Identification of Bulbocodin D and C as novel STAT3 inhibitors and their anticancer activities in lung cancer cells

Cancer stands as one of the predominant causes of mortality globally, necessitating ongoing efforts to develop innovat-ive therapeutics. Historically, natural products have been foundational in the quest for anticancer agents. Bulbocodin D (BD) and Bulbocodin C (BC), two bibenzyls derived from Pleione bulbocodioides (Franch.) Rolfe, have demonstrated notable in vitro antican-cer activity. In human lung cancer A549 cells, the IC50s for BD and BC were 11.63 and 11.71 mu mol center dot L-1, respectively. BD triggered ap-optosis, as evidenced by an upsurge in Annexin V-positive cells and elevated protein expression of cleaved-PARP in cancer cells. Fur-thermore, BD and BC markedly inhibited the migratory and invasive potentials of A549 cells. The altered genes identified through RNA-sequencing analysis were integrated into the CMap dataset, suggesting BD's role as a potential signal transducer and activator of transcription 3 (STAT3) inhibitor. SwissDock and MOE analyses further revealed that both BD and BC exhibited a commendable binding affinity with STAT3. Additionally, a surface plasmon resonance assay confirmed the direct binding affinity between these compounds and STAT3. Notably, treatment with either BD or BC led to a significant reduction in p-STAT3 (Tyr 705) protein levels, regardless of interleukin-6 stimulation in A549 cells. In addition, the extracellular signal-regulated kinase (ERK) was activated after BD or BC treatment. An enhancement in cancer cell mortality was observed upon combined treatment of BD and U0126, the MEK1/2 inhibitor. In conclusion, BD and BC emerge as promising novel STAT3 inhibitors with potential implications in cancer therapy.