Targeting autophagy enhances BO-1051-induced apoptosis in human malignant glioma cells.

Purpose: BO-1051 is an N-mustard derivative that is conjugated with DNA-affinic 9-anilinoacridine. Since BO-1051 was reported to have strong anticancer activity, we investigated the effect and underlying mechanism of BO-1051 in human glioma cell lines.

Methods: Human glioma cell lines U251MG and U87MG were studied with BO-1051 or the combination of BO-1051 and autophagic inhibitors. Growth inhibition was assessed by MTT assay. Apoptosis was measured by annexin V staining followed by flow cytometry and immunoblotting for apoptosis-related molecules. Induction of autophagy was detected by acridine orange labeling, electron microscopy, LC3 localization and its conversion. Transfection of shRNA was used to determine the involvement of Beclin1 in apoptotic cell death.

Results: MTT assay showed that BO-1051 suppressed the viability of four glioma cell lines (U251MG, U87MG, GBM-3 and DBTRG-05MG) in a dose-dependent manner. The IC(50) values of BO-1051 for the glioma cells were significantly lower than the values for primary neurons cultures and normal fibroblast cells. Moreover, BO-1051 not only induced apoptotic cell death, but also enhanced autophagic flux via inhibition of Akt/mTOR and activation of Erk1/2. Importantly, suppression of autophagy by 3-methyladenine or bafilomycin A1 significantly increased BO-1051-induced apoptotic cell death in U251MG and U87MG cells. In addition, the proportion of apoptotic cells after BO-1051 treatment was enhanced by co-treatment with shRNA against Beclin1.

Conclusions: BO-1051 induced both apoptosis and autophagy, and inhibition of autophagy significantly augmented the cytotoxic effect of BO-1051. Thus, a combination of BO-1051 and autophagic inhibitors offers a potentially new therapeutic modality for the treatment of malignant glioma.