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Preclinical evaluation of 68Ga- and 177Lu-Labeled AP-01 for the targeted treatment of prostate cancer with moderate PSMA expression

Year: 2025

Type: article

Abstract: AG10 is a molecule that can bind to the thyroxine (T4) binding pocket of transthyretin (TTR). The reversible association between the hydrophilic peptides and TTR using AG10 could increase the circulation half-life (t 1/2 ). We hypothesized that modifying PSMA-617 with AG10 could extend the t 1/2 of PSMA-617 and mitigate the limitations caused by insufficient uptake. The aim of this study was to develop an optimal AG10-modified radiotherapeutic agent that could maximize both tumor uptake and absorbed dose, thereby enhancing therapeutic efficacy for the treatment of tumors, even with moderate PSMA expression. Lysine was used as a linker for the conjugation of PSMA-617 and AG10 to synthesize AG10-PSMA-617 (AP-01). AP-01 was labeled with 68 Ga to image prostate carcinoma xenografts with moderate PSMA expression, serving as a reference for PSMA radio-ligand therapy (PRLT) based treatments. AP-01 was labeled with 177 Lu for the treatment of prostate carcinoma xenografts with moderate PSMA expression. The binding properties and biodistribution of 68 Ga-AP-01 and 177 Lu-AP-01 were studied both in vitro and in vivo. The cytotoxic effects of the 177 Lu-AP-01 were evaluated in prostate carcinoma xenografts. PSMA-617 was successfully conjugated with AG10 using lysine as the linker and labeled with 177 Lu to produce PRLT radiopharmaceuticals- 177 Lu-AP-01. AP-01 was labeled with 68 Ga for imaging prostate carcinoma with moderate PSMA expression. AP-01 demonstrated a high binding affinity (IC 50 = 3.42 nM) for PSMA in vitro, comparable to that of PSMA-617 (IC 50 = 3.38 nM) ( P = 0.324). PET/CT imaging of 68 Ga-AP-01 demonstrated significantly improved tumor uptake and retention as compared with 68 Ga-PSMA-617. The maximum uptake of 68 Ga-AP-01 and 68 Ga-PSMA-617 by 22Rv1 tumors was 18.07 ± 1.19%ID/g and 9.27 ± 1.20%ID/g at 4 h pi, respectively ( P < 0.05). The in vivo targeting abilities of 177 Lu-AP-01 were evaluated through SPECT/CT imaging. The tumor (maximum)-to-muscle (maximum) (T/Mmax) ratio of 177 Lu-AP-01 was 49.28 ± 7.18 at 72 h pi. However, the T/Mmax ratio of 177 Lu-PSMA-617 was 8.39 ± 8.57 at 48 h pi. Biodistribution studies further confirmed the significantly higher tumor uptake of 177 Lu-AP-01 (4.87 ± 0.91%ID/g) compared to 177 Lu-PSMA-617 (1.12 ± 0.01%ID/g) at 96 h post-injection ( P < 0.05). The inhibitory efficiency of 177 Lu-AP-01 on 22Rv1 tumor xenografts was 88.36%, which was superior to that of 177 Lu-PSMA-617 (73.36%) ( P < 0.05). 177 Lu-AP-01 demonstrated no toxic effects on hepatorenal function, routine blood tests, or major organs in mice when compared to the control group. In this study, AP-01 was successfully synthesized. 68 Ga-AP-01 and 177 Lu-AP-01 were obtained with high radiochemical purity and stability. High binding affinity and PSMA targeting specificity were identified in vitro and in vivo. With significantly enhanced tumor uptake and retention, 177 Lu-AP-01 has the potential to improve therapeutic efficacy for the treatment of prostate cancer with moderate PSMA expression.

Source: European Journal of Nuclear Medicine and Molecular Imaging

DOI: 10.1007/s00259-025-07704-2