Linker Optimization in Lu-177 Labeled αvβ6-Integrin Binding Peptide Trimers for Targeted Radionuclide Therapy of Cancer

High Resolution Image Download MS PowerPoint Slide Theranostic radiopharmaceuticals exploit the same molecular target for diagnosis and therapy. Among emerging pan-cancer targets, αvβ6-integrin is highly expressed on various malignant cell types and can be imaged clinically with Ga-68-Trivehexin. However, therapeutic αvβ6-integrin-directed radioligands remain scarce. Here, Lu-177-labeled multimerics of the cyclic nonapeptides Tyr2, sequence c(YRGDLAYp( N Me)K), were constructed using the tetrafunctional chelator DOTPI by means of CuAAC-based and evaluated as αvβ6-integrin-targeted radiotherapeutics. PEG linkers of increasing length (PEG0, PEG3, PEG7, PEG11) were introduced between the chelator and peptides to modulate pharmacokinetics and cellular processing. The Lu-177-labeled conjugates displayed comparable polarity (log D 7.4 ≈ −2) and αvβ6-integrin affinities determined by ELISA (IC 50 ∼ 0.2–0.5 nM), indicating minimal effects of PEG length on in vitro parameters. In αvβ6-positive H2009 cells, PEG linkers markedly enhanced and prolonged receptor-mediated uptake and internalization, consistent with improved multivalent engagement. In H2009 xenograft mice, PEG linkers reduced early blood-pool activity and increased tumor uptake at 24 h, while gelofusine (4% succinylated gelatin in Ringer’s acetate) efficiently mitigated the elevated renal retention (up to 92% reduction). Performance gains plateaued beyond PEG7, identifying the PEG7 trimer ( P7 ) as the preferred lead due to favorable tumor uptake/retention. P7 exhibited high selectivity (65- to 671-fold) over other integrin subtypes, αvβ6-integrin-dependent radiotoxicity to tumor cells, and sustained tumor retention for up to 6 days according to μSPECT.