Macropa-Based 225Ac-Labeled RGD Peptides for Targeted Alpha Therapy

Macropa has formed more stable complexes with 225Ac, although DOTA has been extensively used as a chelator for 225Ac. This study aimed to design and synthesize two novel 225Ac-labeled RGD peptides, [225Ac]Ac-Macropa-c(RGDyK) ([225Ac]1) and [225Ac]Ac-Macropa-[c(RGDyK)]2 ([225Ac]2), and to evaluate their potential for targeted alpha therapy (TAT) of glioblastoma. Further, whether combination therapy with homoarginine (hArg), a modulator of lysosomal function, could further improve therapeutic efficacy was investigated. In Colon-26 cells, [225Ac]2 demonstrated significantly higher cellular uptake and cytotoxicity than [225Ac]1. In Colon-26 tumor-bearing mice, [225Ac]2 exhibited higher tumor accumulation and significant tumor growth inhibition. In GL261 glioblastoma cells, [225Ac]2 showed comparable cellular uptake to that in Colon-26 cells, and combination with hArg in vitro improved its cytotoxicity. However, no significant difference in therapeutic efficacy was observed between the hArg-treated and control groups in the orthotopic GL261 glioblastoma mouse model. The results of this study indicate the potential of 225Ac-labeled RGD peptides incorporating Macropa as a chelator as promising agents for TAT. However, the further optimization of combination strategies and pharmacokinetics is required.