Cyclophosphamide induces mRNA, protein and enzyme activity of cytochrome P450 in rat

Cyclophosphamide Pharmacogenomic Variation in Cancer Treatment and Its Effect on Bioactivation and Pharmacokinetics

Cyclophosphamide (Cy) is a prodrug that is mainly bioactivated by cytochrome P450 (CYP) 2B6 enzyme. Several other enzymes are also involved in its bioactivation and affect its kinetics. Previous studies have shown the effect of the enzymes' genetic polymorphisms on Cy kinetics and its clinical outcome. These results were controversial primarily because of the involvement of several interacting enzymes in the Cy metabolic pathway, which can also be affected by several clinical factors as well as other drug interactions. In this review article, we present the effect of CYP2B6 polymorphisms on Cy kinetics since it is the main bioactivating enzyme, as well as discussing all previously reported enzymes and clinical factors that can alter Cy efficacy. Additionally, we present explanations for key Cy side effects related to the nature and site of its bioactivation. Finally, we discuss the role of busulphan in conditioning regimens in the Cy metabolic pathway as a clinical example of drug-drug interactions involving several enzymes. By the end of this article, our aim is to have provided a comprehensive summary of Cy pharmacogenomics and the effect on its kinetics. The utility of these findings in the development of new strategies for Cy personalized patient dose adjustment will aid in the future optimization of patient specific Cy dosages and ultimately in improving clinical outcomes. In conclusion, CYP2B6 and several other enzyme polymorphisms can alter Cy kinetics and consequently the clinical outcomes. However, the precise quantification of Cy kinetics in any individual patient is complex as it is clearly under multifactorial genetic control. Additionally, other clinical factors such as the patient's age, diagnosis, concomitant medications, and clinical status should also be considered.

Amelioration of cyclophosphamide toxicity via modulation of metabolizing enzymes by avocado (Persea americana) extract

OBJECTIVES

Cyclophosphamide (CPA) is highly effective in treating several human tumours and autoimmune disorders; but, it triggers deleterious side effects. Avocado, Persea americana (Mill.), is a widely consumed fruit with pronounced nutritional and medicinal value. Though many studies examined the protective mechanisms of natural products against CPA toxicity, almost none investigated the modulation of CPA metabolism as a potential underlying mechanism for protection. Here, we investigated the modulating effect of avocado extract (AE) on certain CPA metabolizing enzymes and its correlation with the extent of CPA-induced pulmonary toxicity and urotoxicity.

METHODS

Rats received oral AE (0.9 g/kg body weight/day) 7 days before a single CPA injection (150 mg/kg body weight) and continued AE intake for 2, 7 or 28 days to study three phases of CPA-induced urotoxicity and pulmonary toxicity.

KEY FINDINGS

CPA acutely elevated then reduced hepatic microsomal cytochrome P450 2B6 (CYP2B6) content and significantly suppressed bladder and lung glutathione-S-transferase activity. Furthermore, CPA elevated lung myeloperoxidase activity, DNA content and hydroxyproline level and bladder blood content. AE ameliorated CPA-induced derangements through suppression of CYP2B6 and myeloperoxidase and augmentation of glutathione-S-transferase activity in CPA-treated rats.

CONCLUSIONS

AE modulation of CPA metabolizing enzymes and potential anti-inflammatory effect may mitigate CPA-induced toxicity.

Galangin Activates Nrf2 Signaling and Attenuates Oxidative Damage, Inflammation, and Apoptosis in a Rat Model of Cyclophosphamide-Induced Hepatotoxicity

