Efficacy of the Wnt/Beta-Catenin pathway inhibitor RXC004 in genetically-defined models of cancer

Background: RXC004, a potent and selective inhibitor of the Wnt/β-Catenin pathway regulator porcupine, is being investigated in a safety and tolerability study in cancer patients with solid tumours (NCT03447470). 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, gastric, pancreatic and biliary cancer. We present pre-clinical data on the direct tumour-targeting effects of RXC004 in genetically-defined models of cancer. Methods: RXC004 in vitro effects on sensitive (RNF43 mutant or RSPO fusion) or insensitive (APC/β-Catenin mutant) colorectal and pancreatic tumour cells lines were assessed against a panel of potential Wnt target genes measured using qPCR. To test if these effects translated in vivo, RXC004 was evaluated in several RNF43 mutant or RSPO fusion tumour line efficacy, PK and PD studies. A range of oral doses and schedules of RXC004 were tested for either 7 or 26 days, for PK/PD or efficacy measurements respectively. Efficacy was measured by tumour volume/weight, RXC004 PK was measured in plasma and tumour, and PD effects were measured by tumour qPCR and histological methods. Results: In sensitive cell lines, RXC004 inhibited expression of the Wnt pathway negative feedback genes Axin2 and RNF43. Decreases in c-Myc correlated with the anti-proliferative effects of RXC004. Additionally, MMP7 and CD44 were downregulated, whilst Mucin gene expression increased. In contrast, RXC004 had no anti-proliferative effects on APC mutant colorectal cancer cells in vitro, and no modulation of these Wnt target genes. In vivo, RXC004 demonstrated significant efficacy and PD effects in multiple RNF43 mutant and RSPO fusion xenograft models. Focusing on an RSPO fusion model, RXC004 reduced tumour volume in a dose-dependent manner at 1.5 and 5 mg/kg QD, and 1.5mg/kg BID. In addition, 1.5mg/kg BID of RXC004 scheduled 5 days on, 2 days off also gave significant efficacy. PK analysis was consistent with the predicted dose response, showing excellent absorption and tumour distribution. PD analysis confirmed the RXC004-induced Wnt target gene changes identified in vitro translated in vivo, whilst histology showed a clear reduction in the proliferation marker Ki67 and concomitant increase in the staining of Mucins, indicative of mucinous differentiation of the tumour cells. Conclusion: Taken together, these data demonstrate that RXC004 monotherapy has the potential to benefit patients with tumours bearing RNF43 mutations or RSPO fusions, supporting a genetically-defined patient selection strategy for ongoing RXC004 clinical studies. Citation Format: Simon Woodcock, Inder Bhamra, Cliff Jones, Alicia Edmenson Cook, Catherine Eagle, Caroline Phillips. Efficacy of the Wnt/Beta-Catenin pathway inhibitor RXC004 in genetically-defined models of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3874.