The diterpene, forskolin, has been shown to affect many membrane proteins including adenylyl cyclase, the glucose transporter, and the P-glycoprotein. Very little information is available about the location of forskolin binding sites on these proteins or the specificity of these binding sites for forskolin and analogs. We have synthesized stable aminoalkylcarbamates of forskolin that are capable of discriminating between different forskolin binding proteins. It is now recognized that adenylyl cyclase represents a family of isoforms that have different amino acid sequences and are differentially regulated by hormones, calcium, and G proteins. Preliminary studies have demonstrated that forskolin interacts differentially with different isoforms of adenylyl cyclase. Eight isotypes of adenylyl cyclase have been described and expressed in sf9 insect cells. Studies for identifying type-specific activators of adenylyl cyclase are being carried out with Dr. Dan Boring, CDER, FDA. These studies involve synthesizing a series of forskolin derivatives in order to define the structure-activity relationships for the different adenylyl cyclases. Progress has been made on understanding the topography of the binding site. Interest has been shown by a group at Lederle Laboratories for collaborating with us to look at the three dimensional computer generated image using binding data generated from our forskolin analogues to gain a better picture of the forskolin binding site. There is still much interest by several commercial enterprises in using forskolin analogues as therapeutic agents. Our collaboration with Dr. Gilman's laboratory in providing us with recombinant adenylyl cyclase isotypes has been fruitful and is on going.