Cyclophosphamide (CP) is a widely used chemotherapeutic agent; however, its clinical application is limited because of its multi-organ toxicity. Galangin (Gal) is a bioactive flavonoid with promising biological activities. This study investigated the hepatoprotective effect of Gal in CP-induced rats. Rats received Gal (15, 30 and 60 mg/kg/day) for 15 days followed by a single dose of CP at day 16. Cyclophosphamide triggered liver injury characterized by elevated serum transaminases, alkaline phosphatase (ALP) and lactate dehydrogenase (LDH), and histopathological manifestations. Increased hepatic reactive oxygen species, malondialdehyde, nitric oxide, and oxidative DNA damage along with declined glutathione and antioxidant enzymes were demonstrated in CP-administered rats. CP provoked hepatic nuclear factor-kappaB (NF-κB) phosphorylation and increased mRNA abundance of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) both expression and serum levels. Gal prevented CP-induced liver injury, boosted antioxidants and suppressed oxidative stress, DNA damage, NF-κB phosphorylation and pro-inflammatory mediators. Gal diminished Bax and caspase-3, and increased B-cell lymphoma-2 (Bcl-2) in liver of CP-administered rats. In addition, Gal increased peroxisome proliferator-activated receptor gamma (PPARγ) expression and activated hepatic nuclear factor erythroid 2-related factor 2 (Nrf2) signaling showed by the increase in Nrf2, NAD(P)H: quinone acceptor oxidoreductase-1 (NQO-1) and heme oxygenase 1 (HO-1) in CP-administered rats. These findings suggest that Gal prevents CP hepatotoxicity through activation of Nrf2/HO-1 signaling and attenuation of oxidative damage, inflammation and cell death. Therefore, Gal might represent a promising adjuvant therapy to prevent hepatotoxicity in patients on CP treatment.

Cytochrome P450 2J2, a new key enzyme in cyclophosphamide bioactivation and a potential biomarker for hematological malignancies

The role of cytochrome P450 2J2 (CYP2J2) in cyclophosphamide (Cy) bioactivation was investigated in patients, cells and microsomes. Gene expression analysis showed that CYP2J2 mRNA expression was significantly (P<0.01) higher in 20 patients with hematological malignancies compared with healthy controls. CYP2J2 expression showed significant upregulation (P<0.05) during Cy treatment before stem cell transplantation. Cy bioactivation was significantly correlated to CYP2J2 expression. Studies in HL-60 cells expressing CYP2J2 showed reduced cell viability when incubated with Cy (half maximal inhibitory concentration=3.6 mM). Inhibition of CYP2J2 using telmisartan reduced Cy bioactivation by 50% and improved cell survival. Cy incubated with recombinant CYP2J2 microsomes has resulted in apparent Km and Vmax values of 3.7-6.6 mM and 2.9-10.3 pmol/(min·pmol) CYP, respectively. This is the first study demonstrating that CYP2J2 is equally important to CYP2B6 in Cy metabolism. The heart, intestine and urinary bladder express high levels of CYP2J2; local Cy bioactivation may explain Cy-treatment-related toxicities in these organs.

Induction of liver cytochrome P450s by Danshen-Gegen formula is the leading cause for its pharmacokinetic interactions with warfarin

ETHNOPHARMACOLOGICAL RELEVANCE

Although the increased usage of herbal medicine leading to herb-drug interactions is well reported, the mechanism of such interactions between herbal medicines with conventionally prescribed drugs such as warfarin is not yet fully understood. Our previous rat in vivo study demonstrated that co-administration of Danshen-Gegen Formula (DGF), a Radix Salvia miltiorrhiza (Danshen) and Radix Puerariae lobatae (Gegen) containing Chinese medicine formula recently developed for the treatment of cardiovascular disease, with warfarin could cause significant herb-drug interactions. The current study aims to explore the pharmacokinetics-based mechanism of the DGF-warfarin interactions during absorption, distribution and metabolism processes.

MATERIALS AND METHODS

Caco-2 cell monolayer model and rat in situ intestinal perfusion model were used to study the DGF-warfarin interactions during the intestinal absorption processes. Male Sprague-Dawley rats were orally administered warfarin in presence and absence of DGF for consecutive 5 days. The microsomal activity and expression of the liver CYP isozymes were determined and compared among different treatment groups. Blood from the rats administered DGF was employed to evaluate effects of DGF on the plasma protein binding of warfarin.

