Abstract
Anti-programmed cell death 1 (aPD1) therapy has yielded limited success in patients with colorectal cancer (CRC). Syndecan binding protein (SDCBP), encodes a PDZ domain-containing protein that is essential for cellular processes, including cell adhesion, migration, and signal transduction. Here, we investigated the effect of SDCBP on tumor progression, immunotherapy, and the tumor microenvironment (TME) in CRC. High expression of SDCBP is associated with non-response to immunotherapy and correlated with poorer disease-free survival (DFS) in CRC patients. Inhibiting SDCBP by transfecting shRNA or using its inhibitor zinc pyrithione (ZnPT) hindered proliferation and metastasis while enhancing the efficacy of aPD1 treatment in a mouse xenograft model and liver metastasis model. The TME of CRC was significantly altered following ZnPT treatment characterized by a reduced amount of M2 macrophages and a heightened percentage of M1 macrophages. The co-culture system of CRC cells and macrophages provided evidence that SDCBP silencing promoted the repolarisation of M2 macrophages into M1. SDCBP promotes the proliferation, metastasis, and immunotherapy resistance of CRC. Thus, ZnPT represents an effective SDCBP inhibitor and exhibits considerable potential for combination with aPD1 to enhance immunotherapy efficacy.