CYP2B6, and knockdown of METTL3/14 induced the condensation of the chromatin structure in this region. In conclusion, we demonstrated that METTL3/14 upregulated CYP2B6 expression by altering the chromatin status.

Targeting CAR and Nrf2 improves cyclophosphamide bioactivation while reducing doxorubicin-induced cardiotoxicity in triple-negative breast cancer treatment

Cyclophosphamide (CPA) and doxorubicin (DOX) are key components of chemotherapy for triple-negative breast cancer (TNBC), although suboptimal outcomes are commonly associated with drug resistance and/or intolerable side effects. Through an approach combining high-throughput screening and chemical modification, we developed CN06 as a dual activator of the constitutive androstane receptor (CAR) and nuclear factor erythroid 2-related factor 2 (Nrf2). CN06 enhances CAR-induced bioactivation of CPA (a prodrug) by provoking hepatic expression of CYP2B6, while repressing DOX-induced cytotoxicity in cardiomyocytes in vitro via stimulating Nrf2-antioxidant signaling. Utilizing a multicellular coculture model incorporating human primary hepatocytes, TNBC cells, and cardiomyocytes, we show that CN06 increased CPA/DOX-mediated TNBC cell death via CAR-dependent CYP2B6 induction and subsequent conversion of CPA to its active metabolite 4-hydroxy-CPA, while protecting against DOX-induced cardiotoxicity by selectively activating Nrf2-antioxidant signaling in cardiomyocytes but not in TNBC cells. Furthermore, CN06 preserves the viability and function of human iPSC-derived cardiomyocytes by modulating antioxidant defenses, decreasing apoptosis, and enhancing the kinetics of contraction and relaxation. Collectively, our findings identify CAR and Nrf2 as potentially novel combined therapeutic targets whereby CN06 holds the potential to improve the efficacy/toxicity ratio of CPA/DOX-containing chemotherapy.

Underlying Anticancer Mechanisms and Synergistic Combinations of Phytochemicals with Cancer Chemotherapeutics: Potential Benefits and Risks

Cancer therapies are associated with various challenges including the emergence of multidrug resistant tumors, toxicological issues, severe side effects, and economic burden. To counteract these effects, natural products as substitutes and adjuvant therapies have received considerable attention owing to their safety, efficacy, and economic aspects. Various preclinical and clinical studies revealed that natural products and their combinations with chemotherapeutics mediate their anticancer effects via modulation of various signaling pathways implicated in promoting apoptosis, inhibiting excessive cellular proliferation, and mobilizing the immune system. Several lead phytochemicals including curcumin, resveratrol, quercetin, and cannabinoids synergistically act with cancer chemotherapeutics reducing cell proliferation and inducing apoptosis and cell cycle arrest. However, clinical studies on the subject matter are limited and need further extensive studies. It has been observed that patients undergoing chemotherapy use alternative therapies to ameliorate the symptoms associated with the use of chemotherapeutic agents. Nevertheless, some of the patients inform their physicians regarding herbal medicine during chemotherapy while others do not, and even most of the patients do not know the composition of herbal medicine they consume during chemotherapy. Herbal interactions with chemotherapeutics are associated with both beneficial and harmful aspects, but the beneficial aspect overweighs the harmful ones in terms of controlling the symptoms associated with the chemotherapy. Nonetheless, a large number of herbal medicines have been demonstrated to have synergistic effect with chemotherapy and alleviate the side effects of chemotherapeutic agents. The concomitant use of the majority of herbal medicines with chemotherapy has been demonstrated to be beneficial in multiple malignant tumors like cancer of blood, lungs, kidneys, liver, skin, and gastrointestinal tract. However, herbal medicines which possess positive interaction and improve the quality of life of patients should be sorted out and integrated with the chemotherapy. There should be a quality control system for the appraisal of herbal medicine, and there should also be an appropriate system of patient-doctor communication to counsel the patients regarding the beneficial and deleterious effects of the herbal medicine in combination with chemotherapy.

CYP2B6 allelic variants and non-genetic factors influence CYP2B6 enzyme function

Human CYP2B6 enzyme although constitutes relatively low proportion (1–4%) of hepatic cytochrome P450 content, it is the major catalyst of metabolism of several clinically important drugs (efavirenz, cyclophosphamide, bupropion, methadone). High interindividual variability in CYP2B6 function, contributing to impaired drug-response and/or adverse reactions, is partly elucidated by genetic polymorphisms, whereas non-genetic factors can significantly modify the CYP2B6 phenotype. The influence of genetic and phenoconverting non-genetic factors on CYP2B6-selective activity and CYP2B6 expression was investigated in liver tissues from Caucasian subjects (N = 119). Strong association was observed between hepatic S-mephenytoin N-demethylase activity and CYP2B6 mRNA expression (P < 0.0001). In less than one third of the tissue donors, the CYP2B6 phenotype characterized by S-mephenytoin N-demethylase activity and/or CYP2B6 expression was concordant with CYP2B6 genotype, whereas in more than 35% of the subjects, an altered CYP2B6 phenotype was attributed to phenoconverting non-genetic factors (to CYP2B6-specific inhibitors and inducers, non-specific amoxicillin + clavulanic acid treatment and chronic alcohol consumption, but not to the gender). Furthermore, CYP2B6 genotype–phenotype mismatch still existed in one third of tissue donors. In conclusion, identifying potential sources of CYP2B6 variability and considering both genetic variations and non-genetic factors is a pressing requirement for appropriate elucidation of CYP2B6 genotype–phenotype mismatch.

Pharmacogenomics in Children

Historically genetics has not been considered when prescribing drugs for children. However, it is clear that genetics are not only an important determinant of disease in children but also of drug response for many important drugs that are core agents used in the therapy of common problems in children. Advances in therapy and in the ethical construct of children's research have made pharmacogenomic assessment for children much easier to pursue. It is likely that pharmacogenomics will become part of the therapeutic decision-making process for children, notably in areas such as childhood cancer where weighing benefits and risks of therapy is crucial.

