An optimized integrin α6-targeted peptide for positron emission tomography/magnetic resonance imaging of pancreatic cancer and its precancerous lesion Dear Editor, Recently, we successfully developed a radiolabeled probe targeting integrin α6 for the positron emission tomography (PET)/magnetic resonance (MR) imaging of pancreatic ductal adenocarcinoma (PDAC) and its precancerous lesion, pancreatic intraepithelial neoplasia (PanIN). Most pancreatic cancers are PDAC. 1 Standard approaches for detecting PDAC at early stage are lacking with most diagnosed patients at advanced stage. 2 Tumortargeted molecular imaging significantly improved the tumor-detection rate, 3 which may also enhance the early diagnosis of PDAC. Considering the genetic complexity of PDAC, a PDAC-specific target with highly adaptability, sensitivity, and specificity is required. We selected integrin α6 as the target of PDAC as it was overexpressed in pancreatic cancer cells 4,5 and cancerous tissue of patients with PDAC 4,6,7 with an overexpression rate up to 92%. 4 Increased integrin α6 levels were associated with stronger PDAC cell invasiveness 5 and poorer prognosis for patients. 6,7 Furthermore, the integrin α6β4 dimer was overexpressed in PanIN even at a stage as early as PanIN 1A. 4 Here, we confirmed that integrin α6 was overexpressed in human PDAC (Figure 1A,B) and increased integrin α6 had poorer prognosis for PDAC patients (Figure 1C). Recently, a peptide CRWYDENAC (dubbed RWY) targeting integrin α6 has been identified 8 and employed for nanotherapeutics of nasopharyngeal carcinoma 8 and for PET imaging of hepatocellular carcinoma by our team. 9 Here, we used the Ala scanning mutagenesis to modify the RWY peptide. R, W, and Y were the three key amino acids within the RWY peptide, since their replacement by an alanine reduced the cellular binding ability of this peptide, both in vitro and in vivo. Interestingly, the alanine substitution of E resulted in the CRWYDANAC (dubbed S5) peptide with an approximately 1.5-fold enhanced tumor binding ability (Figure 1D,E). The This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.