The present disclosure generally relates to a circularized peptide for treating cancer. An cyclic peptide is disclosed that has an amino acid sequence selected from Lys-X5-Glu-X1-X2-Gln-Met-Glu-Asp-Asp-X3-X4 (SEQ ID NO: 3), (SEQ ID NO: 4), Lys-Gly-X6-Val-Leu-Gln-Met-X7-X8-X9-Leu-Val (SEQ ID NO: 5), Lys-X5-Glu-X1-X2-Gln-X12-Glu-Asp-Asp-X3-X4 (SEQ ID NO: 9), and X10-X5-X6-Val-Leu-Gln-Met-Glu-Asp-X9-X3-X4 (SEQ ID NO: 10). The amino acids X1, X2, X3, and X4 can be each independently valine, leucine, isoleucine, or alanine； X5 can be glycine, alanine, leucine, isoleucine, or valine； X6, X7, X8, and X9 can be each independently glutamic acid or asparagine； X10 can be lysine or arginine； X11 can be methionine or cysteine； and X12 can be methionine or norleucine. The cyclic peptide can have the amino acid sequence Lys-Gly-Glu-Val-Leu-Gln-Met-Glu-Asp-Asp-Leu-Val (SEQ ID NO: 1).
