Time-dependent induction of rat hepatic CYP1A1 and CYP1A2 expression after single-dose administration of the anti-angiogenic agent TSU-68

In vitro differences in toddalolactone metabolism in various species and its effect on cytochrome P450 expression

CONTEXT

Toddalolactone, the main component of Toddalia asiatica (L.) Lam. (Rutaceae), has anticancer, antihypertension, anti-inflammatory, and antifungal activities.

OBJECTIVE

This study investigated the metabolic characteristics of toddalolactone.

MATERIALS AND METHODS

Toddalolactone metabolic stabilities were investigated by incubating toddalolactone (20 μM) with liver microsomes from humans, rabbits, mice, rats, dogs, minipigs, and monkeys for 0, 30, 60, and 90 min. The CYP isoforms involved in toddalolactone metabolism were characterized based on chemical inhibition studies and screening assays. The effects of toddalolactone (0, 10, and 50 µM) on CYP1A1 and CYP3A5 protein expression were investigated by immunoblotting. After injecting toddalolactone (10 mg/kg), in vivo pharmacokinetic profiles using six Sprague-Dawley rats were investigated by taking 9-time points, including 0, 0.25, 0.5, 0.75, 1, 2, 4, 6 and 8 h.

RESULTS

Monkeys showed the greatest metabolic capacity in CYP-mediated and UGT-mediated reaction systems with short half-lives (T_1/2) of 245 and 66 min, respectively, while T_1/2 of humans in two reaction systems were 673 and 83 min, respectively. CYP1A1 and CYP3A5 were the major CYP isoforms involved in toddalolactone biotransformation. Induction of CYP1A1 protein expression by 50 μM toddalolactone was approximately 50% greater than that of the control (0 μM). Peak plasma concentration (C_max) for toddalolactone was 0.42 μg/mL, and T_max occurred at 0.25 h post-dosing. The elimination t_1/2 was 1.05 h, and the AUC_0-t was 0.46 μg/mL/h.

CONCLUSIONS

These findings demonstrated the significant species differences of toddalolactone metabolic profiles, which will promote appropriate species selection in further toddalolactone studies.

LC-MS-based assay of granisetron 7-hydroxylation activity for the evaluation of CYP1A1 induction from diesel particulate matter-exposed hepatic and respiratory cell lines

Particulate matter (PM) generally consists of aggregated particles containing trace metals and polycyclic aromatic hydrocarbons (PAHs). Cytochrome P450 (CYP) 1A1, one of the extensively investigated biomarkers, is highly inducible when PAHs activate the aryl hydrocarbon receptor (AhR). The present study focused on developing a LC-MS/MS-based assay to evaluate CYP1A1 induction potential following PM exposure. This assay adapted a CYP1A1 selective reaction of granisetron 7-hydroxylation in response to an AhR inducer, 6-formylindolo[3,2-b]carbazole (FICZ), in HepaRG and A549 cell lines. Exposure to FICZ (10 nM) increased the levels of granisetron 7-hydroxylation significantly, whereas no elevation of ethoxyresorufin-O-deethylation (EROD) activity was found in HepaRG cells. In A549 cells, granisetron 7-hydroxylation showed a better dose-response from 0 to 10000 nM FICZ treatment than EROD. EROD Additionally, the application of the assay with diesel PM exposure showed a concentration-dependent induction of CYP1A1 in HepaRG, A549, and human nasal epithelial cells. The granisetron assay has better selectivity for CYP1A1 than the conventional EROD assay, which is overlapped reaction with CYP1A2 and CYP1B1, with high correlations between AhR activation and CYP1A1 mRNA levels. Accompanying the great application potential to different organs and cell culture systems, future studies will implement the granisetron assay for the respiratory toxicity evaluation.

Sudden infant death syndrome caused by cardiac arrhythmias: only a matter of genes encoding ion channels?

