Abstract 4491: Development of IRE-1 inhibitors for B cell cancer therapy
Authors: Shao Andong , Tang Chih-Hang Anthony , Valle Juan R. Del , Hu Chih-Chi Andrew 
Published: March 2024

Abstract
In response to the endoplasmic reticulum (ER) stress, the IRE-1 kinase/RNase splices the mRNA of the XBP-1 gene, resulting in the spliced XBP-1 (XBP-1s) mRNA that encodes the functional XBP-1s transcription factor. XBP-1s is critically important for the growth and survival of B cell leukemia, lymphoma, and multiple myeloma. When compared with other inhibitors targeting IRE-1, the tricyclic chromenone-based inhibitors B-I09 and D-F07, prodrugs harboring an aldehyde-masking group, emerged as the very reliable inhibitors for potent suppression of the XBP-1s protein. Protection of the aldehyde as a 1,3-dioxane acetal led to strong fluorescence emitted by the coumarin chromophore, enabling both B-I09 and D-F07 to be tracked inside the cell. We installed a photolabile structural cage on the hydroxy group of D-F07 to generate PC-D-F07. Such a modification significantly stabilized the 1,3-dioxane acetal protecting group, allowing for specific stimulus-mediated control of the inhibitory activity. Upon photoactivation, the re-exposed hydroxy group triggered the aldehyde-protecting 1,3-dioxane acetal to slowly decompose, leading to the inhibition of the RNase activity of IRE-1. Since chemical modifications of the hydroxy group could be used to tune 1,3-dioxane prodrug stability, we installed reactive oxygen species (ROS)-sensitive boronate cage groups onto B-I09 (BC-B-I09) and D-F07 (BC-D-F07) to achieve stimuli-responsive activities and improve tumor-targeting efficiency based on that cancerous B cells indeed produced higher levels of ROS than normal B cells. These boronate caged compounds could be further combined with the FDA-approved Auranofin, a thioredoxin reductase inhibitor, to achieve synergistic cancer-killing effects. These results led us to further develop a novel prodrug, TC-D-F07, in which a thiol-reactive dinitrobenzenesulfonyl (Dns) cage was installed onto the hydroxy group of D-F07. The electron-withdrawing Dns group in TC-D-F07 similarly stabilized the neighboring 1,3-dioxane acetal, allowing for stimulus-mediated control of its inhibitory activity. TC-D-F07 exhibited high sensitivity to intracellular thiols produced by cancerous B cells. In addition, when TC-D-F07 was decomposed into D-F07, we observed that a dinitrophenyl cysteine adduct resulting from cleavage of the Dns group could induce the ER stress, causing cancerous B cells to increase the expression of XBP-1s. However, the accumulated levels of D-F07 from TC-D-F07 and its gradual decomposition into the active IRE-1 inhibitor could eventually deprive cancer cells of all XBP-1s, leading to more severe apoptosis in TC-D-F07-treated than in D-F07-treated cells. Thus, TC-D-F07 with both ER stress-inducing and XBP-1s-inhibiting activities represents an IRE-1-targeting caged prodrug that can be used to treat B cell cancer effectively.
Citation Format: Andong Shao, Chih-Hang Anthony Tang, Juan R. Del Valle, Chih-Chi Andrew Hu. Development of IRE-1 inhibitors for B cell cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4491.