Acetyl-bufalin shows potent efficacy against non-small-cell lung cancer by targeting the CDK9/STAT3 signalling pathway.

BACKGROUND Cyclin-dependent kinase 9 (CDK9) is a promising prognostic marker and therapeutic target in cancers. Bufalin is an effective anti-tumour agent; however, the clinical application of bufalin is limited due to its high toxicity. Acetyl-bufalin, the bufalin prodrug, was designed and synthesised with higher efficiency and lower toxicity. METHODS Three non-small-cell lung cancer (NSCLC) cell lines, a xenograft model and a patient-derived xenograft (PDX) model were used to examine the effects of acetyl-bufalin. CDK9/STAT3 involvement was investigated by knockdown with siRNA, proteome microarray assay, western blot analysis and co-immunoprecipitation experiments. Acute toxicity test and pharmacokinetics (PK) study were conducted to assess the safety and PK. The human NSCLC tissues were analysed to verify high CDK9 expression. RESULTS We showed that CDK9 induced NSCLC cell proliferation and that this effect was associated with STAT3 activation, specifically an increase in STAT3 phosphorylation and transcription factor activity. Acetyl-bufalin is an effective and safety inhibitor of the CDK9/STAT3 pathway, leading to the impediment of various oncogenic processes in NSCLC. Molecular docking and high-throughput proteomics platform analysis uncovered acetyl-bufalin directly binds to CDK9. Consequently, acetyl-bufalin impaired the complex formation of CDK9 and STAT3, decreased the expressions of P-STAT3, and transcribed target genes such as cyclin B1, CDC2, MCL-1, Survivin, VEGF, BCL2, and it upregulated the expression levels of BAX and caspase-3 activity. Acetyl-bufalin inhibited tumour growth in NSCLC xenograft and PDX models. CONCLUSIONS Acetyl-bufalin is a novel blocker of the CDK9/STAT3 pathway thus may have potential in therapy of NSCLC and other cancers.