Our Science – Burke Website
Terrence R. Burke Jr., Ph.D.
Bioorganic Medicinal Chemistry and the Modulation of Kinase-Dependent Signal Transduction
Pharmacological agents are being developed to modulate phosphotyrosyl (pTyr)-dependent cell signaling. Emphasis is on inhibitors of pTyr-dependent binding interactions which are mediated by src homology 2 (SH2) domains and on protein-tyrosine phosphatase (PTP) inhibitors. Central to both of these efforts is the development of new pTyr mimetics that afford either increased stability toward enzymatic degradation by PTPs or increased affinity. In the SH2 domain area, development of cell-permeable growth factor receptor-bound 2 (Grb2) antagonists is being undertaken as potential new therapeutics for a variety of cancers including erbB-2- and MET-dependent cancers, including breast cancer. For this work, peptidomimetics have been designed as conformationally constrained analogs of natural Grb2 SH2 domain-bound pTyr-containing peptides.
In related work, a series of new pTyr-mimicking amino acid analogs have also been prepared to enhance cell permeability. Among these are medium-size, nonphosphate-containing analogs which exhibit low nanomolar Grb2 SH2 domain inhibition constants. Promising analogs exhibit potent inhibition of Grb2 binding in whole cell systems and display good cytostatic effects against breast cancer cells grown in culture or in soft agar. Studies are currently under way to examine the utility of the agents in combination therapies directed against breast cancer. Preliminary cell studies indicate that nontoxic concentrations of our synthetic Grb2 inhibitors can act cooperatively with certain standard cytotoxic chemotherapeutic agents to significantly reduce the growth inhibitory dose. In other cellular studies, our synthetic Grb2 inhibitors have been shown to inhibit human growth factor (HGF)-induced cell migration in Met containing fibroblasts. Work is currently in progress to examine these agents in whole animal metastasis models.
In the phosphatase area, a structure-based approach toward inhibitor design is being pursued. Using an epidermal growth factor receptor (EGFR)-derived pTyr-containing peptide sequence as a platform, we have examined a large number of novel nonphosphorus-containing pTyr mimetics for inhibitory potency against PTP1B. Highly potent motifs identified in this fashion have served as models for small molecule peptidomimetic design. The most potent of these low molecular weight inhibitors is currently undergoing cocrystallography with PTP1B for x-ray crystal structure determination. The aim of this work is to identify high affinity small molecule inhibitors with improved bioavailability as tools for studying cellular signal transduction and as potential therapeutic agents. Inhibitors of HIV integrase are being developed as potential anti-AIDS drugs in collaboration with the Laboratory of Molecular Pharmacology, CCR, NCI. Lead inhibitor structures have initially been derived from several sources, including three-dimensional pharmacophore searching of the more than 250,000 compounds contained within the NCI's chemical repository. Promising compounds have been systematically explored through chemical synthesis of analogs to determine structure-activity relationships (SAR) responsible for integrase inhibition. Information generated in this fashion has been applied to the design and preparation of new analogs having higher potency, reduced collateral cytotoxicity, and greater antiviral protective effects in HIV-infected cells. One lead structure in these studies has been provided by chicoric acid, which is a natural product previously reported to exhibit potent HIV integrase inhibition as well as protective effects in HIV-infected cells. Through a large number of synthetic analogs, we established important SAR parameters for this class of integrase inhibitor. In further work, we have prepared a series of sulfur-containing bisaroyl hydrazines which show potent inhibition of HIV integrase in extracellular assays and are capable of exhibiting 100 percent protection of HIV-infected cells at micromolar concentrations. Collaborative studies are under way to examine HIV integrase inhibition in whole cell systems.
In separate studies, collaborative efforts are under way to obtain x-ray structures of inhibitors bound to the HIV integrase enzyme. Information obtained from such x-ray structures should provide a starting point for the computer-assisted design of potent new inhibitors. In one approach, synthetic modification of potent inhibitors has been undertaken to render them water soluble and more suitable for cocrystallization with HIV integrase. In an alternate approach, promising inhibitors are being synthetically modified in ways that will allow them to bind irreversibly to the enzyme active site. This has required the development of new synthetic chemistry that allows the introduction of highly reactive functionality in latent, nonreactive form, which can be unmasked to the active species in a final step prior to incubation with the enzyme.
This page was last updated on 2/19/2013.