Center for Radiopharmaceutical Science ETH-PSI-USZ, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
Mol Pharm. 2010 Apr 5;7(2):597-604. doi: 10.1021/mp900296k.
Administration of certain antifolates before radiofolate application has previously proven to have a positive effect on undesired kidney uptake of radiofolates in mice bearing human tumor xenografts. The aims of this study were to (i) test the effects of the antifolates, pemetrexed and CB3717, on tissue distribution of the clinically investigated radiofolate, (99m)Tc-EC20, and (ii) to determine if pemetrexed's kidney-selective blocking effect also functions in mice bearing syngeneic tumors. Relative binding affinities of pemetrexed and CB3717 were determined in folate receptor (FR)-positive KB cells at 0 and 37 degrees C using (3)H-folic acid. In vivo studies were performed in nude mice with KB tumor xenografts (A) and in Balb/c mice bearing FR-positive M109 tumor grafts (B). (99m)Tc-EC20 was prepared via a kit formulation. The antifolates pemetrexed and CB3717 (20 mumol/kg body weight) were administered intravenously 1 h before injection of (99m)Tc-EC20 (67 nmol/kg body weight). Similar to previously published data we found that FR-binding affinities of pemetrexed and CB3717 at 0 degrees C were in the same range as that of folic acid. Interestingly, experiments performed at 37 degrees C showed that pemetrexed has a nearly approximately 700-fold lower FR-affinity than CB3717. Tissue distribution of (99m)Tc-EC20 was largely comparable in both animal models (A and B). Radiofolate accumulation was found in FR-positive tumors (A, 8.92 +/- 2.14% ID/g; B, 15.02 +/- 0.95% ID/g) and FR-positive kidneys (A, 59.10 +/- 8.03% ID/g; B, 69.44 +/- 4.66% ID/g, 4 h p.i.). Preinjection of pemetrexed resulted in a significant decrease of (99m)Tc-EC20 uptake in kidney (A, 18.80 +/- 2.73% ID/g; B, 15.27 +/- 2.64% ID/g; 4 h p.i), whereas uptake in the tumors was unaltered. However, administration of the CB3717 resulted in a reduction of (99m)Tc-EC20 uptake in both the kidney and tumor (<1% ID/g, 4 h p.i.). We have thus demonstrated that pemetrexed effectively reduces kidney uptake of radiofolates not only in xenografted mice but also in a syngeneic tumor mouse model, thereby indicating that the kidney-specific blocking effect is not based on differences between human and murine FRs that are expressed in xenografts and kidneys, respectively. This effect was not observed with the antifolate, CB3717, which targets the FR selectively in contrast to pemetrexed that is predominantly transported into cells through carrier systems.
Administration of certain antifolates before radiofolate application has previously proven to have a positive effect on undesired kidney uptake of radiofolates in mice bearing human tumor xenografts. 预先给予某些抗叶酸药物，然后再给予放射性叶酸，先前已被证明可对荷有人源肿瘤异种移植物的小鼠体内放射性叶酸的非预期肾脏摄取产生积极影响。
