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* These authors contributed equally
The present protocol describes the implantation and evaluation of melanoma in the murine choroid utilizing optical coherence tomography.
Establishing experimental choroidal melanoma models is challenging in terms of the ability to induce tumors at the correct localization. In addition, difficulties in observing posterior choroidal melanoma in vivo limit tumor location and growth evaluation in real-time. The approach described here optimizes techniques for establishing choroidal melanoma in mice via a multi-step sub-choroidal B16LS9 cell injection procedure. To enable precision in injecting into the small dimensions of the mouse uvea, the complete procedure is performed under a microscope. First, a conjunctival peritomy is formed in the dorsal-temporal area of the eye. Then, a tract into the sub-choroidal space is created by inserting a needle through the exposed sclera. This is followed by the insertion of a blunt needle into the tract and the injection of melanoma cells into the choroid. Immediately after injection, noninvasive optical coherence tomography (OCT) imaging is utilized to determine tumor location and progress. Retinal detachment is evaluated as a predictor of tumor site and size. The presented method enables the reproducible induction of choroid-localized melanoma in mice and the live imaging of tumor growth evaluation. As such, it provides a valuable tool for studying intraocular tumors.
Uveal melanoma (UM) is the most frequent intraocular primary malignancy in adults. Approximately 90% of ocular melanomas originate from melanocytes in the choroid region of the uveal tract1. UM is a major cause of morbidity and mortality, as it is estimated that close to 50% of patients develop metastatic disease, with the liver being the major site of metastasis2. Early treatment of primary lesions may reduce the chance of metastases, yet no effective treatment prevents metastases formation3.
The standard treatment of uveal melanoma includes irradiation therapy, which is associated with loss of vision due to optic neuropathy, retinopathy, dry eye syndrome, and cataract. Surgical resection is typically delayed until the growth of the lesion is recognized and characterized. However, such a delay may allow metastatic disease development4. In some cases, futile enucleation is required. Of course, this radical procedure compromises vision and results in dramatic aesthetic deterioration.
There have been many efforts dedicated to developing experimental models to study uveal melanoma. Preclinical animal models that allow accurate assessment of this malignancy are key for investigating novel diagnostic and therapeutic strategies for uveal melanoma. Experimental animal models of ocular melanoma are mainly based on the inoculation of tumor cells in mice, rats, and rabbits5,6. Mouse models are cost-effective and widely used for melanoma studies due to their rapid reproduction rate and high genome similarity to humans. The murine cutaneous melanoma cell line B16 is commonly utilized to inoculate C57BL6 mice and induce syngeneic tumors. When using this model to induce uveal melanoma, tumor-bearing eyes typically need to be enucleated 7-14 days after inoculation. Further, B16 is a highly invasive model. The immune-privileged nature of the eye supports metastasis, and metastases may typically be detected 3-4 weeks after tumor cell inoculation. Subcultures of the original B16 line display distinct metastatic properties6. For example, the Queens melanoma line has a high metastatic rate7,8. The B16LS9 cell line has dendritic cell morphology and was derived from liver metastases of C57BL/6 mice injected with the parental cutaneous melanoma line B16F19. When injected into the posterior compartment of the eye, these cells were shown to form intraocular tumors, which histologically resemble human uveal melanoma and form liver-specific metastases in C57BL/6, but not Balb/C, mice10,11,12. Genetically, the cells are characterized by higher expression of the c-met proto-oncogene, which acts as a cellular receptor for hepatocyte growth factor13. In contrast, B16F10, the 10th passage of the parental B16, primarily metastasizes to the lungs when inoculated intraocularly14. Both B16F10 and B16LS9 are pigmented12.
Several key challenges limit the success of murine uveal melanoma models. First, tumor cell reflux may lead to extraocular or subconjunctival melanoma. Second, tumor growth after intraocular inoculation of melanoma cells is often highly variable, posing difficulties in evaluating treatment and progress. Another major difficulty is the limited ability to follow tumor growth in vivo. While bioluminescent imaging, such as of luciferase expressing tumors, is commonly used to monitor ocular tumor growth15,16, it cannot provide information on the intraocular location of the tumor. Therefore, evaluation of the tumor is typically performed following enucleation of the eye10,17. This greatly limits the ability to characterize tumor progression and response to treatments extensively. Another major hurdle in studying uveal melanoma is the difficulty in monitoring lesions in pigmented mice. New approaches, which overcome these difficulties, are required to promote the research of uveal melanoma in animal models.
