Abstract 3335: A novel and potent IRE1α RNase inhibitor, HM100168 as a promising therapeutic strategy in solid cancers
Authors: Kim Jisook , Jung Seung Hyun , Kim Minjeong , Park Wongi , Byun Jooyun , Park Soonki , Lee Miyoung , Kim Yu-Yon , Park Junghwa , Hong Seokhyun , Kim Minhwa , Ahn Young Gil 
Published: March 2024

Abstract
Protein folding homeostasis in the endoplasmic reticulum (ER) is regulated by a signaling network called the unfolded protein response (UPR). Inositol-requiring enzyme 1α (IRE1α) is an ER membrane-resident kinase/RNase that mediates signal transmission in the most evolutionarily conserved way of the UPR. The IRE1α-XBP1 pathway, one of the most essential branches of the UPR, is activated in various types of cancer. When IRE1α is activated, the spliced form of XBP1 (XBP1s) is generated to activate the transcription of many pro-survival genes to prevent cellular death and relieve cellular stress. IRE1α plays an instrumental pro-tumoral role in various cancers, such as glioblastoma, myeloma, lung adenocarcinoma, and breast cancers, as well as high IRE1α activity is associated with poor prognoses. Moreover, IRE1-XBP1 plays an essential role in the UPR and ER stress responses, which have been implicated in the development of drug resistance. Thereby, blockade of the IRE1α-XBP1 pathway is crucial as it is considered as a potential anti-cancer strategy. Here, we developed a potent and selective IRE1α RNase inhibitor, which have a hydroxy-aryl-aldehydes (HAA) moiety that binds to IRE1α within the RNase catalytic site. Our lead compound, HM100168, potently inhibited the RNase activity of human IRE1α at nanomolar concentrations without affecting its kinase activity. Experiments were performed on MCF7 breast cancer cells to confirm the inhibitory effect in the mRNA and protein levels of XBP1s, which was increased by tunicamycin (TM), a ER stress inducer. HM100168 strongly inhibited ​​XBP1s levels in a dose-dependent manner, displaying the potent IC50 values. We tested cell growth inhibition activity in 3D as well as 2D cell culture condition of various cancer cell lines. Interestingly, HM100168 effectively inhibited cell proliferation of diverse cancer cell lines in both 2D and 3D culture condition. In addition, we explored the promising anti-cancer effects of HM100168 and its synergistic potential when combined with anti-tumorigenic agents. As a result, HM100168 in combination with anti-tumorigenic agents significantly enhanced suppression of tumor growth in human cancer cell transplanted mice. In conclusion, we have identified a novel compound with unique properties that specifically blocked the endonuclease activity of IRE1α. HM100168 inhibited IRE1α endonuclease activity, without affecting its kinase activity after endoplasmic reticulum stress in vitro. The identification of this novel IRE1α inhibitor supports the hypothesis that the IRE1α-XBP1 axis is a promising target for anticancer therapy. Also, co-targeting of IRE1α-XBP1 in combination with anti-tumorigenic agents can be considered a novel approach to overcome cancer resistance. Further preclinical studies will be performed and reported soon after the establishment of a preclinical candidate.
Citation Format: Jisook Kim, Seung Hyun Jung, Minjeong Kim, Wongi Park, Jooyun Byun, Soonki Park, Miyoung Lee, Yu-Yon Kim, Junghwa Park, Seokhyun Hong, Minhwa Kim, Young Gil Ahn. A novel and potent IRE1α RNase inhibitor, HM100168 as a promising therapeutic strategy in solid cancers [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 3335.