In-vivo imaging tool for assessing tumor growth in mouse models of intraocular melanoma

Abstract

Purpose : Uveal melanoma (UM) and conjunctival melanoma (CM) are ocular malignancies that give rise to life threatening metastases. Although there is some success with radiation and chemotherapy treatments, it is usually at the cost of significant vision impairment and they are not effective against the metastatic disease. Hence, therapeutic approach for treating ocular melanoma that also prevents metastases is an unmet need.
Very few mouse models of metastatic CM and UM are available for research. One of the challenges is to follow tumor growth in-vivo and determine the right size for treatment, mainly of the posterior, choroidal melanoma. Hence, the purpose of this study was to establish a simple, noninvasive imaging tool that will simplify visualization and tumor follow-up in mouse models of CM and UM.

Methods : Tumors were induced by inoculation of B16LS9 murine cutaneous melanoma cells into the sub-conjunctival or the posterior, sub-choroidal space of C57BL6 mouse eye under a surgical microscope. Five to ten days following injection, tumor size was assessed by Phoenix Micron^TM image-guided Optical Coherence Tomography (OCT) imaging system, including a real-time camera view and OCT scan of the conjunctiva and the retina. In addition, tumor depth and size were evaluated by longitudinal and sagittal ultrasound sections and histopathological examination of eye sections.

Results : Injection of seven or seventy thousand cells sub-conjunctively or sub-choroidally, respectively, lead to tumor growth within 5-7 days. A clear tumor mass was detected at these regions using the Micron^TM imaging system camera view and OCT scans. H&E staining of eye sections confirmed the presence of tumoral tissue in the retro-bulbar and sub-retinal areas, which was characterized by atypical large pleomorphic epithelioid cells with large nuclei and prominent nucleoli, representing malignant melanoma. Tumor size, as determined by the OCT scans, was confirmed by an ultrasound scan and by the histopathological examination.

Conclusions : Using a simple, non-invasive imaging tool we were able to follow intraocular tumor growth of both CM and UM, and to define a grading scale to evaluate tumor size: small, medium or large. This tool may be utilized for evaluation of new mouse models for CM and UM, as well as for testing new therapies for these diseases.

This is a 2020 Imaging in the Eye Conference abstract.