Abstract 998: Mechanism of action of RXC004, a Wnt pathway inhibitor, in genetically-defined models of cancer

Abstract

Abstract Background: RXC004 is a porcupine inhibitor, and thus a potent and selective inhibitor of Wnt ligand-dependent signalling. RXC004 is currently being investigated in a safety and tolerability study in cancer patients with solid tumours (NCT03447470). Certain Wnt pathway alterations, including loss-of-function RNF43 mutations and RSPO gene fusions, result in higher levels of the Wnt receptor Fzd on the cell surface increasing Wnt-ligand dependent signalling. These alterations are implicated in colorectal and pancreatic cancer. We present pre-clinical data on the effects of RXC004 in genetically defined models of cancer. Methods: RXC004 in vitro effects on the metabolic activity of both sensitive (genetically selected RNF43 mutant or RSPO fusion models) and insensitive (beta-catenin mutant model) colorectal and pancreatic tumour cells lines were assessed. To test if these effects translated in vivo, RXC004 was also evaluated in an in vivo FDG-PET study in an RSPO fusion tumour cell line. In addition, as we had previously noted that RXC004 caused cell differentiation in an RSPO fusion model, we studied if pre-treatment with RXC004 would affect subsequent tumour growth post RXC004 induced cell differentiation in vivo. Results: In tumour cell lines in vitro, RXC004 significantly reduced glucose uptake only in genetically selected tumour cell lines. In vivo FDG-PET studies also showed a reduction in FDG-PET signals post 7 days treatment of 5mg/kg QD RXC004. Imaging demonstrated that MaxSUV (maximum standardised uptake value) decreased by 31% in RXC004 treated versus vehicle treated tumours, furthermore biodistribution of PET ligand was significantly inhibited in tumours post 7 days RXC004 treatment. Pre-treatment of RXC004 in an in vivo mouse xenograft model for 7 days resulted in a significant reduction in tumour growth when tumour fragments from these pre-treated mice were re-implanted into naïve mice (P<0.05). Conclusion: These data demonstrate that RXC004 monotherapy results in tumour cell differentiation accompanied by reduced metabolic activity in genetically selected tumours. RXC004-induced cell differentiation may therefore continue to provide patient benefit even post dosing. Moreover, FDG-PET imaging in clinical studies may allow early detection of the positive effects of RXC004 in a non-invasive manner, and prior to any changes in tumour volume by conventional RECIST measurements. Citation Format: Caroline Phillips, Simon Woodcock, Catherine Eagle, Andrew Saunders, Craig Tilston, Inder Bhamra, Richard Armer. Mechanism of action of RXC004, a Wnt pathway inhibitor, in genetically-defined models of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 998.