Introduction Ovarian cancer (OVCA) is a lethal gynecologic malignancy. Patients with high-grade and low-grade disease carry a poor prognosis from chemoresistance and decreased induction of apoptosis. We hypothesized persistent activation of the unfolded protein response (UPR) with upregulation of CHOP and XAF-1 arms, would overcome apoptotic arrest, leading to death in chemo-sensitive and resistant OVCA.

Methods Patient-derived and commercially available HG and LG OVCA cells were cultured and treated with celastrol, a potent UPR activator. Cell viability was assessed using Incucyte. Protein lysates of cells treated with celastrol were analyzed using Western blot and Caspase-Glo. RNA was analyzed using real-time PCR. Transient knock down (KD) of XAF-1 and CHOP was performed using siRNA.

Results Celastrol induced cell death in chemo-sensitive and resistant OVCA lines in the nanomolar range. Celastrol induced the UPR.

CHOP was preferentially upregulated upstream of mitochondrial depolarization and induction of the intrinsic apoptotic pathway. There was a reciprocal rise in XAF-1 RNA/protein levels and fall in XIAP with UPR activation. KD of XAF-1 decreased the cytotoxic effect of celastrol. KD of CHOP resulted in a lack of rise in XAF-1 with UPR activation.

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Abstract 337 Figure 1

Conclusions Activating UPR with agents that upregulate the CHOP/XAF-1 axis induce death in chemo-sensitive/resistant OVCA lines. XAF-1 is presumptively regulated by CHOP and a major effector of UPR, required for full cytotoxic activity. The CHOP/XAF-1 arm of UPR is a promising targetable pathway for treating HG/LG OVCA.