Jia Fang, Balaji Baghavathy S, Gallazzi Fabio, Lewis Michael R
Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, MO, 65211.
Molecular Biology Program, University of Missouri, Columbia, MO, 65211.
Nucl Med Biol. 2015 Nov;42(11):809-15. doi: 10.1016/j.nucmedbio.2015.06.002. Epub 2015 Jun 9.
The bcl-2 gene is overexpressed in non-Hodgkin's lymphoma (NHL). We have reported micro-SPECT/CT imaging of Mec-1 human lymphoma xenografts in SCID mice, using [(111)In]DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate. In order to reduce normal organ accumulation and improve imaging contrast, modified monomers with neutral hydrophilic (serine, TS) or negatively charged (aspartic acid, TD) residues were synthesized as substitutes for glycine at T(14) in the PNA sequence. The parent and modified PNA-peptide conjugates were labeled with (64)Cu and evaluated in biodistribution studies and high resolution PET/CT imaging of SCID mice bearing bcl-2-positive Mec-1 xenografts as well as bcl-2-negative Ramos xenografts.
Mice were administered the (64)Cu-labeled conjugates for biodistribution and imaging studies. Biodistributions were obtained from 1 to 48 h post-injection. Mice were imaged from 1 to 48 h post-injection.
The parent glycine conjugate and two modified conjugates all showed selective tumor uptake in Mec-1 xenografts. The liver uptake of the serine conjugate was significantly reduced compared to the two other PNA conjugates. Its kidney uptake was highest of the three at 47.1% ID/g at 1h and dropped to 20.6% ID/g at 24h. [Copper-64]DOTA-anti-bcl-2-TS-PNA-Tyr(3)-octreotate showed tumor uptake of 1.38% ID/g at 1h and 1.06% ID/g at 24h. The tumor-to-blood ratio was increased by factor of 2 from 1h to 24h. This compound detected Mec-1 tumors by micro-PET/CT as early as 1h post-injection and at time points out to 48 h. However, the negative control Ramos tumor could not be detected.
These (64)Cu-labeled, amino acid-modified PNA conjugates showed selective tumor targeting in vivo, and tumor xenografts were detected by micro-PET/CT as early as 1h post-injection, suggesting that bcl-2 expression at the mRNA level can detected by PET in mouse models of NHL. Advances in knowledge and implications for patient care Down-regulating bcl-2, an anti-apoptotic proto-oncogene, is a mechanism to reverse chemotherapy resistance in humans with NHL. Thus, bcl-2 overexpression might be considered a new independent prognostic parameter in NHL, aiding in the identification of patients at risk for treatment failure. We have developed [(64)Cu]DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate conjugates for targeted antisense PET imaging. Our preclinical studies identified an effective combination of antisense and radionuclide imaging, with the goal of future clinical trials in patients. This imaging modality may improve clinical care by identifying patients who might respond better to conventional chemotherapy.
bcl-2基因在非霍奇金淋巴瘤（NHL）中过表达。我们曾报道使用[(111)In]DOTA-抗bcl-2-PNA-Tyr(3)-奥曲肽对SCID小鼠体内的Mec-1人淋巴瘤异种移植瘤进行微SPECT/CT成像。为了减少正常器官摄取并提高成像对比度，合成了具有中性亲水性（丝氨酸，TS）或带负电荷（天冬氨酸，TD）残基的修饰单体，以替代PNA序列中T(14)处的甘氨酸。将亲本和修饰的PNA-肽缀合物用(64)Cu标记，并在荷bcl-2阳性Mec-1异种移植瘤以及bcl-2阴性Ramos异种移植瘤的SCID小鼠的生物分布研究和高分辨率PET/CT成像中进行评估。
给小鼠注射(64)Cu标记的缀合物以进行生物分布和成像研究。在注射后1至48小时获得生物分布数据。在注射后1至48小时对小鼠进行成像。
亲本甘氨酸缀合物和两种修饰缀合物在Mec-1异种移植瘤中均显示出选择性肿瘤摄取。与其他两种PNA缀合物相比，丝氨酸缀合物的肝脏摄取显著降低。其肾脏摄取在三者中最高，在1小时时为47.1% ID/g，在24小时时降至20.6% ID/g。[铜-64]DOTA-抗bcl-2-TS-PNA-Tyr(3)-奥曲肽在1小时时肿瘤摄取为1.38% ID/g，在24小时时为1.06% ID/g。肿瘤与血液的比值从1小时到24小时增加了2倍。该化合物在注射后1小时以及直至48小时的时间点通过微PET/CT均可检测到Mec-1肿瘤。然而，阴性对照Ramos肿瘤未被检测到。
这些(64)Cu标记的、氨基酸修饰的PNA缀合物在体内显示出选择性肿瘤靶向性，并且通过微PET/CT在注射后1小时即可检测到肿瘤异种移植瘤，这表明在NHL小鼠模型中PET可检测到mRNA水平的bcl-2表达。知识进展及对患者护理的意义下调抗凋亡原癌基因bcl-2是逆转NHL患者化疗耐药性的一种机制。因此，bcl-2过表达可能被视为NHL中一个新的独立预后参数，有助于识别有治疗失败风险的患者。我们已开发出[(64)Cu]DOTA-抗bcl-2-PNA-Tyr(3)-奥曲肽缀合物用于靶向反义PET成像。我们的临床前研究确定了反义与放射性核素成像的有效组合，目标是未来对患者进行临床试验。这种成像方式可能通过识别可能对传统化疗反应更好的患者来改善临床护理。
