Epidermal Growth Factor Receptor as a Radiotheranostic Target in Orthotopic Models of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) remains a leading cause of cancer-related mortality, with a 5-y survival rate of approximately 20%. Although glypican-3–targeted radiotheranostics are under development, a plurality of patients with HCC lack glypican-3 expression, underscoring the need for alternative targetable antigens. Epidermal growth factor receptor (EGFR) is overexpressed in 50%–70% of HCC tumors and represents a clinically validated therapeutic target. Here, we developed and evaluated a panitumumab-based EGFR-targeted radiotheranostic pair, [89Zr]Zr-desferrioxamine-panitumumab ([89Zr]Zr-Pani) for immuno-PET and [225Ac]Ac-Macropa-panitumumab ([225Ac]Ac-Pani) for targeted α-particle therapy, in clinically relevant orthotopic HCC models. Methods: Panitumumab was conjugated with desferrioxamine or Macropa chelators and radiolabeled with 89Zr or 225Ac, respectively. EGFR expression was characterized across a panel of HCC cell lines. Binding affinity, biodistribution, and tumor specificity were assessed in subcutaneous and orthotopic Huh-7 models, with EGFR-mediated targeting confirmed by blocking (200-fold molar excess of unlabeled panitumumab). Therapeutic efficacy was evaluated in mice bearing orthotopic Huh-7-Luc+ tumors (n = 6 per group) after a single 9.3 kBq dose of [225Ac]Ac-Pani, with longitudinal monitoring by bioluminescence imaging, [89Zr]Zr-Pani immuno-PET, and blood chemistry. Results: [89Zr]Zr-Pani exhibited high-affinity binding to EGFR (dissociation constant, 0.35 nM) and demonstrated robust tumor accumulation in both subcutaneous Huh-7 (20.6 ± 2.6 %IA/g) and orthotopic Huh-7-Luc+ tumors (19.3 ± 2.0 %IA/g) at 120–192 h postinjection. Biodistribution of [225Ac]Ac-Pani closely mirrored that of [89Zr]Zr-Pani across organs and tumors, with tumor uptake reduced approximately 5-fold by blocking (21.7 ± 1.1 vs. 4.5 ± 0.6 %IA/g; P < 0.0001), confirming EGFR-specific targeting. A single 9.3 kBq administration of [225Ac]Ac-Pani induced substantial early tumor regression and significantly prolonged median survival (70 d) compared with vehicle (28 d) and blocking (35 d) groups (log-rank P < 0.0001), with no clinically meaningful hepatotoxicity or renal toxicity. However, tumor regrowth eventually occurred in all treated mice. Conclusion: [89Zr]Zr-Pani and [225Ac]Ac-Pani represent a radiotheranostic pair that enables EGFR-specific imaging and targeted α-particle therapy in orthotopic HCC models. These findings establish EGFR as a promising radiotheranostic target in HCC, broadening the patient population eligible for image-guided radiopharmaceutical interventions for liver cancer.