Toyocamycin (hydrate)

Toyocamycin is a natural adenosine analog first isolated from Streptomyces and shown in early studies to be cytotoxic to bacteria, fungi, and cancer cells and to have antiviral activities. Toyocamycin prevents IRE1α-induced mRNA cleavage (IC₅₀ = 80 nM) and inhibits constitutive activation of XBP1 in multiple myeloma cell lines.¹ It is used to study IRE1α action in the endoplasmic reticulum stress response, particularly in the context of cancer.^2,3 It also inhibits phosphatidylinositol kinase in vitro (IC₅₀ = 3.3 µg/ml), but not in cells, and blocks the ribosomal RNA-processing kinase Rio1 (IC₅₀ = ~30 nM).^4,5

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1. Ri, M., Tashiro, E., Oikawa, D., et al. Identification of Toyocamycin, an agent cytotoxic for multiple myeloma cells, as a potent inhibitor of ER stress-induced XBP1 mRNA splicing. Blood Cancer J. 2(7), (2016).

2. Chien, W., Ding, L.W., Sun, Q.Y., et al. Selective inhibition of unfolded protein response induces apoptosis in pancreatic cancer cells. Oncotarget 5(13), 4881-4894 (2014).

3. Sun, H., Lin, D.C., Guo, X., et al. Inhibition of IRE1α-driven pro-survival pathways is a promising therapeutic application in acute myeloid leukemia. Oncotarget 7(14), 18736-18749 (2016).

4. Nishioka, H., Sawa, T., Hamada, M., et al. Inhibition of phosphatidylinositol kinase by toyocamycin. J. Antibiot. (Tokyo) 43(12), 1586-1589 (1990).

5. Kiburu, I.N., and LaRonde-LaBlanc, N. Interaction of Rio1 kinase with toyocamycin reveals a conformational switch that controls oligomeric state and catalytic activity. PLoS One 7(5), (2016).