Synthesis and Preclinical Evaluation of [Ga]SP94 for Micro-PET Imaging of GRP78 Expression in Hepatocellular Carcinoma.

Glucose-regulated protein 78 (GRP78) is overexpressed in a wide variety of solid tumors, serving as a well-characterized target for tumor imaging or therapy. In this work, we developed a GRP78-responsive radiotracer (DOTA-Ga)-Gly-Gly-Gly-Ser-Phe-Ser-Ile-Ile-His-Thr-Pro-Ile-Leu-Pro-Leu-Gly-Gly-Cys ([Ga]SP94) for hepatocellular carcinoma (HCC) micro-PET imaging. DOTA-SP94 was synthesized by solid phase synthesis and then radiolabeled with GaCl with >99% radiochemical purity. The expression levels of GRP78 in HepG cells were confirmed by Western blotting. In vitro and in vivo study of [Ga]SP94 showed high stability and high uptake in GRP78-overexpressing HepG cells and tumor, fast clearance, and low nontarget uptake. Micro-PET images showed excellent tumor accumulation of [Ga]SP94 in the HepG-implanted nude mice tumor model. Additionally, the radiotracer uptake in HepG tumors can be blocked by unlabeled DOTA-SP94, suggesting that the tracer uptake by HCC was receptor-mediated. We envision that our radiotracer can be used for noninvasive imaging of HCC and is worthy of further clinical investigations.