Kapoor Vaishali, Dadey David Y A, Nguyen Kim, Wildman Scott A, Hoye Kelly, Khudanyan Arpine, Bandara Nilantha, Rogers Buck E, Thotala Dinesh, Hallahan Dennis E
Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri.
Medical Scientist Training Program, Washington University in St. Louis, St. Louis, Missouri.
J Nucl Med. 2016 Dec;57(12):1991-1997. doi: 10.2967/jnumed.115.165118. Epub 2016 Jul 21.
Cancer-specific targeting sparing normal tissues would significantly enhance cancer therapy outcomes and reduce cancer-related mortality. One approach is to target receptors or molecules that are specifically expressed on cancer cells. Peptides as cancer-specific targeting agents offer advantages such as ease of synthesis, low antigenicity, and enhanced diffusion into tissues. Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum stress chaperone that regulates the unfolded protein response and is overexpressed in various cancers. In this study, we evaluated GIRLRG peptide that specifically targets GRP78 for cancer-specific binding (in vitro) and noninvasive tumor imaging (in vivo).
GIRLRG peptide was modeled into the GRP78 ATPase domain using computational modeling. Surface plasmon resonance studies were performed to determine the affinity of GIRLRG peptide to GRP78 protein. GIRLRG was conjugated with PEG to prolong its circulation in mice. Tumor binding efficacy of PEG-GIRLRG peptide was evaluated in nude mice bearing heterotopic cervical (HT3), esophageal (OE33), pancreatic (BXPC3), lung (A549), and glioma (D54) tumors. Nano-SPECT/CT imaging of the mice was performed 48 and 72 h after injection with In-labeled PEG-GIRLRG or PEG-control peptide. Post-SPECT biodistribution studies were performed 96 h after injection of the radiolabeled peptides.
Using molecular modeling and surface plasmon resonance, we identified that GIRLRG was binding with an affinity constant of 2.16 × 10 M in the ATPase domain of GRP78. GIRLRG peptide specifically bound to cervical, lung, esophageal, and glioma cells. SPECT imaging revealed that In-PEG-GIRLRG specifically bound to cervical, esophageal, pancreatic, lung, and brain tumors. Post-SPECT biodistribution data also validated the SPECT imaging results.
GIRLRG peptide specifically binds to the ATPase domain of GRP78. Radiolabeled PEG-GIRLRG could be used to target various cancers. Further studies would be required to translate PEG-GIRLRG peptide into the clinic.
癌症特异性靶向并保护正常组织可显著提高癌症治疗效果并降低癌症相关死亡率。一种方法是靶向癌细胞上特异性表达的受体或分子。肽作为癌症特异性靶向剂具有合成简便、抗原性低以及增强向组织内扩散等优点。葡萄糖调节蛋白78（GRP78）是一种内质网应激伴侣蛋白，可调节未折叠蛋白反应，且在多种癌症中过度表达。在本研究中，我们评估了特异性靶向GRP78用于癌症特异性结合（体外）和非侵入性肿瘤成像（体内）的GIRLRG肽。
使用计算建模将GIRLRG肽模拟到GRP78 ATP酶结构域中。进行表面等离子体共振研究以确定GIRLRG肽与GRP78蛋白的亲和力。GIRLRG与聚乙二醇（PEG）偶联以延长其在小鼠体内的循环时间。在携带异位宫颈癌（HT3）、食管癌（OE33）、胰腺癌（BXPC3）、肺癌（A549）和胶质瘤（D54）肿瘤的裸鼠中评估PEG - GIRLRG肽的肿瘤结合效果。在注射铟标记的PEG - GIRLRG或PEG对照肽后48小时和72小时对小鼠进行纳米单光子发射计算机断层扫描/计算机断层扫描（Nano - SPECT/CT）成像。在注射放射性标记肽后96小时进行SPECT后生物分布研究。
使用分子建模和表面等离子体共振，我们确定GIRLRG在GRP78的ATP酶结构域中以2.16×10⁻⁶ M的亲和常数结合。GIRLRG肽特异性结合宫颈癌、肺癌、食管癌和胶质瘤细胞。SPECT成像显示铟 - PEG - GIRLRG特异性结合宫颈癌、食管癌、胰腺癌、肺癌和脑肿瘤。SPECT后生物分布数据也验证了SPECT成像结果。
GIRLRG肽特异性结合GRP78的ATP酶结构域。放射性标记的PEG - GIRLRG可用于靶向多种癌症。需要进一步研究将PEG - GIRLRG肽转化应用于临床。
