Abstract 2566: Pre-clinical efficacy of the Wnt pathway inhibitor RXC004 in combination with anti-cancer therapies
Authors: Kelly James , Woodcock Simon , Bhamra Inder , Jones Cliff , Armer Richard , Robertson Jane , Phillips Caroline 
Published: June 2022

Background: RXC004, a potent and selective inhibitor of the Wnt pathway regulator Porcupine, is being investigated in phase 2 studies in patients with advanced cancers (NCT04907851 and NCT04907539). Wnt pathway alterations, including loss-of-function RNF43 mutations and RSPO gene fusions, result in higher levels of the Wnt receptor Frizzled (Fzd) on the cell surface increasing Wnt-ligand dependent signaling. These alterations, which have been shown to be sensitive to Porcupine inhibitors, are implicated in colorectal, gastric and pancreatic cancer. Pre-clinical in vivo data on the effects of RXC004 in combination with clinically relevant anti-cancer therapies have not previously been described in genetically-defined models of cancer.

Methods: RXC004 was evaluated as a monotherapy, and in combination with clinically relevant chemotherapy regimens, in an RSPO-fusion colorectal xenograft model (SNU-1411). RXC004, dosed at 5mg/kg QD (5 days on/2 days off), was evaluated in combination with either the clinically relevant colorectal triplet chemotherapy regimen (5-fluorouracil 5-FU (25mg/kg), irinotecan (50mg/kg) and oxaliplatin (5mg/kg)) or doublet chemotherapy regimen (5-FU (25mg/kg), irinotecan (50mg/kg)). Each chemotherapy regimen was dosed once a week for 3 to 4 weeks either alone or in combination with RXC004, which was dosed from day 8 onwards at 5mg/kg QD (5 days on/2 days off). Efficacy was measured by tumor volume and survival endpoint. In addition, RXC004 was studied in vitro, as monotherapy and in combination with a PARP inhibitor in genetically selected cell lines with both RSPO-fusion and RNF43 mutation. Combination and monotherapy effects on proliferation and effects on downstream signaling were investigated.

Results: RXC004 in combination with the triplet chemotherapy regimen led to significantly increased survival compared to either treatment alone (p&lt;0.005) and significant tumor volume reduction measured at Day 22 (p&lt;0.001). RXC004 in combination with the doublet chemotherapy also increased survival compared to either treatment alone (p&lt;0.05), and the combination led to significantly decreased tumor volume measured at Day 25 (p&lt;0.05). RXC004 treatment in genetically defined cell lines with RSPO fusions or RNF43 mutations led to a significant reduction in BRCA1 and BRCA2 gene expression. In in vitro proliferation studies a synergistic effect of RXC004 and a PARP inhibitor was demonstrated in genetically defined cell lines.

Conclusion: These data demonstrate that RXC004 in combination with clinically relevant standard of care chemotherapy regimens can lead to potential benefit over chemotherapy alone. The RXC004 induced downregulation of DNA repair pathway genes observed in vitro could contribute to the beneficial effect seen in combination with a PARP inhibitor in vitro as well as the combination effect observed in vivo with standard of care chemotherapy agents.

Citation Format: James Kelly, Simon Woodcock, Inder Bhamra, Cliff Jones, Richard Armer, Jane Robertson, Caroline Phillips. Pre-clinical efficacy of the Wnt pathway inhibitor RXC004 in combination with anti-cancer therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2566.