Drug delivery strategies in maximizing anti-angiogenesis and anti-tumor immunity

Metronomic chemotherapy has been shown to elicit anti-tumor immune response and block tumor angiogenesis distinct from that observed with maximal tolerated dose (MTD) therapy. This review delves into the mechanisms behind anti-tumor immunity and seeks to identify the differential effect of dosing regimens, including daily low-dose and medium-dose intermittent chemotherapy (MEDIC), on both innate and adaptive immune populations involved in observed anti-tumor immune response. Given reports of VEGF/VEGFR blockade antagonizing anti-tumor immunity, drug choice, dose, and selective delivery determined by advanced formulations/vehicles are highlighted as potential sources of innovation for identifying anti-angiogenic modalities that may be combined with metronomic regimens without interrupting key immune players in the anti-tumor response. Engineered drug delivery mechanisms that exhibit extended and local release of anti-angiogenic agents both alone and in combination with chemotherapeutic treatments have also been demonstrated to elicit a potent and potentially systemic anti-tumor immune response, favoring tumor regression and stasis over progression. This review examines this interplay between various cancer models, the host immune response, and select anti-cancer agents depending on drug dosing, scheduling/regimen, and delivery modality.

Human Family 1-4 cytochrome P450 enzymes involved in the metabolic activation of xenobiotic and physiological chemicals: an update

This is an overview of the metabolic activation of drugs, natural products, physiological compounds, and general chemicals by the catalytic activity of cytochrome P450 enzymes belonging to Families 1-4. The data were collected from > 5152 references. The total number of data entries of reactions catalyzed by P450s Families 1-4 was 7696 of which 1121 (~ 15%) were defined as bioactivation reactions of different degrees. The data were divided into groups of General Chemicals, Drugs, Natural Products, and Physiological Compounds, presented in tabular form. The metabolism and bioactivation of selected examples of each group are discussed. In most of the cases, the metabolites are directly toxic chemicals reacting with cell macromolecules, but in some cases the metabolites formed are not direct toxicants but participate as substrates in succeeding metabolic reactions (e.g., conjugation reactions), the products of which are final toxicants. We identified a high level of activation for three groups of compounds (General Chemicals, Drugs, and Natural Products) yielding activated metabolites and the generally low participation of Physiological Compounds in bioactivation reactions. In the group of General Chemicals, P450 enzymes 1A1, 1A2, and 1B1 dominate in the formation of activated metabolites. Drugs are mostly activated by the enzyme P450 3A4, and Natural Products by P450s 1A2, 2E1, and 3A4. Physiological Compounds showed no clearly dominant enzyme, but the highest numbers of activations are attributed to P450 1A, 1B1, and 3A enzymes. The results thus show, perhaps not surprisingly, that Physiological Compounds are infrequent substrates in bioactivation reactions catalyzed by P450 enzyme Families 1-4, with the exception of estrogens and arachidonic acid. The results thus provide information on the enzymes that activate specific groups of chemicals to toxic metabolites.

Assessment of Cannabidiol and Δ9-Tetrahydrocannabiol in Mouse Models of Medulloblastoma and Ependymoma

Simple Summary

Phytocannabinoids Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) have been demonstrated to exhibit anti-cancer activity in preclinical models of brain cancer leading to new clinical trials for adults with glioblastoma. We describe here the first report that has investigated a role for THC and CBD in pediatric brain cancer. Cannabinoids had cytotoxic activity against medulloblastoma and ependymoma cells in vitro, functioning in part through the inhibition of cell cycle progression and the induction of autophagy. Despite these effects in vitro, when tested in orthotopic mouse models of medulloblastoma or ependymoma, no impact on animal survival was observed. Furthermore, cannabinoids neither enhanced nor impaired conventional chemotherapy in a medulloblastoma mouse model. These data show that while THC and CBD do have some effects on medulloblastoma and ependymoma cells, are well tolerated, and have minimal adverse effects, they do not appear to elicit any survival benefit in preclinical models of pediatric brain cancer.

Abstract

Children with medulloblastoma and ependymoma are treated with a multidisciplinary approach that incorporates surgery, radiotherapy, and chemotherapy; however, overall survival rates for patients with high-risk disease remain unsatisfactory. Data indicate that plant-derived cannabinoids are effective against adult glioblastoma; however, preclinical evidence supporting their use in pediatric brain cancers is lacking. Here we investigated the potential role for Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) in medulloblastoma and ependymoma. Dose-dependent cytotoxicity of medulloblastoma and ependymoma cells was induced by THC and CBD in vitro, and a synergistic reduction in viability was observed when both drugs were combined. Mechanistically, cannabinoids induced cell cycle arrest, in part by the production of reactive oxygen species, autophagy, and apoptosis; however, this did not translate to increased survival in orthotopic transplant models despite being well tolerated. We also tested the combination of cannabinoids with the medulloblastoma drug cyclophosphamide, and despite some in vitro synergism, no survival advantage was observed in vivo. Consequently, clinical benefit from the use of cannabinoids in the treatment of high-grade medulloblastoma and ependymoma is expected to be limited. This study emphasizes the importance of preclinical models in validating therapeutic agent efficacy prior to clinical trials, ensuring that enrolled patients are afforded the most promising therapies available.

The Role of Cannabinoids as Anticancer Agents in Pediatric Oncology

Simple Summary

The endocannabinoid system (ECS) is a complex signaling pathway system involved in the regulation of multiple functions in both normal tissues and cancer. Δ9-tetrahydrocannabinol and cannabidiol are plant-derived cannabinoids that possess some efficacy against adult cancer, in part via modulation of the ECS, and may be less toxic agents compared to other treatments used in oncology. To date, there are minimal studies that have investigated these drugs in the pediatric cancer setting. Indeed, there are currently no preclinical or clinical studies examining the effects of cannabinoids in pediatric brain cancer, although there is some evidence that they can alleviate symptoms associated with childhood cancer therapy, such as vomiting and nausea. Given there is accumulating evidence that cannabis use during adolescence is associated with poor mental and cognitive health, there is a present and urgent need to investigate the safety and efficacy of cannabinoids in pediatric oncology to provide guidance to families and physicians.

