Lung and bladder cancers are mostly incurable because of the early development of drug resistance and metastatic dissemination. Hence, improved therapies that tackle these two processes are urgently needed to improve clinical outcome. We have identified RSK4 as a promoter of drug resistance and metastasis in lung and bladder cancer cells. Silencing this kinase, through either RNA interference or CRISPR, sensitized tumor cells to chemotherapy and hindered metastasis in vitro and in vivo in a tail vein injection model. Drug screening revealed several floxacin antibiotics as potent RSK4 activation inhibitors, and trovafloxacin reproduced all effects of RSK4 silencing in vitro and in/ex vivo using lung cancer xenograft and genetically engineered mouse models and bladder tumor explants. Through x-ray structure determination and Markov transient and Deuterium exchange analyses, we identified the allosteric binding site and revealed how this compound blocks RSK4 kinase activation through binding to an allosteric site and mimicking a kinase autoinhibitory mechanism involving the RSK4's hydrophobic motif. Last, we show that patients undergoing chemotherapy and adhering to prophylactic levofloxacin in the large placebo-controlled randomized phase 3 SIGNIFICANT trial had significantly increased (P = 0.048) long-term overall survival times. Hence, we suggest that RSK4 inhibition may represent an effective therapeutic strategy for treating lung and bladder cancer.
Bibliographical noteFunding Information:
The authors acknowledge infrastructure support from the Cancer Research UK Imperial Centre, the Imperial Experimental Cancer Medicine Centre, and the National Institute for Health Research Imperial Biomedical Research Centre. O.E.P., M.J.S., and F.P. thank Cancer Research UK (CRUK) for funding S.C., U.M., and F.P. and CTRT for funding R.R. M.M.U.A. acknowledges CRUK funding (C33269/A11161 and C33269/A20752). S.N.Y. and M.B. acknowledge Engineering and Physical Sciences Research Council (EPSRC) grant EP/ N014529/1 supporting the EPSRC Centre for Mathematics of Precision Healthcare. D.J.P. thanks the Wellcome Trust Strategic Fund (PS3416). J.D. is funded by the Francis Crick Institute, which receives its core funding from Cancer Research UK (FC001070), the U.K. Medical Research Council (FC001070), and the Wellcome Trust (FC001070).
Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science.
ASJC Scopus subject areas