Abstract 5420: Antitumor activity of nemorosone against pancreatic cancer cells and xenografts

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Polycyclic polyprenylated acylphloroglucinols (PPAPs) are secondary plant metabolites with fascinating structures and a wide variety of biological activites including pronounced anticancer properties. In this study, the cytotoxic potential of the PPAP nemorosone was assessed on three cell lines derived from pancreatic adenocarcinoma, a cancer type with a poor prognosis due to its chemoresistance, and on normal fibroblasts. Transcription profiling using microarrays comprising a set of 4000 genes was used to identify important gene-regulatory networksassociated with the mode of action of nemorosone. Additionally, a xenograft mouse tumor model was established to assess bioavailability and in vivo antitumor activity of this PPAP. Cell viability and apoptosis assays demonstrated a dose- and time-dependent cytotoxic effect of nemorosone on all pancreatic cancer cell lines and a significantly lower activity against normal fibroblasts. Cytotoxicity was found to be characterized by cell cycle arrest and induction of caspase-dependent intrinsic apoptosisthrough the release of cytochrome c from mitochondria. More detailed analyses revealed a rapid and dose-dependent depletion of endoplasmic reticulum (ER) calcium stores with a concomitant depolarization of the mitochondrial membrane within seconds after onset of treatment. These results suggest an immediate ionophoric effect of nemorosone together with disturbance of the ER ion homeostasis. As determined by microarray analysis, nemorosone altered the expression of 336 genes, most of which were found to be associated with the regulation of cell cycle and apoptosis or the cellular response to stress. 75 genes were concomitantly differentially regulated in all three cancer cell lines and were suspected to be related to the primary mechanism of action of nemorosone. Using a pathway modeling approach, many of them were identified to play a role in the ER stress-induced unfolded protein response(UPR). Using RNAi-mediated gene silencing of the central pro-apoptotic UPR transcription factor DDIT3, nemorosone-induced apoptosis could partially be abrogated, thus confirming the involvement of UPR signaling in nemorosone's mode of action. Since up-regulation of UPR components was not observed in fibroblasts, a preferential effect on cancer cells can be assumed. Treatment of pancreatic cancer xenograft-bearing nude mice with nemorosone resulted in a complete inhibition of tumor growth accompanied by a good tolerability. Immunohistochemical staining of xenograft sections confirmed the growth-inhibiting and apoptosis-inducing effects of nemorosone in vivo. It can be concluded from the results of this study that nemorosone is a potential lead compound with a novel mechanism of action which should be further explored for the treatment of pancreatic cancer and also other tumor entities. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5420. doi:10.1158/1538-7445.AM2011-5420