Purpose: Axitinib (AG-013736) is a potent and selective inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases 1to 3 that is in clinical development for the treatment of solid tumors. We provide a comprehensive description of its in vitro characteristics and activities, in vivo antiangiogenesis, and antitumor efficacy and translational pharmacology data. Experimental Design: The potency, kinase selectivity, pharmacologic activity, and antitumor efficacy of axitinib were assessed in various nonclinical models. Results: Axitinib inhibits cellular autophosphorylation of VEGF receptors (VEGFR) with picomolar IC 50 values. Counterscreening across multiple kinase and protein panels shows it is selective for VEGFRs. Axitinib blocks VEGF-mediated endothelial cell survival, tube formation, and downstream signaling through endothelial nitric oxide synthase, Akt and extracellular signal-regulated kinase. Following twice daily oral administration, axitinib produces consistent and dose-dependent antitumor efficacy that is associated with blocking VEGFR-2 phosphorylation, vascular permeability, angiogenesis, and concomitant induction of tumor cell apoptosis. Axitinib in combination with chemotherapeutic or targeted agents enhances antitumor efficacy in many tumor models compared with single agent alone. Dose scheduling studies in a human pancreatic tumor xenograft model show that simultaneous administration of axitinib and gemcitabine without prolonged dose interruption or truncation of axitinib produces the greatest antitumor efficacy. The efficacious drug concentrations predicted in nonclinical studies are consistent with the range achieved in the clinic. Although axitinib inhibits platelet-derived growth factor receptors and KIT with nanomolar in vitro potencies, based on pharmacokinetic/pharmacodynamic analysis, axitinib acts primarily as a VEGFR tyrosine kinase inhibitor at the current clinical exposure. Conclusions: The selectivity, potency for VEGFRs, and robust nonclinical activity may afford broad opportunities for axitinib to improve cancer therapy.

ABSTRACT:Studies were designed to quantitatively assess the mRNA expression of 1) 10 cytochrome P450 (P450) enzymes in human cornea, iris-ciliary body (ICB), and retina/choroid relative to their levels in the liver, and of 2) 21 drug transporters in these tissues relative to their levels in human small intestine, liver, or kidney. Potential species differences in mRNA expression of PEPT1, PEPT2, and MDR1 were also assessed in these ocular tissues from rabbit, dog, monkey, and human. P450 expression was either absent or marginal in human cornea, ICB, and retina/choroid, suggesting a limited role for P450-mediated metabolism in ocular drug disposition. In contrast, among 21 key drug efflux and uptake transporters, many exhibited relative expression levels in ocular tissues comparable with those observed in small intestine, liver, or kidney. This robust ocular transporter presence strongly suggests a significant role that transporters may play in ocular barrier function and ocular pharmacokinetics. The highly expressed efflux transporter MRP1 and uptake transporters PEPT2, OCT1, OCTN1, and OCTN2 may be particularly important in absorption, distribution, and clearance of their drug substrates in the eye. Evidence of cross-species ocular transporter expression differences noted in these studies supports the conclusion that transporter expression variability, along with anatomic and physiological differences, should be taken into consideration to better understand animal ocular pharmacokinetic and pharmacodynamic data and the scalability to human for ocular drugs.

ABSTRACT:Sunitinib is an oral multitargeted tyrosine kinase inhibitor approved for the treatment of advanced renal cell carcinoma, imatinibrefractory gastrointestinal stromal tumor, and advanced pancreatic neuroendocrine tumors. The current studies were conducted to characterize the pharmacokinetics, distribution, and metabolism of sunitinib after intravenous and/or oral administrations of

