Bromodeoxyuridine hypersensitivity of metastatic melanoma cells

A model system for testing the efficacy of chemotherapy protocols for metastatic melanoma was established using cell cultures from two brain and three lymph node metastases of melanoma from five different patients. Continuously growing cultures which were positive for tyrosinase activity were analysed regarding their proliferation rate by continuous bromodeoxyuridine (BrdU) labelling and subsequent Hoechst-33258/ethidium bromide flow cytometry. Melanoma cell cultures exhibit a strong sensitivity to BrdU: at 5% oxygen, 50% growth inhibition is attained with 360 +/- 130 microM BrdU (range: 130-520; n = 11) vs 650 +/- 50 microM BrdU (n = 3) for diploid human fibroblasts and 570 +/- 20 microM BrdU (n = 6) for human lymphoid cell lines. Moreover, BrdU sensitivity of melanoma cells is clearly oxygen dependent: 50% growth inhibition at 200 +/- 55 microM (range: 65-400 microM) for 20% oxygen vs 360 +/- 130 microM BrdU for 5% oxygen. The cell cycle kinetic mechanism of BrdU-induced growth inhibition is accumulation of cells in the first cycle G2 phase. On the basis of these results we suggest testing BrdU in chemotherapy protocols for the treatment of metastatic melanoma.