Tetrandrine blocks autophagic flux and induces apoptosis via energetic impairment in cancer cells

Abstract

Lysosomes are acidic organelles that have a crucial role in degrading intracellular macromolecules and organelles during the final stage of autophagy. Tetrandrine (Tet), a bisbenzylisoquinoline alkaloid, was reported as an autophagy activator. Here, in contrast with previous studies, we show that Tet is a potent lysosomal deacidification agent and is able to block autophagic flux in the degradation stage. Single-agent Tet induces significant apoptosis both in vitro and in xenograft models. In the presence of Tet, apoptosis was preceded by a robust accumulation of autophagosomes and an increased level of microtubule-associated protein 1 light chain 3, type II (LC3-II). However, Tet increased the level of sequestosome 1 and decreased the turnover of LC3, indicating the blockade of autophagic flux in the degradation stage. As blockade of autophagic flux decreases the recycling of cellular fuels, Tet reduces the uptake of glucose in cancer cells. These effects lead to insufficient substrates for tricarboxylic acid (TCA) cycle and impaired oxidative phosphorylation. Blunting autophagosome formation using 3-methyladenine or genetic knockdown of Beclin-1 failed to rescue cells upon Tet treatment. By contrast, addition of methyl pyruvate to supplement TCA substrates protected Tet-treated tumor cells. These results demonstrate that energetic impairment is required in Tet-induced apoptosis. Tet, as a potent lysosomal inhibitor, is translatable to the treatment of malignant tumor patients.

Tetrandrine triggers an alternative autophagy in DU145 cells

“…As alternative transcripts of autophagy related 5 (ATG5) lack one or two exons in DU145 cells, and this causes the autophagy pathway to be genetically impaired (12). By contrast, DU145 cells exhibited the highest sensitivity to Tet in all of the 11 cancer cell lines that were previously tested by the authors of the present study (1), implying that impairment in autophagy may increase Tet-induced cell death. In order to investigate the role of autophagy on Tet-induced cell death in DU145 cells, the ultrastructural changes following Tet treatment were observed by transmission electron microscopy (TEM).…”

“…Previously, the present authors have demonstrated that Tet induces cell death in 11 cancer cell lines (1). Tet directly neutralizes the lysosomal acidity, blocks the autophagic flux in the degradation step and causes energetic impairment, which eventually results in cell death (1). By contrast, Tet also acts as an autophagy agonist by inducing the synthesis of reactive oxygen species (3,4,(9)(10)(11), indicating that Tet may function as a multi-target drug to regulate autophagy in cancer cells.…”

“…By contrast, Tet also acts as an autophagy agonist by inducing the synthesis of reactive oxygen species (3,4,9-11), indicating that Tet may function as a multi-target drug to regulate autophagy in cancer cells. Regardless of the Tet target, the present authors and other groups have previously consistently observed that Tet increases the number of autophagosomes, levels of microtubule-associated protein 1 light chain 3, type II (LC3-II) and the number of enhanced green fluorescent protein-LC3 puncta in cancer cells (1,3,9). DU145, a commonly used prostate cancer cell line for research, is different from PC-3 and LNCaP cells in terms of autophagy regulation (12).…”

“…Tetrandrine (Tet), a natural product isolated from Stephania tetrandra, has been reported to be an anti-tumor and anti-inflammatory drug (1)(2)(3)(4)(5)(6)(7)(8). Previously, the present authors have demonstrated that Tet induces cell death in 11 cancer cell lines (1).…”

“…Previously, the present authors have demonstrated that Tet induces cell death in 11 cancer cell lines (1). Tet directly neutralizes the lysosomal acidity, blocks the autophagic flux in the degradation step and causes energetic impairment, which eventually results in cell death (1).…”