Increasing evidence exposes a subpopulation of cancer cells, known as cancer stem cells (CSCs), to be critical for the progression of several human malignancies, including glioblastoma multiforme (GBM). CSCs are highly tumorigenic, capable of self-renewal, and resistant to conventional therapies, and thus considered to be one of the key contributors to disease recurrence. In order to elucidate the poorly understood evolutionary path of tumor recurrence and the role of CSCs in this process, we developed patient-derived xenograft GBM recurrent models induced by anti-glioma chemotherapy, temozolomide (TMZ). In this model, we observed a significant phenotypic shift towards an undifferentiated population. We confirmed these findings in vitro as sorted CD133-negative populations cultured in differentiation-forcing media were found to acquire CD133 expression following chemotherapy treatment. To investigate this phenotypic switch at the single cell level, GSC-specific promoter-based reporter systems were engineered to track changes in the GSC population in real time. We observed the active phenotypic and functional switch of single non-stem glioma cells to a stem-like state and that TMZ therapy significantly increased the rate of single-cell conversions. Importantly, we showed the therapy induced HIF1α and HIF2α play key roles in allowing non-stem glioma cells to acquire stem-like traits, as the expression of both HIFs increase upon TMZ therapy and knockdown of HIFs expression inhibits the interconversion between non-stem glioma cells and GSCs post-therapy. Based on our results, we propose that anti-glioma chemotherapy promotes the accumulation of HIFs in the GBM cells that induces the formation of therapy-resistant GSCs responsible for recurrence.
- Received August 13, 2015.
- Revision received September 23, 2016.
- Accepted September 25, 2016.
- Copyright ©2016, American Association for Cancer Research.