Omaveloxolone and TX63682 are hepatoprotective in the STAM mouse model of nonalcoholic steatohepatitis

Omaveloxolone is a potent activator of Nrf2, a master transcriptional regulator of a multitude of cytoprotective functions, including antioxidative, anti-inflammatory, and mitochondrial bioenergetic effects. Some of the most potent known effects of Nrf2 involve hepatoprotective functions. The purpose of this study was to evaluate the effects of omaveloxolone and TX63682, a closely related structural analog with similar oral bioavailability, in the STAM mouse model of nonalcoholic steatohepatitis (NASH). C57Bl/6 mice received a single subcutaneous injection of streptozotocin two days after birth and were fed a high-fat diet from 4 to 9 weeks of age. Omaveloxolone and TX63682 were orally administered at doses of 1, 3, and 10 mg/kg/d from 6 to 9 weeks of age. Consistent with the beneficial effects of Nrf2 on hepatoprotection and improved lipid handling, both omaveloxolone and TX63682 decreased hepatic fat deposition, hepatocellular ballooning, inflammatory cell infiltration, and collagen deposition. Omaveloxolone and TX63682 also improved blood glucose control, as evidenced by reductions in nonfasting blood glucose and glycated hemoglobin A1C concentrations. Reductions in liver and serum triglycerides with omaveloxolone and TX63682 treatment were also observed. Both omaveloxolone and TX63682 decreased leptin and increased adiponectin in serum, which is consistent with the anti-inflammatory and antifibrotic effects observed in the liver. These results were associated with significant induction of Nrf2 target gene expression in the liver, including NAD(P)H:quinone oxidoreductase 1, sulfiredoxin 1, and ferritin heavy chain 1. Overall, these data suggest that omaveloxolone and related Nrf2 activators may be useful for the treatment of NASH.

Bardoxolone methyl analog attenuates proteinuria-induced tubular damage by modulating mitochondrial function

Multiple clinical studies have shown that bardoxolone methyl, a potent activator of nuclear factor erythroid 2–related factor 2 (Nrf2), is effective in increasing glomerular filtration rate in patients with chronic kidney disease. However, whether an Nrf2 activator can protect tubules from proteinuria-induced tubular damage via anti-inflammatory and antioxidative stress mechanisms is unknown. Using an Institute of Cancer Research–derived glomerulonephritis (ICGN) mouse model of nephrosis, we examined the effects of dihydro-CDDO-trifluoroethyl amide (dh404), a rodent-tolerable bardoxolone methyl analog, in protecting the tubulointerstitium; dh404 markedly suppressed tubular epithelial cell damage in the renal interstitium of ICGN mice. The tubular epithelial cells of ICGN mice showed a decrease in the size and number of mitochondria, as well as the breakdown of the crista structure, whereas the number and ultrastructure of mitochondria were maintained by the dh404 treatment. To further determine the effect of dh404 on mitochondrial function, we used human proximal tubular cells in vitro. Stimulation with albumin and free fatty acid increased mitochondrial reactive oxygen species (ROS). However, dh404 administration diminished mitochondrial ROS. Our data show that dh404 significantly reduced proteinuria-induced tubular cell mitochondrial damage, suggesting that improved redox balance and mitochondrial function and suppression of inflammation underlie the cytoprotective mechanism of Nrf2 activators, including bardoxolone methyl, in diabetic kidney disease.—Nagasu, H., Sogawa, Y., Kidokoro, K., Itano, S., Yamamoto, T., Satoh, M., Sasaki, T., Suzuki, T., Yamamoto, M., Wigley, W. C., Proksch, J. W., Meyer, C. J., Kashihara, N. Bardoxolone methyl analog attenuates proteinuria-induced tubular damage by modulating mitochondrial function.

Pharmacokinetics and pharmacodynamics of the novel Nrf2 activator omaveloxolone in primates

Background

Omaveloxolone is a synthetic oleanane triterpenoid that pharmacologically activates Nrf2, a master transcription factor that regulates genes with antioxidative, anti-inflammatory, and mitochondrial bioenergetic properties, and is being evaluated in patients with Friedreich’s ataxia.

Methods

The present study evaluated the pharmacokinetics (PK) and tissue distribution of omaveloxolone in monkeys after single and multiple oral doses, and then compared these data to initial results in Friedreich’s ataxia patients. Pharmacodynamic (PD) evaluations in monkeys consisted of Nrf2 target gene mRNA expression in peripheral blood mononuclear cells (PBMCs), liver, lung, and brain. A PK/PD model was generated with the monkey data, and used to further evaluate the Friedreich’s ataxia patient PK profile.

Results

Oral administration of omaveloxolone to monkeys was associated with dose-linear plasma PK and readily measureable and dose-proportional concentrations in liver, lung, and brain. Dose-dependent induction of Nrf2 target genes in PBMCs and tissues was also observed. Clinically, oral administration of omaveloxolone to Friedreich’s ataxia patients at incremental doses from 2.5 to 300 mg produced dose-proportional systemic exposures. Clinical doses of at least 80 mg were associated with meaningful improvements in neurological function in patients and generated plasma omaveloxolone concentrations consistent with those significantly inducing Nrf2 target genes in monkeys, as shown with the monkey PK/PD model.