Abstract

Cannabinoids are a group of chemicals that bind to receptors in the human body and, in turn, modulate the endocannabinoid system (ECS). They can be endogenously produced, synthetic, or derived from the plant Cannabis sativa L. Research over the past several decades has shown that the ECS is a cellular communication network essential to maintain multiple biological functions and the homeostasis of the body. Indeed, cannabinoids have been shown to influence a wide variety of biological effects, including memory, pain, reproduction, bone remodeling or immunity, to name a few. Unsurprisingly, given these broad physiological effects, alterations of the ECS have been found in different diseases, including cancer. In recent years, the medical use of cannabis has been approved in different countries for a variety of human conditions. However, the use of these compounds, specifically as anticancer agents, remains controversial. Studies have shown that cannabinoids do have anticancer activity in different tumor types such as breast cancer, melanoma, lymphoma and adult brain cancer. Specifically, phytocannabinoids Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) has been shown to induce apoptosis and inhibit proliferation of adult cancer cells, as well as modulate angiogenesis and metastasis. Despite increasing evidence that cannabinoids elicit antitumor effects in adult cancers, there is minimal data available on their effects in children or in pediatric cancers despite public and clinical demand for information. Here we describe a comprehensive and critical review of what is known about the effects of cannabinoids on pediatric cancers, highlight current gaps in knowledge and identify the critical issues that need addressing before considering these promising but controversial drugs for use in pediatric oncology.

A Review: Effects of Macrolides on CYP450 Enzymes

As a kind of haemoglobin, cytochrome P450 enzymes (CYP450) participate in the metabolism of many substances, including endogenous substances, exogenous substances and drugs. It is estimated that 60% of common prescription drugs require bioconversion through CYP450. The influence of macrolides on CYP450 contributes to the metabolism and drug-drug interactions (DDIs) of macrolides. At present, most studies on the effects of macrolides on CYP450 are focused on CYP3A, but a few exist on other enzymes and drug combinations, such as telithromycin, which can decrease the activity of hepatic CYP1A2 and CYP3A2. This article summarizes some published applications of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. And the article may subsequently guide the rational use of drugs in clinical trials. To a certain extent, poisoning caused by adverse drug interactions can be avoided. Unreasonable use of macrolide antibiotics may enable the presence of residue of macrolide antibiotics in animal-origin food. It is unhealthy for people to eat food with macrolide antibiotic residues. So it is of great significance to guarantee food safety and protect the health of consumers by the rational use of macrolides. This review gives a detailed description of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. Moreover, it offers a perspective for researchers to further explore in this area.

CITCO as an Adjuvant Facilitates CHOP-Based Lymphoma Treatment in hCAR-Transgenic Mice

Non-Hodgkin's lymphoma (NHL) is a malignant cancer originating in the lymphatic system with a 25-30% mortality rate. CHOP, consisting of cyclophosphamide (CPA), doxorubicin, vincristine, and prednisone, is a first-generation chemotherapy extensively used to treat NHL. However, poor survival rates among patients in advanced stages of NHL shows a need to improve this standard of care treatment. CPA, an integral component of CHOP, is a prodrug that requires CYP2B6-mediated bioactivation to 4-hydroxy-CPA (4-OH-CPA). The expression of CYP2B6 is transcriptionally regulated by the constitutive androstane receptor (CAR, NRi13). We have previously demonstrated that the induction of hepatic CYP2B6 by CITCO, a selective human CAR (hCAR) agonist, results in CHOP's enhanced antineoplastic effects in vitro. Here, we investigate the in vivo potential of CITCO as an adjuvant of CPA-based NHL treatment in a hCAR-transgenic mouse line. Our results demonstrate that the addition of CITCO to the CHOP regimen leads to significant suppression of the growth of EL-4 xenografts in hCAR-transgenic mice accompanied by reduced expression of cyclin-D1, ki67, Pcna, and increased caspase 3 fragmentation in tumor tissues. CITCO robustly induced the expression of cyp2b10 (murine ortholog of CYP2B6) through hCAR activation and increased plasma concentrations of 4-OH-CPA. Comparing to intraperitoneal injection, oral gavage of CITCO results in optimal hepatic cyp2b10 induction. Our in vivo studies have collectively uncovered CITCO as an effective facilitator for CPA-based NHL treatment with a pharmacokinetic profile favoring oral administration, promoting CITCO as a promising adjuvant candidate for CPA-based regimens.

Predicting Metabolism-Related Drug-Drug Interactions Using a Microphysiological Multitissue System

Drug-drug interactions (DDIs) occur when the pharmacological activity of one drug is altered by a second drug. As multimorbidity and polypharmacotherapy are becoming more common due to the increasing age of the population, the risk of DDIs is massively increasing. Therefore, in vitro testing methods are needed to capture such multiorgan events. Here, a scalable, gravity-driven microfluidic system featuring 3D microtissues (MTs) that represent different organs for the prediction of drug-drug interactions is used. Human liver microtissues (hLiMTs) are combined with tumor microtissues (TuMTs) and treated with drug combinations that are known to cause DDIs in vivo. The testing system is able to capture and quantify DDIs upon co-administration of the anticancer prodrugs cyclophosphamide or ifosfamide with the antiretroviral drug ritonavir. Dosage of ritonavir inhibits hepatic metabolization of the two prodrugs to different extents and decreases their efficacy in acting on TuMTs. The flexible MT compartment design of the system, the use of polystyrene as chip material, and the assembly of several chips in stackable plates offer the potential to significantly advance preclinical substance testing. The possibility of testing a broad variety of drug combinations to identify possible DDIs will improve the drug development process and increase patient safety.

