Determination of tebufelone, a new anti-inflammatory drug, in plasma and tissue using capillary gas chromatography/stable isotope dilution mass spectrometry

Interspecies scaling of tebufelone pharmacokinetic data and application to preclinical toxicology

PURPOSE

Retrospective application of allometric scaling techniques to tebufelone, a nonsteroidal antiinflammatory agent, in order to better understand the systemic exposure relationships between the doses administered to the species used in toxicology studies and the doses given to human subjects and patients in clinical studies.

METHODS

Non-compartmental estimates of tebufelone's total body volume of distribution during the terminal phase (Vz) and clearance (CL) obtained from intravenous dosing to rat, monkey, dog, and human were allometrically scaled to body weight, and body weight and brain weight, respectively. AUCs determined from single or multiple dose pharmacokinetic studies and from preclinical toxicology studies were plotted versus dose adjusted for bioavailability and divided by allometrically scaled clearance to produce an allometric relationship suggesting a non-linear increase in AUC with dose across the four species.

RESULTS

Segmental linear regression analysis of this relationship indicates a change point associated with an AUC of approximately 2,300 ng-hr/mL. Elevations in serum levels of various liver enzymes or associated signs of hepatic toxicity occur in some, but not all of the animals exposed for more than three weeks in repeat dosing studies at the actual dose that this represents.

CONCLUSIONS

The analysis suggests that doses producing tebufelone plasma levels above a certain threshold AUC and duration of exposure to parent tebufelone are associated with increased risks of hepatic effects. Whether this is because metabolic shifts occur at these doses cannot be determined from these data.

Effects of tebufelone (NE-11740), a new anti-inflammatory drug, on arachidonic acid metabolism

Tebufelone is a novel nonsteroidal anti-inflammatory drug (NSAID), of the di-tert-butylphenol (DTBP) class, which displays potent anti-inflammatory, analgesic and anti-pyretic properties in a variety of animal models. In this report, the effects of Tebufelone on arachidonic acid (AA) metabolism are reviewed. Tebufelone potently inhibits the formation of prostaglandins (PGE2) a key mediator of pain and inflammation, in isolated enzyme preparations (IC50 = 1.5 microM, KI = 0.35 microM), two in vitro cellular systems: rat peritoneal macrophages (IC50 = 0.02 microM) and human whole blood (IC50 = 0.08 microM), and ex vivo in man. In addition to PGE2 inhibition, which is common to all NSAIDs, higher concentrations of Tebufelone block the in vitro formation of products of the lipoxygenase pathway [leukotrienes (LTB4)] in rat macrophages (IC50 = 20 microM) and human whole blood (IC50 = 22 microM). Substrate incorporation studies (14C-AA) indicate that Tebufelone reversibly inhibits cyclooxygenase (CO) and 5-lipoxygenase (5-LO) enzymes rather than regulating the release of AA. Tebufelone was shown to be a more potent CO inhibitor than indomethacin and a less potent 5-LO inhibitor than RG-5901. Comparisons to structurally related compounds under development (E-5110, Esai; KME-4, Kanagafuchi), found Tebufelone to be the most potent CO inhibitor in vitro. All three DTBP compounds were equipotent 5-LO inhibitors. It is likely that Tebufelone's inhibitory effects on AA metabolism are, in part, responsible for its in vivo efficacy and enhanced safety profile.

Comparison of tebufelone distribution in rat blood plasma and inflamed and noninflamed tissues following peroral and intravenous administration

It is recognized that some acidic nonsteroidal antiinflammatory drugs (NSAIDs) accumulate in the synovial fluids of inflamed joints. The distribution of tebufelone, a member of the di-tert-butylphenol class of NSAIDs, between rat plasma and paw tissues (inflamed and noninflamed) was determined. Tebufelone was administered (doses providing 80% maximal effectiveness) perorally (po, 10 mg/kg) or intravenously (i.v., 0.5 mg/kg) to Sprague-Dawley rats just prior to injection of an inflammatory adjuvant (carrageenan) into one of the hind paws. Levels of the drug were measured in plasma, inflamed paws, and noninflamed paws at prescribed times postdosing by capillary gas chromatography/stable isotope dilution mass spectrometry. Tebufelone levels, as determined from areas under the curves of concentration versus time were sevenfold (po) and 11-fold (i.v.) higher in paw tissue than in plasma. Inflamed and noninflamed tissues have equal affinity for the drug. Calculated terminal-phase half-lives of tebufelone in paw tissue were similar following i.v. and po dosing (approximately 14 h) and equivalent to the plasma half-life of the drug after po dosing (approximately 10 h). The plasma half-life determined following i.v. dosing was considerably lower (2.8 h). The anti-inflammatory activity of tebufelone appears to correlate more closely with tissue distribution profiles than plasma drug levels at the dose levels examined.

Absorption, bioavailability, and pharmacokinetics of tebufelone in the rat

Tebufelone (NE-11740) is a member of the new di-tert-butylphenol class of anti-inflammatory agents. It exhibits good inhibitory activity against cyclooxygenase and 5-lipoxygenase in vitro. It also shows excellent anti-inflammatory activity and inhibits bone resorption in vivo in the rat adjuvant arthritis model at an oral dose level of 1 to 2 mg/kg. The absorption, bioavailability, and pharmacokinetics of tebufelone were investigated in male Sprague-Dawley rats. Tebufelone labeled with carbon-14 was administered intravenously at doses of 0.5 and 2 mg/kg and perorally at doses of 2 and 10 mg/kg to fasted rats. Plasma samples taken from the rats at timed intervals were analyzed for total radiolabel by scintillation counting and for tebufelone by a mass spectrometric method. Comparison of the total radiolabel and tebufelone areas under the curves (AUCs) of concentration of tebufelone versus time from the 2-mg/kg intravenous and 2-mg/kg oral doses indicates that tebufelone is completely absorbed and 100% bioavailable at this dose level in the rat. The AUCs are a linear function of dose at the 0.5- and 2-mg/kg dose levels, but the AUC of the 10-mg/kg dose exhibits a nonproportional increase, suggesting saturation of elimination processes at this higher dose.