KATZENELLENBOGEN, John A.

Department of Chemistry
Ph.D. (1969) Harvard University

Research Topics

Steroid Structure and Function
Molecular Probes for the Steroid Receptors
Novel Ligand Design and Combinatorial Chemistry
Fluorescent Steroids
Positron Emitting Imaging Agents

Research Interests: Nuclear Hormone Receptors

A. Steroid Receptor Structure and Function, Dynamics and Interactions – We are interested in studying the structure and function of steroid receptors, the estrogen receptor, in particular, using a variety of chemical probe, mutagenesis, spectroscopic, and biophysical methods, such as fluorescnece and X-ray crystallography. Using molecular biological methods, we have developed methods for site-specific labeling of the ligand binding domains of nuclear receptors with fluorophores. These modified proteins are powerful tools to study receptor conformation, conformational dynamics, and interactions with coregulator proteins, and how these processes are modulated by ligand binding and should lead to a clearer understanding of the molecular events that underlie the actions of hormonal agonist and antagonists. These components can also be used to prepare microarrays of receptor or coregulator proteins through which ligand binding and relevant protein-protein interactions can be studied in a high throughput fashion.

B. Novel Ligands for Nuclear Hormone Receptors Developed by Combinatorial Chemistry – We are using structural motif analysis of ligands for steroid receptors to conceive of novel heterocyclic and bridged bicyclic systems that can form molecular scaffolds for high affinity receptor ligands. These scaffolds are then elaborated by combinatorial chemical methods, often involving synthesis of solid phase, to prepare libraries of candidate ligands that are then evaluated by receptor binding and cell-based transcription assays. This approach is leading to the expedited discovery of high affinity ligands for these receptors that are structurally novel and have unusual pharmacological characteristics. In fact, some of these novel ligands have very high selectivity for one of the two estrogen receptor subtypes, ERą and ERβ. This approach should lead to the development of new estrogens that are optimally suited for medical uses in women’s health (menopausal hormone replacement, and breast cancer prevention and treatment).

C. Inhibitors of Receptor-Coactivator Interaction – The action of steroid hormones involves the interaction of the hormone-receptor complex with coactivator proteins. We are synthesizing and evaluating small molecules that are designed to act as inhibitors of receptor-coactivator interaction. Such agents might function as novel inhibitors of steroid hormone action, useful in to treatment of hormone-responsive cancers,that could not be surmounted by the normal hormone resistance mechanisms.

D. Radio-Emitting Steroids – We are preparing estrogens, progestins, androgens, and corticosteroids labeled with the positron-emitting radionuclides, fluorine-18, bromine-76,77, iodine-124, technetium-94m, and the single photon emitter, technetium-99m, as receptor-based imaging agents for hormone-responsive tumors of the breast and prostate. In collaboration with workers at Washington University Medical School, we have already demonstrated that target tissues and tumors that contain estrogen and androgen receptors can be imaged with F-18 labeled estrogens. This project involves computer-based design of ligand structure, organic and radiochemical synthesis, tracer level chemistry and microanalysis, receptor binding studies, and, through collaboration, in vivo and imaging studies in experimental animals and ultimately human cancer patients. This work should lead to the development of novel diagnostic agents for breast and prostate cancer that might permit a much more complete diagnostic evaluation of the disease than simple biochemical assay of receptor in tumor biopsy homogenates, and a rapid assessment of response to hormone therapy.

E. Fluorescent Probes – We are developing fluorescent estrogens and progestins that can be used in conjunction with flow cytometry, fluorescence microscopy or fluorescence dynamics methods, to assay the estrogen receptor content of individual cells. Since the receptor content of individual cell is very small, we have developed ligands for receptor that are optimized both in terms of their high affinity for the receptor and their low affinity for non-specific binding sites, and in terms of their fluorescent properties. These agents should enable characterization of cells from breast tumors in terms of their responsiveness to hormone therapy to enable a more definitive prediction of the course of hormone therapy.

Key Words Steroid Receptor Structure and Function, Hormones, Diagnostic Reagents, Pharmaceuticals, Site-Directed Mutagenesis, Protein Purification and Characterization, Active Sites and Receptors, Molecular Modeling, Natural Products, Structural Biology, X-Ray Crystallography, NMR, Organic Synthesis, Combinatorial Chemistry.

Current Research Funding NIH, DOE, U.S. Army

BTC Members