肿瘤显像剂S^11C-甲基-L-半胱氨酸的细胞摄取机制研究

Mechanism in cellular uptake of S-UC-methyl-L-cysteine as a tumor imaging agent

目的探讨肿瘤细胞摄取S^11C-甲基-L-半胱氨酸（^11C-MCYS）的机制。方法将Hepal-6肝癌细胞分为Na^＋依赖组（NaCl组）及非Na^＋依赖组（氯化胆碱组）进行氨基酸转运实验。每组又分为对照组、L-氨基酸转运载体抑制剂2-氨基二环．2，2，1-庚烷-2-羧酸（BCH）组、转运系统A和ASC的抑制剂α-甲基-氨基异丁酸（MeAIB）组、MeAIB＋丝氨酸组，分别加入^11C-MCYS（400μl0．925MBq／ml）、^11C—MCYS（200μl1．85MBq／ml）＋阻滞剂BCH（200μl 15mmol／L）、^11C-MCYS（200μl1．85MBq／ml）＋阻滞剂MeAIB（200Ixl15mmol／L）以及“C．MCYS（200斗11．85MBq／ml）＋阻滞剂MeAIB＋丝氨酸（200斗l15mmol／L）。作用4min后终止培养应用1计数仪测量细胞放射性活度。将Hepal一6肝癌细胞分为5组，各组均加入200μl^11C—MCYS（1．85MBq／ml）后分别加入50、100、200、300、350μmol／L浓度不等的MCYS进行竞争抑制实验。培养4min后终止培养应用γ计数仪测量细胞放射性活度。结果无论是否有Na^＋存在，对照组、BCH组、MeAIB及MeAIB＋丝氨酸组对^11C—MCYS摄取的差异均无统计学意义（均P〉0．05）。MeAIB组和MeAIB＋丝氨酸组中的NaCl组细胞放射性活性与氯化胆碱组相比差异均无统计学意义（18958．18±97．32比20582．27±196．32，18385．24±122．96比21620比±131．41，均P〉0．05），两者均不能抑制Na^＋非依赖性氨基酸转运载体的转运。而BCH组中的NaCl组细胞放射性活性高于氯化胆碱组（2587．21±＋30．25比2340．61±21．09，P〈0．05），可见BCH能明显抑制Na^＋非依赖性氨基酸转运体对^11C-MCYS的转运。不同浓度MCYS（50～350μmol／L）作用下肿瘤细胞对^11C-MCYS摄取差异无统计学意义（均P〉0．05）。结论肿瘤细胞摄取^11C-MCYS是通过非Na^＋依赖的L-氨基酸转运系统进行转运的，极少涉及氨基酸转运系统A和ASC。

Objective To investigate the mechanism in uptake of S-11C-methyl-L-cysteine（11C- MCYS） by tumor cells. Methods Hepal-6 cells were divided into Na^＋ dependent （NaC1 group） and non- Na^＋ dependent （choline chloride group） groups for amino acids transport experiment. The two groups were then divided into control group, 2′-aminobicyclo（2, 2, 1） - heptane-2′-carboxylic acid （BCH, L-amino acid transporter inhibitor） , N-methylamino-isobutyric acid （MeAIB, transport system inhibitor of A and ASC） and MeAIB＋serine groups. All the groups were added with ^11C-MCYS （400 μl 0.925 MBq/ml）, HC- MCYS（200 μl 1.85 MBq/ml）＋ BCH（200 μl 15 mmol/L）, ^11C-MCYS（200 μl 1.85 MBq/ml）＋ MeAIB（200 μl 15 mmol/L）, ^11C-MCYS（200 μl 1.85 MBq/ml）＋ MeAIB＋serine（200 μl 15 mmol/L） respectively. After 4 min, the incubation was discontinued, and the cell radioactivity was measured with γ counter. Thereafter,Hepa 1-6 cells were classified into five groups which were added with 200 μl ^11C-MCYS （1.85 MBq/ml）and then different concentrations of MCYS （50, 100, 200, 300, 350 μmol/L） for a competitive inhibition experiment. γcounter was used to measure the radioactivity at 4 mins after incubation. Results There were no significant differences in uptake of ^11C- MCYS by control, BCH, MeAIB and MeAIB＋serine groups with or without the presence of Na ^＋ （P〉0.05）. In MeAIB and MeAIB ＋ serine groups, the NaCl and choline chloride sub- groups showed no significant differences in radioactivity （18 958.18±97.32 vs 20 582.27± 196.32, 18 385.24 ± 122.96 vs 21 620.54 ± 131.41, both P〉0.05） and could not inhibit the transportation of non-Na^＋ dependent amino acid carrier. However in BCH group, the radioactivity in NaCl group was higher than that in choline chloride group （2587.21± 30.25 vs 2340.61 ±21.09, P〈0.05）. Thus, BCH could significantly inhibit the transportation of ^11C-MCYS by non-Na^＋ dependent amino acid carrier. No significant differences were found in uptake of ^11C-MCYS by tumor cells under different concentrations of MCYS（50 - 350 μmol/L） （all P〉0.05）. Conclusion The uptake of nC-MCYS is the result of transportation through non- Na^＋ dependent L-amino acid transport system, with minimal involvement of amino acid transport system A and ASC.