Abstract
1414
Objectives: Low pH inserted peptide (pHLIP) can cross tumor cell membrane in the extracellular acidic microenvironment, which makes it a potential carrier for anti-tumor drug. However, few studies have been reported for longtermly monitoring in vivo distribution of pHLIP. In our study, highly stabilized near-infrared fluorescence was labeled onto pHLIP for analyzing its dynamic distribution in the transplanted breast tumors during 7 days p.i.
Methods: The red fluorescent dye Rhodamine B and near-infrared fluorescent dye Cy5 (Cy5-pHLIP) were respectively labeled at the hydroxyl terminal of pHLIP for imaging in vitro and in vivo. The fluorescent intensity in the MDA-MB-231 cells and cell vitality were analyzed under the different pH values. In vivo dynamic fluorescent intensities in the regions of interesting of tumor and normal organs were calculated, and then fluorescence imaging of the isolated tissues was finally performed.
Results: Fluorescent intensity in the MDA-MB-231 cells was highest at pH 6.6 (100 ± 9.7%), and 69.9 ± 5.5%, 19.8 ± 1.4%, 0.4 ± 0.04% at pH 7.0, 7.4 and 7.8 (P < 0.05). pHLIP has no significant toxic effect on cell vitality. After Cy5-pHLIP injection, the fluorescent intensity of tumor gradually decreased, but the tumor-to-background ratios were stable (3.42 ± 0.27, 3.00 ± 1.23, 3.38 ± 0.62, and 3.51 ± 0.37 at 2 h, 24 h, 72 h, and 7 days) (Fig. 1A). Besides the urinary collection system, the large intestine physiologically secreted a large amount of pHLIPs (Fig.1B).
Conclusions: Cy5-labeled pHLIP could longtermly and stably imaging the accumulation of pHLIP in the transplanted breast tumor, which provides an alternative method for in vivo monitoring pHLIP as a drug carrier. However, high secretion of pHLIP in the large intestine increased the interpretation complexity of tumor imaging.
