(111) designed a hexapeptide based on the combination of AGR2 with the largest subunit of RNA Polymerase II (RNAPII) in a peptide motif dependent manner, which interfered with RNAPII by competitively destroying the AGR2-RNAPII complex, leading to RNAPII dysfunction and accompanied by the activation of DNA damage response in early tumor lesions, and proved to be effective in the treatment of breast cancer. Here, AGR2 is linked to breast cancer.