Repurposed floxacins targeting RSK4 prevent chemoresistance and metastasis in lung and bladder cancer.

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.

Regenerative repair after endoluminal injury in mice with specific antagonism of protease activated receptors on CD34+ vascular progenitors.

Tissue factor (TF) and thrombin are involved in intimal hyperplasia (IH) and remodelling following vascular injury. Because many neointimal smooth muscle cells (VSMCs) derive from circulating vascular progenitors (VPs), we investigated how thrombin influences VP phenotype and function. Following wire-induced carotid artery injury in mice, the majority of circulating VPs expressed TF, were capable of initiating clotting in vitro, and had protease-activated receptors (PAR)-1, -2, and -4. Thrombin, through PAR-1, inhibited apoptosis and caused proliferation, resulting in the outgrowth of VP coexpressing markers of activated endothelial cells and VSMCs, even in the presence of growth factors. These mixed-phenotype VPs circulated as a minority population after injury and shared a similar phenotype with many neointimal cells. Labeled CD34(+) cells, injected up to 2 weeks after injury, could be detected in the injured vessel wall, suggesting that continued recruitment may contribute to progressive IH. Finally, CD34(+) cells incubated with thrombin prior to injection promoted florid neointimal lesions, whereas those incubated with PAR antagonists inhibited IH and promoted regenerative repair characterized by the development of a quiescent endothelium. We conclude that IH after vascular injury is due to the direct actions of thrombin on mobilized VPs.