The anti-CEACAM1 agonistic antibody CCM5.01 inhibits colon cancer cell lines growth in 2D and 3D models.

Abstract Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a transmembrane glycoprotein that functions as an inhibitory receptor (IR). CEACAM1 is expressed on various normal and tumor cells, which exploit these IRs to suppress immune cell-mediated anti-tumor immunity via heterophilic interactions. CEACAM1 exists in two main isoforms: CEACAM1-Long (L), which contains two immune receptor tyrosine-based inhibitory motifs (ITIMs) and mediates inhibition, and CEACAM1-Short (S), lacking any signal transduction motifs; the function of S remains unclear. Previously, we developed an agonistic anti-CEACAM1 monoclonal antibody (mAb), CCM5.01, and evaluated its binding and inhibitory effects on melanoma cells in vitro and in vivo. In this study, we examined the function of CCM5.01 on CEACAM1-expressing human colon cancer cell lines in vitro (MTT) and analyzed its isoform ratio (RT-PCR). Then, we transfected HT-29 cells with either L or S expression vectors to assess their individual responses to CCM5.01. Our results revealed that following activation by CCM5.01, CEACAM1-L induced phosphorylation of SHP1, p53, and activation of caspase-3, namely cell inhibition, while CEACAM1-S exhibited an activating cell response. Similar outcomes were observed in 3D spheroid models. Our findings suggest that targeting CEACAM1 on colon cancer cells may be a promising strategy for colon cancer treatment.