Pharmacogenomics in Pediatric Oncology: Mitigating Adverse Drug Reactions While Preserving Efficacy

Cancer is the leading cause of death in American children older than 1 year of age. Major developments in drugs such as thiopurines and optimization in clinical trial protocols for treating cancer in children have led to a remarkable improvement in survival, from approximately 30% in the 1960s to more than 80% today. Short-term and long-term adverse effects of chemotherapy still affect most survivors of childhood cancer. Pharmacogenetics plays a major role in predicting the safety of cancer chemotherapy and, in the future, its effectiveness. Treatment failure in childhood cancer-due to either serious adverse effects that limit therapy or the failure of conventional dosing to induce remission-warrants development of new strategies for treatment. Here, we summarize the current knowledge of the pharmacogenomics of cancer drug treatment in children and of statistically and clinically relevant drug-gene associations and the mechanistic understandings that underscore their therapeutic value in the treatment of childhood cancer.

The importance of both CYP2C19 and CYP2B6 germline variations in cyclophosphamide pharmacokinetics and clinical outcomes

Cyclophosphamide is an alkylating agent used in the treatment of solid and haematological malignancies and as an immunosuppressive agent. As a prodrug, it is dependent on bioactivation to the active phosphoramide mustard metabolite to elicit its therapeutic effect. This focused review will highlight the evidence for the role of germline pharmacogenetic variation in both plasma pharmacokinetics and clinical outcomes. There is a substantial indication from 13 pharmacokinetic and 17 therapeutic outcome studies, in contexts as diverse as haematological malignancy, breast cancer, systemic lupus erythematosus and myeloablation, that pharmacogenetic variation in both CYP2C19 and CYP2B6 influence the bioactivation of cyclophosphamide. An additional role for pharmacogenetic variation in ALDH1A1 has also been reported. Future studies should comprehensively assess these 3 pharmacogenes and undertake appropriate statistical analysis of gene-gene interactions to confirm these findings and may allow personalised treatment regimens.

Nitrogen Mustards as Anticancer Chemotherapies: Historic Perspective, Current Developments and Future Trends

Nitrogen mustards, a family of DNA alkylating agents, marked the start of cancer pharmacotherapy. While traditionally characterized by their dose-limiting toxic effects, nitrogen mustards have been the subject of intense research efforts, which have led to safer and more effective agents. Even though the alkylating prodrug mustards were first developed decades ago, active research on ways to improve their selectivity and cytotoxic efficacy is a currently active topic of research. This review addresses the historical development of the nitrogen mustards, outlining their mechanism of action, and discussing the improvements on their therapeutic profile made through rational structure modifications. A special emphasis is made on discussing the nitrogen mustard prodrug category, with Cyclophosphamide (CPA) serving as the main highlight. Selected insights on the latest developments on nitrogen mustards are then provided, limiting such information to agents that preserve the original nitrogen mustard mechanism as their primary mode of action. Additionally, future trends that might follow in the quest to optimize these invaluable chemotherapeutic medications are succinctly suggested.

DL5050, a Selective Agonist for the Human Constitutive Androstane Receptor

The constitutive androstane receptor (CAR) is a xenobiotic sensor governing the transcription of genes involved in drug disposition, energy homeostasis, and cell proliferation. However, currently available human CAR (hCAR) agonists are nonselective, which commonly activate hCAR along with other nuclear receptors, especially the closely related human pregnane X receptor (hPXR). Using a well-known hCAR agonist CITCO as a template, we report our efforts in the discovery of a potent and highly selective hCAR agonist. Two of the new compounds of the series, 18 and 19 (DL5050), demonstrated excellent potency and selectivity for hCAR over hPXR. DL5050 preferentially induced the expression of CYP2B6 (target of hCAR) over CYP3A4 (target of hPXR) on both the mRNA and protein levels. The selective hCAR agonist DL5050 represents a valuable tool molecule to further define the biological functions of hCAR, and may also be used as a new lead in the discovery of hCAR agonists for various therapeutic applications.

Microfluidic Multitissue Platform for Advanced Embryotoxicity Testing In Vitro

The integration of metabolic competence in developmental toxicity assays in vitro is of fundamental importance to better predict adverse drug effects. Here, a microfluidic hanging-drop platform is presented that seamlessly integrates liver metabolism into the embryonic stem cell test (EST). Primary human liver microtissues (hLiMTs) and embryoid bodies (EBs) are combined in the same fluidic network, so that hLiMT-generated metabolites are directly transported to the EBs. Gravity-driven flow through the network enables continuous intertissue communication, constant medium turnover, and, most importantly, immediate exchange of metabolites. As a proof of concept, the prodrug cyclophosphamide is investigated and a fourfold lower ID50 concentration (50% inhibition of EB differentiation) is found after biotransformation, which demonstrates the potentially adverse effects of metabolites on embryotoxicity. The metaEST platform provides a promising tool to increase the predictive power of the current EST assay by more comprehensively including and better reflecting physiological processes in in vitro tests.

