Inhibition of P4HB sensitizes GBM cells to TMZ-mediated cell death. (A) Western blot confirmed siP4HB knockdown after 48 h and 120 h of transfection in D54-R and U87-R cells. β-Actin was used as a reference control. Two different siRNAs against different exons of P4HB were tested (ie, siP4HB_1 and siP4HB_2), and a nonspecific siRNA (siCtrl) was used in parallel. (B) Decrease in cell viability after knockdown of P4HB in D54-R and U87-R cells when compared to the siCtrl. This trend of effect is augmented in TMZ dose-dependent manner (250, 500, 1000 and 2000 µM). *P = .05; **P = .01. (C) Colony formation assay shows a decrease in cell growth after P4HB knockdown in TMZ-treated D54-R and U87-R cells (upper panel). Western blot confirmed P4HB expression was still inhibited after the incubation period of 14 days (lower panel). (D) P4HB inhibitor (bacitracin, BAC) decreased the percentage of GBM cell viability. Effect is significantly augmented at TMZ concentrations of 500 and 1000 μM. (E) Representative clonogenic pictures showing few colonies of D54-R and U87-R formed after treatment with BAC and TMZ at 500 and 1000 µM.