Table 1.

Summary of studies investigating CSC and TMZ

Author	serum free medium used?	Key findings (on TMZ and CSC)	Problems
Eramo et al. (2006)	Yes	High resistance of neurosphere cultures to different drugs	No detailed investigation of stem cell properties.
Liu et al. (2006)	Initial culture with serum	Differential susceptibility of CD133+ as compared to CD133- cells	No confirmation in vivo, non-physiological TMZ concentrations
Clement et al. (2007)	Yes	Reduced clonogenicity by TMZ.	Study did not investigate TMZ effects in detail.
Ghods et al. (2007)	No	Gliosarcoma cells grown as neurospheres were more resistant to TMZ than the same cells grown as monolayer.	Study did not control for different growth conditions (spheres vs. monolayer).
Chua et al. (2008)	No	Increase of SP cell population after TMZ treatment.	No in vivo study on tumorigenicity, serum cultured cell lines (U87).
Beier et al. (2008)	Yes	Depletion of clonogenic and tumorigenic cells by TMZ.	Only a few concentrations investigated.
Bleau et al. (2009)	No (serum-free medium only for neurosphere experiments)	Increased tumorigenicity of glioma cell derived from murine glioma model after long term TMZ treatment (14d). First study that proved that TMZ may increase the tumorigenicity of gliomas.	Murine cells, no information on MGMT methylation status.
Blough et al. (2010)	Yes	Susceptiblity of CSC lines dependent on MGMT expression and promoter status.	No detailed assessement of stem cell properties.
Larmoral-Theys et al. (2010)	No	Decreased tumorigenicity of an oligodendroglial cell line after long-term TMZ treatment.	Serum cultured cell lines; no detailed assessment of stem cell properties.
Glas et al. (2010)	Yes	Differential susceptibility of peripheral and central CSC lines to TMZ. No constant difference between central and peripheral samples.	No systematic assessment of stem cell properties and MGMT status. Conflicting data to Pistolatto et al.
Pistolatto et al. (2010)	Yes	Higher resistance of central, hypoxic CD133 CSC as compared to cells derived from the periphery due to increased MGMT expression.	No validation in a larger set of samples. Conflicting data to Glas et al.
Mihaliak et al. (2010)	Yes	Initial reduction of neurosphere-like growth after TMZ challenge; recovery in 4/5 CSC lines.	No assessment of the MGMT status; only a few concentrations investigated.
Gilbert et al. (2010)	Yes	Initial reduction of neurosphere-like growth after TMZ challenge; inhibition of neurosphere recovery using by NOTCH inhibition.	See comment on Milhaliak et al.
Villalva et al. (2011)	Yes	Decreased clonogenicity after treatment with TMZ.	Study did not investigate TMZ effects in detail.
Hsieh et al. (2010)	Yes	Activation of IGF or shh increases the resistance of CSC to TMZ. Differentiated CSC (with 10% serum) were more susceptible to acute TMZ toxicity than CSC lines.	No controls for different growth conditions (spheres vs. monolayer and serum vs. stem cell medium) mentioned.