Sudden infant death syndrome is the unexpected demise of a child younger than 1 year of age which remains unexplained after a complete autopsy investigation. Usually, it occurs during sleep, in males, and during the first 12 weeks of life. The pathophysiological mechanism underlying the death is unknown, and the lethal episode is considered multifactorial. However, in cases without a conclusive post-mortem diagnosis, suspicious of cardiac arrhythmias may also be considered as a cause of death, especially in families suffering from any cardiac disease associated with sudden cardiac death. Here, we review current understanding of sudden infant death, focusing on genetic causes leading to lethal cardiac arrhythmias, considering both genes encoding ion channels as well as structural proteins due to recent association of channelopathies and desmosomal genes. We support a comprehensive analysis of all genes associated with sudden cardiac death in families suffering of infant death. It allows the identification of the most plausible cause of death but also of family members at risk, providing cardiologists with essential data to adopt therapeutic preventive measures in families affected with this lethal entity.

A phase II open-label randomized multicenter trial of TSU-68 in combination with S-1 and oxaliplatin versus S-1 in combination with oxaliplatin in patients with metastatic colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the fourth leading cause of cancer-related deaths worldwide. The combination of oxaliplatin-based treatments (oxaliplatin plus infusional 5-fluorouracil and leucovorin [FOLFOX] or oxaliplatin plus capecitabine [CapeOX]) and bevacizumab is a standard chemotherapy regimen for metastatic CRC (mCRC). However, several clinical studies that tested S-1 plus oxaliplatin (SOX) indicate that SOX is also a treatment option for mCRC. TSU-68 is an oral compound that inhibits vascular endothelial growth factor receptor and platelet-derived growth factor receptor. The recommended dose of TSU-68 + SOX was previously determined in a phase I study of mCRC patients. The goal of this trial was to evaluate the efficacy of TSU-68 in combination with SOX.

METHODS

This open-label multicenter randomized phase II trial was performed in Korea. Treatment-naive mCRC patients with a performance status of 0 or 1 were randomized in a 1:1 ratio to receive either TSU-68 + SOX or SOX alone. The primary endpoint was progression-free survival (PFS).

RESULTS

A total of 105 patients (TSU-68 + SOX, 52 patients; SOX alone, 53 patients) were randomized. The median PFS was 7.0 months in the TSU-68 + SOX group (hazard ratio [HR], 1.057) and 7.2 months in the SOX group (p = 0.8401). The most frequent grade 3 and 4 adverse events were thrombocytopenia (9.6 % [TSU-68 + SOX] vs. 26.4 % [SOX]), neutropenia (13.5 % [TSU-68 + SOX] vs. 15.1 % [SOX]), and anemia (3.8 % [TSU-68 + SOX] vs. 13.2 % [SOX]). We observed a difference between the 2 groups for all grades of anemia (15.4 % [TSU-68 + SOX] vs. 32.1 % [SOX]), diarrhea (30.8 % [TSU-68 + SOX] vs. 47.2 % [SOX]), vomiting (50.0 % [TSU-68 + SOX] vs. 26.4 % [SOX]), and chromaturia (23.1 % [TSU-68 + SOX] vs. 0.0 % [SOX]). Analysis using a Cox proportional hazard model showed that baseline interleukin 6 (IL-6) levels were associated with a survival benefit of TSU-68 (p = 0.012).

CONCLUSION

TSU-68 + SOX had a favorable safety profile. However, TSU-68 did not have a synergistic effect on the efficacy of SOX. The baseline serum IL-6 level could be a prognostic factor for TSU-68 efficacy.

RO4938581, a GABAAα5 modulator, displays strong CYP1A2 autoinduction properties in rats

