Chick Chorioallantoic Membrane as a Patient-Derived Xenograft Model for Uveal Melanoma: Imaging Modalities for Growth and Vascular Evaluation

SIMPLE SUMMARY: The objective of the present study is to establish a new in vivo patient-derived xenograft (PDX) model for uveal melanoma (UM) based on the chick chorioallantoic membrane (CAM) assay. Furthermore, various implantation techniques and monitoring tools, such as different ultrasound modalities, optical coherence tomography and angiography, fluorescein angiography, image analysis, as well as fluorescent immunohistochemistry, were investigated for the assessment of the growth, vascularity, and, therefore, the viability of the implanted grafts. The results suggested an increase in the size parameters of the UM specimens and comparable data for the applied monitoring instruments, resulting in the CAM-based PDX model becoming an alternative step in translational cancer research for novel diagnostic and therapeutic experimentation in the field of ocular melanoma. ABSTRACT: Background: Patient-derived tumor xenografts (PDXs) have emerged as valuable preclinical in vivo models in oncology as they largely retain the polygenomic architecture of the human tumors from which they originate. Although animal models are accompanied by cost and time constraints and a low engraftment rate, PDXs have primarily been established in immunodeficient rodent models for the in vivo assessment of tumor characteristics and of novel therapeutic cancer targets. The chick chorioallantoic membrane (CAM) assay represents an attractive alternative in vivo model that has long been used in the research of tumor biology and angiogenesis, and can overcome some of these limitations. Methods: In this study, we reviewed different technical approaches for the establishment and monitoring of a CAM-based uveal melanoma PDX model. Forty-six fresh tumor grafts were acquired after enucleation from six uveal melanoma patients and were implanted onto the CAM on ED7 with Matrigel and a ring (group 1), with Matrigel (group 2), or natively without Matrigel or a ring (group 3). Real-time imaging techniques, such as various ultrasound modalities, optical coherence tomography, infrared imaging, and imaging analyses with Image J for tumor growth and extension, as well as color doppler, optical coherence angiography, and fluorescein angiography for angiogenesis, were performed on ED18 as alternative monitoring instruments. The tumor samples were excised on ED18 for histological assessment. Results: There were no significant differences between the three tested experimental groups regarding the length and width of the grafts during the development period. A statistically significant increase in volume (p = 0.0007) and weight (p = 0.0216) between ED7 and ED18 was only documented for tumor specimens of group 2. A significant correlation of the results for the cross-sectional area, largest basal diameter, and volume was documented between the different imaging and measurement techniques and the excised grafts. The formation of a vascular star around the tumor and of a vascular ring on the base of the tumor was observed for the majority of the viable developing grafts as a sign of successful engraftment. Conclusion: The establishment of a CAM-PDX uveal melanoma model could elucidate the biological growth patterns and the efficacy of new therapeutic options in vivo. The methodological novelty of this study, investigating different implanting techniques and exploiting advances in real-time imaging with multiple modalities, allows precise, quantitative assessment in the field of tumor experimentation, underlying the feasibility of CAM as an in vivo PDX model.