The insulin-line activity of vanadium compounds is currently of great interest given the recent Phase 1 clinical trial using oral organic vanadium (IV) (KP-102) treatment of diabetes. The organic vanadium compounds are superior to the simple vanadium salts (vanadate and vanadyl sulfate) with respect to their insulin-like effects and lower toxicity. This proposal has two goals. One goal is to characterize the mode of action of two different classes of organic vanadium compounds. The second goal is to identify new vanadium compounds with superior insulin-like activities and lower toxicity. The conventional wisdom on how vanadium compounds produce their insulin-enhancing effects is through inhibition of a tyrosine protein phosphatase acting on the insulin receptor and/or at points distal to the receptor in the insulin signaling pathway. Since no correlation has been reported for compound efficacy in animals and inhibition of a protein phosphatase, and recognizing the amounts of data available, it is appropriate at this time to entertain the hypothesis that no one target is sufficient to describe the mode of action of vanadium compounds. The multi-factor approach proposed here is developed on the premise that protein phosphatase inhibition and some other as yet unidentified parameter(s) combined are responsible for the mode of vanadium compounds. A systematic multi-factor mechanistic analysis of compound effects requires that effects are organized in categories (insulin-like, toxicity, pharmacology, cellular environment and chemical properties) each containing several parameters in a framework of compound profiles. The design of new compounds (Aim 1) will be used as a tool to test mechanistic hypotheses that will be developed based on data obtained in 11 assays (Aim 2). In addition, libraries of compounds prepared by combinatorial synthesis will be screened using 4 in vitro and cellular assays to identify superior compounds (Aim 2). Iterative evaluation of the performance of each compound/combinatorial library will lead to identification of key structural units. Finally, the compound profiles will guide selection of four compounds for detailed pharmacokinetic and distribution analysis (Aim 3).
The Specific Aims we propose are:
Aim 1. Preparation of Individual Vanadium Compounds and Combinatorial Libraries of Vanadium Compounds. The aqueous hydrolytic and redox chemistry of biologically active compounds will be characterized.
Aim 2. Assays to Evaluate the Effects of Vanadium Compounds in Biological Systems In Vitro (Part A, phosphatase inhibition, protein interaction, lipophilicity and effects of cellular reducing agents), In Cell Culture (Part B, cell growth and viability, speciation of vanadium compounds in cells, stimulation by insulin receptor phosphorylation in normal and vanadium compound treated cells) and In Vanadium Treated Normal and STZ- Induced Diabetic Rats (Part C, efficacy for lowered elevated plasma glucose levels, insulin sensitivity, absorption of total vanadium into serum at steady state and phosphorylation of insulin receptor phosphorylation).
Aim 3. Pharmacokinetic and Distribution Profiles of Organic Vanadium Compounds. Four vanadium compounds will be evaluated in a STZ-induced diabetic rabbit model. Our approach combine Chemical and Biological Experiments to develop superior vanadium compounds for the treatment of diabetes and simultaneously elucidate the mode of action of these compounds. The proposed studies will lead to an in-depth understanding of both the chemical and pharmacological properties of known and new vanadium compounds inducing insulin-like action.
