Antileukaemic activity of treosulfan in xenografted human acute lymphoblastic leukaemias (ALL).

Treosulfan (L-threitol-1,4-bis-methanesulphonate; Ovastat(R)) is a bifunctional alkylating drug indicated for the treatment of advanced ovarian carcinoma. Recent data revealed immunosuppressive characteristics and substantial haematopoietic stem cell toxicity after repeated dosing of mice. Therefore, treosulfan is considered to be an alternative conditioning agent to busulfan (for example) administered prior to allogeneic/autologous stem cell transplantation of patients with haematological malignancies. An antineoplastic activity for treosulfan has been previously shown in preclinical models of melanoma, breast, lung and renal-cell carcinomas. Here, in vivo antileukaemic activity of treosulfan is compared with the activity of equitoxic doses of cyclophosphamide or busulfan for the first time using human acute lymphoblastic leukaemia (ALL)-models of paediatric origin xenotransplanted into non-obese diabetic (NOD)/severe combined immunodeficient (SCID) mice. Treosulfan treatment achieved an optimum treated to control (T/C) value of 159% (survival time) against B-ALL-SCID 7 and a T/C value of 0% (tumour growth) against T-ALL-SCID 4 and proB-ALL-SCID 19, respectively. Complete regression of established subcutaneously (s.c.) growing nodules of ALL-SCID 4 and 19 was obvious and long-term survivors without tumour re-growth were observed. Equitoxic doses of busulfan (ALL-SCID 4, 7, 19) or cyclophosphamide (ALL-SCID 19) were less effective with regard to the numbers of complete regressions and the number of cured animals. Side-effects included myelotoxicity and a small reduction in body weight, but these were tolerable. Treosulfan can be considered a highly active antileukaemic drug whose corresponding clinical value is to be tested in appropriate protocols with leukaemic patients.