Purpose

The present study describes the analysis of amino acid transporters ASCT1, ASCT2, LAT1, and x_c⁻ in breast cancer under normoxic and hypoxic conditions. [¹⁸F]FDOPA-PET and [¹⁸F]FSPG-PET were used as imaging biomarkers to probe l-type amino acid transporter (LAT1) and cystine-glutamate antiporter (x_c⁻) in breast cancer models.

Procedures

LAT1 and x_c⁻ transporters were studied under normoxic and hypoxic conditions with radiotracers [¹⁸F]FDOPA and [¹⁸F]FSPG in estrogen receptor–positive (ER+) MCF7 and triple-negative MDA-MB231 cells and in human mammary epithelial MCF10A control cells. Protein expression was analyzed using Western blot and immunohistochemistry.

Results

ASCT1 protein expression levels were comparable in all three cell lines, while noticeable ASCT2 expression levels were only found in MCF10A control cells. Higher LAT1 protein expression was detected in ER+ MCF7 cells. High x_c⁻ protein expression levels were detected in MDA-MB231 cells. Uptake of [¹⁸F]FDOPA through LAT1 was significantly higher in MCF7 versus MDA-MB231 cells, while the uptake of [¹⁸F]FSPG through x_c⁻ resulted in the opposite confirming expression and functional differences for both amino acid transporters in different breast cancer models. Hypoxia significantly increased [¹⁸F]FDOPA uptake in MCF7 cells and [¹⁸F]FSPG uptake in MDA-MB231 cells. In vivo PET imaging revealed substantially higher tumor uptake of [¹⁸F]FDOPA in MCF7 tumors as well as [¹⁸F]FSPG uptake in MDA-MB231 tumors confirming differences detected in vitro.

Conclusions

ER+ breast cancer cells express higher levels of amino acid transporter LAT1, whereas triple-negative breast cancer cells express more x_c⁻. Cellular uptake and PET imaging experiments with [¹⁸F]FDOPA and [¹⁸F]FSPG confirmed functional LAT1 and x_c⁻ expression profiles. There was initial evidence that hypoxia regulates the function of both amino acid transporters in breast cancer. The results further indicated that [¹⁸F]FDOPA and [¹⁸F]FSPG are suitable radiotracer to distinguish between ER+ and triple-negative breast cancer types.

中文翻译：

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L 型氨基酸转运蛋白 (LAT1) 和胱氨酸-谷氨酸逆向转运蛋白 (xc-) 与 [18F]FDOPA 和 [18F]FSPG 在乳腺癌模型中的 PET 成像。

目的

本研究描述了在常氧和缺氧条件下对乳腺癌中氨基酸转运蛋白 ASCT1、ASCT2、LAT1 和 x _c ^{- 的}分析。[ ¹⁸ F]FDOPA-PET 和[ ¹⁸ F]FSPG-PET 被用作成像生物标志物，以探测乳腺癌模型中的l型氨基酸转运蛋白 (LAT1) 和胱氨酸-谷氨酸逆向转运蛋白 (x _c ^- )。

程序

在常氧和缺氧条件下，使用放射性示踪剂 [ ¹⁸ F] FDOPA 和 [ ¹⁸ F] FSPG 在雌激素受体阳性 (ER+) MCF7 和三阴性 MDA-MB231 细胞以及人乳腺上皮 MCF10A 对照中研究LAT1 和 x _c ^-转运蛋白细胞。使用蛋白质印迹和免疫组织化学分析蛋白质表达。

结果

ASCT1 蛋白表达水平在所有三种细胞系中相当，而明显的 ASCT2 表达水平仅在 MCF10A 对照细胞中发现。在 ER+ MCF7 细胞中检测到更高的 LAT1 蛋白表达。在 MDA-MB231 细胞中检测到高 x _c ^-蛋白表达水平。与MDA-MB231 细胞相比，MCF7 通过 LAT1摄取 [ ¹⁸ F]FDOPA 显着更高，而通过 x _c ^-摄取 [ ¹⁸ F] FSPG导致相反，证实了不同乳房中两种氨基酸转运蛋白的表达和功能差异癌症模型。缺氧显着增加 [ ¹⁸ F] FDOPA 在 MCF7 细胞和 [ ¹⁸F] MDA-MB231 细胞中的 FSPG 摄取。体内PET 成像显示MCF7 肿瘤中 [ ¹⁸ F] FDOPA 的肿瘤摄取显着更高，MDA-MB231 肿瘤中的[ ¹⁸ F] FSPG 摄取证实了体外检测到的差异。

结论

ER+ 乳腺癌细胞表达更高水平的氨基酸转运蛋白 LAT1，而三阴性乳腺癌细胞表达更多 x _c ^-。使用[ ¹⁸ F]FDOPA 和[ ¹⁸ F]FSPG 的细胞摄取和PET 成像实验证实了功能性LAT1 和x _c ^-表达谱。有初步证据表明，缺氧可调节乳腺癌中两种氨基酸转运蛋白的功能。结果进一步表明[ ¹⁸ F]FDOPA 和[ ¹⁸ F]FSPG 是区分ER+ 和三阴性乳腺癌类型的合适放射性示踪剂。