Wuzhi capsule regulates chloroacetaldehyde pharmacokinetics behaviour and alleviates high-dose cyclophosphamide-induced nephrotoxicity and neurotoxicity in rats

High-dose cyclophosphamide (HD-CTX) treatment often leads to severe nephrotoxicity and neurotoxicity, which are mainly caused by one of its metabolites, chloroacetaldehyde (CAA). However, there are no effective antidotes to prevent these side effects. The objective of this study was to evaluate the effect of Wuzhi Capsule (WZC) on the pharmacokinetics of CTX and its metabolites in rats, and the attenuation of CAA induced kidney and brain injuries, which was produced at equimolar with 2-dechloroethylcyclophosphamide. Rats were treated with single- or multiple-dose of WZC when giving HD-CTX, and the plasma concentration of CTX and its metabolites were quantitated by UHPLC-MS/MS Single-dose, not multiple-dose of WZC co-administration (300 mg/kg) significantly reduced C_max and AUC_0→24 h of DC-CTX by 33.10% and 35.51%, respectively. Biochemical assay suggested oxidative stress was involved in kidney and brain injuries by HD-CTX, which were attenuated by single-dose WZC (300 mg/kg) pre-treatment, with increased glutathione, glutathione peroxidase and superoxide dismutase contents/or activities in both tissues and plasma (P < 0.05). Meanwhile, WZC pre-treatment could also significantly decrease the plasma levels of creatinine, blood urea nitrogen and malondialdehyde (P < 0.05). Additionally, WZC treatment improved the morphology and pathology condition of the kidneys and brains in rats. In conclusion, single-dose WZC co-administration decreased CAA production and exerted protective effect on CTX-induced oxidative stress in kidney and brain, whereas repetitive WZC co-administration with CTX was probably not recommended.

Kinetics of Cyclophosphamide Metabolism in Humans, Dogs, Cats, and Mice and Relationship to Cytotoxic Activity and Pharmacokinetics

Cyclophosphamide (CP), a prodrug that is enzymatically converted to the cytotoxic 4-hydroxycyclophosphamide (4OHCP) by hepatic enzymes, is commonly used in both human and veterinary medicine to treat cancers and modulate the immune system. We investigated the metabolism of CP in humans, dogs, cats, and mice using liver microsomes; apparent K M, V max, and intrinsic clearance (V max/K M) parameters were estimated. The interspecies and intraspecies variations in kinetics were vast. Dog microsomes were, on average, 55-fold more efficient than human microsomes, 2.8-fold more efficient than cat microsomes, and 1.2-fold more efficient than mouse microsomes at catalyzing CP bioactivation. These differences translated to cell-based systems. Breast cancer cells exposed to 4OHCP via CP bioactivation by microsomes resulted in a stratification of cytotoxicity that was dependent on the species of microsomes measured by IC50: dog (31.65 μM), mouse (44.95 μM), cat (272.6 μM), and human (1857 μM). The contributions of cytochrome P450s, specifically, CYP2B, CYP2C, and CYP3A, to CP bioactivation were examined: CYP3A inhibition resulted in no change in 4OHCP formation; CYP2B inhibition slightly reduced 4OHCP in humans, cats, and mice; and CYP2C inhibition drastically reduced 4OHCP formation in each species. Semiphysiologic modeling of CP metabolism using scaled metabolic parameters resulted in simulated data that closely matched published pharmacokinetic profiles, determined by noncompartmental analysis. The results highlight differential CP metabolism delineated by species and demonstrate the importance of metabolism on CP clearance.

Hypoxia increases chemoresistance in human medulloblastoma DAOY cells via hypoxia‑inducible factor 1α‑mediated downregulation of the CYP2B6, CYP3A4 and CYP3A5 enzymes and inhibition of cell proliferation

Medulloblastomas are among the most frequently diagnosed pediatric solid tumors, and drug resistance remains as the principal cause of treatment failure. Hypoxia and the subsequent activation of hypoxia-inducible factor 1α (HIF-1α) are considered key factors in modulating drug antitumor effectiveness, but the underlying mechanisms in medulloblastomas have not yet been clearly understood. The aim of the present study was to determine whether hypoxia induces resistance to cyclophosphamide (CPA) and ifosfamide (IFA) in DAOY medulloblastoma cells, whether the mechanism is dependent on HIF-1α, and whether involves the modulation of the expression of cytochromes P450 (CYP)2B6, 3A4 and 3A5 and the control of cell proliferation. Monolayer cultures of DAOY medulloblastoma cells were exposed for 24 h to moderate (1% O₂) or severe (0.1% O₂) hypoxia, and protein expression was evaluated by immunoblotting. Cytotoxicity was studied with the MTT assay and by Annexin V/PI staining and flow cytometry. Cell proliferation was determined by the trypan-blue exclusion assay and cell cycle by propidium iodide staining and flow cytometry. Hypoxia decreased CPA and IFA cytotoxicity in medulloblastoma cells, which correlated with a reduction in the protein levels of CYP2B6, CYP3A4 and CYP3A5 and inhibition of cell proliferation. These responses were dependent on hypoxia-induced HIF-1α activation, as evidenced by chemical inhibition of its transcriptional activity with 2-methoxyestradiol (2-ME), which enhanced the cytotoxic activity of CPA and IFA and increased apoptosis. Our results indicate that by stimulating HIF-1α activity, hypoxia downregulates the expression of CYP2B6, CYP3A4 and CYP3A5, that in turn leads to decreased conversion of CPA and IFA into their active forms and thus to diminished cytotoxicity. These results support that the combination of HIF-1α inhibitors and canonical antineoplastic agents provides a potential therapeutic alternative against medulloblastoma.

Schisandra chinensis extract decreases chloroacetaldehyde production in rats and attenuates cyclophosphamide toxicity in liver, kidney and brain

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis (Turcz.) Baill (S. chinensis) has been used for thousands years in China, and is usually applied in treatment of urinary tract disorders and liver injury. S. chinensis extract (SCE) has board protective effects on liver, kidney and nervous system. Schisandra lignans are generally considered as the bioactive components of SCE.

AIM OF THE STUDY

To investigate the pharmacokinetic herb-drug interactions (HDIs) between SCE and cyclophosphamide (CTX). To evaluate the protective effects of SCE against CTX induced damage in rat liver, kidney and brain.

MATERIALS AND METHODS

The pharmacokinetic HDIs between SCE and CTX were investigated by determining plasma concentrations of CTX and three metabolites, namely 4-ketocyclophosphamide (4-Keto), 2-dechloroethylcyclophosphamide (DCCTX) and carboxyphosphamide (CPM) using a previously developed UPLC-MS/MS method. To evaluate the protective effects of SCE pretreatment, toxicity and oxidation stress assessments along with histology investigations were carried out in rat liver, kidney and brain.

