Justicidin A inhibits AKT/mTOR and activates type III PI3K/beclin 1 signaling pathways leading to autophagy of human colorectal cancer cells

Abstract

Justicidin A (JA), a pure compound isolated from Justicia procumbens, is a traditional herbal remedy for treatment of fever, pain, and cancer in Taiwan. Treatment of JA not only increased the expression of autophagic marker microtubule‐associated protein 1 light chain‐II by immunoblotting and confocal microscopy, but also augmented the formation of acidic vesicular organelles by flow cytometry in HT‐29 cells. Further study indicated that the expression of p‐AKT, p‐mTOR, p‐p70S6k was decreased whereas that of type III PI3K, becline 1, and Atg5‐Arg12 was increased in JA‐treated cells. Annexin V‐FITC and propidium iodine staining followed by flow cytometry revealed that induction of early apoptosis was displayed at 12 h that was later than the induction of autophagy. Of note, pre‐treatment of the cells with autophagy inhibitor 3‐methyladenine reduced JA‐induced early apoptotic rate. Oral administration of JA (6.2 mg/kg) once a day for 56 consecutive days was shown to suppress the growth and induce apoptosis and autophagy of HT‐29 cells transplanted to NOD‐SCID mice, suggesting chemotherapeutic potential of JA on human colorectal cancer cells.(Supported in part by National Science Council, Taipei, Taiwan, No. NSC 96‐2313‐B‐309‐001‐MY2 and NSC 98‐2313‐B‐003‐002‐MY3).