Decrease in Plasma Concentrations of Antiangiogenic Agent TSU-68 ((Z)-5-[(1,2-Dihydro-2-oxo-3H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-propanoic acid) during Oral Administration Twice a Day to Rats

Identification and characterization of in vitro and in vivo metabolites of steroidal alkaloid veratramine

Veratramine, a steroidal alkaloid originating from Veratrum nigrum L., has demonstrated distinct anti-tumor and anti-hypertension effects, however, its metabolism has rarely been explored. The objective of the current study was to provide a comprehensive investigation of its metabolic pathways. The in vitro metabolic profiles of veratramine were evaluated by incubating it with liver microsomes and cytosols. The in vivo metabolic profiles in plasma, bile, urine and feces were monitored by UPLC-MS/MS after oral (20 mg/kg) and i.v. (50 µg/kg) administration in rats. Meanwhile, related P450s inhibitors and recombinant P450s and SULTs were used to identify the isozymes responsible for its metabolism. Eleven metabolites of veratramine, including seven hydroxylated, two sulfated and two glucuronidated metabolites, were characterized. Unlike most alkaloids, the major reactive sites of veratramine were on ring A and B instead of on the amine moiety. CYP2D6 was the major isozyme mediating hydroxylation, and substrate inhibition was observed with a Vmax , Ki and Clint of 2.05 ± 0.53 nmol/min/mg, 33.08 ± 10.13 µ m and 13.58 ± 1.27 µL/min/mg. SULT2A1, with Km , Vmax and Clint values of 19.37 ± 0.87 µ m, 1.51 ± 0.02 nmol/min/mg and 78.19 ± 8.57 µL/min/mg, was identified as the major isozyme contributing to its sulfation. In conclusion, CYP2D6 and SULT2A1 mediating hydroxylation and sulfation were identified as the major biotransformation for veratramine.

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.

AhR activation underlies the CYP1A autoinduction by A-998679 in rats

Xenobiotic-mediated induction of cytochrome P450 (CYP) drug metabolizing enzymes (DMEs) is frequently encountered in drug discovery and can influence disposition, pharmacokinetic, and toxicity profiles. The CYP1A subfamily of DMEs plays a central role in the biotransformation of several drugs and environmental chemicals. Autoinduction of drugs through CYP3A enzymes is a common mechanism for their enhanced clearance. However, autoinduction via CYP1A is encountered less frequently. In this report, an experimental compound, A-998679 [3-(5-pyridin-3-yl-1,2,4-oxadiazol-3-yl) benzonitrile], was shown to enhance its own clearance via induction of Cyp1a1 and Cyp1a2. Rats were dosed for 5 days with 30, 100, and 200 mg/kg/day A-998679. During the dosing period, the compound's plasma AUC decreased at 30 mg/kg (95%) and 100 mg/kg (80%). Gene expression analysis and immunohistochemistry of the livers showed a large increase in the mRNA and protein levels of Cyp1a, which was involved in the biotransformation of A-998679. Induction of CYP1A was confirmed in primary rat, human, and dog hepatocytes. The compound also weakly inhibited CYP1A2 in human liver microsomes. A-998679 activated the aryl hydrocarbon receptor (AhR) in a luciferase gene reporter assay in HepG2 cells, upregulated expression of genes associated with AhR activation in rat liver and enhanced nuclear migration of AhR in HepG2 cells. Collectively these results demonstrate that A-998679 is an AhR activator that induces Cyp1a1 and Cyp1a2 expression, resulting in an autoinduction phenomenon. The unique properties of A-998679, along with its novel structure distinct from classical polycyclic aromatic hydrocarbons (PAHs), may warrant its further evaluation as a tool compound for use in studies involving AhR biology and CYP1A-related mechanisms of drug metabolism and toxicity.

Phase I, pharmacokinetic, and biological studies of TSU-68, a novel multiple receptor tyrosine kinase inhibitor, administered after meals with solid tumors

PURPOSE

TSU-68 is a low molecular weight inhibitor of the tyrosine kinases for vascular endothelial growth factor receptor 2, platelet-derived growth factor receptor β, and fibroblast growth factors receptor 1. In this study, we assessed the recommended dose with TSU-68 administration of twice-daily (b.i.d.) or thrice-daily (t.i.d.) after meals for 4 weeks in Japanese patients with solid tumors based on the safety and tolerability and investigated the relationship between angiogenesis biomarker and clinical outcomes.

METHODS

The study design was a dose-escalation method with alternating enrollment of b.i.d. administration and t.i.d. administration after meal by traditional three-patient cohort.

