PET and MRI of metastatic peritoneal and pulmonary colorectal cancer in mice with human epidermal growth factor receptor 1-targeted 89Zr-labeled panitumumab.

Unlabelled: Human epidermal growth factor receptor 1 (HER1) plays an important role in the pathogenesis of colorectal cancer. Panitumumab is an anti-HER1 monoclonal antibody approved for use in colorectal cancer. However, few data exist regarding HER1 status in the corresponding distant metastases, and little corresponding information is available regarding the localization of panitumumab at primary and metastatic lesions. The utility of PET and MRI using (89)Zr-panitumumab to assess the status of HER1 in distant metastases with different metastasis models is presented in this study.

Methods: In vivo biodistribution and PET studies were performed in HER1-expressing LS-174T and HER1-negative A375 tumor xenografts. Additionally, studies were performed in different models of intraperitoneal and pulmonary metastases. MRI studies were performed for metastatic models to characterize the targeting potential of (89)Zr-panitumumab at different lesion sites.

Results: HER1-mediated targeting was achieved in all HER1-expressing models. The LS-174T tumor area under the curve (AUC) was 3.7-fold greater than the AUC for A375. The LS-174T tumor AUC of 204.13 ± 9.67 was significantly greater (P < 0.001) than the LS-174T tumor AUC of 36.45 ± 1.39 obtained from mice coinjected with 0.1 mg of panitumumab for blocking the target. Differences were observed in 2 intraperitoneal models; tumor uptake in mice with a 3-d tumor burden was more than 2-fold greater than the mice with a 7-d tumor burden. PET and MRI studies revealed HER1-mediated tumor targeting in all metastatic models. However, significant differences were observed between different LS-174T tumor models. Peak tumor uptake of approximately 40 percentage injected dose per gram (%ID/g) was observed at 3-4 d after injection for the subcutaneous tumor model, in contrast to approximately 75 %ID/g at 2 d after injection for the thoracic tumors and approximately 95 %ID/g at 1-2 d after injection for the intraperitoneal tumors.

Conclusion: The potential utility of (89)Zr-panitumumab in assessing HER1 status in distant metastases and understanding the variations in antibody uptake at different lesion sites is demonstrated in this study. (89)Zr-panitumumab can play a vital role in patient stratification and immunotherapy and therefore warrants further investigation for clinical translation.