Step 1: Selecting the Target

Epidermal Growth Factor Receptor (EGFR) is a transmembrane receptor tyrosine kinase and a member of the HER (human epidermal growth factor receptor) family. EGFR is overexpressed or mutated in various epithelial tumors, such as Non-Small Cell Lung Cancer (NSCLC), Head and Neck Squamous Cell Carcinoma, and Colorectal Cancer. EGFR activates its tyrosine kinase activity by binding with ligands, thereby activating downstream signaling pathways such as RAS-RAF-MEK (MAPK/ERK), PI3K-AKT-mTOR, and JAK/STAT, regulating cell proliferation, differentiation, migration, and survival. The presence of EGFR mutations makes tumors more sensitive to specific targeted therapeutic drugs, such as the first-generation EGFR Tyrosine Kinase Inhibitors (TKIs) Erlotinib and Gefitinib. However, almost all patients receiving EGFR-TKIs will eventually develop resistance, with the most common mechanism being the T790M mutation. Because of this, research on EGFR-targeted therapeutic drugs has progressed rapidly, reaching the fourth generation.

Example Figure: This figure illustrates the Epidermal Growth Factor Receptor (EGFR) signaling pathway and its role in colorectal cancer. The EGFR signaling pathway plays a critical role in the development and progression of colorectal cancer, involving multiple molecules and steps.
Paper Title: Targeting the EGFR signalling pathway in metastatic colorectal cancer.

Existing EGFR-TKIs have achieved certain efficacy in treating EGFR-mutant tumors, but the development of resistance limits their long-term application. Furthermore, for tumors that have already developed resistance, especially those with complex mutation profiles such as T790M and C797S mutations, the effects of existing treatments are limited. Therefore, developing novel therapeutic strategies such as nuclear drugs may provide new treatment options for these patients. Radioimmunotherapy, as an emerging treatment modality, has potential synergistic effects and may be combined with existing targeted and immunotherapies to provide a more comprehensive treatment plan.

Paper Title: Radiolabeling and Preclinical Evaluation of Therapeutic Efficacy of 225Ac-ch806 in Glioblastoma and Colorectal Cancer Xenograft Models.

In the study, 225Ac-ch806 was prepared using different chelators, including [225Ac]Ac-macropa-tzPEG3Sq-ch806 and [225Ac]Ac-DOTA-dhPzPEG4-ch806. The research team quantified the radiochemical yield, purity, apparent specific activity, and serum stability of 225Ac-ch806. They systematically evaluated the in vitro cell killing effect and studied the biodistribution and therapeutic effect of 225Ac-ch806 in mice bearing U87MG.de2-7 and DiFi tumors. Pharmacodynamic analysis was performed on tumors after treatment, including gH2AX detection for DNA double-strand breaks via immunofluorescence, and immunohistochemical analysis of proliferation, cell cycle arrest, and apoptosis.

Step 2: Synthesis, Labeling, and Detailed Characterization

This figure illustrates the biodistribution of ²²⁵Ac-ch806 and ²²⁵ Ac-IgG1 in U87MG.de2-7 (glioblastoma) and DiFi (colorectal cancer) xenograft models. The data show that tumor uptake of ²²⁵ Ac-ch806 peaked on day 2 post-injection in the U87MG.de2-7 model, whereas tumor accumulation gradually increased until day 7 in the DiFi model. These results highlight the tumor-specific targeting capability of ²²⁵ Ac-ch806, as well as its potential therapeutic application across different tumor models.

This figure presents the therapeutic outcomes of ²²⁵ Ac-ch806 in the U87MG.de2-7 model, including tumor growth curves, survival curves, and immunofluorescence staining for γγ H2AX (a molecular marker of DNA double-strand breaks). Mice treated with ²²⁵ Ac-ch806 exhibited long-term suppression of tumor growth and 100% survival. Furthermore, higher levels of DNA double-strand breaks were observed in ²²⁵ Ac-ch806-treated tumors compared to the control group, confirming both the therapeutic efficacy of ²²⁵ Ac-ch806 and its ability to induce DNA damage.

This figure presents the therapeutic outcomes of ²²⁵ Ac-ch806 in the DiFi model, including tumor growth curves, survival curves, and immunofluorescence staining for γγ H2AX. Despite relatively low accumulation of ²²⁵ Ac-ch806 in DiFi tumors, mice treated with ²²⁵ Ac-ch806 showed a steady decline in tumor volume, with 7 mice achieving a complete response and 1 showing a partial response. The survival curve demonstrated prolonged survival in the ²²⁵ Ac-ch806-treated group. Additionally, higher levels of DNA double-strand breaks were observed in treated tumors compared to the control group, further confirming the therapeutic efficacy of ²²⁵ Ac-ch806.

This figure presents immunohistochemical analyses of U87MG.de2-7 and DiFi tumors using Hematoxylin and Eosin (H&E) staining, as well as Ki-67, p21, and cleaved caspase 3 staining, to assess tumor architecture, proliferation capacity, cell cycle, and apoptosis. Compared with the control group, ²²⁵ Ac-ch806-treated tumors exhibited reduced Ki-67 staining, indicating decreased proliferation. In the U87MG.de2-7 model, p21 expression was significantly upregulated by ²²⁵ Ac-ch806, suggesting potential cell cycle arrest induced by DNA double-strand breaks. In the DiFi model, ²²⁵ Ac-ch806-treated tumors showed significantly increased levels of apoptosis, indicating that ²²⁵ Ac-ch806 promotes cell death via the apoptotic pathway.