Conclusion

Overall, the monkey data demonstrate a well-characterized and dose-proportional PK and tissue distribution profile after oral administration of omaveloxolone, which was associated with Nrf2 activation. Further, systemic exposures to omaveloxolone that produce Nrf2 activation in monkeys were readily achievable in Friedreich’s ataxia patients after oral administration.

RTA 1701 is an oral RORγt inhibitor that suppresses the IL-17A response in non-human primates

RTA 1701 is an orally-bioavailable, selective RORγt inhibitor. RORγt orchestrates the differentiation of Th17 cells and contributes to autoimmune disease pathogenesis. Inhibition of RORγt suppresses Th17 cells and the associated secretion of the effector pro-inflammatory cytokine IL-17A. As such, RTA 1701 is highly efficacious in rodent models of rheumatoid arthritis and multiple sclerosis. This study was conducted to evaluate the pharmacokinetics of RTA 1701 and its effects on ex vivo stimulation of IL-17A production in whole blood after oral administration to naïve healthy cynomolgus monkeys. Monkeys received a single administration of RTA 1701 (0.3, 3, 30, or 300 mg/kg). After a one-week washout, monkeys received the same doses of RTA 1701 once daily for 14 consecutive days. Blood was collected after a single dose and after 14 days of dosing for analysis of plasma RTA 1701 concentrations through 72 hours post-dose and for evaluation of RTA 1701 effects on ex vivo stimulation of IL-17A at 24, 30, and 72 hours post-dose. RTA 1701 exhibited oral bioavailability in monkeys with dose-dependent increases in exposure over the wide range of doses evaluated. Further, oral administration produced systemic exposure to RTA 1701 at sufficient levels to produce significant and dose-dependent suppression of ex vivo stimulation of IL-17A secretion in whole blood at 24 and 30 hours after single and repeat dosing, with IL-17A levels returning to baseline within 72 hours after a single dose. Collectively, these data demonstrate that RTA 1701 is orally bioavailable in non-human primates and significantly suppresses the IL-17A response. These data also support the future clinical development of RTA 1701 for the potential treatment of autoimmune diseases.

Safety, pharmacokinetics, and pharmacodynamics of oral omaveloxolone (RTA 408), a synthetic triterpenoid, in a first-in-human trial of patients with advanced solid tumors

Background

Omaveloxolone is a semisynthetic oleanane triterpenoid that potently activates Nrf2 with subsequent antioxidant function. We conducted a first-in-human Phase I clinical trial (NCT02029729) with the primary objectives to determine the appropriate dose for Phase II studies, characterize pharmacokinetic and pharmacodynamic parameters, and assess antitumor activity.

Methods

Omaveloxolone was administered orally once daily continuously in a 28-day cycle for patients with stage 4 relapsed/refractory melanoma or non-small cell lung cancer. An accelerated titration design was employed until a grade 2-related adverse event (AE) occurred. A standard 3+3 dose escalation was employed. Single-dose and steady-state plasma pharmacokinetics of the drug were characterized. Downstream Nrf2 activation was assessed in peripheral blood mononuclear cells by quantification of target gene mRNA expression.

Results

Omaveloxolone was tested at four dose levels up to 15 mg given orally once daily. No dose-limiting toxicities were detected, and the maximum tolerated dose was not determined. All drug-related AEs were either grade 1 or 2 in severity, and none required clinical action. The most common drug-related AEs were elevated alkaline phosphatase (18%) and anemia (18%). No drug interruptions or reductions were required. Omaveloxolone was rapidly absorbed and exhibited proportional increases in exposure across dose levels. With some exceptions, an overall trend toward time-dependent and dose-dependent activation of Nrf2 antioxidant genes was observed. No confirmed radiologic responses were seen, although one lung cancer subject did have stable disease exceeding 1 year.

Conclusions

Omaveloxolone has favorable tolerability at biologically active doses, although this trial had a small sample size which limits definitive conclusions. These findings support further investigation of omaveloxolone in cancer.

Topical application of RTA 408 lotion activates Nrf2 in human skin and is well-tolerated by healthy human volunteers

BACKGROUND

Topical application of the synthetic triterpenoid RTA 408 to rodents elicits a potent dermal cytoprotective phenotype through activation of the transcription factor Nrf2. Therefore, studies were conducted to investigate if such cytoprotective properties translate to human dermal cells, and a topical lotion formulation was developed and evaluated clinically.

METHODS

In vitro, RTA 408 (3-1000 nM) was incubated with primary human keratinocytes for 16 h. Ex vivo, RTA 408 (0.03, 0.3, or 3 %) was applied to healthy human skin explants twice daily for 3 days. A Phase 1 healthy volunteer clinical study with RTA 408 Lotion (NCT02029716) consisted of 3 sequential parts. In Part A, RTA 408 Lotion (0.5 %, 1 %, and 3 %) and lotion vehicle were applied to individual 4-cm(2) sites twice daily for 14 days. In Parts B and C, separate groups of subjects had 3 % RTA 408 Lotion applied twice daily to a 100-cm(2) site for 14 days or a 500-cm(2) site for 28 days.

RESULTS

RTA 408 was well-tolerated in both in vitro and ex vivo settings up to the highest concentrations tested. Further, RTA 408 significantly and dose-dependently induced a variety of Nrf2 target genes. Clinically, RTA 408 Lotion was also well-tolerated up to the highest concentration, largest surface area, and longest duration tested. Moreover, significant increases in expression of the prototypical Nrf2 target gene NQO1 were observed in skin biopsies, suggesting robust activation of the pharmacological target.

