Abstract 3571: The Thioredoxin Reductase Inhibitor Chaetocin has Potent Antineoplastic Effects in Solid Tumors

Abstract

Abstract Background: We had previously reported that the natural product chaetocin has potent and selective in vitro, ex vivo and in vivo anti-myeloma activity attributable to the imposition of cellular oxidative stress (ROS) in part mediated via competitive inhibition of the redox enzyme thioredoxin reductase. Having also observed chaetocin-induced cytotoxicity in solid tumor cell lines, we now extend prior work to characterize the effects of chaetocin in solid tumor cell lines and in human umbilical vein endothelial cells (HUVECs). Methods: The effects of chaetocin in solid tumor cell lines were assessed using colony forming assays, trypan blue exclusion assays, apoptosis and autophagy assays, electron microscopy, transcriptional profiling, and the National Cancer Institute 60 cell line screen. Results: Chaetocin demonstrated potent anti-cancer activity in all assessed solid tumor cell lines with IC50 values between 2-10 nM (24 h exposures, colony forming assays). While apoptosis was induced in a cell line-dependant fashion, it was not required for chaetocin-induced cytotoxicity, as ZVAD-fmk prevented apoptosis but not cell death. Markers of autophagy were not altered by chaetocin treatment. Interestingly, results form the NCI 60 cell line screen showed that hematological cell lines were generally more resistant to chaetocin than solid tumor lines despite our prior report indicating the activity of chaetocin in myeloma. Transcriptional profiling results were consistent with those anticipated from an agent producing cell death via imposition of cellular ROS, with heme oxidase-1 prominently induced along with other transcripts in pathways related to inflammatory response and cell death. Results from OxyBlot protein oxidation kit analyses (Millipore, Billerica, MA) confirmed a generalized increase in the carbonyl modification of proteins, a hallmark of cellular oxidative damage, in response to chaetocin treatment. Experiments using Rho0 mitochondrial inactive cells indicated that cellular ROS is induced by chaetocin independent of respiratory functional mitochondria. Chaetocin was also shown to block the interleukin-, fibroblast growth factor- or EGM2 media-induced proliferation of HUVEC cells at low-nanomolar concentrations. Conclusions: Chaetocin has wide-ranging antineoplastic activity across not only hematological, but also solid tumor, cell lines and displays evidence of antiangiogentic activity in HUVEC proliferation assays. Overall, chaetocin appears to be an attractive agent for further development as a candidate anti-cancer therapeutic in a variety of neoplasms. Supported in part by CA125750. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3571.