CD133 as a Biomarker for an Autoantibody-to-ImmunoPET Paradigm for the Early Detection of Small Cell Lung Cancer

Small cell lung cancer (SCLC) is a deadly neuroendocrine tumor for which there are no screening methods sensitive enough to facilitate early, effective intervention. We propose targeting the neuroendocrine tumor neoantigen CD133 via antibody-based early detection and positron emission tomography (immunoPET) to facilitate the earlier and more accurate detection of SCLC. Methods: RNAseq datasets, IHC, flow cytometry, and western blots were used to quantify CD133 expression in healthy and SCLC patients. CD133 was imaged in vivo using near-infrared fluorescence immunoimaging and zirconium-89 immunoPET. Anti(α)-CD133 autoantibody levels were measured in SCLC patient plasma using antibody microarrays. Results: Across 6 publicly available datasets, CD133 mRNA was found to be higher in SCLC tumors compared to other tissues, including healthy or normal adjacent lung and non-SCLC samples. Critically, the upregulation of CD133 mRNA in SCLC was associated with a significant increase (HR 2.62) in death. CD133 protein was expressed in primary human SCLC, in SCLC patient-derived xenografts (PDXs), and in both SCLC cell lines tested (H82 and H69). Using a H82 xenograft mouse model, we first imaged CD133 expression with near-infrared fluorescence (NIRF). Both in vivo and ex vivo NIRF clearly show that a fluorophore-tagged αCD133 homed to lung tumors. Next, we validated the non-invasive visualization of subcutaneous and orthotopic H82 xenografts via immunoPET. An αCD133 antibody labeled with the positron-emitting radiometal zirconium-89 demonstrated significant accumulation in tumor tissue while producing minimal uptake in healthy organs. Finally, plasma αCD133 autoantibodies were found in subjects from cohort studies up to 1 year prior to SCLC diagnosis. Conclusion: In light of these findings, we conclude that the presence of αCD133 autoantibodies in a blood sample followed by CD133-targeted 89Zr-immunoPET could be an effective early detection screening strategy for SCLC.