Nelfinavir mesylate (Viracept, formally AG1343) is a potent and orally bioavailable human immunodeficiency virus (HIV) type 1 (HIV-1) protease inhibitor (K i ‫؍‬ 2 nM) and is being widely prescribed in combination with HIV reverse transcriptase inhibitors for the treatment of HIV infection. The current studies evaluated the presence of metabolites circulating in plasma following the oral administration of nelfinavir to healthy volunteers and HIV-infected patients, as well as the levels in plasma and antiviral activities of these metabolites. The results showed that the parent drug was the major circulating chemical species, followed in decreasing abundance by its hydroxy-t-butylamide metabolite (M8) and 3-methoxy-4-hydroxynelfinavir (M1). Antiviral assays with HIV-1 strain RF-infected CEM-SS cells showed that the 50% effective concentrations (EC 50 ) of nelfinavir, M8, and M1 were 30, 34, and 151 nM, respectively, and that the corresponding EC 50 against another HIV-1 strain, IIIB, in MT-2 cells were 60, 86, and 653 nM. Therefore, apparently similar in vitro antiviral activities were demonstrated for nelfinavir and M8, whereas an approximately 5-to 11-fold-lower level of antiviral activity was observed for M1. The active metabolite, M8, showed a degree of binding to human plasma proteins similar to that of nelfinavir (ca. 98%). Concentrations in plasma of nelfinavir and its metabolites in 10 HIV-positive patients receiving nelfinavir therapy (750 mg three times per day) were determined by a liquid chromatography tandem mass spectrometry assay. At steady state (day 28), the mean plasma nelfinavir concentrations ranged from 1.73 to 4.96 M and the M8 concentrations ranged from 0.55 to 1.96 M, whereas the M1 concentrations were low and ranged from 0.09 to 0.19 M. In conclusion, the findings from the current studies suggest that, in humans, nelfinavir forms an active metabolite circulating at appreciable levels in plasma. The active metabolite M8 may account for some of the antiviral activity associated with nelfinavir in the treatment of HIV disease.

ABSTRACT:The recently introduced Clonetics human corneal epithelium (cHCE) cell line is considered a promising in vitro permeability model, replacing excised animal cornea to predict corneal permeability of topically administered compounds. The purpose of this study was to further characterize cHCE as a corneal permeability model from both drug metabolism and transport aspects. First, good correlation was found in the permeability values (P app ) obtained from cHCE and rabbit corneas for various ophthalmic drugs and permeability markers. Second, a previously established realtime quantitative polymerase chain reaction method was used to profile mRNA expression of drug-metabolizing enzymes (major cytochromes P450 and UDP glucuronosyltransferase 1A1) and transporters in cHCE in comparison with human cornea. Findings indicated that 1) the mRNA expression of most metabolizing enzymes tested was lower in cHCE than in excised human cornea, 2) the mRNA expression of efflux transporters [multidrug resistantassociated protein (MRP) 1, MRP2, MRP3, and breast cancer resistance protein], peptide transporters (PEPT1 and PEPT2), and organic cation transporters (OCTN1, OCTN2, OCT1, and OCT3) could be detected in cHCE as in human cornea. However, multidrug resistance (MDR) 1 and organic anion transporting polypeptide 2B1 was not detected in cHCE; 3) cHCE was demonstrated to possess both esterase and ketone reductase activities known to be present in human cornea; and 4) transport studies using probe substrates suggested that both active efflux and uptake transport may be limited in cHCE. As the first detailed report to delineate drug metabolism and transport characteristics of cHCE, this work shed light on the usefulness and potential limitations of cHCE in predicting the corneal permeability of ophthalmic drugs, including ester prodrugs, and transporter substrates.Topical instillation is the desired route of administration for ophthalmic drugs to treat diseases in the anterior segment of the eye including glaucoma, inflammations, infections, and dry eye. The primary pathway of drug permeation from the tear fluid to the anterior chamber of the eye is via the transcorneal route. The cornea has a multilayered structure constituted primarily of corneal epithelium, stroma, and endothelium. However, passage through the corneal epithelium is considered to be the rate-limiting step in the transcorneal penetration of most ophthalmic drugs (Maurice and Mishima, 1984).In the past decade, several in vitro corneal permeability models that can substitute for the isolated cornea to predict ocular absorption and facilitate ophthalmic drug discovery have been developed (Reichl and Becker, 2008). These models evolved from primary cultures using rabbit corneas and immortalized rabbit cell lines to the immortalized human corneal epithelial (HCE) cell lines, and even include complex systems such as human corneal constructs (summarized in Table 1). Given the pros and cons of each model, HCE cell lines seem to be most appealing owing to their human o...