Endoplasmic reticulum (ER) stress and the subsequent adaptive cellular response, termed the unfolded protein response (UPR), have been implicated in several diseases, including cancer. In this review, I present a brief introduction to ER stress and the UPR and then summarize the importance of the IRE1α-XBP1 branch as a target for anticancer drug discovery. In addition, I introduce our approach to the identification of inhibitors against the IRE1α-XBP1 branch from microbial cultures. As a result of our screening, toyocamycin has been identified and toyocamycin showed anticancer activity against multiple myeloma.
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