Combinations of Salmonella typhimurium A1-R, Recombinant Methioninase, and Chloroquine, Each Targeting Fundamental Cancer Hallmarks, Are Selectively Effective on Colon Cancer Cells Compared to Normal Fibroblasts

Background/Aim: Metastatic colon cancer is a recalcitrant disease. Previous studies have shown efficacy of Salmonella typhimurium A1-R (A1-R), recombinant methioninase (rMETase), and chloroquine (CQ) on cancer cells as they target fundamental hallmarks of cancer. The present study examined these agents alone and all combinations against colon-cancer cells compared to normal fibroblasts. Materials and Methods: The in vitro cytotoxicity and synergy of A1-R, rMETase, and CQ were assessed on the HCT116 colon-cancer cell line and Hs-27 normal fibroblasts. Cell viability was measured using the WST-8 assay. IC30 and IC50 values were determined. Combination treatments were performed at IC30 concentrations to evaluate synergistic efficacy of all combinations of A1-R, rMETase, and CQ on each cell type. Results: A1-R alone and rMETase alone showed significantly higher cytotoxicity on HCT116 cells than on Hs-27 fibroblasts. Combination of A1-R with either rMETase or CQ demonstrated selective cytotoxicity toward HCT116 cells compared to normal Hs-27 fibroblasts. The triple combination selectively eradicated the cancer cells. Conclusion: Tumor-targeting with A1-R combined with methionine restriction (rMETase) or autophagy inhibition (CQ) resulted in selective and synergistic cytotoxicity against colon-cancer cells compared to normal fibroblasts. The present findings support the clinical potential of the combination of A1-R, rMETase, and CQ for recalcitrant colon cancer.