Inhibition of SPARC expression in LN443 suppresses pro-apoptotic signaling, increases colony forming efficiency, eliminates SPARC-induced pro-death signaling in temozolomide (TMZ), and has no effect on survival in TMZ. A. Representative Western blots of LN443 cells treated with control siRNA (Csi) or SPARC siRNA (SPARCsi) for 72 hr. Equal numbers of siRNA-treated cells were plated overnight in growth serum, and then treated with 0 (0.1% DMSO control), or 40, 80 or 100 μM TMZ for 2 days before lysing. Arrows indicate ≥ 2-fold increases or decreases due to SPARC siRNA treatment. Asterisks indicate ≥ 2-fold increases or decreases due to TMZ treatment. B. Means for colony forming efficiency ± SD of LN443 ± SPARC siRNA plating 375 cells/60-mm dish. * p = 0.018. C. Means for surviving fraction ± SD of LN443 ± SPARC siRNA ± increasing concentrations of TMZ plating 375 cells/60-mm dish. Plating 750 cells gave similar results.