PD08-11: Targeting Porcupine, a Critical Node for Wnt Signalling in Cancer.

Abstract

Abstract Wnt ligands were first discovered based upon their transforming activity in the setting of mouse mammary tumor virus (MMTV) induced mammary carcinogenesis. Wnt signalling is required for normal development of the mammary gland and dysregulated Wnt signalling is implicated in cancers of the breast and colon among others. Furthermore, lobular breast cancer commonly shows reduced expression of E-cadherin that can lead to release of membrane-bound b-catenin into the cytoplasm and potentially increase Wnt signalling in the presence of Wnt ligand. To date, however, low-molecular weight therapeutic inhibitors of the Wnt pathway have not been developed. We set out to discover key points of intervention in the Wnt pathway and to develop low molecular weight inhibitors against such nodes. To this end, a cellular high-throughput screen for small molecule inhibitors of the Wnt pathway was performed. In this assay, cells secreting Wnt3a were co-cultured with cells harboring a luciferase reporter driven by the Wnt/beta-catenin responsive elements. Potent and specific Wnt pathway inhibitors were identified from this screen. To discern the mechanism of action of these compounds, a lead inhibitor was radiolabeled and used to probe protein targets in a radioligand binding assay. From these assays a candidate target of the inhibitor was identified as Porcupine. Porcupine is a membrane bound O-acyltransferase enzyme that is required for and dedicated to palmitoylating Wnt ligands, a necessary step in the process of Wnt ligand secretion. Inhibition of Porcupine blocks Wnt dependent activities, including LRP6 phosphorylation and the expression of Wnt target genes, such as Axin2, which in turn reduces the growth of cancer cells dependent on autocrine or paracrine Wnt signaling. A selective and orally bioavailable Porcupine inhibitor (NVP-LGK974) that inhibits the Wnt pathway in vitro and in vivo was developed through medicinal chemistry optimization. In preclinical evaluation, the compound robustly suppressed Wnt pathway signaling in vivo resulting in tumor regression in a murine breast cancer model driven by MMTV-Wnt1. In addition, this inhibitor attenuated tumor growth as a single agent and induced tumor regression in combination with Taxol in a human primary breast tumor model. Wnt signalling is also important for the maintenance and homeostasis of normal tissues including gastrointestinal tissue. However, preclinical rodent efficacy models of cancer demonstrate that intermittent pharmacological inhibition of Porcupine can be effective against the tumor and mostly spare the normal gastrointestinal tissue, with an acceptable therapeutic window. A Phase I dose escalation study of NVP-LGK974 in patients with melanoma and lobular breast cancer to evaluate the safety, tolerability, PK, and PD properties is expected to begin this year. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD08-11.