UA62784; a Putative Inhibitor of CENP-E Kinesin-like Protein and its Effects on Human Pancreatic Cancer Cells

Abstract

UA62784 is a novel fluorenone identified in a biologic screen of compounds that are selectively cytotoxic in DPC4 (deleted in pancreatic cancer)-deleted pancreatic cancer cells. We sought to determine the mechanism of action of UA62784, and discovered it to be a potent mitotic inhibitor. UA62784 affects the ATPase activity of the mitotic kinesin centromere protein E (CENP-E), but does not affect other known mitotic kinesins. This inhibition of ATPase activity is not caused by an inhibition of microtubule binding nor is it caused by a failure of the kinesin to translocate to the nucleus during mitosis. Despite the anti-cancer properties of this drug, UA62784 is relatively insoluble and is not suitable as a lead compound for further development.Once we determined the mechanism of action of UA62784, we sought to determine if analogs would demonstrate the same potent mitotic inhibition while also offering properties such as increased solubility. A small library of chemical analogs was generated wherein each compound was a slight variation of UA62784 (termed the DPC series). Several potential leads were identified which exhibited increased solubility and/or increased cytotoxic activity. When tested for CENP-E ATPase inhibition, some compounds were noted to inhibit other kinesins as well. We therefore created a screen where each of the DPC compounds was tested for activity in Eg5, CENP-E, MKLP-1, MCAK, and KIF3C kinesins. Within these data, there is a correlation between cellular IC50 and kinesin ATPase inhibition for CENP-E and MKLP-1. A few compounds emerged from these studies, including DPC046, which has a low cellular IC50 and inhibits all five kinesins to some degree. DPC046 was used in a mouse xenograft study to determine in vivo efficacy, but no significant tumor shrinkage was seen, likely due to solubility limitations affecting the amount of bioavailable compound.From these studies we conclude that the cytotoxic effects seen in UA62784 and its analogs are due, at least in part, to their inhibition of kinesin proteins. We demonstrate that compounds that inhibit CENP-E and other kinesin proteins hold promise in cytotoxically targeting pancreatic cancer cells. Further development is needed to optimize DPC046 compound solubility in order to increase in vivo efficacy.