Probing Vasoreactivity and Hypoxic Phenotype in Different Tumor Grafts Grown on the Chorioallantoic Membrane of the Chicken Embryo In Ovo Using MRI

SIMPLE SUMMARY: Fertilized chicken eggs can be used to study tumors. During their development, chicken eggshells are fenestrated, and the chicken embryo that is enwrapped by a highly vascularized membrane becomes accessible. Tumor cells are then planted onto this membrane, which supports tumor growth and, after one week, the tumor graft is studied using magnetic resonance imaging. To characterize the tumor in living chicken embryos, a gas tube can be fixed into the eggshell window and the chicken embryo and hence, the tumor graft is exposed to air, carbon dioxide-enriched air, or oxygen enriched with carbon dioxide. Different tumor types react differently to such gas challenges, which can be quantitatively measured and related to the tumor grafts’ vascular functioning and oxygenation. ABSTRACT: Tumor grafts grown on the chorioallantoic membrane (CAM) of chicken embryos represent a transition between cell culture and mammalian in vivo models. Magnetic resonance imaging (MRI) started to harness this potential. Functional gas challenge is feasible on the CAM. Using quantitative T1 and T2* mapping, we characterized the response of MC-38 colon, A549, and H460 adeno-carcinoma cell grafts to hypercapnic (HC) and hypercapnic-hyperoxic (HCHO) gas challenges, pertaining to the grafts’ vascular and oxygenation phenotypes. MR imaging revealed that larger T1 and T2* were located in the center of H460 and MC-38 tumors. Quantitative analysis showed a significant reduction in T1 and a significant increase in T2* in response to HCHO for A549 grafts, while H460 and MC-38 tumors did not respond to either gas challenge. Different tumor grafts respond differentially to HC and HCHO conditions. A549 tumor grafts, with higher vessel density and smaller tumor diameter compared with H460 and MC-38 grafts, had a significant response in T1 for HCHO and T2* increased slightly during HC and significantly under HCHO, consistent with a normoxic phenotype and functional vasoreactivity. Therefore, gas challenges enable differential characterization of tumor grafts with respect to their vascular and oxygenation status.