Abstract 1654: Pre-clinical activity of the Wnt/Beta-catenin pathway inhibitor RXC004 in models of biliary tract cancer
Authors: Woodcock Simon A. , Keppel Dorottya , Eagle Catherine , Bhamra Inder , Platt Eleanor , Frost Lucy , Randall Kevin , Armer Richard , Robertson Jane , Marshall Gayle , Phillips Caroline 
Published: April 2023

Abstract
Background: RXC004 is a potent and selective inhibitor of the Wnt pathway regulator Porcupine, and is currently being investigated in phase 2 studies in patients with advanced cancers, including Biliary Tract Cancers (BTCs) +/- Pembrolizumab (NCT04907851 and NCT04907539). Whilst genetically-defined ‘upstream’ Wnt pathway alterations, including loss-of-function RNF43 mutations and RSPO gene fusions, sensitise Gastrointestinal (GI) cancers to RXC004, other non-genetic factors remain to be determined. Wnt pathway mutations are rare in BTCs, however these tumors have been shown to overexpress various Wnt ligands, with evidence that this high expression is associated with worse prognosis.
Methods: RXC004 was evaluated as a monotherapy against a panel of patient-derived xenograft (PDX) models of Biliary Tract Cancer for efficacy and pharmacodynamic (PD) activity. RXC004 was dosed at 5mg/kg QD and efficacy was measured by tumor volume, tumor weight and survival endpoint, whilst tumor pharmacodynamic (PD) effects were measured by quantitative Real-Time PCR (qPCR) for gene expression and histological staining methods. Baseline transcriptome characteristics of the PDX models were determined against the PanCancer Pathways and PanCancer IO360 codesets using Nanostring nCounter analysis.
Results: RXC004 monotherapy was efficacious in multiple PDX models of Biliary Tract Cancer, significantly reducing tumor volume and tumor weight (range p&lt;0.05 to p&lt;0.0001). Tumor PD effects of RXC004 treatment on gene expression by qPCR included Wnt pathway genes (AXIN2, cMYC), differentiation genes (MUC2, MUC4, MUC5AC) and secreted Wnt pathway regulators (sFRPs, DKKs), and on histology included Ki67 and Mucin (periodic acid-Schiff’s (PAS)/Alcian blue staining). Hierarchical clustering of the PDX models was performed based on the expression of Wnt signalling genes in the Nanostring analysis. Furthermore, the gene expression profiles were used to predict whether models were likely to be RXC004 sensitive using Random Forest machine learning algorithms.
Conclusion: These data demonstrate that (1) RXC004 is efficacious in pre-clinical PDX models of BTC, (2) RXC004 induces multiple PD effects in BTC models at the level of gene expression, cell proliferation and cell differentiation, and (3) PDX models of BTC can be clustered based on baseline transcriptomic profiles of Wnt signalling genes and predict RXC004 sensitivity.
Citation Format: Simon A. Woodcock, Dorottya Keppel, Catherine Eagle, Inder Bhamra, Eleanor Platt, Lucy Frost, Kevin Randall, Richard Armer, Jane Robertson, Gayle Marshall, Caroline Phillips. Pre-clinical activity of the Wnt/Beta-catenin pathway inhibitor RXC004 in models of biliary tract cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1654.