ChemBioChem 2003, 4, 379±385 DOI: 10.1002/cbic.200200468 ¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 379 Signaling Effects of Demethylasterriquinone B1, a Selective Insulin Receptor Modulator Nicholas J. G. Webster,* [a] Kaapjoo Park, [b] and Michael C. Pirrung [b] A possible breakthrough in the treatment of diabetes was made with the discovery that a fungal natural product, demethylasterri- quinone B1 (DAQ B1), is an orally active, small-molecule mimic of insulin. Subsequent work has shown that the glucose-lowering effects of DAQ B1 are not accompanied by enhanced vascular proliferation, which is a side effect of chronic insulin administration that can lead to arteriosclerosis. Our recent short and modular total synthesis of DAQ B1 could be readily modified to create congeners and afforded ample supplies of the natural product, which permitted intracellular signal transduction of DAQ B1 to be examined. The activities of DAQ B1 and over a dozen related structures were studied for insulin receptor (IR) and insulin receptor substrate-1 phosphorylation. Examination of the effect of DAQ B1 on kinases downstream of the IR in insulin signal transduction showed selective activation of Akt kinase (a metabolic effect) but not of extracellular-regulated kinase (a proliferative effect). The influence of DAQ B1 on gene expression (determined by a microarray study) was also divergent from that of insulin, which activates both proliferative and metabolic pathways. The action of DAQ B1 as a selective insulin receptor modulator can be accounted for by its ability to selectively activate one kinase among the many emanating from insulin receptor autophosphorylation and its reduced effects on gene expression. KEYWORDS: gene expression ¥ insulin ¥ kinases ¥ microarray ¥ natural products Introduction A long-sought goal in the growth factor receptor field, [1] attainment of small molecule agonists, was realized with the discovery of demethylasterriquinone B1 (DAQ B1), an insulin receptor (IR) activator. [2] Oral administration of DAQ B1 causes Figure 1. Insulin signal transduction begins with the binding of insulin to the extracellular domain of the dimeric receptor formed from the smaller a chain and the extracellular domain of the b chain. Phosphorylation of tyrosine residues in the intracellular domain of the b chains occurs, which permits phosphorylation of insulin receptor substrates such as IRS-1. It is believed that DAQ B1 directly promotes phosphorylation of the intracellular tyrosine kinase domain of the IR. The phosphotyrosine residues in the IR or IRS-1 can recruit phosphatidylinositol-3- kinase (PI3K) to the cell membrane through adapter protein interactions with SH2 domains. Production of phosphatidylinositol-3,4,5-tris-phosphate activates Akt for phosphorylation of GLUT4 for glucose transport and GSK-3 for glycogen synthesis. Phosphatases such as PTEN inhibit some insulin (and other prolifer- ative) actions by dephosphorylating lipid phosphate groups. Protein tyrosine phosphatase 1B (PTP1B) can inhibit some insulin actions by dephosphorylating IR and IRS-1. Bad  pro-apoptotic BCL-2 family member. lowering of glucose levels in diabetic mice without causing proliferation of vascular smooth muscle, [3] and thus may qualify as the first selective insulin receptor modulator (SIRM). In other animal models, DAQ B1 lowers glucose levels only in the presence of low levels of insulin. [4, 5] The initial stages of transmembrane signaling that lead to insulin's metabolic effects are shown in Figure 1. A key control molecule is Akt, which supervises glucose transport by GLUT4 as well as glycogen synthase by glycogen synthase kinase-3 (GSK- 3). Insulin also affects other signal-transduction molecules, including the Ras proliferative pathways. We recently completed a brief, modular total synthesis of the natural product DAQ B1. [6] In order to better understand the in vivo actions of this molecule, its metabolic and transcriptional effects were studied in cellular models. In rat fibroblasts that over-express human IR, DAQ B1 shows similar activation of the extracellular-regulated kinase (ERK) from the MAP kinase family to that achieved by insulin, but enhanced activation of the Akt [a] Prof. N. J. G. Webster Department of Medicine 0673 University of California-San Diego, 9500 Gilman Drive La Jolla, California 92093 (USA) and San Diego Veterans Healthcare System, CA 92161 (USA) Fax: ( 1)858534-6653 E-mail: nwebster@ucsd.edu [b] K. Park, Prof. M. C. Pirrung Department of Chemistry Levine Science Research Center Duke University, Durham, North Carolina 27708 (USA) Supporting information for this article is available on the WWW under http://www.chembiochem.org or from the author.