Background

Glioblastoma multiforme (GBM) remains a challenge for clinicians due to resistance to conventional treatment with the DNA-damaging agent temozolomide (TMZ) and radiation. Developing new therapeutic approaches is imperative and there is a growing interest in targeting cancer cell metabolism. Based on work from our group and others, the metabolic autophagy pathway has emerged as a promising therapeutic target as demonstrated by the large number of clinical trials based on the autophagy inhibitor hydroxychloroquine (HCQ) and chloroquine (CQ), including a multi-centre Phase II study set up by our institution. While in established GBM cell lines autophagy acts as a pro-survival signal upon radiation, its role in response to genotoxic stress in primary GBM cells is unknown. The main objective of the present work is to investigate the role of autophagy in regulation of TMZ sensitivity in primary GBM cells. This is important given the ongoing clinical trials but also in the design of future trials.

Method

We inhibited autophagy both by pharmacological means and stable knockdown of the essential autophagy gene ATG7 in primary GBM cells. To study the effect of autophagy inhibition on response to TMZ, we used viability assays, growth curves and clonogenic assays.

Results

Inhibition of autophagy did not significantly alter growth properties of primary GBM cells at steady state. In contrast, in a subset of primary GBM lines inhibiting autophagy increased cytotoxicity of TMZ. Notably, the differential response to autophagy suppression is linked to correction of TMZ-induced DNA adducts.

Conclusion

This work implicates autophagy in regulation of TMZ sensitivity in primary GBM cells. Further investigation of mechanisms underlying the response to autophagy inhibition could lead to identification of new biomarkers for patient stratification in future clinical studies based on autophagy inhibitors and TMZ.