RESULTS

The equimolar produced metabolite DCCTX was chosen to reflect chloroacetaldehyde (CAA, a toxic metabolite of CTX) production in rats. Single-dose pretreatment of SCE significantly reduced CAA production and decreased the C_max and AUC_0-24h of DCCTX by 69% and 49% respectively (P < 0.05). After pretreated with SCE for 7 consecutive days, the C_max and AUC_0-24h of DCCTX were still decreased (-25% and -37%, P < 0.05) when compared with CTX alone group. Parallel toxicity and oxidation stress investigations showed that single-dose SCE pretreatment significantly decreased plasma BUN and Cr levels (-12% and -46%, respectively) and reduced liver AST activity (-32%). Moreover, SCE pretreatment potently increased the brain GSH content by 7.8-fold, and reduced MDA levels in rat liver, kidney and brain by 39%, 28% and 31%, respectively (compared with CTX alone group). The protective effects of SCE were also supported by histological observations.

CONCLUSION

Our experiment results suggest that S. chinensis may find use as a complementary medicine in CTX treatment.

The role of melatonin on chemotherapy-induced reproductive toxicity

Objectives

Reproductive malfunctions after chemotherapy still are a reason of reducing fertility and need specialized intensive care. The aim of this review was to investigate the effect of melatonin on the reproductive system under threatening with chemotherapeutic drugs.

Methods

To find the role of melatonin in the reproductive system during chemotherapy, a full systematic literature search was carried out based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines in the electronic databases up to 17 April 2017 using search terms in the titles and abstracts. A total of 380 articles are screened according to our inclusion and exclusion criteria. Finally, 18 articles were included in this study.

Key findings

It has been cleared that melatonin has bilateral effects on reproductive cells. Melatonin protects normal cells via mechanisms, including decrease in oxidative stress, apoptosis, inflammation and modulating mitochondrial function, and sexual hormones. Furthermore, melatonin with antiproliferative properties and direct effects on its receptors improves reproductive injury and function during chemotherapy. On the other hand, melatonin sensitizes the effects of chemotherapeutic drugs and enhances chemotherapy-induced toxicity in cancerous cells through increasing apoptosis, oxidative stress and mitochondrial malfunction.

Conclusions

The study provides evidence of the bilateral role of melatonin in the reproductive system during chemotherapy.

Effects of ketoconazole on cyclophosphamide metabolism: evaluation of CYP3A4 inhibition effect using the in vitro and in vivo models

Cyclophosphamide (CP) is widely used in anticancer therapy regimens and 2-dechloroethylcyclophosphamide (DECP) is its side-chain dechloroethylated metabolite. N-dechloroethylation of CP mediated by the enzyme CYP3A4 yields nephrotoxic and neurotoxic chloroacetaldehyde (CAA) in equimolar amount to DECP. This study aimed to evaluate the inhibitory effect of ketoconazole (KTZ) on CP metabolism through in vitro and in vivo drug-drug interaction (DDI) research. Long-term treatment of KTZ induces hepatic injury; thus single doses of KTZ at low, middle, and high levels (10, 20, and 40 mg/kg) were investigated for pharmacokinetic DDI with CP. Our in vitro human liver microsome modeling approach suggested that KTZ inhibited CYP3A4 activity and then decreased DECP exposure. In addition, an UHPLC-MS/MS method for quantifying CP, DECP, and KTZ in rat plasma was developed and fully validated with a 4 min analysis coupled with a simple and reproducible one-step protein precipitation. A further in vivo pharmacokinetic study demonstrated that combination use of CP (10 mg/kg) and KTZ (10, 20, and 40 mg/kg) in rats caused a KTZ dose-dependent decrease in main parameters of DECP (C_max, T_max, and AUC_0-∞) and provided magnitude exposure of DECP (more than a 50% AUC decrease) as a consequence of CYP3A inhibition but had only a small effect on the CP plasma concentration. Our results suggested that combination usage of a CYP3A4 inhibitor like KTZ may decrease CAA exposure and thus intervene against CAA-induced adverse effects in CP clinical treatment.

Metabolism of megestrol acetate in vitro and the role of oxidative metabolites

1. There is limited knowledge regarding the metabolism of megestrol acetate (MA), as it was approved by FDA in 1971, prior to the availability of modern tools for identifying specific drug-metabolizing enzymes. We determined the cytochrome P450s (P450s) and UDP-glucuronosyltransferases (UGTs) that metabolize MA, identified oxidative metabolites and determined pharmacologic activity at the progesterone, androgen and glucocorticoid receptors (PR, AR and GR, respectively). 2. Oxidative metabolites were produced using human liver microsomes (HLMs), and isolated for mass spectral (MS) and nuclear magnetic resonance (NMR) analyses. We screened recombinant P450s using MA at 62 μM (HLM K_m for metabolite 1; M1) and 28 μM (HLM K_m for metabolite 2; M2). UGT isoforms were simultaneously incubated with UDPGA, nicotinamide adenine dinucleotide phosphate (NADPH), CYP3A4 and MA. Metabolites were evaluated for pharmacologic activity on the PR, AR and GR. CYP3A4 and CYP3A5 are responsible for oxidative metabolism of 62 μM MA. 3. At 28 μM substrate concentration, CYP3A4 was the only contributing enzyme. Mass spectral and NMR data suggest metabolism of MA to two alcohols. After oxidation, MA is converted into two secondary glucuronides by UGT2B17 among other UGTs. MA, M1 and M2 had significant pharmacologic activity on the PR while only MA showed activity on the AR and GR.

