Peptides are biomolecules that have been associated with various physiological responses and have great potential for the diagnosis or treatment of diseases, including various types of tumors. Several studies have shown that biologically active peptides containing the RGD domain have a high affinity with the αvβ3 integrin adhesion molecule overexpressed in tumor cells, assisting in molecular imaging or targeted radionuclide therapy (TRT) as an anti-tumor agent.

To obtain an anti-integrin peptide fragment modified by incorporating two spacers — hexa-aminocaproic acid (C6) or dodeca-aminocaproic acid (C12) — and by adding the chelating agent DOTA for subsequent radiolabeling with yttrium-86 (86Y).

The modified peptides were synthesized by the solid-phase peptide synthesis method using the Fmoc/tBut strategy. In this strategy, the Fmoc group removal step was carried out with 20% 4-methylpiperidine / 80% DMF, and the amino acid coupling step is usually performed with the diisopropylcarbodiimide/1-hydroxybenzotriazole (DIC/HOBt) acylation mixture. In this step, an excess of Fmoc-amino acids and acylating agents of 2.5 times were used relative to the synthesis scale utilized in mmol/g. Peptide cleavage from the resin and removal of side chain protecting groups were carried out using a mixture containing a high concentration of TFA (reagent K). After synthesis and cleavage, the peptides underwent characterization and purification process through high-performance liquid chromatography (HPLC) and mass spectrometry. The radiolabeling process was conducted utilizing cyclotron-produced 86Y, employing a NaOAc buffer (pH = 5.5). The radiochemical reaction was performed at 95°C for 30 min, followed by filtration through a Sep-Pak C18 cartridge for purification and determination of the radiolabeling yield.

The DOTA-C6-anti-integrin and DOTA-C12-anti-integrin peptides were efficiently synthesized, and the yields obtained were approximately 12.7% and 26.4%, respectively. Chromatographic analyses obtained by HPLC, as well as mass spectrometry, showed that the entire synthesis, cleavage, and characterization process were carried out properly with visualization of profiles and molecular masses of 1165.3 g/mol and 1249.1 g/mol for the DOTA-C6-anti-integrin and DOTA-C12-anti-integrin peptides, respectively. After the purification process, 14.6 mg and 66.2 mg of pure peptides were obtained. The preliminary 86Y-labeling data indicated a radiochemical yield of approximately 97% for both peptides.

The proposed modified anti-integrin peptides were efficiently synthesized, characterized, and purified. Preliminary radiolabeling studies with 86Y demonstrated a high radiochemical yield, paving the way for further exploration in radiochemical studies and assays of affinity to tumor cells.