Abstract 5071: Inhibition of Porcupine reduces Wnt-dependent colony formation and/or proliferation in both autocrine and paracrine cell models

Abstract Aberrant activation of the pro-survival Wnt signalling pathway is a key determinant in numerous cancers (Nusse and Varmus, 2012) and therefore constituents of this pathway are potentially promising therapeutic targets. The membrane-bound o-acyltransferase porcupine (PORCN) is required for post-translational modification of all Wnts, and is vital for Wnt secretion (Herr et. al., 2012). Due to the complex and varied oncogenic roles of the known Wnt ligands, prevention of active ligand secretion provides an effective mechanism for inhibiting canonical and non-canonical Wnt signalling in both paracrine and autocrine systems. Here we show that a novel inhibitor of porcupine potently inhibits both autocrine and paracrine models of Wnt/β-catenin signalling. Treatment of the pancreatic cancer cell line CAPAN-2 with REDX05562 resulted in a significant decrease of axin 2 mRNA expression by qPCR (10.4 fold, 10nM). This reduction in expression was partially reversed by the addition of recombinant human Wnt-3A (100ng.ml−1). The decrease in axin 2 expression was concomitant with an inhibition of CAPAN-2 proliferation (IC50 1.4nM +/- 0.8nM). Conversely treatment of MCF-7 mammospheres with REDX05562 did not inhibit sphere forming efficiency (SFE). However, when stimulated with recombinant Wnt-3A an increase in anoikis resistance was observed suggesting a potential paracrine influence. In vivo the presence of cancer associated fibroblasts (CAFs) are a likely source of paracrine Wnt (Green et. al., 2013). Indeed, conditioned media taken from primary CAFs (isolated from fresh mastectomies) increased anoikis resistance in MCF-7 cells without any discernible effect on CAF proliferation. This effect was significantly inhibited when MCF-7 cells were incubated with conditioned media taken from primary CAFs treated with REDX05562. Moreover, immunofluorescent labelling of PORCN revealed that PORCN expression is markedly higher in CAFs than in MCF-7s. This is consistent with the hypothesis that different mechanisms underpin Wnt-signalling in breast and pancreatic cancer. The above data show that the novel PORCN inhibitor REDX05562 effectively reduces the impact of pro-survival Wnt ligand-mediated signalling in both paracrine and autocrine models. This further emphasises the broad therapeutic potential of PORCN inhibition in Wnt-dependent cancers. Citation Format: Ben A. Thompson, Kate J. Messenger, Emily Linnane, Sarah E. Coupland, Peter J. Calcraft. Inhibition of Porcupine reduces Wnt-dependent colony formation and/or proliferation in both autocrine and paracrine cell models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5071. doi:10.1158/1538-7445.AM2015-5071