CONCLUSIONS

Overall, these data suggest RTA 408 Lotion is well-tolerated, activates Nrf2 in human skin, and appears suitable for continued clinical development.

The use of the African green monkey as a preclinical model for ocular pharmacokinetic studies

PURPOSE

This investigation evaluated the ocular and systemic pharmacokinetics of besifloxacin in African green monkeys compared with cynomolgus monkeys following topical ocular dosing.

METHODS

A suspension formulation containing 0.6% besifloxacin was administered to African green and cynomolgus monkeys. Animals were euthanized at predetermined time intervals, and ocular tissue and systemic blood samples were collected and analyzed by LC/MS/MS.

RESULTS

In both African green and cynomolgus monkeys, high concentrations of besifloxacin were detected in anterior segment tissues, while levels in posterior segment tissues and plasma were low. Mean concentration versus time profiles of besifloxacin were generally similar between species, with rapid absorption into ocular tissues after a single dose. In anterior segment tissues, concentrations of besifloxacin were measurable throughout the 24-h sampling period in both species. Quantitatively, concentrations were consistently higher in the conjunctiva of African green monkeys compared with cynomolgus monkeys. Besifloxacin levels were also higher during the first 3 h following dosing in the tear fluid of African green monkeys, but lower in the iris/ciliary body during this timeframe. However after the 3-h time point, concentrations in the tear fluid and iris/ciliary body were similar between species. Exposure in cornea tended to be higher in African green monkeys, but the difference was less pronounced than for conjunctiva. Exposure in aqueous humor was comparable between species. In posterior segment tissues, exposure to besifloxacin tended to be higher in cynomolgus monkeys. Systemic exposure also tended to be higher in cynomolgus monkeys, but measurable levels were present in the plasma of both species throughout the 24-h sampling period. With the exception of iris/ciliary body and vitreous humor, mean ocular tissue weights were generally similar between species although a small, but statistically significant, difference was also observed in the choroid.

CONCLUSIONS

African green monkeys may be a suitable model for preclinical ocular pharmacokinetic studies. Additional studies using a variety of compounds would be useful in determining whether the quantitative differences in ocular exposures and ocular tissue weights observed in the present investigation reflect slight variations in the procedures used in these separate experiments, or true physiological and anatomical differences between species.

Ocular pharmacokinetics/pharmacodynamics of besifloxacin, moxifloxacin, and gatifloxacin following topical administration to pigmented rabbits

PURPOSE

The purpose of this investigation was to evaluate the ocular pharmacokinetic/pharmacodynamic (PK/PD) relationship for besifloxacin, moxifloxacin, and gatifloxacin using rabbit ocular PK data, along with in vitro minimum inhibitory concentration (MIC90) values against methicillin- and ciprofloxacin-resistant Staphylococcus aureus (MRSA-CR) and Staphylococcus epidermidis (MRSE-CR).

METHODS

Rabbits received a topical instillation of Besivance™ (besifloxacin ophthalmic suspension, 0.6%), Vigamox (moxifloxacin hydrochloride ophthalmic solution, 0.5% as base), or Zymar (gatifloxacin ophthalmic solution, 0.3%), and ocular tissues and plasma were collected from 4 animals/treatment/collection time at 8 predetermined time intervals during the 24h after dosing. Ocular levels of each agent were measured by LC/MS/MS, and PK parameters (Cmax, Tmax, and AUC₀₋₂₄) were determined. AUC₀₋₂₄/MIC₉₀ ratios were calculated for tears, conjunctiva, cornea, and aqueous humor using previously reported MIC₉₀values for MRSA-CR and MRSE-CR.

RESULTS

All of the fluoroquinolones tested demonstrated rapid penetration into ocular tissues after a single instillation. Besifloxacin demonstrated the highest exposure in tear fluid, while exposure in conjunctiva was comparable for all 3 compounds. Peak concentrations of all fluoroquinolones in aqueous humor were at or below ~1g/mL. In comparison with their MIC₉₀values against MRSE-CR and MRSA-CR, besifloxacin achieved an AUC₀₋₂₄/MIC₉₀ ratio of ~800 in tears, compared with values of ≤10 for moxifloxacin and gatifloxacin. In cornea, conjunctiva, and aqueous humor, the AUC₀₋₂₄/MIC₉₀ ratios were <10 for all compounds. However, in these tissues AUC₀₋₂₄/MIC₉₀ ratios for besifloxacin were 1.5- to 38-fold higher than moxifloxacin and gatifloxacin.

CONCLUSIONS

In rabbits, besifloxacin demonstrates a nonclinical ocular PK profile characterized by high and sustained concentrations in tear fluid, resulting in AUC₀₋₂₄/MIC₉₀ ratios of ~800 for ciprofloxacin-resistant MRSE and MRSA after a single administration. Although besifloxacin had the highest AUC₀₋₂₄/MIC₉₀ratios for intraocular tissues, the ratios for all of the drugs were below the target values needed for effective bacterial killing of ciprofloxacin-resistant MRSE and MRSA. Taken together, these nonclinical data indicate that besifloxacin has a favorable ocular PK/PD profile, consistent with the reported clinical efficacy of besifloxacin in the treatment of bacterial conjunctivitis, and consistent with the profile needed for ocular surface sterilization.

