Development of an early biomarker for the ovarian liability of selective estrogen receptor modulators in rats.

Selective estrogen receptor modulators (SERMs) have the potential to treat estrogen sensitive diseases such as uterine leiomyoma and endometriosis, which are prevalent in reproductive age women. However, SERMs also increase the risk of developing ovarian cysts in this population, a phenomenon that is not seen in postmenopausal women. It is believed that current SERMs partially block estradiol's ability to downregulate gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus thereby interfering with estradiol's negative feedback, leading to increased ovarian stimulation by gonadotropins, and cyst formation. It has been postulated that a SERM with poor brain exposure would have less negative effect on the HPO axis, therefore reducing the risk of developing ovarian cysts. In order to test this hypothesis, we identified an early marker of SERM-dependent ovarian effects: upregulation of Cyp17a1 mRNA. SERMs known to cause ovarian cysts upregulate Cyp17a1 after only 4 days of dosing and suppression of the HPO axis prevented this regulation, indicating that ovarian expression of Cyp17a1 was secondary to SERM's effect on the brain. We then characterized three SERMs with similar binding affinity and antagonist effects on the uterus for their relative brain/plasma exposure and ovarian effects. We found that the degree of brain exposure correlated very well with Cyp17a1 expression.

A rat pharmacokinetic/pharmacodynamic model for assessment of lipopolysaccharide-induced tumor necrosis factor-alpha production.

INTRODUCTION: Tumor necrosis factor-alpha (TNFalpha) participates in many inflammatory processes. TNFalpha modulators show beneficial effects for the treatment of many diseases including rheumatoid arthritis. The purpose of this study was to validate a rat pharmacokinetic/pharmacodynamic (PK/PD) model for rapid assessment of drug candidates that intended to interrupt TNFalpha synthesis or release. METHODS: Rats received intravenous (IV) or oral administrations of test article or dose vehicle, followed by LPS challenge. Plasma levels of test article and TNFalpha were determined. The areas under the concentration-time curves (AUC(drug) and AUC(TNFalpha)) were calculated. The overall percentage of inhibition on TNFalpha release in vivo was calculated by comparing AUC(TNFalpha) of the test article treated group against that for the vehicle control group. RESULTS: The dosing vehicles tested in this study did not increase plasma TNFalpha level. At IV dose of up to 100 microg/kg, LPS did not alter the pharmacokinetics of the compound tested. Using a selective TNFalpha converting enzyme (TACE) inhibitor as model compound, this PK/PD model demonstrated its ability to correlate plasma test article concentration with its biological activity of lowering the LPS-induced TNFalpha plasma levels in vivo. DISCUSSION: A rat PK/PD model for evaluation of the effect of drug candidates on LPS-induced TNFalpha synthesis and/or release has been investigated. This model provides integrated information on pharmacokinetics and in vivo potency of the test articles.

In vitro-in vivo correlation on delivery of drug candidates to articular cartilage.

PURPOSE: In the treatment of osteoarthritis (OA), some of the therapeutic approaches require delivery of drug(s) to the diseased cartilage. Presence of adequate drug levels in the cartilage is one of the important criteria in selection and ranking of lead compounds. The purpose of this study was to investigate the correlation in cartilage compound levels between in vitro experiments and in vivo animal studies. MATERIALS AND METHODS: Bovine cartilage samples were incubated with test compounds of various concentrations in a culture medium, in the absence or presence of 25 mg/ml of serum albumin which served as an artificial synovial fluid (SF). The test compounds were also dosed to rabbits, the animal model used for efficacy studies, over a six-week treatment period. Test article concentrations in plasma, SF, and cartilage were determined by LC/MS/MS analysis. RESULTS AND CONCLUSIONS: A correlation in cartilage drug concentration was observed between in vitro and in vivo studies. Plasma protein binding and the test article's affinity to cartilage were the major determining factors for drug delivery to cartilage in vivo.

Effect of von Willebrand factor on the pharmacokinetics of recombinant human platelet glycoprotein Ibalpha-immunoglobulin G1 chimeric proteins.

PURPOSE: Recombinant human platelet glycoprotein Ibalpha-immunoglobulin G1 chimeric proteins (GPIbalpha-Ig) have varying levels of anti-thrombotic activities based on their ability to compete for platelet mediated adhesion to von Willebrand Factor (vWF). Valine substituted GPIbalpha-Ig chimeras, at certain position, increase the binding affinity to vWF over its "wild-type" GPIbalpha-Ig analog. The purpose of this study was to determine the pharmacokinetics of two valine substituted GPIbalpha-Ig chimeras, GPIbalpha-Ig/1V (valine substitution at 239 position) and GPIbalpha-Ig/2V (double valine substitution at 233 and 239 position), in mice, rats and dogs. METHODS: Head-to-head comparisons of pharmacokinetics of GPIbalpha-Ig/1V and GPIbalpha-Ig/2V were investigated in rats and dogs after intravenous administration. Since vWF precipitates in the serum but not in plasma preparation, the concentration-time profiles of GPIbalpha-Ig/2V in rats were examined from the same blood samples for determination of matrix effect. The disposition of GPIbalpha-Ig/2V was also compared in vWF-deficient versus wild-type mice. RESULTS: For GPIbalpha-Ig/2V, the serum clearances were 2.62+/-0.27 ml/hr/kg in rats and 1.97+/-0.24 ml/hr/kg in dogs. The serum clearances of less potent GPIbalpha-Ig/1V were 1.08+/-0.08 and 0.97+/-0.19 ml/hr/kg in rats and dogs, respectively. In addition, the serum clearance of GPlbalpha-Ig/2V of 1.53 ml/hr/kg in vWF-deficient mice was lower than that in wild-type mice of 2.79 ml/hr/kg. CONCLUSION: The difference in disposition for valine substituted forms of GPIbalpha-Ig in laboratory animals are likely affected by their enhanced binding affinity for circulating vWF.