Purpose. Extracellular acidity is a marker of highly aggressive breast cancer (BC). pH-low insertion peptides (pHLIPs) target the acidic tumor microenvironment. This study evaluates the distribution and therapeutic efficacy of radioiodine-labeled pHLIP variant 3 (Var3) in a mouse model of BC. Methods. The binding of fluorescein isothiocyanate (FITC)- or radioiodine-125 (¹²⁵I) labeled Var3-pHLIP to MDA-MB-231, 4T1, and SK-BR-3 BC cell lines under different pH values was evaluated in vitro. The distribution of ¹²⁵I-labeled Var3-pHLIP and wild-type- (WT-) pHLIP in tumor-bearing mice was analyzed in vivo using micro-SPECT/CT imaging. The therapeutic efficacy of radioiodine-131 (¹³¹I)-labeled Var3-pHLIP in MDA-MB-231 xenografts was evaluated by relative tumor volume measurement and immunohistochemical analysis. Results. The binding ability of FITC- or ¹²⁵I-labeled Var3-pHLIP to tumor cells increased with the decrease in pH. The tumor-to-background ratio of ¹²⁵I-Var3-pHLIP in BC xenografts showed the best imaging contrast at 24 h or 48 h postinjection. The uptake of ¹²⁵I-Var3-pHLIP in MDA-MB-231 xenografts at 2 h postinjection was significantly higher than that of ¹²⁵I-WT-pHLIP ( vs. %ID/g, ). The relative tumor volume in MDA-MB-231 xenografts was significantly lower in the ¹³¹I-Var3-pHLIP-treated group than in the groups treated with Var3-pHLIP (), ¹³¹I (), and saline (). The ¹³¹I-Var 3-pHLIP group presented a lower expression of Ki67 and a higher expression of caspase 3. Conclusion. Radioiodine-labeled Var3-pHLIP effectively targeted BC cells in an acidic environment and inhibited the growth of MDA-MB-231 xenografts by ionizing radiation.

中文翻译：

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放射性碘标记的 pH 低插入肽变体 3 在乳腺癌小鼠模型中的体内分布和治疗效果

目的。细胞外酸度是高度侵袭性乳腺癌 (BC) 的标志。低 pH 插入肽 (pHLIP) 靶向酸性肿瘤微环境。本研究评估了放射性碘标记的 pHLIP 变体 3 (Var3) 在 BC 小鼠模型中的分布和治疗效果。方法。在体外评估了不同 pH 值下异硫氰酸荧光素 (FITC) 或放射性碘 125 ( ¹²⁵ I) 标记的 Var3-pHLIP 与 MDA-MB-231、4T1 和 SK-BR-3 BC 细胞系的结合。使用 micro-SPECT/CT 成像在体内分析了¹²⁵ I 标记的 Var3-pHLIP 和野生型 (WT-) pHLIP 在荷瘤小鼠中的分布。放射性碘131（¹³¹通过相对肿瘤体积测量和免疫组织化学分析评估 MDA-MB-231 异种移植物中 I) 标记的 Var3-pHLIP。结果。FITC 或¹²⁵ I 标记的 Var3-pHLIP 与肿瘤细胞的结合能力随着 pH 值的降低而增加。^{BC 异种移植物中125} I-Var3-pHLIP的肿瘤与背景比在注射后 24 小时或 48 小时显示出最佳的成像对比度。^{MDA-MB-231 异种移植物注射后 2 h 对125} I-Var3-pHLIP的摄取显着高于¹²⁵ I-WT-pHLIP (对比%ID/克，）。MDA-MB-231 异种移植物中的相对肿瘤体积在¹³¹ I-Var3-pHLIP 治疗组中显着低于 Var3-pHLIP 治疗组（), ¹³¹我 ()和生理盐水 (）。¹³¹ I-Var 3-pHLIP组Ki67表达较低，caspase 3表达较高。结论。放射性碘标记的 Var3-pHLIP 在酸性环境中有效靶向 BC 细胞，并通过电离辐射抑制 MDA-MB-231 异种移植物的生长。