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

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.