Development of sirtuin and calmodulin-dependent protein kinase inhibitors as anti-cancer therapeutics

Abstract

Small molecule inhibitors of the human sirtuins and calmodulin-dependent protein kinases have shown promising anti-cancer activity in cell-based screens and animal models. We have synthesized analogues of these compounds, identifying more selective sirtuin inhibitors and more potent calmodulin-dependent protein kinase inhibitors.The sirtuins are a family of NAD+-dependent deacetylases that regulate cellular aging and gene silencing in simple organisms and appear to play important regulatory roles in human cells that make them attractive anti-cancer targets. We have previously identified the compound cambinol, an inhibitor of the human sirtuins SIRT1 and SIRT2, which is selectively toxic to Burkitt's lymphoma cells. In order to determine which sirtuin is the relevant target, we screened analogues of cambinol, identifying compounds that exhibited moderate selectivity for both SIRT1 and SIRT2. The compound JP136 is ten-fold more selective in vitro for SIRT1 over SIRT2, with respective IC50's of 13 muM and 125 muM, and it is far less potent against the Daudi Burkitt's lymphoma cell line than cambinol. Conversely, the compound ADS010, which is selective for SIRT2 in cell-based assays, is slightly more toxic to Daudi cells than cambinol. Like cambinol, ADS010 has been found to be toxic only to B-cell lymphomas. SIRT2 appears to be the relevant target for cambinol-induced Daudi cell toxicity.KN-62, an inhibitor of the calmodulin-dependent protein kinases (CaMKs), enhances the terminal differentiation of retinoic acid sensitive human myeloid leukemia cell lines. In an effort to identify additional CaMK inhibitors that exhibit more potent activity in triggering leukemia cell differentiation, we synthesized 45 analogues of KN-62 and determined their ability to induce HL-60 cell differentiation. Sixteen of these novel analogues exhibited significant differentiation-inducing activity, and one analogue, AS-004, was five times more potent than KN-62 in inhibiting proliferation and inducing differentiation of HL--60 cells. Such KN-62 analogues and/or related compounds may prove useful in treating promyelocytic leukemia.