RESULTS

Absorption studies demonstrated that DGF could potentially increase the intestinal absorption of warfarin (32% and 75% increase of warfarin Papp in Caco-2 and intestinal perfusion models, respectively) via altering the regional pH environment in GI tract. DGF administration could lead to significant increase in liver microsomal activity and mRNA expression of CYP1A1 and CYP2B1, indicating the potential induction on the liver metabolism of warfarin by DGF. Moreover, it has been proven by ex vivo study that the single-dose administration of DGF could decrease the protein binding of warfarin in plasma by at least 11.6%.

CONCLUSION

Collectively, current study demonstrated that DGF could significantly induce the liver phase I metabolism of warfarin, and to a less extent, potentially increase the intestinal absorption and decrease the plasma protein binding of warfarin. The inductive effects of DGF on the liver phase I metabolism of warfarin may be dominantly responsible for the DGF-warfarin pharmacokinetics interactions.

The role of constitutive androstane receptor in oxazaphosphorine-mediated induction of drug-metabolizing enzymes in human hepatocytes

PURPOSE

To investigate the roles of the constitutive androstane receptor (CAR) in cyclophosphamide (CPA)- and ifosfamide (IFO)-mediated induction of hepatic drug-metabolizing enzymes (DME).

METHODS

Induction of DMEs was evaluated using real-time RT-PCR and Western blotting analysis in human primary hepatocyte (HPH) cultures. Activation of CAR, pregnane X receptor (PXR), and aryl hydrocarbon receptor by CPA and IFO was assessed in cell-based reporter assays in HepG2 cells and/or nuclear translocation assays in HPHs.

RESULTS

CYP2B6 reporter activity was significantly enhanced by CPA and IFO in HepG2 cells co-transfected with CYP2B6 reporter plasmid and a chemical-responsive human CAR variant (CAR1 + A) construct. Real-time RT-PCR and Western blotting analysis in HPHs showed that both CPA and IFO induced the expressions of CYP2B6 and CYP3A4. Notably, treatment of HPHs with CPA but not IFO resulted in significant nuclear accumulation of CAR, which represents the initial step of CAR activation. Further studies in HPHs demonstrated that selective inhibition of PXR by sulforaphane preferentially repressed IFO- over CPA-mediated induction of CYP2B6.

CONCLUSION

These results provide novel insights into the differential roles of CAR in the regulation of CPA- and IFO-induced DME expression and potential drug-drug interactions.

The Effect of Repeated Administration of Cyclophosphamide on Cytochrome P450 2B in Rats

PURPOSE

The prodrug cyclophosphamide (CPA) is activated by cytochrome P450 (CYP) enzymes. CPA is one of the corner stones in all cancer treatment. We have studied the effect of repeated doses of CPA given at different time intervals on the mRNA, protein levels, and enzyme activity of CYPs in rats.

EXPERIMENTAL DESIGN

Two groups of animals (A-75 and A-150) were treated with four doses of CPA (75 and 150 mg/kg, respectively) at short time intervals (6 h). The third group of animals (B-150) was treated with 150 mg/kg at 24-h intervals. Three animals were killed 30 min after administration, and three animals immediately before the next dose.

RESULTS

CYP2B1 and CYP2B2 mRNAs were significantly induced at 6 h after each dose in group A-75 (maximum of 2100-fold and 60-fold after the third dose, respectively), whereas the mRNA levels measured at 6 h postadministration in group A-150 were 1,490-fold and 36-fold after the second dose. In group B-150, no significant induction of mRNA levels was observed. CYP2B1 and CYP2B2 protein levels also increased with increased mRNAs. Plasma levels of 4-hydroxy-CPA measured at 30 min after dose correlated well with the increase in protein levels.

CONCLUSION

Up-regulation of CYP2B mRNA, with a concomitant increase in protein expression and activity, were observed after repeated administration of low doses of CPA compared with that found using higher doses, possibly due to toxicity counteracting induction. These results may help in designing more effective dosing schedules for CPA.