RESULTS

We enrolled 24 patients at doses of 200, 400, and 500 mg/m(2) b.i.d. or 200 and 400 mg/m(2) t.i.d. No dose-limiting toxicity (DLT) occurred in the 200 mg/m(2) b.i.d. or t.i.d., and 3 patients experienced DLTs at 400 mg/m(2) b.i.d. or 400 mg/m(2) t.i.d. As main toxicity, blood albumin decreased, malaise, diarrhea, alkaline phosphatase increased, anorexia, abdominal pain, nausea, and vomiting were observed as almost all grade 1-2. There were no apparent differences in pharmacokinetic parameters between days 2 and 28 after the repeated b.i.d. and t.i.d. doses. Although tumor shrinkage was not observed, the disease control rate was 41.7%. As an angiogenesis-related factor of stratified analysis, plasma vascular endothelial growth factor and plasminogen activator inhibitor-1 were detected as a significant increase with progressive disease patients.

CONCLUSIONS

A recommended dosage of TSU-68 for this administration schedules was estimated to be 400 mg/m(2) or less b.i.d.

Phase I and pharmacokinetic study of TSU-68, a novel multiple receptor tyrosine kinase inhibitor, by twice daily oral administration between meals in patients with advanced solid tumors

PURPOSE

A single-agent dose-escalating phase I and pharmacokinetic study on TSU-68, a novel multiple receptor tyrosine kinase inhibitor, was performed to determine the safety profile, maximum-tolerated dose for Japanese patients with advanced solid tumors and to define the recommended dose of phase II studies.

METHODS

Study design was a dose escalation method on a three-patient cohort. TSU-68 was given orally twice daily (bid) between meals without interruption; the estimation of dose escalation was based on the toxicity within 4 week administration at each dose level.

RESULTS

Fifteen patients were enrolled into the study. Dose levels studied were 200, 400, 800, and 1,200 mg/m(2) bid. Grade 3 arrhythmia and anemia/thrombocytopenia were observed in 1 patient each at 800 mg/m(2) bid. Three patients discontinued continuous oral administration for 4 weeks at 400 and 800 mg/m(2) bid. At 1,200 mg/m(2) bid, 2 patients discontinued the treatment over 4 weeks for intolerable fatigue and abdominal pain, respectively. No serious drug-related toxicities have been observed. Grade 1-2 toxicity included urinary/feces discoloration, diarrhea, fatigue, anorexia, abdominal/chest pain, and edema. Tumor shrinkage was observed in 1 patient of NSCLC. In the pharmacokinetics, at any dose levels, C(max) and AUC(0-t) after repeated administration of TSU-68 on days 8 and 29 were ~2-fold lower that those after the first administration on day 1; these parameters are similar between days 8 and 28. In addition, no obvious dose-dependent increase in plasma exposure to TSU-68 repeatedly administered was observed over the four dose levels, including the higher dose levels.

CONCLUSIONS

The tolerable dose in this administration schedule for continuing treatment is thought to be 800 mg/m(2) or less bid.

Structure, function, regulation and polymorphism and the clinical significance of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g., benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids). CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances, and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close link between CYP1A1 and 1A2 sharing a common 5'-flanking region. The human CYP1A2 gene spans almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of 1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate binding platforms on either side of the cavity. A large interindividual variability in the expression and activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of them have been associated with altered drug clearance and response and disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.

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.

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

The anti-angiogenic agent TSU-68 is known to rapidly induce cytochrome P450 activity responsible for its own hydroxylation in rats. In this study, we identified CYP1A1 and CYP1A2 as the TSU-68-induced P450 and temporally characterized the rapid induction of these isoforms. Protein and mRNA levels of CYP1A1 and CYP1A2 along with CYP1A activities were examined in rat liver after a single oral administration of 500 mg/kg TSU-68. CYP1A-mediated ethoxyresorufin O-deethylation and TSU-68 hydroxylation activities reached the maximum at 12 hr. The activities were maintained up to 24 hr and then slowly decreased down to control levels. Protein levels of both CYP1A1 and CYP1A2 were also rapidly induced with temporal profiles similar to the profile of CYP1A activity. In contrast, unlike CYP1A2 mRNA levels, which peaked at 12 hr and almost returned to control levels by 48 hr, CYP1A1 mRNA levels peaked as early as 3 hr and returned to control levels by 24 hr. Thus, CYP1A1 showed more rapid elevation and turnover of its mRNA than CYP1A2. In conclusion, TSU-68 administered to rats rapidly induced mRNA and protein of CYP1A1 and CYP1A2 as well as CYP1A activity. Furthermore, the data showed a difference in the time-dependent induction between CYP1A1 and CYP1A2 mRNAs.