GAPDH and neoplasm: Moreover, adding 35 μM TMZ after knockdown of defense genes further lysed tumor sphere-initiating cells (Fig. 3a, a; Additional file 1: Figure S2), which was not seen in those transfected with siRNA targeting housekeeping gene, glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) (Fig. 3a, a).