Selective inhibition of HDAC6 promotes bladder cancer radiosensitization without inducing CXCL1 signalling

Although bladder-preserving trimodality therapy is recognized for patients with muscle-invasive bladder cancer (MIBC), chemotherapy can have toxic effects. Inhibitors to histone deacetylases (HDACis) have been identified as an effective strategy to enhance the radiotherapy (RT) effect, and several of them have clinical efficacy in BC. However, little is known about how a specific HDAC6 inhibitor (HDAC6i) acts in concert with RT. Knockdown of HDAC6 enhanced the radiosensitization of BC cells and increased γH2AX accumulation, similar to the effect of panobinostat, a pan-HDACi. Applying tubacin, a selective HDAC6i, to T24 cells induced H3K9ac and α-tubulin acetylation, and significantly decreased clonogenic cell survival when combined with RT. Further transcriptomic analysis of shHDAC6-transduced T24 cells under irradiation showed that genes that were highly downregulated compared to the levels in response to RT alone were significantly enriched in the inflammatory response. Moreover, HDAC6 knockdown counteracted the RT-induced mRNA expression of CXCL1, SERPINE1, SDC1 and SDC2. Importantly, tubacin suppressed RT-promoted invaded/migrated T24 cells, whereas panobinostat elevated RT-induced CXCL1 expression and invasion/migration abilities. This phenotype was significantly abrogated by the CXCL1 antibody, indicating that RT-induced CXCL1 is the key regulator contributing to BC malignancy. Immunohistochemical evaluation of tumours from BC patients supported the correlation between CXCL1 overexpression and poor prognosis. Unlike the pan-HDACi, the selective HDAC6i tubacin can enhance BC radiosensitization and suppress RT-induced oncogenic CXCL1-Snail signalling, thus further advancing the therapeutic potential of tubacin with RT. RNAs were extracted from T24 cell line and profiled by RNA-seq