gms | German Medical Science

Objective: Malignant brain tumours contain a distinct sub-population of tumorigenic cells generally termed “brain tumour initiating cells” (BTICs) that possess biological features of adult neural stem cells. Recent findings indicate that BTICs comprise the major cellular component determining the invasive phenotype and resistance of malignant brain tumours to radio- and chemotherapy. Accordingly, BTICs have now emerged as the most relevant cell target for glioma therapy. The primary aim of our study is to isolate the BTIC populations from biopsy specimens and established glioma cell lines as well as characterizing their radioresponse in vitro and in vivo.

Methods: Neurosphere cultures were propagated under serum-free conditions. To select for radioresistance, cell populations were selected by exposing BTICs cultures to repetitive rounds of clinically relevant doses of ionizing radiation (IR). A tumorigenic potential of the BTICs cultures was evaluated by using an orthotopic glioma mouse model.

Results: Neurosphere cultures capable of a long-term self-renewal under serum-free cell culture conditions have been established from six glioma biopsy specimens and from well characterized glioma cell lines. Out of fifteen glioma cell lines tested, three (U251, G112 and G28) show a BTIC phenotype and form invasive intracranial tumours in an orthotopic glioma mouse model. Neurosphere cultures derived either from glioma specimens or from glioma cell lines display a radioresistant phenotype in response to IR. We selected a radioresistant population from the G112-BTIC culture and compared their radioresponse in vivo with that of the parental culture. Nude mice implanted with the IR-selected G112-BTIC population and treated with clinically relevant doses of IR had a significantly (P < 0.02) shorter average survival time than IR treated mice implanted with the parental G112-BTIC culture (60 days and 100 days, respectively).

Conclusions: Glioma-derived BTICs exposed to sublethal radiation doses accquire a radiation resistant phenotype, which is associated in vivo with increased invasive behavior and accelerated tumor progression. This model system provides a basis for targetting radio- and chemoresistant cell populations in GBM.