Thomas Poulos
Molecular Biology & Biochemistry
School of Biological Sciences
Phone: (949)824-7020
Email: poulos@uci.edu
http://www.faculty.uci.edu/profile.cfm?faculty_id=2699
http://crystal.bio.uci.edu/~poulos/lab_website/intro.html
Poulos Lab Web Site
Thomas Poulos
Two projects in the lab relate directly to cancer: cytochrome P450 and nitric oxide synthase.
P450 – Cytochromes P450 are the primary enzymes involved in detoxifying a wide range of xenobiotics including drugs. An unfortunate consequence of P450 oxidation reactions is the conversion of some aromatic hydrocarbons into potent carcinogens. Dr. Poulos’ research has centered on structure determination of various P450s and related redox partners with a special emphasis on protein-protein interactions. More recently they have been working on aromatase, a key P450 involved in sex hormone biosynthesis. Aromatase catalyzes 3 consecutive hydroxylations that convert C19 androgens to aromatic C18 estrogenic steroids. The production of estrogens by aromatase in breast cancer cells promotes tumor growth and hence, inhibition of aromatase offers therapeutic potential in breast cancer. In fact, aromatase is one of the more clearly defined P450 drug targets in mammals. They are collaborating with Dr. Shiuan Chen at the City of Hope on aromatase His group has made significant advances in expressing functional aromatase in E. coli. Over the years the main limitation in this project has been that aromatase, like all mammalian P450s, is membrane bound so the expression of soluble, monodisperse samples has been difficult. However, the recent advances made in Dr. Chen’s lab as well as the advances made in the lab of Eric Johnson on how to re-engineer membrane bound P450s for increased solubility and monodispersity has increased the level of optimism for moving forward on the aromatase structure.
Nitric Oxide Synthase (NOS) – NOS is the enzyme responsible for the production of NO, a potent signaling molecule critical in a number of physiological systems. Humans produce 3 isoforms called inducible NOS (iNOS), neuronal NOS (nNOS), and endothelial NOS (eNOS). NO derived from eNOS is important in controlling blood pressure and maintaining vascular tone, NO produced by nNOS is involved in neural transmission, while iNOS participates in the immune response where NO acts as a cytoxic molecule used to kill pathogens.
NO also has been found to stimulate breast cancer tumor growth while NOS inhibitors have been shown to block tumor growth. Although studies on the relationship between NO and breast cancer is still in its infancy, the available data indicate a clear connection. In certain breast cancer cell lines there is a good correlation between tumor growth and NO production indicating that NO may provide a positive growth signal within the tumor. In another study, immune stimulatory agents like interferon and LPS enhance NO production by stimulating the formation of iNOS which was shown to enhance tumor growth in vivo. In this same study it was shown that NOS inhibitors can slow tumor growth. There is a correlation between the presence of NOS and axillary lymph node metastasis while NOS inhibitors also limit osteolytic bone metastses, a frequent clinical problem in breast cancer. NO and its reaction product with superoxide, peroxynitrite, have been shown to be causative factors in toxic anemia in breast cancer patients. There also is a complex interplay between tamoxifen effects on breast cancer cells and NO production suggesting the involvement of NOS. In all these examples the isoform responsible for the NO effects is iNOS. However, in at least one study there is a link between eNOS and breast cancer. High levels of NO production in endothelial cells in normal tissue surrounding the tumor correlates with longer overall survival. As in other non-cancer related pathological conditions, it appears that in breast cancer eNOS is the “good” NOS while iNOS is the “bad” NOS. Taken together these studies strongly suggest that isoform specific inhibition of iNOS could prove of some benefit in controlling breast cancer.
An important goal in NOS research is to develop isoform-selective NOS inhibitors. Selectivity is important since in most cases the target NOS is nNOS or iNOS but not eNOS since eNOS is critical in blood pressure control. Dr. Poulos has successfully used structure based inhibitor design to develop novel NOS inhibitors that bind up to 4,000 time more tightly to nNOS than to eNOS. Moreover, some of these compounds do very well in animal trials where it was found that nNOS inhibitors block ischemic injury during hypoxia. This effort require proein crystallography and computer modeling here at UCI and synthetic organic chemistry and animal testing with collaborators at Northwestern University.
Selected Publications:
Li, H., Igarashi, J., Jamal, J., Yang, W., and Poulos, T. L. (2006). Structural studies of constitutive nitric oxide synthases with diatomic ligands bound. J Biol Inorg Chem 11(6), 753-68.
Kuznetsov, V. Y., Poulos, T. L., and Sevrioukova, I. F. (2006). Putidaredoxin-to-cytochrome P450cam electron transfer: differences between the two reductive steps required for catalysis. Biochemistry 45(39), 11934-44.
Kimmich, N., Das, A., Sevrioukova, I., Meharenna, Y., Sligar, S. G., and Poulos, T. L. (2007). Electron transfer between cytochrome P450cin and its FMN-containing redox partner, cindoxin. J Biol Chem 282(37), 27006-11.
Levin, A. M., Murase, K., Jackson, P. J., Flinspach, M. L., Poulos, T. L., and Weiss, G. A. (2007). Double barrel shotgun scanning of the caveolin-1 scaffolding domain. ACS Chem Biol 2(7), 493-500.
Seo, J., Igarashi, J., Li, H., Martasek, P., Roman, L. J., Poulos, T. L., and Silverman, R. B. (2007). Structure-based design and synthesis of N(omega)-nitro-L-arginine-containing peptidomimetics as selective inhibitors of neuronal nitric oxide synthase. Displacement of the heme structural water. J Med Chem 50(9), 2089-99. |
