177Lu-labeling of nuclear localization sequence (NLS)-grafted HER2-receptor affine peptide

Tagging of cell permeable nuclear localization sequence (NLS) with receptor targeting peptide vectors is an attractive strategy for selectively targeted translocation of therapeutic cargoes. The present study aimed at grafting nuclear localization sequence (NLS) onto breast cancer targeting rL-A9 peptide. Molecular docking analysis revealed higher binding affinity of the peptide, DOTA-NLS-rL-A9 (−26.1 kJ/mol) towards HER2 receptor in comparison to DOTA-rL-A9 peptide (−22.2 kJ/mol). Confocal microscopy data suggested significantly enhanced cellular internalization of NLS-tagged peptide. The engineered HER2-selective, DOTA-NLS-rL-A9 peptide scaffold was radiolabeled with Lu-177 for intracellular delivery of the theranostic radionuclide into tumor cells. [¹⁷⁷Lu]Lu-DOTA-NLS-rL-A9 exhibited significantly enhanced binding affinity (4.58 ± 1.77 nM) towards human breast carcinoma SKBR3 cells and cellular internalization (85 % at 24 h) compared to its original analog, [¹⁷⁷Lu]Lu-DOTA-rL-A9. In vivo biodistribution studies showed consistent retention of [¹⁷⁷Lu]Lu-DOTA-NLS-rL-A9 in the tumor with negligible washout of radioactivity (∼4.1 % ID/g at 48 h). Prolonged tumor activity with rapid off-target tissue clearance resulted in significantly high tumor-to-background ratios. The radiopeptide, [¹⁷⁷Lu]Lu-DOTA-NLS-rL-A9 thus, being precisely confined into HER2-expressing tumor cells and exhibiting favourable pharmacokinetic features is an efficient candidate for further screening.