Purpose: Metastatic uveal melanoma is strongly resistant to chemotherapy, and multidrug resistance (MDR) may be involved. To investigate the role of MDR, the presence of the MDR-associated proteins P-glycoprotein (Pgp), MRP, and lung resistance protein (LRP) was determined on primary choroidal melanomas and cell lines.
Methods: A panel of primary choroidal melanomas was examined for the presence of MDR-associated proteins by immunohistochemical analysis. In cell lines established from four primary choroidal melanomas and one metastatic choroidal melanoma, the expression of MDR-associated proteins was determined with monoclonal antibodies in cytospin preparations and flow cytometry. In addition, the functional capacities of transporter proteins Pgp and MRP as adenosine triphosphate-driven efflux pumps were determined by measuring the cellular accumulation and efflux of the fluorescent dyes rhodamine 123 and calcein-AM, with and without the presence of specific pump inhibitors PSC833 and probenecid.
Results: Low levels of Pgp and MRP were detected in most primary tumors and in some cell lines. Measurable transporter function of Pgp could be determined in cell line OCM-1. Lung-resistance protein was present in all primary tumors and cell lines and showed high expression levels.
Conclusions: This study revealed the involvement of LRP and at least a minor role of Pgp and MRP in chemoresistance of choroidal melanoma. Compared with cutaneous melanomas, uveal melanomas appear to express slightly higher levels of Pgp. These findings provide insights into the drug-resistant phenotype of this disease and can aid in the design of therapeutic protocols.