Autoinduction in drug metabolism is a known phenomenon observed when a drug induces the enzymes responsible for its own metabolism. The potency, rate and extent of autoinduction following a given treatment paradigm may have therapeutic implications in clinic as well as for in vivo pharmacological assessments in animals. RO4938581, an imidazo-triazolo-benzodiazepine, is a novel GABAAα5 negative modulator recently pursued for the treatment of cognitive dysfunctions. As circulating plasma levels of RO4938581 were shown to decrease rapidly after repeated dosing in rats, with CYP1A2 being involved in the metabolism of the compound, we examined the potential role of RO4938581-mediated autoinduction of CYP1A2. Incubation of rat hepatocytes with RO4938581 revealed potent CYP1A2 induction with significant increase in enzymatic activity at concentrations of 0.1nM and RO4938581 was shown to be 700-fold more potent than β-napththoflavone. Ex vivo studies revealed a 7-fold increase in metabolic CYP1A2 activity in liver microsomes prepared from rats administered with 0.1mg/kg of RO4938581 24h before. This induction profile was reflected in vivo in pharmacokinetic studies in rats where an 8-fold reduction in plasma exposure was observed after a second dose. The reduction in plasma exposures due to CYP1A2 autoinduction were confirmed functionally in contextual fear conditioning paradigm in rats, where a positive pharmacological effect observed after acute drug administration disappeared completely after sub-chronic dosing. Together, these findings suggest that RO4938581 possesses potent CYP1A2 autoinductive properties in rats and may serve as a tool for mechanistic metabolism or drug-drug interaction studies encircling this enzyme in rats.

Hepatic Drug-Metabolizing Enzyme Induction and Implications for Preclinical and Clinical Risk Assessment

Hepatic drug metabolizing enzyme (DME) induction complicates the development of new drugs owing to altered efficacy of concomitant treatments, reduction in exposure resulting from autoinduction, and potential generation of toxic metabolites. Risk assessment of DME induction during clinical evaluation is confounded by several uncertainties pertaining to hazard identification and dose response analysis. Hepatic DME induction rarely leads to clinical evidence of altered metabolism and toxicity in the patient, which typically occur only if the DME induction is relatively severe. High drug doses are associated with a greater likelihood of hepatic DME induction and downstream effects; therefore, drugs of low potency requiring higher dosing tend to lead to a greater risk of drug–drug interactions. Vigilance in clinical trials for increased or diminished drug effect and, specifically, pharmacokinetic studies in the presence of other drugs and concomitant diseases are necessary for a drug risk assessment profile.

Efforts to remove hepatic DME-inducing drugs from development can be facilitated with current in vitro and in vivo assessments and will improve with the development of newer technologies. A carefully tailored case-by-case approach will lead to the development of efficacious drugs with an acceptable risk/benefit profile available to patients.

3-aminobenzanthrone, a human metabolite of the carcinogenic environmental pollutant 3-nitrobenzanthrone, induces biotransformation enzymes in rat kidney and lung

3-aminobenzanthrone (3-ABA) is the metabolite of the carcinogenic air pollutant 3-nitrobenzanthrone (3-NBA). 3-ABA was investigated for its ability to induce cytochrome P450 1A1 (CYP1A1) and NAD(P)H:quinone oxidoreductase (NQO1) in kidney and lung of rats, and for the influence of such induction on DNA adduct formation by 3-ABA and 3-NBA. NQO1 is the enzyme that reduces 3-NBA to N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) and CYP1A enzymes oxidize 3-ABA to the same intermediate. When activated by cytosolic and and/or microsomal fractions isolated from rat lung, the target organ for 3-NBA carcinogenicity, and kidney, both compounds generated the same DNA-adduct pattern, consisting of five adducts. When pulmonary cytosols isolated from rats that had been treated i.p. with 40 mg/kg bw of 3-ABA were incubated with 3-NBA, DNA adduct formation was up to 1.7-fold higher than in incubations with cytosols from control animals. This increase corresponded to an increase in protein level and enzymatic activity of NQO1. In contrast, no induction of NQO1 expression by 3-ABA treatment was found in the kidney. Incubations of 3-ABA with renal and pulmonary microsomes of 3-ABA-treated rats led to an increase of up to a 4.5-fold in DNA-adduct formation relative to controls. The stimulation of DNA-adduct formation correlated with a higher protein expression and activity of CYP1A1 induced by 3-ABA. These results show that by inducing lung and kidney CYP1A1 and NQO1, 3-ABA increases its own enzymatic activation as well as that of the environmental pollutant, 3-NBA, thereby enhancing the genotoxic and carcinogenic potential of both compounds.