Ocular pharmacokinetics of mapracorat, a novel, selective glucocorticoid receptor agonist, in rabbits and monkeys

Mapracorat is a selective glucocorticoid receptor agonist in development for the treatment of a variety of ocular diseases. The purpose of this investigation was to evaluate the ocular pharmacokinetics of mapracorat after topical dosing over a range of dose levels in rabbits and monkeys. Mapracorat was administered over a range of doses from 0.01 to 3000 μg/eye (rabbit) or 50 to 3000 μg/eye (monkey). All animals received a single instillation, and monkeys also received repeated (three times per day for 4 days) instillations. At predetermined intervals through at least 24 h after dosing, ocular tissues and plasma were collected and analyzed for mapracorat by liquid chromatography-tandem mass spectrometry. Mapracorat was rapidly absorbed and widely distributed into ocular tissues after topical ocular administration, with measurable levels sustained through ≥24 h. In both species, mapracorat concentrations were highest in tears followed by conjunctiva and cornea, with lower levels observed in iris/ciliary body and aqueous humor. Mapracorat concentrations in conjunctiva, cornea, and iris/ciliary body increased linearly with increasing dose levels. Ocular exposure was higher after repeated dosing to monkeys than after a single dose. Systemic exposure to mapracorat was low after a single administration, with an average maximal concentration of ≤2.0 ng/ml at the highest dose tested (3000 μg/eye). In comparison with the traditional glucocorticoids, dexamethasone (0.1%) and prednisolone acetate (1%), mapracorat (3%) demonstrated similar or higher levels in ocular tissues with lower systemic exposure. The favorable pharmacokinetic profile of mapracorat supports further clinical investigation and suggests that a convenient daily dosing regimen may be efficacious for this novel ophthalmic anti-inflammatory therapy.

Concentrations of besifloxacin, gatifloxacin, and moxifloxacin in human conjunctiva after topical ocular administration

PURPOSE

To evaluate the pharmacokinetic properties of besifloxacin, gatifloxacin, and moxifloxacin in the conjunctival tissue of healthy volunteers after topical application.

METHODS

One-hundred eight (108) subjects were randomly assigned to receive one drop of besifloxacin (0.6% suspension), gatifloxacin (0.3% solution), or moxifloxacin (0.5% solution) ophthalmic formulations in one eye prior to conjunctival biopsy. Conjunctival samples were taken from subjects at either 15 minutes, 30 minutes, 2 hours, 6 hours, 12 hours, or 24 hours after dosing.

RESULTS

All three fluoroquinolones reached a peak mean concentration 15 minutes after dosing. The mean concentrations of besifloxacin, gatifloxacin, and moxifloxacin at 15 minutes were 2.30 +/- 1.42 mug/g, 4.03 +/- 3.84 mug/g, and 10.7 +/- 5.89 mug/g, respectively. Concentrations decreased with each subsequent time point. At 24 hours after dosing, concentrations of besifloxacin were measurable in 4 of 6 subjects, compared with 3 of 6 subjects for gatifloxacin and 2 of 6 subjects for moxifloxacin. Besifloxacin had the greatest mean residence time (4.7 hours) in the conjunctival tissue. With regard to methicillin-resistant strains of Staphylococcus aureus and Staphylococcus epidermidis, besifloxacin had the greatest area-under-the-curve (AUC) to MIC(90) ratio. Nine percent (9%) of study subjects (N = 7) experienced a transient reduction in visual acuity.

CONCLUSION

All three fluoroquinolones were well tolerated and reached levels in the conjunctiva above the MIC(90)s of methicillin-sensitive S. aureus and S. epidermidis for at least 2 hours.

Ocular pharmacokinetics of besifloxacin following topical administration to rabbits, monkeys, and humans

PURPOSE

Studies were conducted to evaluate the ocular penetration and systemic exposure to besifloxacin, a fluoroquinolone antibiotic, following topical ocular administration to animals and humans.

METHODS

Besifloxacin ophthalmic suspension (0.6%) was administered as a topical ocular instillation to pigmented rabbits, cynomolgus monkeys, and human subjects. At predetermined intervals after dosing, samples of ocular tissues and plasma were collected and analyzed for besifloxacin levels using HPLC/MS/MS methods.

RESULTS

Besifloxacin demonstrated good ocular penetration in rabbits and monkeys, with rapid absorption and sustained concentrations observed in anterior ocular tissues through 24 h after a single administration. Maximum besifloxacin concentrations in conjunctiva, cornea, and aqueous humor of monkeys were 6.43 microg/g, 2.10 microg/g, and 0.796 microg/mL, respectively, after a single topical dose, and concentrations declined in these tissues with an apparent half-life of 5-14 h. Following a single topical ocular administration to humans, the maximum besifloxacin concentration in tears was 610 microg/g with concentrations decreasing to approximately 1.6 microg/g at 24 h. The resulting pharmacokinetic parameters for besifloxacin in human tears were evaluated relative to the MIC(90) values (microg/mL) for besifloxacin against Streptococcus pneumoniae (0.125), Staphylococcus aureus (0.25), Staphylococcus epidermidis (0.5), and Haemophilus influenzae (0.06). Following a single topical administration, the C(max)/MIC(90) ratios for besifloxacin in human tears were > or =1,220, and the AUC((0-24))/MIC(90) ratios were > or =2,500 for these relevant ocular pathogens. Following repeated 3-times daily (TID) topical ocular administration to human subjects with clinically diagnosed bacterial conjunctivitis, maximum besifloxacin concentrations in plasma were less than 0.5 ng/mL, on average.

