Abstract LB-400: Tannic acid induces prostate cancer cell death via unfolded protein response (UPR) and modulation of CHOP
Authors: Hatami Elham , Nagesh Prashanth Kumar Bhusetty , Chowdhury Pallabita , Kashyap Vivek K. , Khan Sheema , Hafeez Bilal , Jaggi Meena , Chauhan Subhash C. , Yallapu Murali M. 
Published: August 2018

Objectives: Endoplasmic reticulum (ER) is an intricate organelle that is crucial for cellular function and survival. Cellular environments that interfere with ER functioning can lead to the accumulation of unfolded proteins, which are sensed by transmembrane sensors that instigate the unfolded protein response (UPR) to reinstate ER proteostasis. When the UPR is perturbed or not sufficient to deal with the stress conditions, apoptotic cell death is ensued. Often, prostate tumor cells (PrCa) are exposed to intrinsic and external factors that alter protein homeostasis producing endoplasmic reticulum (ER) stress. IRE1, PERK, and ATF6 are key signaling stems of the UPR during ER stress. At molecular level, dimerization of PERK kinase phosphorylates eIF2α, resulting in translation attenuation. This selectively enhances translation of the ATF4 transcription factor. Also, activated IRE1 stimulates the nuclear translocation of XBP1. Both ATF4 and XBP1 induces expression of UPR genes. The UPR stimulates and protects tumor cells against stressful conditions within the tumor microenvironment. Therapeutic intervention on this aspect ER Stress mediated apoptosis is much needed. Here, we examined the mechanistic role of tannic acid (TA) through novel targeting inhibition of UPR via modulation of ER stress in PrCa cell death.

Methods: In vitro therapeutic perspective of tannic acid was evaluated using clinically relevant human prostate cancer cell line models (C4-2, PC3 and DU145) through cell proliferation and clonogenic assays. The anti-metastatic potential of TA in PrCa cells was determined using invasive and migration studies. The phase arrest and concomitant apoptosis in PrCa cells were examined using Propidium Iodide based flow cytometric studies. TA induced ER stress-mediated UPR cellular apoptotic activity was confirmed using Western blot, real-time studies, and nuclear distortion studies.

Results: Protein profiling results have showed yin approach of inhibition ER stress during TA treatments with the inhibition of CHOP protein. Also, we observed TA treated PrCa cells was able to induce ER stress response proteins, such as PERK and IRE1. Its downstream signaling events include the induction of XBP1, EIF2α expression key mediators by alteration of Bcl2/Bax ratio from shifting survival towards apoptosis. With this line we assessed the expression profile of apoptosis-associated markers such as Bid and Bim (upregulated), and Bcl-2 and Bcl-xL which ratifies the induction of apoptosis during treatments. TA exhibited prominent growth arrest at G1 phase and increase of concentration led to elevated sub G1, annotating the increase of apoptotic cells. The expression of P18 and P21 were increased during TA treatments and cyclin D1 expression was inhibited supporting the G1 phase cell arrest. The expression of MMP2 and MMP9 were reduced, signifying the superior anti-metastatic ability of this compound. Cell proliferation studies showed a dose-dependent inhibitory profile of TA. Distinct results of anti-migratory and anti-metastatic effects of TA was observed during treatments.

Conclusion: This study suggests that TA can efficiently induce UPR and promote ER stress signaling in cells that renders apoptosis in PrCa cells by the over expression of CHOP. We believe this novel therapeutic paradigm have clinical significance in advanced PrCa.

Citation Format: Elham Hatami, Prashanth Kumar Bhusetty Nagesh, Pallabita Chowdhury, Vivek K. Kashyap, Sheema Khan, Bilal Hafeez, Meena Jaggi, Subhash C. Chauhan, Murali M. Yallapu. Tannic acid induces prostate cancer cell death via unfolded protein response (UPR) and modulation of CHOP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-400.