IN-VITRO STUDIES ON INTERACTION OF 4-HYDROPEROXYIFOSFAMIDE AND 2-MERCAPTOETHANESULFONATE IN MALIGNANT GLIOMAS

Drug interference of ifosfamide and sodium 2-mercaptoethanesulphonate (MESNA) was studied in three malignant glioma cell cultures (HTZ-17, H TZ-209B, and HTZ-243) by a recently developed in vitro method for eval uation of multimodal treatment interactions. Glioma cell cultures were treated in monolayer 96-well tissue-culture plates for 2 h each, with 4-hydroperoxyifosfamide and MESNA combined in both sequences, or alon e. Concentrations ranged from 0.01 muM to 50 muM in single-modality ex posures, and from 0.01 muM to 10 muM in combination exposures. After f ive population doubling times, DNA synthesis was determined by a stand ard [H-3]Tdr-incorporation liquid-scintillation-counting protocol. Dat a points were evaluated for mono- and combined treatment dose effects (adapted with a probit function), and a model-free three-dimensional r esponse surface was created that was compared to the theoretical addit ive, anticipated response surface. Local additivity was analysed for a ny ratio of combined treatment. No tumour effects were seen with MESNA in single-drug exposure, whereas ifosfamide resulted in more than 90% inhibition of tumour DNA synthesis. In combination experiments, MESNA could be confirmed to be inert: the anticipated theoretical combinati on response surfaces formed a three-dimensional extension of the singl e-drug ifosfamide dose/response curves - the experimental combination response surfaces displayed an identical appearance (P less-than-or-eq ual-to 0.05). In conclusion, these results indicate no drug interferen ce of MESNA and ifosfamide in malignant glioma cells.