Inhibition of ER stress–associated IRE-1/XBP-1 pathway reduces leukemic cell survival
Chih-Hang Anthony Tang, … , Juan R. Del Valle, Chih-Chi Andrew Hu
Chih-Hang Anthony Tang, … , Juan R. Del Valle, Chih-Chi Andrew Hu
Published May 8, 2014
Citation Information: J Clin Invest. 2014;124(6):2585-2598. https://doi.org/10.1172/JCI73448.
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Research Article Oncology

Inhibition of ER stress–associated IRE-1/XBP-1 pathway reduces leukemic cell survival

Abstract

Activation of the ER stress response is associated with malignant progression of B cell chronic lymphocytic leukemia (CLL). We developed a murine CLL model that lacks the ER stress–associated transcription factor XBP-1 in B cells and found that XBP-1 deficiency decelerates malignant progression of CLL-associated disease. XBP-1 deficiency resulted in acquisition of phenotypes that are disadvantageous for leukemic cell survival, including compromised BCR signaling capability and increased surface expression of sphingosine-1-phosphate receptor 1 (S1P1). Because XBP-1 expression requires the RNase activity of the ER transmembrane receptor IRE-1, we developed a potent IRE-1 RNase inhibitor through chemical synthesis and modified the structure to facilitate entry into cells to target the IRE-1/XBP-1 pathway. Treatment of CLL cells with this inhibitor (B-I09) mimicked XBP-1 deficiency, including upregulation of IRE-1 expression and compromised BCR signaling. Moreover, B-I09 treatment did not affect the transport of secretory and integral membrane-bound proteins. Administration of B-I09 to CLL tumor–bearing mice suppressed leukemic progression by inducing apoptosis and did not cause systemic toxicity. Additionally, B-I09 and ibrutinib, an FDA-approved BTK inhibitor, synergized to induce apoptosis in B cell leukemia, lymphoma, and multiple myeloma. These data indicate that targeting XBP-1 has potential as a treatment strategy, not only for multiple myeloma, but also for mature B cell leukemia and lymphoma.

Authors

Chih-Hang Anthony Tang, Sujeewa Ranatunga, Crystina L. Kriss, Christopher L. Cubitt, Jianguo Tao, Javier A. Pinilla-Ibarz, Juan R. Del Valle, Chih-Chi Andrew Hu

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Figure 5

IRE-1 inhibitors with masked aldehyde moieties potently suppress XBP-1s expression and leukemic growth.

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IRE-1 inhibitors with masked aldehyde moieties potently suppress XBP-1s ...
(A) WaC3 CLL cells were treated with indicated compounds for 24 hours and lysed for RNA extraction. Human unspliced XBP1 (XBP1u), spliced XBP1 (XBP1s), and actin were detected by RT-PCR using specific primers. Data are representative of 3 experiments. (B) Mouse B cells were stimulated with LPS for 48 hours to allow for XBP-1s expression, and then treated with indicated inhibitors for 24 hours. Lysates were immunoblotted for XBP-1s and p97. Data are representative of 3 experiments. (C) LPS-stimulated B cells were treated with 0, 1.25, 2.5, 5, 10, 20, 40, 80, or 160 mM B-H09 for 24 hours. Equal amounts of lysates were immunoblotted for XBP-1s. The XBP-1s protein band intensity was determined using ImageJ. The percentage of inhibition was determined by comparing with the untreated group. Data from 3 experiments were plotted as mean ± SEM. (D) Mouse CD3–IgM+CD5+ Eμ-TCL1 CLL cells were treated with DMSO or indicated inhibitors for 3 days and subjected to XTT assays. Percentages of growth were determined by comparing inhibitor-treated with DMSO-treated groups. Data from 4 identical experimental groups were plotted as mean ± SD. Results are representative of 3 experiments. (E and F) Primary CLL cells from 2 human patients were treated with DMSO or indicated inhibitors (20 μM), subjected to XTT assays, and similarly analyzed. Data from 4 identical experimental groups were plotted as mean ± SD. Results are representative of 3 experiments.