Colorectal cancer (CRC) affects the population worldwide, occupying the first place in terms of death and incidence. Synthetic peptides (SPs) emerged as alternative molecules due to their activity and low toxicity. Proteomic analysis of PepGAT-treated HCT-116 cells revealed a decreased abundance of proteins involved in ROS metabolism and energetic metabolisms, cell cycle, DNA repair, migration, invasion, cancer aggressiveness, and proteins involved in resistance to 5-FU. PepGAT induced earlier ROS and apoptosis in HCT-116 cells, cell cycle arrest, and inhibited HCT-116 migration. PepGAT enhances the action of 5-FU against HCT-116 cells by dropping down 6-fold the 5-FU toward HCT-116 and reduces its toxicity for non-cancerous cells. These findings strongly suggest the multiple mechanisms of action displayed by PepGAT against CRC cells and its potential to either be studied alone or in combination with 5-FU to develop new studies against CRC and might develop new drugs against it.