Identification of RSPO2 Fusion Mutations and Target Therapy Using a Porcupine Inhibitor.

Cancers are driven by a variety of somatic gene mutations and identifying these mutations enables the development of novel target drugs. We have sought to identify abnormalities in Wnt pathway-related genes that are sensitive to Wnt inhibitor treatment. We examined Patient Derived Xenograft (PDX) RNA samples and found new R-Spondin 2 (RSPO2) transcript fusions with the EMC2, PVT1 or HNF4G genes. These fusion events were identified in about 1.4% of the digestive system cancer samples. We then examined the oncogenic effects of the RSPO2-EMC2 fusion gene and confirmed that it can drive oncogenesis, sustain tumor growth and promote metastasis. Finally, we used a Wnt pathway Porcupine inhibitor CGX1321 to treat PDX mouse models containing RSPO2 fusion genes. All the RSPO2 fusion tumors responded to the treatment and stopped progression. Our data show that Wnt pathway inhibition could provide an effective treatment for cancers containing RSPO2 fusion. The RSPO2 fusion will serve as a good biomarker for screening patients to support clinical treatment of digestive system cancers using Wnt pathway inhibitors.