Development of a Cyclic TMTP1-Based PET Probe for Visualization of Hepatocellular Carcinoma

TMTP1 is a tumor-homing peptide that selectively targets highly metastatic tumor cells with XPNPEP2 identified as its potential targeting receptor. Although TMTP1-based molecular probes have been explored for imaging tumors such as hepatocellular carcinoma (HCC), their clinical translation has been hampered by factors including suboptimal tumor uptake and rapid systemic clearance. To study possible solution for addressing these challenges, a cyclic TMTP1 based positron emission tomography (PET) probe, [⁶⁸Ga]Ga-DOTA-cTMTP1, was designed, synthesized, and evaluated for imaging HCC in small animal models. [⁶⁸Ga]Ga-DOTA-cTMTP1 demonstrated favorable aqueous solubility, with a log D _7.4 value of -3.28 ± 0.05, and it exhibited excellent in vitro stability in phosphate buffered saline (PBS) and fetal bovine serum (FBS). Biodistribution studies revealed a certain level of tumor accumulation (0.98 ± 0.14%ID/g at 30 min) and retention (0.40 ± 0.11%ID/g at 120 min). Impressively, [⁶⁸Ga]Ga-DOTA-cTMTP1 maintained high tumor-to-liver contrast over time, with ratios of 2.65 ± 0.45 at 30 min, 2.37 ± 0.07 at 60 min, and 2.14 ± 0.20 at 120 min. It also displayed capability of clear visualization of small HCC foci (<4 mm) in transgenic c-Myc liver tumor mice models, with tumor/liver ratios 2.20 ± 0.10 at 30 min, 2.26 ± 0.11 at 60 min, and 2.55 ± 0.44 at 120 min, respectively. Overall, this study highlights that [⁶⁸Ga]Ga-DOTA-cTMTP1 has favorable pharmacokinetic and in vivo tumor imaging profile, and it is a highly promising probe for visualization of HCC microlesions. Development of PET probes based on cyclic TMTP1 is a promising approach for discovering novel imaging probes.