The morphology of the amelanotic Greene melanoma

The Behavior of Two Cell Lines Obtained from Murine (B16-F10) and Human (G-361) Melanomas Implanted into the Eyes of New Zealand White Rabbits, and their Microscopic, Immunohistochemical and Ultrastructural Appearances

A transcleral inoculation of 15x10(6) melanocytes of the B16-F10 and G-361 cell lines was carried out in the anterior chamber of one eye in New Zealand white rabbits. Tumor growth occurred in 24 eyes (77%) of the B16-F10 group and in 22 (73%) of the G-361 group. The tumors of the latter group were mostly amelanic and showed local aggression with ocular perforation and extrascleral growth one month post-implant, while the tumors of the B16-F10 group were intensely pigmented and grew over the iris although they did not perforate the eyeball. Microscopically, the tumors of both groups were of the mixed type, made up of epithelioid and fusiform melanocytes. S-100 protein and Nki C3 monoclonal immunohistochemical techniques showed a positive immunoreaction in all cases of tumor growth. Ultrastructurally, the G-361 melanocytes showed a few melanosomes corresponding to maturity state II and, occasionally, state III, while totally melanized state IV cells predominated in the B16-F10 group. Aberrant melanosomes were common in both groups. The inoculation of 15x10(6) melanocytes of either cell line was useful to produce ocular melanomas.

Animal Eye Models for Uveal Melanoma

Animal models play an important role in understanding tumor growth and may be used to develop novel therapies against human malignancies. The significance of the results from animal experiments depends on the selection of the proper model. Many attempts have been made to create appropriate animal models for uveal melanoma and its characteristic metastatic behavior. One approach is to use transgenic animal models or to implant tumor cells. A variety of tumor types have been used for this purpose: tumor cells, such as Greene melanoma, murine B16 melanoma, and human uveal melanoma cells, may be implanted in the eyes of hamsters, rats, rabbits, and mice, among others. Various inoculation routes, including into the anterior chamber and posterior compartment, and retro-orbitally, have been applied to obtain tumor growth mimicking ocular uveal melanoma. However, when we choose animal models, we must be conscious of many disadvantages, such as variable tumor growth, or the need for immunosuppression in xenogeneic grafts. In this paper, we will discuss the various eye models.

Comparative study of experimental ocular melanoma using two implantation techniques of B16-F10 melanocytes

OBJECTIVE

The aim of this work was to evaluate the behaviour of B16-F10 melanoma cell cultures implanted in the anterior chamber of the eye of New Zealand white rabbits by studying the clinical-pathological and ultrastructural characteristics of the lesions.

METHODS

One group (A) (consisting of 30 rabbits) was transclerally inoculated (1 mm from sclero-corneal limbus) with 4 x 10(6) melanocytes and another group (B) (also 30 animals) was inoculated once per week for 3 consecutive weeks with 5 x 10(6) cells (total 15 x 10(6)); 30 animals acted as the control group (C). All the lesions were processed for optic and electronic microscopy.

RESULTS

Tumoral growth in group A was 43% (13/30) and in group B 80% (24/30). All lesions were pigmented and none perforated the eyeball. Microscopically, they were a mixture of epithelioid and fusiform cells disposed around the blood vessels. Ultrastructurally, the presence of melanosomes in different stages of maturation and aberrant melanosomes were characteristic.

CONCLUSION

We suggest that the transcleral inoculation of 15 X 10(6) B16-F10 melanocytes into the anterior chamber of the eye of New Zealand white rabbits may be a valid and reproducible method for obtaining an experimental ocular melanoma model.

Heterotransplantation of human uveal melanoma

Cell lines established from the biopsy specimen of a patient with a spindle B choroidal melanoma were transplanted into the posterior choroid of 30 immunosuppressed, pigmented New Zealand rabbits. Growth of the tumor xenografts could be seen 7 to 10 days after transplantation. Tumor xenografts were reproducible and reached an average size of 5 mm in height and 8 mm in their basal dimension by 4 weeks. Histopathology of the original tumor revealed primarily spindle B cells, while the tumor xenografts contained epithelioid, spindle B, and clear cell melanoma cells. Of particular interest was the presence of an extensive and intact vasculature and the absence of a capsule surrounding the lesions in situ. The use of human uveal melanoma cells, the ease of transplantation, and the posterior location of the tumor may make this animal model of use in studies on new diagnostic and therapeutic modalities.

