Wu FengYu, Chen YueHua, Li DaCheng, Wang ZhenGuang, Yu MingMing
Department of Nuclear Medicine, The Affiliated Hospital of Qingdao University, No.59, Haier St., Laoshan District, Qingdao, 266100, China.
Mol Imaging Biol. 2022 Aug;24(4):570-579. doi: 10.1007/s11307-021-01702-0. Epub 2022 Jan 10.
The pH (low) insertion peptide (pHLIP) family can target the tumor microenvironment (TME). If pHLIP can be labeled with radioiodine, the imaging and treatment of tumors can be considered. However, tyrosine and tryptophan can bind with iodine in the insertion region of pHLIP, and radioiodine labeling may affect the formation of α-helix structures in acidic environments; therefore, it is necessary to adjust the structure of pHLIP. This study aims to develop an I-labeled pH (low) insertion peptide variant 7-like peptide (pHLIP (Var7) LP) for imaging the TME in MDA-MB-231 triple-negative breast cancer (TNBC) xenograft tumor models.
Based on pHLIP (Var7), a new peptide sequence, pHLIP (Var7) LP, was obtained by the sequence modification method and then characterized. The binding of pHLIP (Var7) LP to MDA-MB-231 cells was analyzed. pHLIP (Var7) LP was labeled with I by the iodogen iodination method. Serial biodistribution studies and small-animal single photon emission computed tomography (SPECT)/computed tomography (CT) imaging in subcutaneous MDA-MB-231 TNBC-bearing mice were performed using [I] I-pHLIP (Var7) LP.
A novel peptide, pHLIP (Var7) LP, has the characteristics of an α-helix structure, electronegativity, and amphiphilicity. Circular dichroism (CD) spectroscopy showed that the peptide presented a typical pH-dependent transition from an unstructured conformation to an α-helix structure when the pH was reduced from 8.0 to 4.0. The relative fluorescence intensities of 5-carboxytetramethylrhodamine (5-TAMRA)-pHLIP(var7) LP at pH = 6.0, 6.6, and 7.4 were 100.00 ± 5.98%, 72.10 ± 4.65%, and 13.72 ± 1.41%, respectively. The distribution of [I] I-pHLIP (Var7) LP in tumors reached the highest level (8.7 ± 1.6% ID/g) at 2 h after injection, and the tumor-to-muscle ratios and tumor-to-blood ratios increased with time. Of the measured off-target organs, the stomach, kidney, and bladder showed higher uptake levels. SPECT imaging revealed rapid and sustained tumor uptake of [I] I-pHLIP (Var7) LP in breast cancer-bearing mice.
This study showed that [I]I-pHLIP (Var7)LP had rapid and sustained tumor uptake in MDA-MB-231 TNBC and provided a new method for TNBC imaging and further treatment.
pH（低）插入肽（pHLIP）家族可靶向肿瘤微环境（TME）。若pHLIP能用放射性碘标记，则可考虑用于肿瘤的成像和治疗。然而，酪氨酸和色氨酸可在pHLIP的插入区域与碘结合，放射性碘标记可能会影响其在酸性环境中α-螺旋结构的形成；因此，有必要调整pHLIP的结构。本研究旨在开发一种用于在MDA-MB-231三阴性乳腺癌（TNBC）异种移植瘤模型中对TME进行成像的碘标记pH（低）插入肽变体7样肽（pHLIP（Var7）LP）。
基于pHLIP（Var7），通过序列修饰方法获得了一个新的肽序列pHLIP（Var7）LP，然后对其进行表征。分析了pHLIP（Var7）LP与MDA-MB-231细胞的结合情况。采用碘珠碘化法用碘对pHLIP（Var7）LP进行标记。使用[碘-125]碘-pHLIP（Var7）LP在皮下接种MDA-MB-231 TNBC的小鼠中进行了系列生物分布研究和小动物单光子发射计算机断层扫描（SPECT）/计算机断层扫描（CT）成像。
一种新型肽pHLIP（Var7）LP具有α-螺旋结构、电负性和两亲性的特点。圆二色性（CD）光谱表明，当pH从8.0降至4.0时，该肽呈现出从无结构构象到α-螺旋结构的典型pH依赖性转变。5-羧基四甲基罗丹明（5-TAMRA）-pHLIP（var7）LP在pH = 6.0、6.6和7.4时的相对荧光强度分别为100.00 ± 5.98%、72.10 ± 4.65%和13.72 ± 1.41%。[碘-125]碘-pHLIP（Var7）LP在注射后2小时在肿瘤中的分布达到最高水平（8.7 ± 1.6% ID/g），肿瘤与肌肉的比值和肿瘤与血液的比值随时间增加。在所测量的非靶器官中，胃、肾和膀胱显示出较高的摄取水平。SPECT成像显示[碘-125]碘-pHLIP（Var7）LP在荷乳腺癌小鼠的肿瘤中摄取迅速且持续。
本研究表明，[碘-125]碘-pHLIP（Var7）LP在MDA-MB-231 TNBC中对肿瘤的摄取迅速且持续，为TNBC成像及进一步治疗提供了一种新方法。
