The Histone Deacetylase Inhibitor Romidepsin Spares Normal Tissues While Acting as an Effective Radiosensitizer in Bladder Tumors in Vivo

Salome Paillas, Chee K. Then, Susan Kilgas, Jia Ling Ruan, James Thompson, Amy Elliott, Sean Smart, Anne E. Kiltie*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)
4 Downloads (Pure)


Purpose: Muscle-invasive bladder cancer has a 40% to 60% 5-year survival rate with radical treatment by surgical removal of the bladder or radiation therapy–based bladder preservation techniques, including concurrent chemoradiation. Elderly patients cannot tolerate current chemoradiation therapy regimens and often receive only radiation therapy, which is less effective. We urgently need effective chemotherapy agents for use with radiation therapy combinations that are nontoxic to normal tissues and tolerated by elderly patients. Methods and Materials: We have identified histone deacetylase (HDAC) inhibitors as promising agents to study. Pan-HDAC inhibition, using panobinostat, is a good strategy for radiosensitization, but more selective agents may be more useful radiosensitizers in a clinical setting, resulting in fewer systemic side effects. Herein, we study the HDAC class I-selective agent romidepsin, which we predict to have fewer off-target effects than panobinostat while maintaining an effective level of tumor radiosensitization. Results: In vitro effects of romidepsin were assessed by clonogenic assay and showed that romidepsin was effective in the nanomolar range in different bladder cancer cells and radiosensitized these cells. The radiosensitizing effect of romidepsin was confirmed in vivo using superficial xenografts. The drug/irradiation combination treatment resulted in significant tumor growth delay but did not increase the severity of acute (3.75 days) intestinal normal tissue toxicity or late toxicity at 29 weeks. Moreover, we showed that romidepsin treatment impaired both homologous recombination and nonhomologous end joining DNA repair pathways, suggesting that the disruption of DNA repair pathways caused by romidepsin is a key mechanism for its radiosensitizing effect in bladder cancer cells. Conclusions: This study demonstrates that romidepsin is an effective radiosensitizer in vitro and in vivo and does not increase the acute and late toxicity after ionizing radiation. Romidepsin is already in clinical use for the cutaneous T-cell lymphoma, but a phase 1 clinical trial of romidepsin as a radiosensitizer could be considered in muscle-invasive bladder cancer.

Original languageEnglish
Pages (from-to)212-221
Number of pages10
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number1
Early online date8 Apr 2020
Publication statusPublished - 1 May 2020

Bibliographical note

Funding Information:
This work was funded by Cancer Research UK (CRUK; C5255/A23755). J.L.R. was funded by CRUK (project grant C15140/A19817). C.K.T. was funded by a CRUK DPhil Research Training and Support Grant, the Balliol College Alfred Douglas Stone Scholarship, and the University of Oxford Clarendon Fund. S.K. was funded by a CRUK/MRC Oxford Institute of Radiation Oncology CRUK studentship.


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