Induction of cytochrome P450 enzymes in rat liver by two conazoles, myclobutanil and triadimefon

This study was undertaken to examine the inductive effects of two triazole antifungal agents, myclobutanil and triadimefon, on the expression of hepatic cytochrome P450 (CYP) genes and on the activities of CYP enzymes in male Sprague Dawley rats. Rats were dosed with the conazoles at three dose levels by gavage for 14 days: myclobutanil (150, 75, and 10mgkg(-1) body weight day(-1); triadimefon (115, 50, and 10 mg kg(-1) body weight day-'), which included their maximum tolerated dose levels (MTD). Both myclobutanil and triadimefon significantly induced pentoxyresorufin O-depentylase activities at their MTD levels: myclobutanil, 8.1-fold at 150mgkg(-1) body weight day- ; and triadimefon, 18.5-fold at 115mgkg(-1) body weight day-'. Benzyloxyresorufin O-debenzylase activities were similarly increased: myclobutanil, 13.3-fold; triadimefon, 27.7-fold. Quantitative real-time reverse-transcription polymerase chain reaction assays were used to characterize the mRNA expression of specific CYP genes induced by these two conazoles. Myclobutanil and triadimefon treatment at their MTD levels significantly increased rat hepatic mRNA expression of CYP2B1 (14.3- and 54.6-fold), CYP3A23/3A1 (2.2- and 7.3-fold), and CYP3A2 (1.5- and 1.7-fold). Western immunoblots of rat hepatic microsomal proteins identified significantly increased levels of CYP isoforms after myclobutanil or triadimefon treatment at their MTD levels: CYP2BI/2 (4.8- and 5.3-fold), and CYP3A1 (2.2- and 2.9-fold). Triadimefon also increased CYP3A2 immunoreactive protein levels 1.8-fold. These results indicate that triadimefon and myclobutanil, like other triazole-containing conazoles, induced CYP2B and CYP3A families of cytochromes in rat liver.

Gene expression profiles as biomarkers for the prediction of chemotherapy drug response in human tumour cells

Genome profiling approaches such as cDNA microarray analysis and quantitative reverse transcription polymerase chain reaction are playing ever-increasing roles in the classification of human cancers and in the discovery of biomarkers for the prediction of prognosis in cancer patients. Increasing research efforts are also being directed at identifying set of genes whose expression can be correlated with response to specific drugs or drug combinations. Such genes hold the prospect of tailoring chemotherapy regimens to the individual patient, based on tumour or host gene expression profiles. This review outlines recent advances and challenges in using genome profiling for the identification of tumour or host genes whose expression correlates with response to chemotherapy drugs both in vitro and in clinical studies. Genetic predictors of response to a variety of anticancer agents are discussed, including the anthracyclines, taxanes, topoisomerase I and II inhibitors, nucleoside analogs, alkylating agents, and vinca alkaloids.

Fluconazole-induced hepatic cytochrome P450 gene expression and enzymatic activities in rats and mice

This study was undertaken to examine the effects of the triazole antifungal agent fluconazole on the expression of hepatic cytochrome P450 (Cyp) genes and the activities of Cyp enzymes in male Sprague-Dawley rats and male CD-1 mice. Alkoxyresorufin O-dealkylation (AROD) methods were used as measures of Cyp enzyme activities. Western analyses identified specific Cyp isoforms. Quantitative real-time reverse-transcription polymerase chain reaction (quantitative real time-RT-PCR) assays were used to quantitate the mRNA expression of specific Cyp genes induced by this conazole. Rats and mice were administered fluconazole 2, 25, or 50 mg/kg bw/d by gavage daily for 14 days. In rats, fluconazole treatment (50 mg/kg bw/d) significantly induced pentoxyresorufin O-dealkylation (PROD), benzyloxyresorufin O-dealkylation (BROD), and ethoxyresorufin O-dealkylation (EROD) hepatic microsomal activities. Fluconazole treatment significantly increased rat hepatic mRNA expression of CYP2B1 and CYP3A23/3A1 with dose-related responses. The highest dose of fluconazole gave a 128-fold induction of CYP2B1 and a 4.6-fold induction of CYP3A23/3A1 mRNA. CYP3A2 mRNA levels were also overexpressed 5.6-7.2-fold depending on dose. Western immunoblots of rat hepatic microsomal proteins identified Cyp isoforms: CYP1A1, CYP1A2, CYP2B1/2, CYP3A23/3A1, and Cyp3A2 with increased levels of CYP2B1/2 and CYP3A23/3A1 proteins. In mice, fluconazole induced BROD, PROD, EROD, and methoxyresorufin O-dealkylation hepatic microsomal activities after treatment with 25 and 50 mg/kg bw/d. Fluconazole increased mouse hepatic mRNA expression of Cyp2b10 (1.9-fold) and Cyp3a11 (2.6-fold) in the 50 mg/kg bw/d treatment group. In summary, these results indicated that fluconazole, a triazole-containing conazole, clearly induced CYP2B and CYP3A families of isoforms in rat liver and Cyp2b and Cyp3a families of isoforms in mouse liver.

