Metastatic Behaviour of Human Uveal Melanoma Cell Lines in a Rabbit Model

Abstract

Abstract: : Purpose: Malignant uveal melanoma metastasizes through haematogenous dissemination usually to liver and lung. The purpose of this study is to investigate the systemic spread of two human uveal melanoma cell lines of different metastatic potential in an albino rabbit animal model. Methods: 1x10⁶ total cells of either the MKT-BR (low metastatic potential) or 92.1 (high metastatic potential) human melanoma cell line were implanted into the suprachoroidal space of albino rabbits. The two groups of 15 animals each were immunosuppressed using cyclosporine A (CsA). Three days before surgery and during the first week of the experiment, animals received a 30 mg/kg/day dose of CsA, followed by 15 mg/kg/day for the next 3 weeks and 10 mg/kg/day for the last 4 weeks in order to prevent cell rejection. All twenty-eight rabbits surviving beyond the fourth week underwent post-mortem necropsy and the lungs were collected for histopathological study. After 8 weeks, all twenty-three surviving rabbits were euthanised. Formalin-fixed, paraffin-embedded lung sections were H&E stained. All H&E negative cases were further studied by immunohistochemistry using HMB-45 monoclonal antibody to detect possible occult micrometastases. Results: Twenty of the twenty-eight animals showed metastatic disease by H&E staining (71.4%). There was no significant difference in the metastatic behaviour of the two cell lines studied. Metastases were found in nine of thirteen samples from the MKT-BR group (69.2%) and eleven of fifteen from the 92.1 group (73.3%). None of the eight H&E negative cases showed micrometastasis when evaluated by immunohistochemistry with HMB-45. Conclusions: Both cell lines showed unexpected high levels of metastasis considering results of previous rabbit models of uveal melanoma. This is especially true for the MKT-BR cell line, which was thought to be of low metastatic potential. These findings may be explained by the degree to which the animals were immunosuppressed in this particular animal model. Due to the negative results obtained with the HMB-45 marker, we speculate that micrometastasis may be absent in this particular animal model of uveal melanoma.

Keywords: melanoma • animal model • immunohistochemistry