Melatonin and Andrographolide synergize to inhibit the colospheroid phenotype by targeting Wnt/beta-catenin signaling

Abstract

β-catenin signaling, and angiogenesis are associated with colospheroid (CSC), development. CSCs, spheroids derived from colon cancer cells, are responsible for metastasis, drug resistance, and disease recurrence. Whether dysregulating β-catenin and inhibiting angiogenesis reduces CSC growth is unknown. In this study, the molecular mechanism of CSC growth inhibition was evaluated using a novel combination of melatonin (MLT) and andrographolide (AGP). These drugs have anti-carcinogenic, antioxidant, and anti-metastatic properties. CSCs were obtained from two metastatic colon cancer cell lines (HT29 and HCT-15). The viability and stemness were monitored (FDA PI staining and immunoblot for CD44, CD133, Nanog, Sox2 and Oct4). The drug combination synergistically diminished stemness via increased ROS levels, reduced mitochondrial membrane potential and ATP level. MLT+AGP induced cell death by inhibiting β-catenin expression and its downregulatory signals, Cyclin D1, c-Myc. MLT+AGP treated cells exhibited translocation of phospho-β-catenin to the nucleus and de-phosphorylated-β-catenin. Downregulation of β-catenin activation and its transcription factors (TCF4, LEF1) and GTP binding/G-protein related activity were found in the dual therapy. Angiogenic inhibition is consistent with downregulation of VEGF mRNA transcripts (VEGF189), phosphorylated VEGF receptor protein expression, matrigel invasion, and capillary tube inhibition. In vivo, the intravenous injection of MLT+AGP slowed HT29 metastatic colon cancer. Histopathology indicated significant reduction in microvascular density and tumor index. Immunohistochemistry for caspase 7, and β-catenin found increased apoptosis and downregulation of β-catenin signals. The mechanism(s) of decreased colospheroids growth were the inhibition of the Wnt/β-catenin pathway. Our results provide rationale for using MLT in combination with AGP for inhibition of CRCs.