Tumor-Specific Zr-89 Immuno-PET Imaging in a Human Bladder Cancer Model

Tumor-specific molecular imaging is an important tool for assessing disease burden and treatment response. CA19.9 is an important tumor-specific marker in several malignancies, including urothelial carcinoma. [Zr-89]DFO-HuMab-5B1 (MVT-2163) is a CA19.9-specific antibody-based construct that has been validated in preclinical animal models of lung, colorectal, and pancreatic malignancies for positron emission tomography (PET) imaging and is currently in a phase I trial for pancreatic cancer (NCT02687230). Here, we examine whether [Zr-89]DFO-HuMab-5B1 may be useful in defining urothelial malignancies. Surface expression of CA19.9 was confirmed in the human bladder cancer line HT 1197. The radioimmunoconjugate [Zr-89]DFO-HuMab-5B1 was injected into mice bearing HT 1197 xenografts, and followed by PET imaging, ex vivo experiments including biodistribution, histology and autoradiography, and analysis of blood samples for shed antigen levels were performed. [Zr-89]DFO-HuMab-5B1 specifically accumulates in HT 1197 engrafted tumors when imaged with PET. Ex vivo biodistribution of organs and autoradiography of engrafted tumors confirm our construct's specific tumor binding. The target antigen CA19.9 was not found to be shed in vitro or in vivo. [Zr-89]DFO-HuMab-5B1 can be used to delineate urothelial carcinomas by PET imaging and may provide tumor-specific information prior to, during, and after systemic therapies.