CONCLUSIONS

Taken together, the results of the current investigation provide a PK/PD-based rationale that supports the use of besifloxacin for the safe and effective treatment of ocular infections.

Cassette dosing pharmacokinetic studies for evaluation of ophthalmic drugs for posterior ocular diseases

The purpose of this investigation was to evaluate the utility of cassette dosing as a means for increasing throughput and decreasing animal usage for intravitreal ocular pharmacokinetic studies. Pigmented rabbits received a single intravitreal injection of test article containing either a single compound or a mixture of up to five compounds. Samples of vitreous, choroid and retina were collected at predetermined intervals through 7 or 28 days after dosing. Concentrations of each compound were determined by LC/MS/MS, with subsequent pharmacokinetic data analysis. The ocular pharmacokinetic properties of four test compounds administered as a cassette were in agreement with the ocular pharmacokinetics of each compound when administered as a single entity. Cassette dosing was subsequently used to screen an additional 15 compounds, with injection of 5 compounds per study. Based on the results from these cassette-dosing studies, some compounds demonstrated favorable ocular pharmacokinetics, with sustained concentrations above 300 ng/g in retina for at least 1 week after dosing while other compounds showed either considerably less penetration into retina or a shorter residence time in the retina. These findings suggest that the cassette dosing approach can be used in evaluating the intravitreal ocular pharmacokinetic properties of compounds intended for ocular use.

Nonclinical safety and pharmacokinetics of intravitreally administered human-derived plasmin in rabbits and minipigs

The use of plasmin for pharmacologic vitreolysis and the creation of a posterior vitreous detachment offers several potential advantages over surgery. The nonclinical pharmacokinetics and safety of human-derived plasmin was evaluated following single or multiple intravitreal injections to rabbits and minipigs. Single intravitreal injections of plasmin at 45-900 microg resulted in a no adverse effect level (NOAEL) of 45 microg in both species; effects at higher doses included chemosis, mucopurulent discharge, mononuclear cell infiltrates in the iris-ciliary body, and reversible changes in electroretinogram waveforms and parameters. No retinal histopathology abnormalities were observed. Following 4 weekly intravitreal injections at 4-423 microg, a NOAEL of 4 microg was identified. Effects at the higher doses included myosis, iritis, iridolenticular synechiae, and changes in electroretinogram waveforms and parameters that were generally not reversible in the present investigation. Vitreal plasmin concentrations were highest at 30 min after dosing and decreased rapidly; measurable concentrations remained, in some animals, at 24 h. Intravitreal plasmin exposure increased in a less-than-dose-proportional manner and tended to be lower in minipigs than in rabbits. The current findings demonstrate acceptable nonclinical safety and pharmacokinetics of intravitreal human plasmin in rabbits and minipigs and support the clinical development of plasmin for ocular diseases.

DEVELOPMENT OF AN IN VIVO PRECLINICAL SCREEN MODEL TO ESTIMATE ABSORPTION AND FIRST-PASS HEPATIC EXTRACTION OF XENOBIOTICS. II. USE OF KETOCONAZOLE TO IDENTIFY P-GLYCOPROTEIN/CYP3A-LIMITED BIOAVAILABILITY IN THE MONKEY

The effect of P-glycoprotein (Pgp) and/or CYP3A on the disposition of xenobiotics has been extensively investigated and is often of interest during drug discovery lead optimization. We have previously described a monkey pharmacokinetic screen to rapidly estimate absorption and first-pass extraction. In the present work, this monkey screen has been expanded to include an assessment of Pgp/CYP3A effects on absorption and first-pass extraction, using ketoconazole as a prototypic dual Pgp/CYP3A inhibitor. To generate a ketoconazole dosing regimen, the pharmacokinetics of ketoconazole were first determined in the monkey and were found to be consistent with that previously described in the rat, dog, and human. Dose-ranging experiments demonstrated that a single 10-mg/kg intraduodenal ketoconazole dose would provide an appropriate exposure; this dose was used throughout subsequent interaction experiments. Next, erythromycin and propranolol were explored as positive and negative control substrates for Pgp/CYP3A interactions, respectively. As anticipated, ketoconazole produced no change in the absorption or first-pass extraction of propranolol but resulted in a substantial increase in absorption and decrease in first-pass extraction of erythromycin. Finally, this ketoconazole-based monkey screen was deployed in a drug discovery setting, and examples of such use are presented. These experiments have allowed a more complete characterization of ketoconazole as a prototypic dual Pgp/CYP3A inhibitor and its use as a tool in a preclinical setting and further demonstrate the use of the monkey to investigate the role of Pgp/CYP3A in limiting the oral bioavailability of new drug candidates.

