IDDF2024-ABS-0283 De novo discovery of C-Met—targeting peptides for 68Ga-PET imaging of hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is the sixth most common cancer and the fourth leading cause of cancer-related death worldwide. Effective early diagnosis is hampered by the lack of noninvasive methods, with approximately 80% of cases diagnosed late. Mesenchymal-epithelial transition factor (c-Met) plays a critical role in HCC progression and metastasis and serves as a biomarker for tumor aggressiveness. Current PET tracers show poor in vivo performance due to low liver background uptake. In this study, using phage display, we identified three high-affinity c-Met targeting peptides (P3, P4, P5) and developed them into PET agents.

Methods

We synthesized and modified P3 (K_D = 1.98 nM), P4 (K_D = 82.2 nM), and P5 (K_D = 11.7 nM)—with NOTA, purified them via RP-HPLC and radiolabeled with 3.00 mCi of ⁶⁸GaCl₃-HCl solution and sodium acetate buffer at 100 °C for 10 minutes. The radiolabeling yield, specific activity, and radiochemical purity were analysed using radio HPLC. Micro PET/CT scanning was performed on HCCLM3-bearing mice, at 0.5 h,1 h and 2 h after injection of [⁶⁸Ga]-NOTA-P3, [⁶⁸Ga]-NOTA-P4, or [⁶⁸Ga]-NOTA-P5, respectively (150±5 μCi in 300 μL of saline per mouse, n = 2).

Results

The radiolabeling yields of the synthesized [⁶⁸Ga]-NOTA-P3, [⁶⁸Ga]-NOTA-P4, and [⁶⁸Ga]-NOTA-P5 were ≥44%, ≥46%, and ≥51%, and radiochemical purity of all three tracers was ≥95%. As shown in figure 1B, the tumor uptake values were 1.7% ID/g, 3.9% ID/g, and 2.4% ID/g at 1 hour post-injection, respectively. It was observed that [⁶⁸Ga]-NOTA-P3 and [⁶⁸Ga]-NOTA-P5 were primarily metabolized by the kidneys, while [⁶⁸Ga]-NOTA-P4 was significantly metabolized in the liver. The metabolic profiles of the PET tracers correlated well with their measured logP values, with [⁶⁸Ga]-NOTA-P4 being relatively hydrophobic. (IDDF2024-ABS-0283 Figure 1)

Conclusions

We have developed de novo peptide radiopharmaceuticals, which show significant potential as PET tracers for the noninvasive quantification of c-Met in vivo. We will then apply them in the treatment of HCC in the future.