Targeting MAPK14 by lobeline upregulates Slurp1-mediated inhibition of alternative activation of TAM and retards colorectal cancer growth
Colorectal cancer often produces an immunosuppressive microenvironment, which prevents them from responding to immunotherapy. Effective treatment options have not been found yet. Here, based on the observation that Lobeline, an alkaloid from the herbal medicine Lobelia Chinensis, inhibited tumor in MC38 colon cancer xenograft mouse model. We performed single-cell transcriptome sequencing analysis of Lobeline and PBS-treated tumors in mice, and found that Lobeline promoted TAM polarization towards M1-like while inhibited its polarization towards M2-like. In addition, Lobeline upregulated the mRNA level of secreted Ly-6/UPAR-related protein 1 (Slurp1) in cancer cells. The inhibitory effect of Lobeline on tumor load and regulation of TAM polarization disappeard in Slurp1-/- mice or WT mice injected with Slurp1 knockdown adenovirus, suggesting that Slurp1 mediates the process of Lobeline regulates TAM polarization and inhibits tumor progression. Through target responsive accessibility profiling (TRAP), isothermal titration calorimetry (ITC) and microcalorimetric mobility shift assay (MST), we demonstrated that MAPK14 was the target protein of Lobeline. At the mechanistic level, upon binding to MAPK14 in colon cancer cells, Lobeline prevented the nuclear translocation of MAPK14, which decreases the level of phosphorylated p53. Subsequently, the negative transcriptional regulation of Slurp1 by p53 was inhibited, that facilitated the transcription and secretion of Slurp1. Furthermore, the combination of Lobeline and PD-1 antibody showed stronger anti-tumor effect. Thus, these findings suggested that the Lobeline-mediated anti-tumor immune activation might be a promising therapeutic strategy for colorectal cancer. Overall design: scRNA-seq profiling of total tumor cells in MC38 mouse transplanted tumor.