Abstract #2667: What distinguishes a PKC activator like phorbol ester from a PKC functional antagonist like bryostatin 1? Bryologues permit dissection of intermediate patterns of activity

Bryostatin 1, a promising anticancer agent in clinical trials, is a potent PKC activator in vitro that paradoxically often antagonizes the effects of the typical PKC activator phorbol 12-myristate 13-acetate (PMA) in cellular systems. Understanding the underlying mechanism(s) responsible for this functional PKC antagonism should afford a new generation of drugs for PKC, a validated therapeutic target. Here, we characterize biological responses to three synthetic bryostatin look-alikes (bryologues 11, 12, and 13 - JACS 2008, 130, 6660-6661) that differ structurally from bryostatin 1 to only a modest degree. We have examined the behavior of these compounds in multiple biological systems in which PMA induces a response which bryostatin 1 fails to induce and where bryostatin 1 blocks the response to PMA. The responses examined were: 1) cell proliferation and differentiation of U937 human leukemia cells, 2) cell proliferation of K562 human leukemia cells, 3) cell proliferation of LNCaP human prostate cancer cells, 4) apoptosis in LNCaP cells, 5) phosphorylation of PKC delta at position Tyr311 in LNCaP cells, 6) activation of cFos in LNCaP cells, 7) release of arachidonic acid metabolites in CH310T1/2 mouse fibroblasts. We find that the bryologues, like PMA and unlike bryostatin 1, inhibit proliferation of U937 and K562 cells and induce the differentiation (attachment) of U937 cells. On the other hand, in LNCaP cells the three bryologues do not inhibit cell proliferation, unlike PMA, and only partially induce apoptosis. Like PMA, however, they induce tyrosine phosphorylation of PKC delta at position 311, an effect induced very weakly and briefly by bryostatin 1. Finally, the duration of cFos activation by the bryologues in LNCaP cells is intermediate between the transient response to bryostatin 1 and the more sustained response to PMA. In C3H10T1/2 mouse fibroblasts, PMA but not bryostatin 1 induces the rapid release of arachidonic acid metabolites; the bryologues have an effect that is intermediate but closer to that of PMA. We conclude that these bryologues have different extents of phorbol ester or bryostatin 1-like character depending on the cell type and cellular endpoint examined and thus that there are multiple mechanisms responsible for the antagonistic action of bryostatin. The bryologues provide unique tools for now identifying which mechanisms are related to which responses. Finally, these bryologues together with novel derivatives should permit dissection of those structural features linked to their various mechanisms of action. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 2667.