Development of radiolabeled heterobivalent GRPR- and NPY(Y1)R-bispecific peptidic ligands for a highly sensitive and specific visualization of human breast cancer with PET

恶性疾病的功能和特异性成像最常见的是对肿瘤细胞表面过度表达的受体进行定位。放射性标记的受体特异性试剂可以与这些受体结合，从而使肿瘤可视化成为可能，例如通过PET/CT成像。然而，对于几个人类肿瘤实体来说，它们表现出各自靶标受体表达的高度个体间和个体内的变异性。受体表达谱可在肿瘤去分化、转移或肿瘤治疗时发生显著变化，进一步限制受体特异性成像的可实现的敏感性。例如，可以并行或互补地过度表达几种不同受体类型的肿瘤实体是人类乳腺癌，它可以携带相应数量的不同受体类型。对人肿瘤活检组织的系统研究表明，GRPR(胃泌素释放肽受体)和NPY(Y1)R(神经肽Y受体，亚型1)这两种受体类型是最常见的过表达，但其表达率分别只有74%和66-85%。这清楚地表明，使用用于肿瘤靶向的单特异性放射性配体，对人类乳腺癌的可视化不能达到高灵敏度。然而，鉴于93%的病变至少高密度携带这两种受体中的一种，使用能够与这两种受体类型结合的放射性标记异二价配体，可以显著提高使用PET进行特定受体介导的乳腺癌成像的敏感性。因此，本放射化学基础研究项目的目标是开发一种基于GRPR和NPY(Y1)R双功能异二价肽的放射性配基，用于使用PET对人乳腺癌进行特异性和进一步敏感的成像。为了实现该项目，工作组以前开发这类系统的经验可以作为开发新的、结构和药代动力学优化的放射配基的基础。在该项目的过程中，将首先建立复杂目标化合物的化学合成及其68Ga和64Cu的放射性标记。除了异二价的双特异性靶标放射性配体外，还将合成异二价的单特异性和单价参比化合物。然后，对这些物质的亲水性/亲脂性和稳定性以及它们的体外GRPR和NPY(Y1)R受体结合亲和力进行电子计算机检测。最后，将在异种小鼠模型中与参比化合物进行比较，以确定新开发的化合物在临床翻译方面的潜力及其提高人类乳腺癌可视化的敏感性。

The functional and specific imaging of malignant diseases most commonly uses the addressing of receptors overexpressed on the tumor cell surface. To these, radiolabeled receptor-specific agents can bind, thus enabling the visualization of tumors e.g. by PET/CT imaging. However, it was shown for several human tumor entities that they exhibit a high inter- and intraindividual variability of the respective target receptor expression. The receptor expression profile can furthermore considerably change upon tumor de-differentiation, metastasis or tumor therapy, further limiting the achievable sensitivity of receptor-specific imaging.An example of a tumor entity that can overexpress several different receptor types in parallel or complementarily is human breast cancer, which can carry different receptor types in relevant amounts. It could be shown in systematic studies on human tumor biopsies that two receptor types, namely the GRPR (gastrin-releasing peptide receptor) and the NPY(Y1)R (neuropeptide Y receptor, subtype 1) are most frequently overexpressed but also achieve expression rates of only 74% and 66-85%, respectively. This makes clear that a visualization of human breast cancer cannot reach a high sensitivity using a monospecific radioligand for tumor targeting. However, given that 93% of lesions carry at least one of these two receptors in high density, the sensitivity of specific receptor-mediated imaging of human breast cancer using PET could be significantly increased using radiolabeled heterobivalent ligands being able to bind to both receptor types. The aim of this radiochemical basic research project is therefore the development of a GRPR- and NPY(Y1)R-bispecific heterobivalent peptide-based radioligand for specific and furthermore sensitive imaging of human breast cancer using PET.For the realization of the project, previous experiences of the working group in the development of such systems can be used as a basis for the development of new, structurally and pharmacokinetically optimized radioligands.Within the course of the project, the chemical synthesis of the complex target compounds and their radiolabeling with 68Ga and 64Cu will be established first. Besides the heterobivalent bispecific target radioligands, also heterobivalent monospecific and monovalent reference compounds will be synthesized.This is followed by the in silico determination of the hydrophilicity/lipophilicity and stability of the substances as well as the determination of their in vitro GRPR and NPY(Y1)R receptor binding affinities.Finally, the developed radioligands will be examined in a xenograft mouse model in comparison to the reference compounds in order to determine the potential of the newly developed compounds with respect to a clinical translation and their ability to improve the sensitivity of human breast cancer visualization.