We previously found that the K-Ras(G12D)-inhibitory bicyclic peptide KS-58 exhibits antitumor activity against syngeneic colon and orthotopic grafted pancreatic tumors; however, pristine KS-58 is difficult to handle because of low water solubility and it requires frequent administration to obtain sufficient antitumor activity. The gene discussed is KRAS; the disease is pancreatic neoplasm.