A single dose of monoclonal anti-phencyclidine IgG offers long-term reductions in phencyclidine behavioral effects in rats

These studies tested the hypothesis that a single dose of high-affinity anti-phencyclidine monoclonal antibody (anti-PCP mAb) provides long-term protection against behavioral effects of repeated PCP administration in rats. Rats were treated with saline, nonspecific bovine IgG (NS-IgG), or anti-PCP mAb (1.0 g/kg). The next morning, the rats were challenged with escalating i.v. doses of PCP (0.32, 0.56, and 1.0 mg/kg) at 90-min intervals. This regimen was repeated every 3 days for 2 weeks. In the saline and NS-IgG control groups, PCP yielded reproducible and linear dose-dependent effects that remained constant during the experiment. In contrast, the anti-PCP mAb treatment blocked PCP effects on day 1, and sustained significant (P < 0.05) reductions in drug effects for the entire 2-week experiment. Brain PCP concentrations (determined at study termination) were reduced by ~55%, whereas serum concentrations were increased over 4000% compared with controls. Thus, a single dose of antibody medication provided long-term reductions in drug effects and brain concentrations, beyond the expected capacity of the drug-antibody interaction. These data challenge current concepts about in vivo dose dependence and unimolecular interaction between antibody binding sites and small molecules and establish that neuroprotection by mAbs may have an unique mechanism of action.

SB-242235, a selective inhibitor of p38 mitogen-activated protein kinase. I: preclinical pharmacokinetics

1. SB-242235 (1-(4-piperidinyl)-4-(4-fluorophenyl)-5-(2-methoxy-4-pyrimidinyl) imidazole) is a potent and selective p38 MAP kinase inhibitor that may be an effective therapy for cytokine-mediated diseases such as autoimmune or inflammatory diseases. The present studies were conducted to evaluate the pharmacokinetics of SB-242235 in several preclinical species, including rat, dog and monkey. 2. SB-242235 demonstrates generally favourable pharmacokinetic properties in all species examined. Systemic plasma clearance was high in rat, but in the non-rodent species SB-242235 demonstrated low to moderate clearance with plasma half-lives > 4h. Oral bioavailability in each preclinical species was high. In rat and monkey, SB-242235 demonstrated non-linear elimination kinetics that manifested as a decrease in clearance with increasing dose and apparent oral bioavailability > 100% at high oral doses. Furthermore, SB-242235 displayed concentration-dependent plasma protein binding over a concentration range of 1000-10,000 ng ml(-1). 3. In conclusion, SB-242235 demonstrates high oral bioavailability across the major preclinical species, and may thus be a useful tool compound for investigation of the role of p38 inhibition in various disease states. However, the observations of non-linear protein binding and disposition also suggest the need for caution in the design of and data interpretation from such studies.

SB-242235, a selective inhibitor of p38 mitogen-activated protein kinase. II: in vitro and in vivo metabolism studies and pharmacokinetic extrapolation to man

1. Inhibition of p38 MAP kinase has been investigated extensively as a potential therapy for cytokine-mediated diseases such as autoimmune and inflammatory diseases. SB-242235 (1-(4-piperidinyl)-4-(4-fluorophenyl)-5-(2-methoxy-4-pyrimidinyl) imidazole) is a potent and selective p38 MAP kinase inhibitor; the preclinical pharmacokinetics of SB-242235 have been described previously. The present studies were conducted to describe the in vitro metabolic rates and routes of SB-242235 metabolism, to characterize its in vivo preclinical metabolism, and to use these data to aid in the prediction of the pharmacokinetic behaviour of SB-242235 in man. 2. SB-242235 was metabolically stable in rat, dog, monkey and human hepatic microsomes, isolated hepatocytes and liver slices in vitro. The in vivo preclinical metabolism studies were consistent with the in vitro findings; SB-242235 was minimally metabolized, and was primarily excreted unchanged in the urine (45 and 67% of the administered dose in the rat and monkey, respectively). 3. Allometric scaling using various correction factors predicted that SB-242235 would have low clearance in man with a predicted half-life ranging from 11.5 to 18.7h. This prediction was consistent with the observed mean half-life of 16.4h in the first-in-man study for SB-242235. An allometric scaling method with a correction for interspecies differences in glomerular filtration rate provided the most accurate prediction of the pharmacokinetic behaviour of SB-242235 in humans, although the clinical data also highlight potential difficulties in conducting prospective allometry.

SB-239063, a potent and selective inhibitor of p38 map kinase: preclinical pharmacokinetics and species-specific reversible isomerization

PURPOSE

A series of studies was conducted to evaluate the preclinical pharmacokinetics of SB-239063 (trans-1-(4-hydroxycyclohexyl)-4-(4-fluorophenyl)-5-[(2-methoxy)pyrimidin-4-yl] imidazole), a potent and selective p38 MAP kinase inhibitor.

METHODS

SB-239063 was administered both i.v. and p.o. in the rat, dog, cynomolgus monkey, and rhesus monkey, with standard pharmacokinetic parameters generated from the concentration vs. time data.

RESULTS

Initial rat studies suggested possible nonlinear disposition, however, assay refinement revealed an in vivo trans-cis isomerization of SB-239063 to a metabolite with nearly identical chromatographic and mass spectral properties. SB-239063 exhibited low to moderate clearance and good bioavailability in the rat and dog, but poor bioavailability in the cynomolgus monkey. Substantial in vivo trans-cis isomerization occurred in the rat and cynomolgus monkey, but occurred to a far lesser extent in the dog. The isomerization reaction was reversible, with a recycled fraction of 0.20 and 0.0003 in the rat and cynomolgus monkey, respectively. In the rhesus monkey, bioavailability was also poor. but no in vivo isomerization was observed. Conclusions. These studies demonstrate the necessity of exercising vigilance in conducting high-throughput analytical method development, and the importance of using a variety of preclinical species when evaluating the disposition of new drug candidates.

