Abstract
Recently, a tumor model based on the chorioallantoic membrane (CAM) was characterized structurally with Magnetic Resonance Imaging (MRI). Yet, capability of MRI to assess vascular functional reserve and potential of oxygenation-sensitive MRI remain largely unexplored in this model. For this purpose, we compared MC-38 colon and A549 lung adenocarcinoma cell grafts grown on the CAM, using quantitative T1 and T2* MRI readouts as imaging markers. These are associated with vascular functionality and oxygenation status when compared between periods of air and carbogen exposure. Our data show that in A549 lung adenocarcinoma cell grafts T2* values increased significantly upon carbogen exposure (p < 0.004, Wilcoxon test; no change in T1), while MC-38 grafts displayed no changes in T1 and T2*), indicating that the grafts differ in their vascular response. Heterogeneity with regard to T1 and T2* distribution within the grafts was noted. MC-38 grafts displayed larger T1 and T2* in the graft centre, while in A549 they were distributed more towards the graft surface. Finally, qualitative assessment of gadolinium-enhancement suggests that A549 grafts display more prominent enhancement compared to MC-38 grafts. Furthermore, MC-38 grafts had 65% larger volumes than A549 grafts. Histology revealed distinct underlying phenotypes of the two tumor grafts, pertaining to the proliferative status (Ki-67) and cellularity (H&E). In sum, a functional gas challenge with carbogen is feasible through gas exchange on the CAM, and it affects MRI signals associated with vascular reactivity and oxygenation status of the tumor graft planted on the CAM. Different grafts based on A549 lung adenocarcinoma and MC-38 colon carcinoma cell lines, respectively, display distinct phenotypes that can be distinguished and characterized non-invasively in ovo using MRI in the living chicken embryo.
Highlights
The chorioallantoic membrane (CAM) of the developing chicken embryo is an established model that is used in biomedical research in a multitude of different applications[1]
Relaxometry measurements were performed with a RARE sequence at variable repetition times TR (TR 430/800/1500/3000/4500 ms, RARE factor 2, TE 10 ms, acquisition time 6 min) and a multi-echo gradient-echo (MGE) acquisition (TE 4–81 ms, echo spacing 7 ms, 3 averages, TR 1500 ms, acquisition time 5 min) for quantitative T1 and T2* mapping, respectively. qT1 and qT2* relaxation times serve as tissue-dependent markers associated with vascular functionality and oxygenation status when compared between periods of air and carbogen (5% CO2, 95% O2) exposure
We compared MC-38 colon and A549 lung adenocarcinoma cell grafts using quantitative T1 and T2* Magnetic Resonance Imaging (MRI) readouts. These served as imaging markers associated with vascular functionality and oxygenation status when compared between periods of air and carbogen exposure
Summary
The chorioallantoic membrane (CAM) of the developing chicken embryo is an established model that is used in biomedical research in a multitude of different applications[1]. As a natural immunodeficient host with a rich vascular network, the CAM is capable to sustain grafted tissues and implants for tissue engineering applications[15] Most importantly, it provides an advantageous environment for tumor formation and is often used to study tumor development, metastasis and progression in xenotransplanted tumors[16]. Vascular functional reserve and oxygenation-sensitive MRI measures[19,20], remain largely unexplored in this model. Changes in tumor oxygenation can be qualitatively assessed during carbogen breathing[22,23,24]
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