Buthionine sulphoximine alone and in combination with melphalan (L-PAM) is highly cytotoxic for human neuroblastoma cell lines

Buthionine sulphoximine (BSO) selectively inhibits glutathione (GSH) synthesis and may enhance the antineuroblastoma activity of melphalan (L-PAM). We determined the cytotoxicity of BSO (dose range 0–1000 μM) alone and in combination with L-PAM (dose range 0–0 μM) in a panel of 18 human neuroblastoma cell lines. BSO alone was highly cytotoxic with 16/18 neuroblastoma cell lines having IC90 values (range 2.1–>1000 μM) below the clinically achievable steady-state plasma level of 500 μM BSO. Maximal cell killing correlated with GSH levels decreased to less than 10% baseline, and was partially reversed by the addition of exogenous anti-oxidants (GSH, vitamin E and ascorbate). Fluorocytometric analysis of DNA fragments by the Tunnel method detected 92% of a BSO-sensitive cell line in apoptosis after a 48 h exposure to 500 μM BSO. The combination of L-PAM and BSO synergistically enhanced the cell killing of L-PAM alone by >1–3 logs (combination index <1). We conclude that BSO has significant single-agent cytotoxicity against neuroblastoma and enhances cell killing when combined with L-PAM.