Investigating the heterogeneity of alkylating agents' efficacy and toxicity between sexes: A systematic review and meta-analysis of randomized trials comparing cyclophosphamide and ifosfamide (MAIAGE study)

BACKGROUND

A marginal interaction between sex and the type of alkylating agent was observed for event-free survival in the Euro-EWING99-R1 randomized controlled trial (RCT) comparing cyclophosphamide and ifosfamide in Ewing sarcoma. To further evaluate this interaction, we performed an individual patient data meta-analysis of RCTs assessing cyclophosphamide versus ifosfamide in any type of cancer.

METHODS

A literature search produced two more eligible RCTs (EICESS92 and IRS-IV). The endpoints were progression-free survival (PFS, main endpoint) and overall survival (OS). The hazard ratios (HRs) of the treatment-by-sex interaction and their 95% confidence interval (95% CI) were assessed using stratified multivariable Cox models. Heterogeneity of the interaction across age categories and trials was explored. We also assessed this interaction for severe acute toxicity using logistic models.

RESULTS

The meta-analysis comprised 1,528 pediatric and young adult sarcoma patients from three RCTs: Euro-EWING99-R1 (n = 856), EICESS92 (n = 155), and IRS-IV (n = 517). There were 224 PFS events in Euro-EWING99-R1 and 200 in the validation set (EICESS92 + IRS-IV), and 171 and 154 deaths in each dataset, respectively. The estimated treatment-by-sex interaction for PFS in Euro-EWING99-R1 (HR = 1.73, 95% CI = 1.00-3.00) was not replicated in the validation set (HR = 0.97, 95% CI = 0.55-1.72), without heterogeneity across trials (P = 0.62). In the pooled analysis, the treatment-by-sex interaction was not significant (HR = 1.31, 95% CI = 0.89-1.95, P = 0.17), without heterogeneity across age categories (P = 0.88) and trials (P = 0.36). Similar results were observed for OS. No significant treatment-by-sex interaction was observed for leucopenia/neutropenia (P = 0.45), infection (P = 0.64), or renal toxicity (P = 0.20).

CONCLUSION

Our meta-analysis did not confirm the hypothesis of a treatment-by-sex interaction on efficacy or toxicity outcomes.

Quantitative in vitro phenotyping and prediction of drug interaction potential of CYP2B6 substrates as victims

1. Determination of f_{m, CYP} for a compound is critical to assess the potential risk of a drug candidate as a victim of DDI. Several compounds are identified as CYP2B6 substrates, but the f_{m, CYP2B6} values are not determined quantitatively. 2. Two methods of reaction phenotyping, the chemical inhibition method and metabolism in rCYP enzymes, were used to determine the relative contributions of the enzymes. Chemical inhibition method was also conducted in the presence of BSA (0.5% w/v). 3. The results confirm with the earlier studies concerning the identity of the CYP2B6 enzyme. The f_{m, CYP2B6} values for artemisinin, bupropion, clopidogrel, ketamine, selegiline, sertraline and ticlopidine were 0.24, 0.28, 0.15, 0.45, 0.46, 0.42 and 0.54, respectively, in HLM determined by chemical inhibition method. The f_{m, CYP2B6} values for artemisinin, bupropion, clopidogrel, ketamine, selegiline, sertraline and ticlopidine were 0.46, 0.17, 0.15, 0.60, 0.51, 0.66 and 0.77, respectively, in HLM determined by chemical inhibition method in the presence of BSA (0.5% w/v). 4. Bupropion metabolism is majorly mediated by CYP2C19 (0.41) with a minor contribution from CYP2B6 (0.16) in the presence of BSA. Ticlopidine is a time-dependent inhibitor of both CYP2B6 and CYP2C19 that can inhibit the bupropion metabolism by 50-60%.

Assessing genotoxicity of diuron on Drosophila melanogaster by the wing-spot test and the wing imaginal disk comet assay

The aim of this study was to evaluate the genotoxicity of the herbicide diuron in the wing-spot test and a novel wing imaginal disk comet assay in Drosophila melanogaster. The wing-spot test was performed with standard (ST) and high-bioactivation (HB) crosses after providing chronic 48 h treatment to third instar larvae. A positive dose-response effect was observed in both crosses, but statistically reduced spot frequencies were registered for the HB cross compared with the ST. This latter finding suggests that metabolism differences play an important role in the genotoxic effect of diuron. To verify diuron's ability to produce DNA damage, a wing imaginal disk comet assay was performed after providing 24 h diuron treatment to ST and HB third instar larvae. DNA damage induced by the herbicide had a significantly positive dose-response effect even at very low concentrations in both strains. However, as noted for the wing-spot test, a significant difference between strains was not observed that could be related to the duration of exposure between both assays. A positive correlation between the comet assay and the wing-spot test was found with regard to diuron genotoxicity.

Insights into CYP2B6-mediated drug-drug interactions

Mounting evidence demonstrates that CYP2B6 plays a much larger role in human drug metabolism than was previously believed. The discovery of multiple important substrates of CYP2B6 as well as polymorphic differences has sparked increasing interest in the genetic and xenobiotic factors contributing to the expression and function of the enzyme. The expression of CYP2B6 is regulated primarily by the xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in the liver. In addition to CYP2B6, these receptors also mediate the inductive expression of CYP3A4, and a number of important phase II enzymes and drug transporters. CYP2B6 has been demonstrated to play a role in the metabolism of 2%–10% of clinically used drugs including widely used antineoplastic agents cyclophosphamide and ifosfamide, anesthetics propofol and ketamine, synthetic opioids pethidine and methadone, and the antiretrovirals nevirapine and efavirenz, among others. Significant inter-individual variability in the expression and function of the human CYP2B6 gene exists and can result in altered clinical outcomes in patients receiving treatment with CYP2B6-substrate drugs. These variances arise from a number of sources including genetic polymorphism, and xenobiotic intervention. In this review, we will provide an overview of the key players in CYP2B6 expression and function and highlight recent advances made in assessing clinical ramifications of important CYP2B6-mediated drug–drug interactions.

