Evaluation of Fluorophotometry to Assess the Vitreal Pharmacokinetics of Protein Therapeutics.

PURPOSE: In this work, we assessed the ability of fluorophotometry to measure the vitreal pharmacokinetics (PK) of fluorescently-labeled ranibizumab in the rabbit after intravitreal injection. We compared these values to those obtained using enzyme-linked immunosorbent assays (ELISA). Data obtained in this study were also compared to historical ranibizumab ocular PK data, either measured in-house or previously published. METHODS: Three individual in vivo studies were performed in New Zealand White rabbits to assess the feasibility of using fluorophotometry to measure rabbit ocular PK of ranibizumab; explore the dynamic range of dosing fluorescently-labeled ranibizumab; and directly compare ranibizumab concentrations and calculated PK parameters measured by vitreal fluorophotometry to those measured using ELISA. RESULTS: In direct comparisons between fluorophotometry and ELISA, the calculated clearance (CL) values were 0.26 and 0.21 mL/day, the volumes of distribution at steady state (Vss) were 0.80 and 0.94 mL, the half-lives (t1/2) were 3.1 and 2.9 days and the dose normalized areas under the curve (AUC/D) were 4.7 and 3.9 µg·day/mL/µg, respectively. These values fell within the ranges of 0.13 to 0.44 mL/day for CL, 0.5 to 1.8 mL for Vss, 2.8 to 3.5 days for t1/2, and 2.3 to 7.9 µg·day/mL/µg for AUC/D that have been either measured previously in-house or published elsewhere. CONCLUSIONS: Although not suitable for measuring retinal concentrations, fluorophotometry is a valuable, noninvasive method to measure vitreous concentrations of protein therapeutics after intravitreal injection.

A novel p21 attenuator which is structurally related to sorafenib.

p21 is a member of the cyclin kinase inhibitor family of proteins and plays pivotal roles in cellular proliferation as well as in the regulation of apoptosis, and thus has diverse functions in diseases as varied as cancer and atherosclerosis. In light of its pleiotropic effects and potential clinical relevance, new methods of attenuation of p21 protein levels by selective inhibitors are therefore powerful tools to probe malignant, infectious and other diseases. Here we introduce a novel p21 attenuator, UC2288, which possesses consistent and relatively selective activity for p21. UC2288 was synthesized based on the chemical model of sorafenib, a multikinase inhibitor that also attenuates p21, but unlike sorafenib, UC2288 did not inhibit Raf kinases or alter p-ERK protein levels. UC2288 decreased p21 mRNA expression independently of p53, and attenuated p21 protein levels with minimal effect on p21 protein stability. In addition, UC2288 inhibits cell growth in the kidney cancer cell lines (GI50 = approximately 10 µM) as well as multiple other cancer cell lines. Thus, this novel p21 inhibitor will be indispensable for exploring the function of p21, and upon further study may be translatable to the clinic.