Brefeldin A: a Newly Identified Cell Death Inducer Selectively Targets Radio-Resistant Colorectal Cancer Cells by Direct Interacting with Caspase-3

Colorectal cancer is one of the most occurring cancers and is a cause of many deaths worldwide. Treatment of cancer is much dependent on the stage of the disease. The patients at the late stages of colorectal cancer show a very low rate of survival (about 10%). One of the challenges for successful treatment is the resistance to radiotherapy, which is a common intervention in combination with chemotherapy. In this study, we screened a panel of natural products aiming to identify small molecules that selectively kill radio-resistant colon cancer cells. For this, we established a radio-resistant colorectal cancer cell model which displayed overexpression of AMPK and TPP1, two markers of radio-resistant. We showed that these cells are resistant to radiation at doses as high as 12 Gy. The library was screened by measuring the caspase-3 activity. The hit compounds were then tested in cell death assay and titrated to calculate their potency and efficacy. Those compounds with the highest ability to kill radio-resistant HCT116 cells were then tested on radio-sensitive cells. We identified Brefeldin A as a potent inducer of death in radio-resistant cells. Brefeldin A induced death in 90% of radio-resistant cells while it affects 40% of the sensitive cells. Brefeldin A targeted radio-resistant colorectal cancer cells by apoptosis and necrosis. We showed that Brefeldin A directly interacts to caspase-3 but not caspase-9 and -6. Brefeldin A didn’t alter the transcription of apoptotic components. This finding opens new windows toward the treatment of resistant colon tumors and re-sensitizing them for adjuvant therapeutic approaches.