An Experimental Study on [(125)I]I-pHLIP (Var7) for SPECT/CT Imaging of an MDA-MB-231 Triple-Negative Breast Cancer Mouse Model by Targeting the Tumor Microenvironment

OBJECTIVE: To evaluate the diagnostic efficacy of MDA-MB-231 triple-negative breast cancer with (125)I-labeled pHLIP (Var7) by single-photon emission computed tomography/computed tomography (SPECT/CT) imaging. METHODS: The binding fraction of [(125)I]I-pHLIP (Var7) and MDA-MB-231 cells was measured at pH 7.4 and pH 6.0, and tumor-bearing mice were subjected to small-animal SPECT/CT imaging studies. RESULTS: At pH = 6.0, the binding fractions of [(125)I]I-pHLIP (Var7) and MDA-MB-231 cells at 10 min, 40 min, 1 h, and 2 h were 1.9 ± 0.1%, 3.5 ± 0.1%, 6.3 ± 0.8%, and 6.6 ± 0.3%, respectively. At pH = 7.4, there was no measured binding between [(125)I]I-pHLIP (Var7) and MDA-MB-231 cells. Small-animal SPECT/CT imaging showed clearly visible tumors at 1 and 2 h after injection. CONCLUSIONS: [(125)I]I-pHLIP (Var7) could bind to MDA-MB-231 cells in an acidic environment, and small-animal SPECT/CT imaging showed clear tumors at 1 and 2 h after probe injection.