AUTHOR=Chen Yuehua , Su Yuan , Pang Xufeng , Song Xiaoxia , Zhao Wanjun , Yu Mingming 

TITLE=Synthesis and Evaluation of Technetium-99m-Labeled pH (Low) Insertion Peptide Variant 7 for Early Diagnosis of MDA-MB-231 Triple-Negative Breast Cancer by Targeting the Tumor Microenvironment

JOURNAL=Frontiers in Oncology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2022.869260

DOI=10.3389/fonc.2022.869260

ISSN=2234-943X

ABSTRACT=<sec><title>Objective</title><p>To prepare technetium-99m (<sup>99m</sup>Tc)-labeled pH (low) insertion peptide variant 7 [pHLIP (Var7)] and carry out small-animal single-photon-emission computed tomography (SPECT)/computed tomography (CT) imaging of tumor-bearing nude mice <italic>in vivo</italic> to study its value in the early diagnosis of triple-negative breast cancer (TNBC).</p></sec><sec><title>Methods</title><p>The pHLIP (Var7) sequence was synthesized <italic>via</italic> solid-phase peptide synthesis. Four amino acids, Gly-(D)-Ala-Gly-Gly, were attached to the N-terminus of pHLIP (Var7) to form a strong chelating group containing an N4 structure. The peptide was labeled with <sup>99m</sup>Tc using a direct labeling method. We determined the <italic>in vitro</italic> binding fraction of <sup>99m</sup>Tc-pHLIP (Var7) to MDA-MB-231 cells. Serial biodistribution studies and small-animal SPECT/CT imaging in MDA-MB-231 TNBC-bearing mice were performed using <sup>99m</sup>Tc-pHLIP (Var7).</p></sec><sec><title>Results</title><p>The radiochemical yield and purity of <sup>99m</sup>Tc-pHLIP (Var7) were 99.49 ± 0.17% and 99.63 ± 0.44%, respectively. The radiochemical purity was still more than 96% after 24 h in serum. The binding fraction of <sup>99m</sup>Tc-pHLIP (Var7) to MDA-MB-231 cells continuously increased in an acidic environment and was significantly higher than the cell-binding fraction (P &lt; 0.01) at pH = 7.4 and the cell-binding fraction (P &lt; 0.01) of <sup>99m</sup>Tc-kVar7 at different pH values (pH = 6.0, 6.5, 7.0 and 7.4) at each time point (P &lt; 0.01). The distribution of <sup>99m</sup>Tc-pHLIP (Var7) in tumors at each time point was significantly greater than that of <sup>99m</sup>Tc-kVar7 (P &lt; 0.01). SPECT/CT imaging was largely consistent with the biodistribution results; the tumor was clearly imaged at each time point after injection of <sup>99m</sup>Tc-pHLIP (Var7) but could not be imaged after injection of <sup>99m</sup>Tc-kVar7.</p></sec><sec><title>Conclusion</title><p><sup>99m</sup>Tc-pHLIP (Var7) showed a high radiochemical yield and stability and was highly concentrated in tumor tissues. Although there was strong radioactive background in the abdomen of tumor-bearing nude mice, it did not hinder early diagnosis of TNBC.</p></sec>