Small Animal Positron Emission Tomography Imaging of a Triple-Negative Breast Cancer Model Using the ⁶⁸ Ga-Labeled pH (Low) Insertion Peptide-Like Peptide YJL-11

<b><i>Objectives:</i></b> To prepare a novel ⁶⁸Ga-labeled pH (low) insertion peptide-like peptide, YJL-11, and study its ability to be used as a probe for the diagnosis of triple-negative breast cancer (TNBC) via <i>in vivo</i> imaging of tumor-bearing nude mice. <b><i>Methods:</i></b> Circular dichroism (CD) analysis of YJL-11 was performed to assess its secondary structure. YJL-11 was labeled with ⁶⁸Ga, and the <i>in vivo</i> biodistribution of ⁶⁸Ga-YJL-11 in MDA-MB-231 xenograft mice was evaluated. This probe was then applied for small animal positron emission tomography (PET) imaging of tumor-bearing nude mice. <b><i>Results:</i></b> CD analysis of YJL-11 confirmed a typical pH-dependent transition in its secondary structure. The radiochemical yield of ⁶⁸Ga-YJL-11 was 75.5 ± 0.25%, and the radiochemical purity was 95.75 ± 0.15%. Biodistribution studies showed that the tumor uptake of ⁶⁸Ga-YJL-11 was significantly higher than in the control group, 1 and 2 h after injection. Small animal PET imaging results were consistent with the biodistribution data, showing clear images of the tumors and livers 1 and 2 h after injection of ⁶⁸Ga-YJL-11, whereas tumors were not detected in the control group. <b><i>Conclusion:</i></b> ⁶⁸Ga-YJL-11 was prepared with high radiochemical yield and can target TNBC tissues, indicating that it has great potential in the diagnosis of TNBC.