Fusion peptides and methods of inhibiting GrB-EHITSN or a fragment thereof are provided. The fusion peptides include an NPF peptide and a cell-permeable peptide operably connected thereto. Fusion peptides and methods of inhibiting activity of GrB-EHITSN or fragment thereof are provided. An aspect includes a fusion peptide comprising an isolated NPF peptide comprising an amino acid sequence having at least 90% identity to SEQ ID NO: 2 and a cell-permeable peptide operably connected to the isolated NPF peptide, wherein the fusion peptide inhibits activity of GrB-EHITSN or a fragment thereof.