Bone and soft-tissue sarcomas are rare malignant tumors comprising numerous histological subtypes. Novel effective therapies are still required. Recently, endoplasmic reticulum stress (ERs) responses have been suggested to be involved in the malignancy of various cancer types, prompting new studies focused on this area for the development of new therapies. Our previous proteomic study demonstrated an association between the ERs response and malignant behaviors in Ewing sarcomas (ESs). We also found that IRE1α inhibitors exert antitumor activity in ESs (Tanabe Y et al. Oncotarget 2017). To develop novel therapies for osteosarcomas (OSs), we performed comprehensive expression study of ERs genes using ER response arrays. Identified factors based on ER response arrays were investigated to elucidate these functional and antitumor activities using inhibitors of identified ERs in OSs.
To elucidate roles of main ER pathway in OS, we performed ER response arrays using OS cell lines. Based on results of ER response arrays, we conducted reverse transcription polymerase chain reaction (RT-PCR) and quantitative (q)-PCR to elucidate the expression of XBP1 and XBP1 splicing (XBP1s) variants in OS cell lines (143B, MG63, KHOS, KHOSR2, U2OS, U2OSR2) and surgical materials. Furthermore, we also performed XBP1 siRNA and inhibitor assays using several IRE1α-XBP1 inhibitors.
ER response arrays using OS cell lines indicated some other pathways including XBP1 had high expressions in transcriptome levels. As we suggested XBP1played crucial roles in OS cell lines, we conducted functional assay focusing on XBP1 in OS cell lines. Expression of XBP1 was confirmed in OS cell lines and surgical materials by RT-PCR. The knockdown of XBP1 expression by siRNA inhibited the cell proliferation of the OS cell lines. Regarding inhibitor assays using IRE1α-XBP1 inhibitors, toyocamycin exerted a strong anti-tumor effect (IC50 <0.07 [0.04 to 0.07] μM) in the OS cell lines, despite SYO1, synovial sarcoma cell line had resistance of the inhibitor.
We found the association between the ER response and the tumor activity in OS. We also found that IRE1α-XBP1 inhibitors suppressed cell growths in OS.
This study was supported by Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number #19H03789 and 19K22694 to Y.S.; 19K16753 to K.A.; 18K15329 to T.O.; # 18K16634 to Y.K.).
The authors.
This study was supported by Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Number #19H03789 and 19K22694 to Y.S.; 19K16753 to K.A.; 18K15329 to T.O.; # 18K16634 to Y.K.).
All authors have declared no conflicts of interest.