Comparative Evaluation of Radiochemical and Biological Properties of 131I- and [99mTc]Tc(CO)3-Labeled RGD Analogues Planned to Interact with the αvß3 Integrin Expressed in Glioblastoma.

Radiolabeled peptides with high specificity for overexpressed receptors in tumor cells hold great promise for diagnostic and therapeutic applications. In this work, we aimed at comparing the radiolabeling efficiency and biological properties of two different RGD analogs: GRGDYV and GRGDHV, labeled with iodine-131 (131I) and technetium-99m-tricarbonyl complex [99mTc][Tc(CO)3]+. Additionally, we evaluated their interaction with the αvß3 integrin molecule, overexpressed in a wide variety of tumors, including glioblastoma. Both peptides were chemically synthesized, purified and radiolabeled with 131I and [99mTc][Tc(CO)3]+ using the chloramine-T and tricarbonyl methodologies, respectively. The stability, binding to serum proteins and partition coefficient were evaluated for both radioconjugates. In addition, the binding and internalization of radiopeptides to rat C6 glioblastoma cells and rat brain homogenates from normal animals and a glioblastoma-induced model were assessed. Finally, ex vivo biodistribution studies were carried out. Radiochemical yields between 95-98% were reached for both peptides under optimized radiolabeling conditions. Both peptides were stable for up to 24 h in saline solution and in human serum. In addition, the radiopeptides have hydrophilic characteristics and a percentage of binding to serum proteins around 35% and 50% for the [131I]I-GRGDYV and [99mTc]Tc(CO)3-GRGDHV fragments, respectively. Radiopeptides showed the capacity of binding and internalization both in cell culture (C6) and rat brain homogenates. Biodistribution studies corroborated the results obtained with brain homogenates and confirmed the different binding characteristics due to the exchange of radionuclides and the presence of the tricarbonyl complex. Thereby, the results showed that both radiopeptides might be considered for future clinical applications.

Standardization of the [68Ga]Ga-PSMA-11 Radiolabeling Protocol in an Automatic Synthesis Module: Assessments for PET Imaging of Prostate Cancer.

Prostate-specific membrane antigen (PSMA) is a glycoprotein present in the prostate, that is overexpressed in prostate cancer (PCa). Recently, PSMA-directed radiopharmaceuticals have been developed, allowing the pinpointing of tumors with the Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) imaging techniques. The aim of the present work was to standardize and validate an automatic synthesis module-based radiolabeling protocol for [68Ga]Ga-PSMA-11, as well as to produce a radiopharmaceutical for PET imaging of PCa malignancies. [68Ga]Ga-PSMA-11 was evaluated to determine the radiochemical purity (RCP), stability in saline solution and serum, lipophilicity, affinity to serum proteins, binding and internalization to lymph node carcinoma of the prostate (LNCaP) cells, and ex vivo biodistribution in mice. The radiopharmaceutical was produced with an RCP of 99.06 ± 0.10%, which was assessed with reversed-phase high-performance liquid chromatography (RP-HPLC). The product was stable in saline solution for up to 4 h (RCP > 98%) and in serum for up to 1 h (RCP > 95%). The lipophilicity was determined as -3.80 ± 0.15, while the serum protein binding (SPB) was <17%. The percentages of binding to LNCaP cells were 4.07 ± 0.51% (30 min) and 4.56 ± 0.46% (60 min), while 19.22 ± 2.73% (30 min) and 16.85 ± 1.34% (60 min) of bound material was internalized. High accumulation of [68Ga]Ga-PSMA-11 was observed in the kidneys, spleen, and tumor, with a tumor-to-contralateral-muscle ratio of >8.5 and a tumor-to-blood ratio of >3.5. In conclusion, an automatic synthesis module-based radiolabeling protocol for [68Ga]Ga-PSMA-11 was standardized and the product was evaluated, thus verifying its characteristics for PET imaging of PCa tumors in a clinical environment.

Radiochemical and biological properties of peptides designed to interact with EGF receptor: Relevance for glioblastoma.

Radiolabeled peptides with high specificity to receptors expressed on tumor cells hold a great promise as diagnostic and therapeutic tracers. The main objective of this study was to evaluate the radiochemical and biological properties of two [131I]I-peptides, as well as their interaction with the epidermal growth factor receptor (EGFR), overexpressed in a wide variety of tumors, including glioblastoma. The EEEEYFELV peptide and its analogue DEDEYFELV, both designed to interact with EGFR, were chemically synthesized, purified and radiolabeled with iodine-131 ([131I]NaI). The radioiodination was evaluated and optimized using the chloramine-T methodology. The stability, serum proteins binding and partition coefficient were assessed for both radioconjugates. Moreover, the binding and internalization of synthesized radiopeptides with rat glioblastoma cells (C6) and with rat brain homogenates from a glioblastoma induced model were evaluated and ex vivo biodistribution studies were performed. Under optimized radiolabeling conditions, the peptides showed an average radiochemical yield of 90-95%. The stability studies showed that both peptides were stable up to 24 h in reaction medium, saline, and human serum. Furthermore, [131I]I-peptides have hydrophilic features and showed binding percentage to serum proteins of around 50%, which is highly compatible with clinical applications. Moreover, the radiopeptides presented capacity for binding and internalization in both tumor cells (C6) and rat brain tissues after tumor induction. Biodistribution studies corroborated the cell culture studies and confirmed the different binding characteristics derived from a simple change of two amino acids (Glu ➔ Asp1,3) in their sequences. The results obtained are consistent enough to motivate further studies. Thereby, these radiolabeled peptides might be useful for diagnostic applications.