Development of new molecular probes for imaging of cancer

• Autor(a) principal: Belchior, Afonso André Morais
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/158351
• topic: CXCR4; Gallium-67; Imaging; pepRF1; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

The 35-amino acid long peptide pepR, derived from DENVC, presents interesting an-tibacterial and anti-HIV activity. However, peptides undergo proteolytic degradation there-fore, pepR in the presence of human serum, gives one main fragment with 17 amino acid res-idues (LKRWGTIKKSKAINVLR) named pepRF1. Interestingly, this human serum resistant fragment pepRF1 presents a more potent anti-HIV activity than its parent pepR (IC50 1.5 ± 0.4 pepRF1 and IC50 37 ± 3.8 pepR). pepRF1 prevents viral entry into target cells by binding to the viral co-receptor CXCR4, acting as an antagonist as proved in cytosolic calcium release assays. CXCR4, whose cognate ligand is chemokine CXCL12, is a G-protein-coupled receptor that is implicated in diverse pathophysiological processes, including various types of cancers (prostate, ovarian, brain), where it plays a key role in tumor development and metastization. Considering that CXCR4 is both an established druggable receptor and a relevant imaging target, we envisaged the possibility of exploring gallium-67(67Ga)-labeled pepRF1 and pepRF1-derived shorter peptide sequences (PepRF1_C2: LKRWGTIKKSKAINV; PepRF1_C4: LKRWGTIKKSKAI, PepRF1_C6: LKRWGTIKKSK; PepRF1_C8: LKRWGTIKK; and PepRF1_C10: LKRWGTI) as CXCR4-targeted imaging agents. To accomplish that goal, the short peptides were conjugated to the bifuncional chelator NODA-GA, giving the corresponding peptide conjugates of the type PepRF1_X_NOD (X = C2, C4, C6, C8 and C10), which were characterized by RP-HPLC and ESI-MS. Reaction of the peptide conjugates with 67GaCl3 gave radiopeptides of the type 67Ga-PepRF1_X_NOD in high radiochemical yield and purity >95%. The chemical identity of the 67Ga-labeled peptide con-jugates was confirmed by comparing their retention times in the RP-HPLC chromatograms (γ-detection) with those of the non-radioactive analogues (UV-detection). The cell uptake studies in cancer cell lines with different levels of CXCR4 expression have shown that there is no correlation between cellular uptake of the 67Ga-labeled peptide conjugates and CXCR4 expression. Moreover, low uptake values (ca. 1 - 2%) were obtained for all radiopeptides. The biodistribution studies in healthy CD-1 mice have shown that the pharmacokinetic profile of the radiopeptides present a similar trend, relatively fast blood clearance with rapid uptake by the kidneys and liver, and no relevant uptake in any other main organ. A moderate to rapid total excretion (32.6 ± 3.2 to 87.9 ± 5.8 % IA) from the whole animal body predomi-nantly through the urinary tract was observed.