The structurally diverse group of natural toxins including okadaic acid, calyculin, microcystin LR, and tautomycin exert their cytotoxic effects by inhibiting the serine-threonine protein phosphatases PP1 and PP2A. This activity dramatically increases the phosphorylation state of a variety of proteins within the cell, which in turn results in acute toxic effects or unregulated cellular proliferation. The compounds themselves are therefore not only hepatotoxins, but also tumor promoters. Because as a group they inhibit PP1 and PP2A quite potently and specifically relative to other known phosphatases such as PP2B (calcineurin), PP2C, and the tyrosine phosphatases, several members of this group have become important PP1/2A structural/activity probes and, more generally, tools for studying intracellular signaling pathways. However, there is still a demand for new inhibitors with increased selectivity or other desirable properties such as improved membrane permeability. A very recent report that the naturally occurring toxin tautomycetin inhibits PP1 an order of magnitude more selectively (40:1) than tautomycin provides an important new lead in this endeavor. In addition, at about the same time, the structure of the okadaic acid-PP1 complex was published, providing for the first time solid structural information about this inhibitor that will allow us to design analogs that are much more synthetically accessible than okadaic acid itself. While most of the studies in this field have focused on the active sites of PP1 and PP2A, in the past several years some attention has shifted to characterizing an allosteric site on these phosphatases that modulates activity by interacting with a variety of binding (regulatory) proteins. Although small peptide analogues of the regulatory protein binding domains are known to bind to the regulatory site of PP1, there have been no reports of small molecule ligands for the regulatory site. We will therefore prepare libraries of small molecule/peptide hybrids and study their interactions with the regulatory site, opening the door to the design and synthesis of non-protein PP1 activators. Supporting this new area, as well as our ongoing inhibitor design program, we will conduct enzymological and structural studies in collaboration with a prominent X-ray crystallographer, Professor Tom Poulos, in order to obtain detailed structural information concerning the hypotheses upon which our designs are based.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM057550-08
Application #
7218074
Study Section
Medicinal Chemistry Study Section (MCHA)
Program Officer
Fabian, Miles
Project Start
1998-08-01
Project End
2009-03-31
Budget Start
2007-04-01
Budget End
2009-03-31
Support Year
8
Fiscal Year
2007
Total Cost
$256,165
Indirect Cost
Name
University of California Irvine
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92697
Glauber, Kristine M; Dana, Catherine E; Park, Steve S et al. (2013) A small molecule screen identifies a novel compound that induces a homeotic transformation in Hydra. Development 140:4788-96
Tappan, Erin; Chamberlin, A Richard (2008) Activation of protein phosphatase 1 by a small molecule designed to bind to the enzyme's regulatory site. Chem Biol 15:167-74
Hart, Matthew E; Chamberlin, A Richard; Walkom, Cecilia et al. (2004) Modified norcantharidins; synthesis, protein phosphatases 1 and 2A inhibition, and anticancer activity. Bioorg Med Chem Lett 14:1969-73
Gulledge, Brian M; Aggen, James B; Chamberlin, A Richard (2003) Linearized and truncated microcystin analogues as inhibitors of protein phosphatases 1 and 2A. Bioorg Med Chem Lett 13:2903-6
Gulledge, Brian M; Aggen, James B; Eng, Hugo et al. (2003) Microcystin analogues comprised only of Adda and a single additional amino acid retain moderate activity as PP1/PP2A inhibitors. Bioorg Med Chem Lett 13:2907-11
Gulledgea, B M; Aggena, J B; Huangb, H-B et al. (2002) The microcystins and nodularins: cyclic polypeptide inhibitors of PP1 and PP2A. Curr Med Chem 9:1991-2003
Krutzik, Peter O; Chamberlin, A Richard (2002) Rapid solid-phase synthesis of DNA-binding pyrrole-imidazole polyamides. Bioorg Med Chem Lett 12:2129-32
Fischer, W J; Garthwaite, I; Miles, C O et al. (2001) Congener-independent immunoassay for microcystins and nodularins. Environ Sci Technol 35:4849-56
Aggen, J B; Humphrey, J M; Gauss, C M et al. (1999) The design, synthesis, and biological evaluation of analogues of the serine-threonine protein phosphatase 1 and 2A selective inhibitor microcystin LA: rational modifications imparting PP1 selectivity. Bioorg Med Chem 7:543-64