Metabolism and transport of oxazaphosphorines and the clinical implications

The oxazaphosphorines including cyclophosphamide (CPA), ifosfamide (IFO), and trofosfamide represent an important group of therapeutic agents due to their substantial antitumor and immuno-modulating activity. CPA is widely used as an anticancer drug, an immunosuppressant, and for the mobilization of hematopoetic progenitor cells from the bone marrow into peripheral blood prior to bone marrow transplantation for aplastic anemia, leukemia, and other malignancies. New oxazaphosphorines derivatives have been developed in an attempt to improve selectivity and response with reduced toxicity. These derivatives include mafosfamide (NSC 345842), glufosfamide (D19575, beta-D-glucosylisophosphoramide mustard), NSC 612567 (aldophosphamide perhydrothiazine), and NSC 613060 (aldophosphamide thiazolidine). This review highlights the metabolism and transport of these oxazaphosphorines (mainly CPA and IFO, as these two oxazaphosphorine drugs are the most widely used alkylating agents) and the clinical implications. Both CPA and IFO are prodrugs that require activation by hepatic cytochrome P450 (CYP)-catalyzed 4-hydroxylation, yielding cytotoxic nitrogen mustards capable of reacting with DNA molecules to form crosslinks and lead to cell apoptosis and/or necrosis. Such prodrug activation can be enhanced within tumor cells by the CYP-based gene directed-enzyme prodrug therapy (GDEPT) approach. However, those newly synthesized oxazaphosphorine derivatives such as glufosfamide, NSC 612567 and NSC 613060, do not need hepatic activation. They are activated through other enzymatic and/or non-enzymatic pathways. For example, both NSC 612567 and NSC 613060 can be activated by plain phosphodiesterase (PDEs) in plasma and other tissues or by the high-affinity nuclear 3'-5' exonucleases associated with DNA polymerases, such as DNA polymerases and epsilon. The alternative CYP-catalyzed inactivation pathway by N-dechloroethylation generates the neurotoxic and nephrotoxic byproduct chloroacetaldehyde (CAA). Various aldehyde dehydrogenases (ALDHs) and glutathione S-transferases (GSTs) are involved in the detoxification of oxazaphosphorine metabolites. The metabolism of oxazaphosphorines is auto-inducible, with the activation of the orphan nuclear receptor pregnane X receptor (PXR) being the major mechanism. Oxazaphosphorine metabolism is affected by a number of factors associated with the drugs (e.g., dosage, route of administration, chirality, and drug combination) and patients (e.g., age, gender, renal and hepatic function). Several drug transporters, such as breast cancer resistance protein (BCRP), multidrug resistance associated proteins (MRP1, MRP2, and MRP4) are involved in the active uptake and efflux of parental oxazaphosphorines, their cytotoxic mustards and conjugates in hepatocytes and tumor cells. Oxazaphosphorine metabolism and transport have a major impact on pharmacokinetic variability, pharmacokinetic-pharmacodynamic relationship, toxicity, resistance, and drug interactions since the drug-metabolizing enzymes and drug transporters involved are key determinants of the pharmacokinetics and pharmacodynamics of oxazaphosphorines. A better understanding of the factors that affect the metabolism and transport of oxazaphosphorines is important for their optional use in cancer chemotherapy.