Optical coherence tomography (OCT) provides distinctive capabilities to image deep into the different sections of the eye in high resolution, which is unparalleled by other methodologies, including ultrasound18,19. OCT imaging has been used in animal models to study various ocular diseases20. Recently, OCT imaging was demonstrated as noninvasive means to evaluate intraocular tumor growth21. The protocol described here depicts the implantation of melanoma cells in the murine choroid and the utilization of OCT to predict intraocular tumor localization and size at the time of cell inoculation.
The experiments in the protocol were approved by the Israeli National Council on Animal Experimentation and comply with the ARVO Statement for using Animals in Ophthalmic and Vision Research. Female C57BL/6 mice, aged 8-10 weeks, were used for the present study and were exposed to 12/12 h light-dark cycles. The animals were obtained from a commercial source (see Table of Materials).
1. Cell culture
2. Animal preparation
3. Creating a conjunctival peritomy and scleral tract into sub-choroidal space
Figure 1: Tumor cell inoculation. (A) The supero-temporal limbal conjunctiva is held using intraocular forceps and pulled toward an infra-nasal position. (B) The tip of a 30 G needle is inserted to penetrate through the sclera, and excision is made to create a track into the sub-choroidal space. (C) A syringe loaded with cells and mounted with a 32 G needle is inserted into the track, and the cells are injected. Please click here to view a larger version of this figure.
4. Inoculation of melanoma cells
5. Assessing the location of the injection
6. Predicting tumor size based on RD height
7. Postoperative procedures
Eyes were examined via OCT immediately after injection of the B16LS9 cells. Local retinal detachment was observed after injection. The mice exhibited three patterns of RD: focal (Figure 2, upper panel), leakage to the vitreous (Figure 2, middle panel), and extended RD (Figure 2, bottom panel). Extended RD is likely caused by damage from the injection. There was an association between the pattern of RD immediately after inje...
Uveal melanoma is a devastating disease for which novel therapeutic approaches are greatly needed. However, research on uveal melanoma and potential treatments is limited by the technical challenges of uveal melanoma animal models1,25. Ocular tumors, which are induced by intraocular injection of cancer cells, are highly variable in both localization and size, likely due to the small dimensions of the mouse eye. Such variability is an obstacle to the comprehensive...
Marcovich A.L.: Steba Biotech (P), Yeda Weizmann (P), EyeYon Medical (C, P), Mor Isum (P). (C) = Consultant; (P) = Patent. All other authors have no competing interests.
This study was supported in part by grant 1304/20 from the Israel Science Foundation (ISF), Israel, for Arie Marcovich. We thank Shahar Ish-Shalom and Ady Yosipovich, from the Department of Pathology, Kaplan Medical Center, Rehovot, Israel, for histology analysis.
Name | Company | Catalog Number | Comments |
10 μL glass syringe (Hamilton Co., Bonaduz, Switzerland) | Hamilton | 721711 | |
30 G needles | BD Microbalance | 2025-01 | |
Atipamezole hydrochloride | Orion Phrma | ||
B16LS9 cells | from Hans Grossniklaus USA | ||
Buprenorphine | richter pharma | 102047 | |
C57BL/6 female mice | Envigo | ||
Essential vitamin mixture | satorius | 01-025-1A | |
Fetal bovine serum | rhenium | 10270106 | |
HEPES | satorius | 03-025-1B | |
Hydroxyethylcellulose 1.4% eye drops | Fisher Pharmaceutical | 390862 | |
InSight OCT segmentation software | Phoenix Micron, Inc | ||
Ketamine | bremer pharma GMBH (medimarket) | 17889 | |
L-glutamine | satorius | 03-020-1B | |
Medetomidine | zoetis (vetmarket) | 102532 | |
Ofloxacin 0.3% eye drops | allergan | E92170 | |
Optical coherence tomography | Phoenix Micron, Inc | ||
Oxybuprocaine 0.4% | Fisher Pharmaceutical | 393050 | |
Penicillin-streptomycin-amphoteracin | satorius | 03-033-1B | |
Phosphate buffered saline (PBS) | satorius | 02-023-1a | |
RPMI cell media | satorius | 01-104-1A | |
Sodium pyruvate | satorius | 03-042-1B | |
Surgical microscope | Zeiss | OPMI-6 CFC | |
Tropicamide 0.5% | Fisher Pharmaceutical | 390723 |
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