Evaluating pH in the Extracellular Tumor Microenvironment Using CEST MRI and Other Imaging Methods

Figure 6

PET imaging of tumor pHe. (a) A pHLIP peptide inserts into cell membranes in low pHe conditions. (b) PET imaging of ⁶⁴Cu-DOTA-pHLIP showed higher uptake and retention in a subcutaneous mouse model of LNCaP relative to PC-3, indicating that the LNCaP tumor model had lower pHe. MR spectroscopy confirmed that the average pHe values of the LNCap and PC-3 tumor models were 6.78 ± 0.29 and 7.23 ± 0.10, respectively. White circles show the locations of the subcutaneous tumors. (c) A membrane-insertion of a variation of pHLIP shows a sigmoidal dependence on pH. Reproduced with permission from [22–24].

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