The aims of this study were to (i) test the effects of the antifolates, pemetrexed and CB3717, on tissue distribution of the clinically investigated radiofolate, (99m)Tc-EC20, and (ii) to determine if pemetrexed's kidney -selective blocking effect also functions in mice bearing syngeneic tumors. 本研究的目的是：（i）检测抗叶酸药物培美曲塞和 CB3717 对临床研究的放射性叶酸（99mTc-EC20）的组织分布的影响，以及（ii）确定培美曲塞的肾脏选择性阻断作用在荷有同源肿瘤的小鼠中是否同样起作用。
Relative binding affinities of pemetrexed and CB3717 were determined in folate receptor (FR)-positive KB cells at 0 and 37 degrees C using (3)H-folic acid. 采用（3）H-叶酸，在 0 和 37°C 下，在叶酸受体（FR）阳性的 KB 细胞中测定培美曲塞和 CB3717 的相对结合亲和力。
In vivo studies were performed in nude mice with KB tumor xenografts (A) and in Balb/c mice bearing FR -positive M109 tumor grafts (B). （99m）Tc-EC20 是通过试剂盒制剂制备的。在荷有 KB 肿瘤异种移植物的裸鼠（A）和荷有 FR 阳性 M109 肿瘤移植物的 Balb/c 小鼠（B）中进行体内研究。
(99m)Tc-EC20 was prepared via a kit formulation. The antifolates pemetrexed and CB3717 (20 mumol/kg body weight) were administered intravenously 1 h before injection of (99m)Tc-EC20 (67 nmol/kg body weight). （99m）Tc-EC20 通过试剂盒制剂制备。在注射（99m）Tc-EC20（67 nmol/kg 体重）前 1 小时，经静脉给予抗叶酸药物培美曲塞和 CB3717（20 mumol/kg 体重）。
Similar to previously published data we found that FR -binding affinities of pemetrexed and CB3717 at 0 degrees C were in the same range as that of folic acid. 与先前发表的数据相似，我们发现培美曲塞和 CB3717 在 0°C 时的 FR 结合亲和力与叶酸的亲和力相同。
Interestingly, experiments performed at 37 degrees C showed that pemetrexed has a nearly approximately 700 -fold lower FR -affinity than CB3717. 有趣的是，在 37°C 下进行的实验表明，培美曲塞的 FR 亲和力比 CB3717 低近 700 倍。
Tissue distribution of (99m)Tc-EC20 was largely comparable in both animal models (A and B). （99m）Tc-EC20 的组织分布在两种动物模型（A 和 B）中基本相当。
Radiofolate accumulation was found in FR -positive tumors (A, 8.92 +/- 2.14% ID/g; B, 15.02 +/- 0.95% ID/g) and FR -positive kidneys (A, 59.10 +/- 8.03% ID/g; B, 69.44 +/- 4.66% ID/g, 4 h p.i.). 放射性叶酸在 FR 阳性肿瘤（A，8.92 ± 2.14% ID/g；B，15.02 ± 0.95% ID/g）和 FR 阳性肾脏（A，59.10 ± 8.03% ID/g；B，69.44 ± 4.66% ID/g，4 h p.i.）中积累。
Preinjection of pemetrexed resulted in a significant decrease of (99m)Tc-EC20 uptake in kidney (A, 18.80 +/- 2.73% ID/g; B, 15.27 +/- 2.64% ID/g; 4 h p.i), whereas uptake in the tumors was unaltered. 预先给予培美曲塞可导致肾脏摄取（99m）Tc-EC20 显著减少（A，18.80 ± 2.73% ID/g；B，15.27 ± 2.64% ID/g；4 h p.i.），而肿瘤摄取则不变。
However, administration of the CB3717 resulted in a reduction of (99m)Tc-EC20 uptake in both the kidney and tumor (<1% ID/g, 4 h p.i.). 然而，给予 CB3717 可导致肾脏和肿瘤摄取（99m）Tc-EC20 减少（<1% ID/g，4 h p.i.）。
We have thus demonstrated that pemetrexed effectively reduces kidney uptake of radiofolates not only in xenografted mice but also in a syngeneic tumor mouse model, thereby indicating that the kidney -specific blocking effect is not based on differences between human and murine FRs that are expressed in xenografts and kidneys, respectively. 因此，我们证明了培美曲塞不仅可有效降低异种移植小鼠体内放射性叶酸的肾脏摄取，而且还可降低同源肿瘤小鼠模型中放射性叶酸的肾脏摄取，这表明肾脏特异性阻断作用不是基于分别在异种移植物和肾脏中表达的人源和鼠源 FR 之间的差异。
This effect was not observed with the antifolate, CB3717, which targets the FR selectively in contrast to pemetrexed that is predominantly transported into cells through carrier systems. 这种作用在抗叶酸药物 CB3717 中未观察到，与培美曲塞不同，CB3717 特异性靶向 FR，而培美曲塞主要通过载体系统进入细胞。
