A novel anti-breast cancer stemness agent optimized from marine-derived bisindole Calcicamide A targeting the IL-6/JAK2/STAT3 signaling pathway

This study focuses on the optimization of Calcicamide A, a marine-derived bisindole natural product, as a novel anti-breast cancer stemness agent targeting the IL-6/STAT3 signaling pathway. We report the first total synthesis of Calcicamide A, which demonstrates a selective inhibitory effect on breast cancer, and design a series of derivatives to explore their structure-activity relationships (SARs). Among these, XQ-26 emerges as a potent inhibitor of breast cancer (BC) stemness, demonstrating significant anti-proliferative effects on BC cell lines. XQ-26 effectively suppresses colony formation, migration, invasion, and tumorsphere formation of BC cells, while reducing the tumor stemness markers CD133+ and CD44+. It also induces apoptosis and G1 phase cell cycle arrest in BC cells. Mechanistically, XQ-26 targets the IL-6/JAK2/STAT3 signaling pathway by downregulating the protein levels of IL-6 receptors (gp130 and gp80), decreasing phosphorylated JAK2 (p-JAK2) and phosphorylated STAT3 (p-STAT3) levels at Tyr705 and Ser727 residues, and inhibiting STAT3 nuclear translocation, thereby regulating the expression of downstream target genes related to cell cycle (Cyclin D1, CDK4) and apoptosis (Bax, Bcl-2, PARP). In vivo, XQ-26 significantly inhibits 4T1 tumor growth with minimal toxicity and enhances the therapeutic efficacy of cisplatin. These findings highlight XQ-26 as a promising anti-breast cancer stemness agent, offering a potential therapeutic strategy for BC treatment.