Development of an in vivo preclinical screen model to estimate absorption and bioavailability of xenobiotics

The purpose of this study was to develop an in vivo screening method for rapid preclinical characterization of absorption and bioavailability of large numbers of compounds. This effort involved several steps. First, a pharmacokinetic characterization of a reference compound was conducted in the monkey. These data were used to verify theoretical calculations of a maximal portal dose-normalized area under the concentration-time curve. Next, a monkey screen was implemented using mixtures of up to five compounds each (i.e., cassettes) to estimate the bioavailability of approximately 200 compounds. Cassettes were administered as a single intraduodenal dose to a single monkey followed by simultaneous portal and systemic blood sampling. Definitive studies were then conducted to determine absolute bioavailability of 14 of these compounds. The studies with the reference compound demonstrated that the theoretical methodology based on a single intraduodenal dose with portal and systemic sampling provided consistent estimates of bioavailability. In the screen studies, approximately 75% of the test compounds were excluded from further evaluation due to poor absorption. Of the 14 compounds selected for follow-up evaluation from both well and poorly absorbed compounds, the absolute bioavailability of 10 of them were correctly classified from the screening data. The remaining 4 compounds were false positives, which showed low bioavailability; no false negatives were encountered. This approach allows for a rapid and reliable screen to evaluate absorption and bioavailability using a single dose in a preclinical model.

The effect of rate of drug administration on the extent and time course of phencyclidine distribution in rat brain, testis, and serum

The goal of these studies was to examine the relationship between the rate of phencyclidine (PCP) administration and PCP tissue distribution. The time course of PCP distribution in serum, brain, and testis after rapid (i.v.) and slow (s.c.) administration was studied. Brain and serum PCP concentrations after an i.v. bolus dose (1 mg/kg at 900 microg/min) were highest at 30 s and decreased biphasically, with serum concentrations decreasing 30 times faster than brain concentrations during the early phase. Consequently, the brain-to-serum PCP concentration ratio increased from 8:1 at 30 s to 14:1 at 20 min before equilibrating at a ratio of 3:1 that remained constant from 1 to 8 h. In contrast, the testis-to-serum ratio increased slowly from 1:1 to 12:1 over 4 h, and then remained constant. In a separate group of animals, an s.c. infusion of PCP (18 mg/kg/day or 3.6 microg/min) produced a brain-to-serum ratio (6:1) that remained constant throughout the 96-h infusion. Testis-to-serum ratios increased from 4:1 at 1 h to 12:1 at 8 h and then remained constant for 96 h. Steady-state infusion of a pharmacologically inactive dose (2.5 mg/kg/day) produced a brain-to-serum ratio (3:1) that was significantly lower than the ratio (6:1) after infusion of the three pharmacologically active doses (10-25 mg/kg/day). The temporary high brain PCP concentrations and the dynamic disequilibrium between brain and serum concentrations after rapid i.v. administration could provide a better understanding of the preference of the human drug abuser for rapid rates (e.g., i.v. or smoking) of drug administration.

Anti-phencyclidine monoclonal antibodies provide long-term reductions in brain phencyclidine concentrations during chronic phencyclidine administration in rats

These studies examined the hypothesis that a single large dose of monoclonal anti-phencyclidine (PCP) antibody could provide long-term reductions in brain PCP concentrations despite continuous PCP administration. PCP (18 mg/kg/day, s.c.) was infused to steady-state (24 h) and then a mole-equivalent dose of a short-acting anti-PCP antigen-binding fragment (Fab) or a long-acting anti-PCP IgG was administered i.v. The PCP infusion continued for up to 27 days, even though the binding capacity of the single dose of antibody used should have been saturated within the first day. At selected time points after antibody administration, brain, testis, and serum PCP concentrations were measured. Serum PCP concentrations rapidly increased approximately 100- and 300-fold after Fab or IgG administration, respectively. Based on the antibody-bound PCP concentrations in serum, the functional elimination half-life (t(1/2lambdaZ)) values for PCP-Fab and PCP-IgG complexes were 9.4 h and 15.4 days, respectively. Fab and IgG administration produced a complete removal of PCP from the brain within 15 min. Although brain PCP concentrations were significantly decreased for only 4 h in Fab-treated animals, IgG administration resulted in significant decreases in brain PCP concentrations lasting for at least 27 days. In contrast, testis PCP concentrations were not substantially affected by antibody administration, suggesting that redistribution of PCP from the testis is too slow to benefit from a limited dose of antibody. These results indicate that anti-PCP IgG can preferentially protect the brain for approximately 4 weeks after IgG administration, even when the antibody binding capacity should have been saturated with continuously administered PCP.

Pharmacokinetic mechanisms for obtaining high renal coelimination of phencyclidine and a monoclonal antiphencyclidine antigen-binding fragment of immunoglobulin G in the rat

Our purpose was to determine mechanisms and methods for significantly increasing the renal coelimination of phencyclidine (PCP) and an anti-PCP monoclonal antibody binding fragment (anti-PCP Fab). To accomplish this goal, we performed a series of experiments to examine the dose-dependence of Fab elimination, mechanisms for enhancing PCP and Fab urinary coelimination and the antigenicity of repeated Fab administration. The results showed that urinary elimination of PCP and anti-PCP Fab was linear over a 30-fold range of doses. Anti-PCP Fab serum pharmacokinetics were best described using bi- or tri-exponential curves with a terminal elimination half-life of approximately 8 hr. Nevertheless, under all experimental conditions the early, nonterminal phase(s) were responsible for the majority (60%) of intact Fab elimination, with only 40% of the Fab eliminated during the terminal phase. These data suggest that the early rapid decline in Fab serum concentrations was primarily due to passive filtration and excretion of intact Fab, and not due to extravascular distribution as previously described. In comparison of methods for enhancing renal coelimination of Fab and PCP, systemic alkalinization produced a significant increase in Fab urinary elimination, with 69% of the Fab dose and 41% of the PCP dose recovered intact in the urine. Finally, in studies of the antigenicity of Fab, repeated administration of Fab produced no significant immune response or renal impairment. Overall, these experiments suggest that careful attention to the physiological status of the kidney during early time periods is essential for maximum coelimination of Fab and bound chemicals.

