DDIT3 and prostate cancer: δ-tocotrienol induced cytotoxicity, apoptosis and autophagy on prostate cancer cells but not on non-cancerous melanocytes. δ-tocotrienol upregulated ERS markers (Grp78, phosphor-eIF2α & IRE1α) and ERS-related apoptosis markers (ATF4 & CHOP).Salubrinal and 4-phenylbutyrate protected the prostate tumour cells from δ-tocotrienol-induced ERS-mediated apoptosis and autophagy.