In vivo therapeutic potential of combination thiol depletion and alkylating chemotherapy

Abstract

Summary The effect of administering the thiol modulating agent buthionine sulfoximine (BSO) in conjunction with alkylating chemotherapy was investigated in vivo in the mouse KHT sarcomas and bone marrow stem cells. Tumour response to treatment was assessed by an in vivo to in vitro excision assay and bone marrow survival was determined in vitro by CFU-GM. Glutathione (GSH) depletion and recovery kinetics were determined at various times after treatment using high performance liquid chromatography (HPLC) techniques. Following a single 2.5 mmol kg-' dose of BSO, tumour GSH reached a nadir of -40% of control 12-16 h after treatment. Bone marrow GSH was depeleted to -45% of control 4-8 h after treatment but recovered to normal by 16 h. When a range of doses of CCNU, mitomycin C, cyclophosphamide or melphalan (MEL) were given 16 h after mice were exposed to a 2.5 mmol kg-' dose of BSO, only the antitumour efficacy of MEL was effectively enhanced (by a factor of -1.4). This BSO-MEL combination appeared to be selective for the tumour as the bone marrow toxicity was not increased beyond that seen for MEL alone. Since increasing the administered dose of BSO neither increased the extent of thiol depletion in the tumour nor enhanced the antitumour efficacy of MEL, three other protocols for delivering the thiol depletor were explored. BSO was given either as multiple 2.5 mmol kg-' doses administered at 6 or 16 h intervals or continuously at a concentration of 30 mM supplied in the animals' drinking water. Both multi-dose BSO pretreatments were found to increase both the antitumour efficacy and normal tissue toxicity of MEL such that no advantage compared to the single dose combination was achieved. In contrast, maintaining the thiol depletor in the drinking water led to an -1.7-fold increase in the antitumour efficacy of MEL without any corresponding increase in bone marrow stem cell toxicity. For the various pretreatment strategies it was possible, in all cases, to account for the presence or absence of a net therapeutic benefit on the basis of the tumour and bone marrow GSH depletion and recovery kinetics.

Clinically Evaluated Cancer Drugs Inhibiting Redox Signaling

“…Thus, lowering GSH has been sought by specific inhibition of c-glutamylcysteine ligase, a key enzyme of GSH biosynthesis. Such an inhibitor, L-S,R buthionine sulfoximine (BSO) (38), was shown to enhance the cytotoxicity to cancer cells of chemotherapeutic agents experimentally both in vitro and in vivo (42,95). Early clinical trials of BSO evaluated its ability to enhance the cytotoxicity of chemotherapeutic agents (6).…”

PRIMA-1Met induces myeloma cell death independent of p53 by impairing the GSH/ROS balance

“…15 BSO (30 mM) was evaluated in combination with melphalan. 31 Mice were treated with 10 mM BSO in drinking water because this concentration was shown to reduce GSH content in the liver. 32 Treatments were performed daily for 4 days, stopped for 2 days, and then performed again for another 4 days (as indicated by arrows in Figure 6A).…”

Synergistic cytotoxicity of buthionine sulfoximine (BSO) and intensive melphalan (L-PAM) for neuroblastoma cell lines established at relapse after myeloablative therapy

“…[9][10][11] Buthionine sulfoxi-mine (BSO), a specific inhibitor of ␥-glutamyl cysteine synthetase (the rate-limiting enzyme in GSH synthesis), depletes GSH, and can reverse alkylator resistance. 9,[12][13][14][15] We have previously reported that BSO, as a single agent, is highly cytotoxic for neuroblastoma cell lines in vitro and results in apoptosis due to increased generation of reactive oxygen species (ROS). 16,17 The combination of BSO with clinically achievable (non-myeloablative) concentrations of L-PAM was synergistic for neuroblastoma cell lines established at diagnosis or following non-myeloablative therapy.…”