A COMPARISON OF THE EFFECTS OF IFOSFAMIDE VS MAFOSFAMIDE TREATMENT ONINTRACELLULAR GLUTATHIONE LEVELS AND IMMUNOLOGICAL FUNCTIONS OF IMMUNOCOMPETENT LYMPHOCYTE SUBSETS

This study compares the effects of ifosfamide treatment with those of mafosfamide treatment with respect to important immunological function s and intracellular glutathione (GSH) levels of immunocompetent lympho cyte subsets such as cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. The proliferative and cytotoxic capacity of human periphe ral blood lymphocyte (PBL) subsets was measured by a standard [H-3] th ymidine uptake assay and a [Cr-51] release assay; the intracellular gl utathione levels were determined by using an established HPLC method d escribed by Reed. Following incubation of human PBLs with the activate d forms of ifosfamide (4-OH-IF) and mafosfamide (4-OH-CP), the prolife rative capacity of recombinant interleukin 2 (rIL-2)-stimulated PBLs w as reduced by both drugs in a dose-dependent manner. However, a threef old higher concentration of ifosfamide compared with mafosfamide is ne eded to achieve a comparable inhibition rate in the proliferative capa city of theses lymphocytes. Separation of PBLs into a CD3(+) CTL and a CD3(-) NK subpopulation revealed that proliferative activity was redu ced in both subpopulations in a dose-dependent manner by ifosfamide an d mafosfamide. However, growth inhibition was much more pronounced in the CD3(+) CTL compared with the CD3(-) NK cells. The intracellular GS H level in CTL, and to a lower extent in NK cells, was reduced more su bstantially following an ifosfamide treatment compared with a mafosfam ide treatment. With respect to our previous finding that an ifosfamide -induced reduction of intracellular GSH levels correlates with decreas ed cytotoxic function, in this study we compared the effects of ifosfa mide treatment with those of mafosfamide treatment on the cytolytic ac tivity of lymphocyte subpopulations. The cytotoxic activity of CD3(+) CTL against allogeneic target cells (B-lymphoblastoid cells) was signi ficantly reduced after preincubation with either activated ifosfamide or mafosfamide. In contrast, the lysis of NK-sensitive tumor target ce lls (K562), mediated by CD3(-) NK cells is only affected if the effect or cells are exposed to high concentrations (100 mu M) of activated if osfamide. The cytotoxic activity of NK cells pretreated with high conc entrations of activated mafosfamide (33 mu M) had no significant inhib itory effect on the cytotoxic function. Taken together, our findings w ere as follows: 1) A threefold higher concentration of activated ifosf amide compared with mafosfamide results in a comparable inhibition of the proliferative activity, in vitro. 2) The intracellular GSH levels of unseparated rIL-2 activated lymphocytes were reduced by ifosfamide and mafosfamide at concentrations above 16 mu M. 3) Separated NK cells compared with CTLs are more resistant to treatment with ifosfamide wi th respect to their intracellular GSH levels. This phenomenon is even more pronounced after treatment with mafosfamide. 4) The reduction in intracellular GSH levels after treatment with ifosfamide and mafosfami de could be correlated with a reduction in the cytotoxic activity.