Chemotherapeutic approaches to brain tumors. Experimental observations with dianhydrogalactitol and dibromodulcitol

Dianhydrogalactitol (DAG) or its active cell-killing moiety has a relatively long biological half-life in 9L cells cultured in vitro. The shape of the DAG dose-response curves was similar to that of those observed for most oncolytic agents. The prominent shoulder on the 24-h dose-response curve indicates that 9L cells can accumulate a reasonable amount of DAG-induced sublethal damage before they are killed. The appearance of 9L colonies in petri dishes was delayed 3-5 days after a DAG treatment that killed more than 99% of the cells, an observation not previously made with radiation, hyperthermia, the nitrosoureas, or other chemotherapeutic agents. Comparison of the in vitro exposure integral and the in vivo tumor tissue integral indicated that DAG would have to be administered at a dose in excess of its LD10 to achieve an in vivo 2 log cell kill. The lack of a significant increase in lifespan after a LD10 dose confirmed this prediction. While DAG alone is active against IC ependymoblastoma, it had very limited activity against IC glioma 26; however, the combination of DAG with BCNU was curative in 85%-100% of animals at 120 days. BCNU alone achieved no more than 4%-16% survival at 120 days. The combination of DBD and BCNU was not consistently better than BCNU alone against IC glioma 26. It appears that DAG may have a limited place in CNS chemotherapy for specific kinds of tumors. BCNU-DAG combination studies suggest that we may, under the right conditions, enhance the antitumor activity of the hexitol epoxides by drug combination therapies, although the mechanism for this enhanced antitumor activity is presently unknown.