Metabolism-based isolation of invasive glioblastoma cells with specific gene signatures and tumorigenic potential.

BACKGROUND: Glioblastoma (GBM) is a highly aggressive brain tumor with rapid subclonal diversification, harboring molecular abnormalities that vary temporospatially, a contributor to therapy resistance. Fluorescence-guided neurosurgical resection utilizes the administration of 5-aminolevulinic acid (5-ALA) generating individually fluorescent tumor cells within a background population of non-neoplastic cells in the invasive tumor region. The aim of the study was to specifically isolate and interrogate the invasive GBM cell population using a novel 5-ALA-based method. METHODS: We have isolated the critical invasive GBM cell population by developing 5-ALA-based metabolic fluorescence-activated cell sorting. This allows purification and study of invasive cells from GBM without an overwhelming background "normal brain" signal to confound data. The population was studied using RNAseq, real-time PCR, and immunohistochemistry, with gene targets functionally interrogated on proliferation and migration assays using siRNA knockdown and known drug inhibitors. RESULTS: RNAseq analysis identifies specific genes such as SERPINE1 which is highly expressed in invasive GBM cells but at low levels in the surrounding normal brain parenchyma. siRNA knockdown and pharmacological inhibition with specific inhibitors of SERPINE1 reduced the capacity of GBM cells to invade in an in vitro assay. Rodent xenografts of 5-ALA-positive cells were established and serially transplanted, confirming tumorigenicity of the fluorescent patient-derived cells but not the 5-ALA-negative cells. CONCLUSIONS: Identification of unique molecular features in the invasive GBM population offers hope for developing more efficacious targeted therapies compared to targeting the tumor core and for isolating tumor subpopulations based upon intrinsic metabolic properties.

Light at the end of the tunnel: the learning curve associated with endoscopic transsphenoidal skull base surgery.

Endoscopic transsphenoidal resection of skull base lesions has been introduced widely as an alternative to microscopic transmucosal approaches. We report the introduction of this technique to our unit, including the learning curve recognized for this procedure, comparing techniques in a concurrent case-control fashion. All patients operated on for sellar, suprasellar, or clival lesions were considered for endoscopic surgery, with 51 patients undergoing endoscopic surgery and 46 having microscopic surgery with the operating method determined by the availability of the ear, nose, and throat surgeon involved with the procedures. Endoscopic surgery compared favorably with microscopic surgery with respect to endocrine control, length of stay, diabetes insipidus, and cerebrospinal fluid leakage. A learning curve was found with a significant fall in complication rates between the first third and most recent third of the cohort. Endoscopic skull base surgery has superior results to microscopic approaches once the initial learning curve is overcome, but this can be done quickly and safely.