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

恶性疾病的功能性和特异性成像最常使用肿瘤细胞表面上过表达的受体的寻址。放射性标记的受体特异性试剂可以与这些结合，从而使肿瘤可视化，例如通过PET/CT成像。然而，对于几种人类肿瘤实体，它们显示出各自靶受体表达的高个体间和个体内变异性。此外，受体表达谱在肿瘤去分化、转移或肿瘤治疗时会发生显著变化，进一步限制了受体特异性成像可达到的灵敏度。在对人类肿瘤活检的系统研究中可以显示，两种受体类型，即GRPR（胃泌素释放肽受体）和NPY（Y1）R（神经肽Y受体，亚型1）最常过表达，但也分别仅达到74%和66- 85%的表达率。这清楚地表明，使用单特异性放射性配体用于肿瘤靶向，人乳腺癌的可视化不能达到高灵敏度。然而，考虑到93%的病变以高密度携带这两种受体中的至少一种，使用能够结合两种受体类型的放射性标记的异二价配体可以显著增加使用PET的特异性受体介导的人乳腺癌成像的灵敏度。因此，该放射化学基础研究项目的目的是开发基于GRPR和NPY（Y1）R双特异性异二价肽的放射性配体，用于使用PET对人类乳腺癌进行特异性和更灵敏的成像。为了实现该项目，工作组在开发此类系统中的先前经验可以用作开发新的，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用68 Ga和64 Cu的放射性标记。除了异二价双特异性靶放射性配体之外，还将合成异二价单特异性和单价参考化合物。随后通过计算机确定物质的亲水性/亲脂性和稳定性，以及确定其体外GRPR和NPY（Y1）R受体结合亲和力。最后，将在异种移植小鼠模型中检查所开发的放射性配体，并与参比化合物进行比较，以提高人类乳腺癌可视化的灵敏度。

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.