Recent data have suggested that mitochondria play a supportive role in maintaining the tumorigenic phenotype. Indeed, antimitochondrial agents have been hypothesized to be potential chemosensitizers to human
malignancy. We assessed the utility of this approach by characterizing the antimitochondrial activity of 3,5-di-tert-butyl-4-hydroxybenzylidene-malononitrile (AG17), in combination with
1,3-bis(2-chloroethyl)-1-nitrosourea (
BCNU) in two human
glioblastoma cell lines. AG17 (NSC 242557) is a
tyrphostin that has been thought to have some antimitochondrial activity, with limited
tyrosine kinase antagonism, and was used at noncytotoxic and nongrowth-inhibitory concentrations (0.25 microM).
Glioblastoma cells were incubated in AG17, and changes in mitochondrial activity were determined.
Tumor cells became auxotrophically dependent on
uridine and
pyruvate, indicating the lack of a functioning respiratory chain. Despite this, cells continued to exhibit no growth-inhibitory effects. Exposure to AG17 was associated with significant depolarization of the mitochondrial membrane potential and decreases in mitochondrial mass in both
glioblastoma cell lines, correlating with the finding of auxotrophic dependence. In contrast, normal human astrocytes treated with the same dose of AG17 did not show changes in growth, mitochondrial membrane potential, or mass. Indeed, auxotrophic dependence on
uridine and
pyruvate could not be established in these cells.
Glioblastoma cells became significantly more responsive to
BCNU chemotherapy with AG17 pretreatment; a linear relationship was noted that correlated the number as well as percentage of polarized mitochondria with
glioblastoma cell survival at the highest dose of
BCNU used (144 microg/ml). Normal human astrocytes did not change with regard to the dose response to
BCNU with previous incubation with AG17. No difference was found in the type of cellular death (apoptosis) in either of the
glioblastoma cell lines, with
BCNU treatment alone, or with the combination AG17 and
BCNU, despite the decrease in polarized mitochondria and mitochondrial mass. AG17 has antimitochondrial properties when used at low dose in human
glioblastoma, which are relatively specific to
tumor cells when compared with normal astrocytes. The use of AG17 as a chemosensitizer, with drugs such as
BCNU, offers a new and possibly effective approach to be developed in patients with glial
tumors.