Lysine Specific Demethylase-1 (LSD-1) overexpression correlates with undifferentiated prostate cancer and predicts poor survival. Demethylation of lysine residues on histone protein by LSD-1 also mediates Epithelial-Mesenchymal Transition (EMT) and resistance to chemotherapy by genome-wide reprogramming of large heterochromatin domains (Large Organized Chromatin K (lysine) modifications or “LOCKs”) to a state of reduced H3 Lys9 dimethylation (H3K9Me2), a repressive mark. This leads to a more stem cell like state of chromatin and enables transcription of genes that confer survival advantage in a given cellular environment. Activation of c-Myc signaling is downstream from several different oncogenic survival pathways and has been shown to mediate EMT and docetaxel resistance in prostate cancer cells. In this study, we investigate the effect of LSD-1 inhibition on sensitivity to docetaxel in docetaxel resistant prostate cancer cells, PC-3D12 (donated to us by Dr. William Watson and Dr. Amanda O’Neill, University College Dublin, Ireland), using HCI2509, a reversible LSD-1 inhibitor. We also investigate LSD-1 and c-Myc expression in PC-3D12 cells in comparison to the docetaxel sensitive parent cell line PC-3, and the effect of LSD-1 inhibition on H3K9Me2 and c-Myc signaling in these cells.
We performed cell viability assays on PC-3 and PC-3D12 cells with increasing concentrations of HCI2509 alone and docetaxel alone. We then pretreated PC-3D12 cells with a sub-toxic dose of HCI2509 for 48 hours and performed cell viability assays with increasing concentrations of docetaxel in continued presence of the constant sub-toxic dose of HCI2509. Next, western blot analysis was performed for LSD-1, c-Myc, H3K9me2 and GAPDH using whole cell lysates from PC-3D12 and PC-3 cells treated with vehicle and increasing doses of HCI2509 for 48 hours.
PC-3D12 cells were more resistant to treatment with docetaxel than PC-3 cells with an approximately 10-fold difference in sensitivity. HCI2509 pretreated PC-3D12 cells had an approximately 10-fold improvement in chemosensitivity to docetaxel, to a range similar to the chemosensitive PC-3 cells. Western Blot analyses of whole cell lysates of untreated PC-3 and untreated PC-3D12 cells showed higher LSD-1 protein and c-Myc protein levels in PC-3D12 cells compared to PC-3 cells. Treatment with HCI2509 resulted in a dose dependent decrease in c-Myc levels and an increase in H3K9me2 mark in PC-3D12 cells.
We conclude that LSD-1 overexpression correlates with chemoresistance in prostate cancer. LSD-1 inhibition rescues chemosensitivity to docetaxel with inhibition of c-Myc signaling in docetaxel resistant prostate cancer cell line and can be developed as a potential treatment strategy in docetaxel resistant prostate cancer.
Citation Format: Sumati Gupta, Alexis Weston, Jared Bearrs, Raffaella Soldi, Sunil Sharma. Effect of LSD-1 inhibition on docetaxel resistance in prostate cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 96. doi:10.1158/1538-7445.AM2015-96