Experimental study on the fractionation schedule for proton irradiation of uveal melanoma

Greene melanoma in the anterior chamber of rabbits was irradiated by protons to find the isoeffect curve for proton irradiation fractionated into one, two, three or four doses. The isoeffect curve for tumor tissue remained constant between one- and three-dose fractionations and rose with four-dose fractionation. The isoeffect curve for normal tissue approximately followed the Ellis equation. Therefore, the optimal irradiation schedule should be in the range of three fractions because this best spares normal tissue while delivering a tumoricidal dose to the lesion. The relative reduction of the total dose from four- to one-dose fractions of intraoperative irradiation should be 20%.

The effects of pre-enucleation irradiation on the development of metastases from intraocular Greene melanoma in hamsters

Using intraocular Greene melanoma in a hamster model, we studied the effect of pre-enucleation irradiation on the development of melanoma metastases. One group (No. = 111) was treated with 1,210 to 1,600 rads of cobaltous chloride Co 60 gamma irradiation before enucleation and the second group (No. = 100) received no irradiation. The groups did not differ with respect to presence of metastases in the 106 days after tumor implantation (chi 2 = 3.05; P = .08). However, Kaplan-Meier survival curves gave a longer time to melanoma-related death in the irradiated animals compared with the controls (log rank test, P = .0008).

Hematoporphyrin derivative photoradiation induced damage to normal and tumor tissue of the pigmented rabbit eye

Cytotoxicity induced by hematoporphyrin derivative (HpD) photoradiation in both normal and experimental tumor tissue of pigmented rabbit eyes has been examined. In addition, documentation of HpD induced fluorescence in ocular structures has also been obtained. Acute normal ocular tissue toxicity studies demonstrated that HpD (1-10 mg HpD/kg) followed 48 hours later by a transpupil irradiation of red light (635 nm, 36-90 J/cm2) resulted in demarcated areas of retinal damage. Long term (chronic) toxicity studies have shown that the initial damage to the retina was permanent but that no damage to the cornea, lens or vitreous could be observed during a 16 month follow-up. Visual and histological documentation have been obtained, following HpD photoradiation therapy (PRT), in rabbit eyes having heterotransplanted single nodule amelanotic melanomas. A toxic effect characterized by tumor blanching, edema and hemorrhage was observed within 24 hours of treatment. Histological examination obtained 24 hours following HpD PRT illustrated massive tumor tissue necrosis and vascular disruption. HpD PRT at clinically relevant doses was also shown to be effective in selectively curing the highly malignant amelanotic iris melanoma. It is concluded that HpD PRT may prove to be an effective modality for treating certain ocular tumors.

Rabbit model of uveal Greene melanoma: morphologic studies of metastatic lesions

We studied the morphology of metastatic tumors in three rabbits with implanted choroidal Greene melanoma. The tumor-bearing eyes were perforated and destroyed by the expanding tumors 10 to 12 weeks after implantation. The animals then lost body weight and became cachectic; they were suspected of having metastases and were sacrificed. The interval between the destruction of the eye and the discovery of metastases was 1 to 14 weeks. Widespread metastases involved the liver, lungs, kidneys, and subcutaneous tissue, with the greatest number of tumors in the liver and lungs. Histopathologic findings in the metastases and primary tumors were identical. This model may be considered appropriate for study of human uveal melanoma because (1) the biological behavior is similar to that of human uveal melanoma, (2) the primary and metastatic tumors are histologically similar, and (3) the large size of the rabbit's eye facilitates observation and manipulation.

[Experiments concerning tumor angiogenesis ]

Cells of human choroidal melanoma were implanted in the cornea of rabbits. A few days later corneal neovascularization onto the tumor can be observed. When the tumor is vascularized, rapid tumor growth follows. Macroscopic, histologic, and angiographic aspects are presented. The role of prostaglandin E2 (PGE2) as a cause of angiogenesis is discussed.