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

During the last 10-15 years, cytochrome P450 (CYP) 2C8 has emerged as an important drug-metabolizing enzyme. CYP2C8 is highly expressed in human liver and is known to metabolize more than 100 drugs. CYP2C8 substrate drugs include amodiaquine, cerivastatin, dasabuvir, enzalutamide, imatinib, loperamide, montelukast, paclitaxel, pioglitazone, repaglinide, and rosiglitazone, and the number is increasing. Similarly, many drugs have been identified as CYP2C8 inhibitors or inducers. In vivo, already a small dose of gemfibrozil, i.e., 10% of its therapeutic dose, is a strong, irreversible inhibitor of CYP2C8. Interestingly, recent findings indicate that the acyl-β-glucuronides of gemfibrozil and clopidogrel cause metabolism-dependent inactivation of CYP2C8, leading to a strong potential for drug interactions. Also several other glucuronide metabolites interact with CYP2C8 as substrates or inhibitors, suggesting that an interplay between CYP2C8 and glucuronides is common. Lack of fully selective and safe probe substrates, inhibitors, and inducers challenges execution and interpretation of drug-drug interaction studies in humans. Apart from drug-drug interactions, some CYP2C8 genetic variants are associated with altered CYP2C8 activity and exhibit significant interethnic frequency differences. Herein, we review the current knowledge on substrates, inhibitors, inducers, and pharmacogenetics of CYP2C8, as well as its role in clinically relevant drug interactions. In addition, implications for selection of CYP2C8 marker and perpetrator drugs to investigate CYP2C8-mediated drug metabolism and interactions in preclinical and clinical studies are discussed.

Human P450 Microarrays for In Vitro Toxicity Analysis: Toward Complete Automation of Human Toxicology Screening

The development of a tool that can provide early-stage predictive toxicology data may accelerate the identification of safer drug candidates, and thereby improve the clinical progression of drug candidates to pharmaceuticals. Such a system would require an accurate and reliable technique that is amenable to the large number of drug candidates that must be screened in the lead discovery and optimization stages of drug development. A key component of predictive toxicology is the ability to harness the metabolite-generating capacity of human cytochromes P450, which are involved in first-pass drug metabolism function of the liver. We have miniaturized P450 catalysis into a microarray format consisting of up to 11,200 isolated P450 reactions, each in 5 nL sol-gel spots, on a single functionalized glass microscope-size biochip. This dramatic scale down from more conventional 96 and 384-well plate scales (at least a 1000-fold reduction in volume) did not adversely affect P450 catalytic activity. Based on the functionality of the P450-containing microarray, we developed the metabolizing enzyme toxicology assay Chip (MetaChip), which combines high-throughput P450 catalysis with cell-based screening on a microscale platform. Proof of concept was demonstrated using anticancer prodrugs cyclophosphamide and Tegafur, as well as the analgesic acetaminophen. The MetaChip may provide a high-throughput microscale alternative to currently used in vitro methods for human metabolism and toxicology screening.

Drug metabolism and clearance system in tumor cells of patients with multiple myeloma

Resistance to chemotherapy is a major limitation of cancer treatments with several molecular mechanisms involved, in particular altered local drug metabolism and detoxification process. The role of drug metabolism and clearance system has not been satisfactorily investigated in Multiple Myeloma (MM), a malignant plasma cell cancer for which a majority of patients escapes treatment. The expression of 350 genes encoding for uptake carriers, xenobiotic receptors, phase I and II Drug Metabolizing Enzymes (DMEs) and efflux transporters was interrogated in MM cells (MMCs) of newly-diagnosed patients in relation to their event free survival. MMCs of patients with a favourable outcome have an increased expression of genes coding for xenobiotic receptors (RXRα, LXR, CAR and FXR) and accordingly of their gene targets, influx transporters and phase I/II DMEs. On the contrary, MMCs of patients with unfavourable outcome displayed a global down regulation of genes coding for xenobiotic receptors and the downstream detoxification genes but had a high expression of genes coding for ARNT and Nrf2 pathways and ABC transporters. Altogether, these data suggests ARNT and Nrf2 pathways could be involved in MM primary resistance and that targeting RXRα, PXR, LXR and FXR through agonists could open new perspectives to alleviate or reverse MM drug resistance.

Activation of the Constitutive Androstane Receptor Increases the Therapeutic Index of CHOP in Lymphoma Treatment

The constitutive androstane receptor (CAR and NR1i3) is a key regulator of CYP2B6, the enzyme predominantly responsible for the biotransformation of cyclophosphamide (CPA) to its pharmacologically active metabolite, 4-hydroxycyclophosphamide (4-OH-CPA). Previous studies from our laboratory illustrated that CAR activation increases the formation of 4-OH-CPA; however, CPA is rarely used clinically outside of combination therapies. Here, we hypothesize that including a selective human CAR activator with the CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) regimen can improve the efficacy without exacerbating off-target toxicity of this regimen in non-Hodgkin lymphoma treatment. In this study, we have developed a novel multiorgan coculture system containing human primary hepatocytes for hepatic metabolism, lymphoma cells as a model target for CHOP, and cardiomyocytes as a major site of off-target toxicity associated with this regimen. We found that a selective human CAR activator, CITCO (6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime), altered expression of key drug-metabolizing enzymes and transporters in human hepatocytes, which positively affects the metabolic profile of CHOP. Coadministration of CITCO and CHOP in the coculture model led to significantly enhanced cytotoxicity in lymphoma cells but not in cardiomyocytes. Moreover, the beneficial effects of CITCO were abrogated when CAR knockout HepaRG cells were used in the coculture model. Importantly, synergistic anticancer effects were observed between CITCO and CHOP, in that inclusion of CITCO alongside the CHOP regimen offers comparable antineoplastic activity toward lymphoma cells at significantly reduced drug concentrations, and the decreased CHOP load attenuates cardiotoxicity. Overall, these findings provide a potentially promising novel strategy for facilitating CHOP-based chemotherapy.