Pharmacodynamics of a monoclonal antiphencyclidine Fab with broad selectivity for phencyclidine-like drugs

The development of treatment strategies for drug intoxication has been hindered in part by the lack of clinically useful antagonists. Consequently, the major goal of these studies was to determine whether a monoclonal antibody Fab fragment (of IgG) could be used as an effective drug class-selective antagonist and to understand better the dose-response relationships for reversing CNS drug toxicity. Changes in drug-induced locomotor effects in a rat model were used to assess the ability of the antiphencyclidine (anti-PCP) Fab to reverse the behavioral effects of PCP and other potent arylcyclohexylamines. In experiments to determine the pharmacodynamics of Fabinduced antagonism of behavioral effects, the Fab completely reversed all PCP-induced locomotor effects in a Fab dose-dependent manner with a minimal effective dose of 0.18 mole-equivalents of Fab and an ED50 value of about one-third mole-equivalent. The anti-PCP Fab also completely reversed the locomotor effects induced by two other structurally related potent analogs of PCP: 1-[1-(2-thienyl)cyclohexyl]piperidine and N-ethyl-1-phenylcyclohexylamine. In addition, pharmacological and immunological selectivity was further tested by treatment of the behavioral effects induced by the structurally unrelated locomotor stimulant (+)methamphetamine. The antibody did not effectively reverse the effects of methamphetamine-induced locomotor activity. These results indicate that antibody-based medications can be developed to treat toxicity caused by classes of drugs as well as by individual drugs.

Nitric oxide generation by renal proximal tubules: role of nitric oxide in the cytotoxicity of lipid A

Lipid A, the biologically active component of lipopolysaccharide, stimulated nitric oxide (NO) production by isolated rat proximal tubules (as measured by NO2- release) in a time-dependent manner. At a concentration of 50 micrograms/ml, lipid A stimulated NO2- generation and guanosine 3',5'-cyclic phosphate (cGMP) production within 5 min. Both of these effects were blocked by NG-methyl-L-arginine (L-NMMA), an inhibitor of NO synthase or by 8-(N,N'-diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8), an inhibitor of intracellular Ca++ release. Because an increase in NO production may be cytotoxic, we examined the cytotoxic potential of lipid A. At 90 min, lipid A (50 micrograms/ml) produced significant lactate dehydrogenase release (42 +/- 5%) compared to control (25 +/- 5%; P < .05). Both L-NMMA (1 mM) and TMB-8 (100 microM) completely protected against lipid A-induced cytotoxicity. TMB-8 but not L-NMMA inhibited the rise intracellular Ca++ concentration ([Ca++]i) in isolated proximal tubules elicited by lipid A. L-NMMA but not TMB-8 inhibited proximal tubule soluble NO synthase activity. Thus, in the proximal tubule, lipid A stimulates a rise in [Ca++]i that in turn activates constitutive NO synthase. Furthermore, these events lead ultimately to NO-dependent cytotoxicity. Therefore, these findings suggest the potential for lipopolysaccharide to have a direct impact on proximal tubule physiology and renal function in vivo and support the potential therapeutic benefits of NO synthase inhibitors in the treatment of endotoxemia.

Effects of lipid A on calcium homeostasis in renal proximal tubules

It is clear that lipopolysaccharides (LPS) are responsible for the multiorgan failure often associated with endotoxemia. However, little is known of the direct effects of LPS on kidney cells. We examined the effects of lipid A, the biologically active component of LPS, on rat proximal tubule Ca++ homeostasis. Lipid A produced a rapid, transient, concentration-dependent rise in intracellular Ca++ concentration, [Ca++]i, as monitored by fura-2. At 50 micrograms/ml [Ca++]i rose to 138 +/- 12 nM (n = 4) above basal [Ca++]i levels. The response to lipid A was not significantly inhibited by chelating extracellular Ca++ with EGTA (5 mM). However, the rise in [Ca++]i was significantly inhibited by 8-(N,N-dimethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride) and thapsigargin (17 +/- 7 nM and 13 +/- 9 nM rise, respectively; P < .05). These data indicate that the rise in [Ca++]i induced by lipid A is due to release of intracellular stores, and not extracellular influx. We also examined the role of inositol 1,4,5-trisphosphate in the lipid A response. Lipid A caused a time-dependent increase in inositol 1,4,5-trisphosphate that paralleled the rise in [Ca++]i, suggesting the release in [Ca++]i is through an inositol 1,4,5-trisphosphate-mediated release of intracellular stores. The ability of lipid A to alter Ca++ homeostasis suggests a potential for LPS to directly alter proximal tubule physiology and renal function in vivo.