Tetrandrine triggers an alternative autophagy in DU145 cells.

Tetrandrine (Tet), a potent lysosomal inhibitor, blocks autophagic flux and induces cancer cell death. Previously, the present authors identified the prostate cancer cell line DU145 to exhibit high sensitivity towards Tet in 11 cancer cell lines. In the present study, autophagy in Tet-treated DU145 cells was investigated. Similar to other cell lines, such as PC-3 and 786-O cells, Tet neutralized the acidity of lysosome and blocked autophagy in DU145 cells. However, Tet failed to induce microtubule-associated protein 1 light chain 3 (LC3) conversion in DU145 cells. By contrast, it was observed by transmission electron microscopy that Tet induced an accumulation of autophagosomes in the cytoplasm. These contrasting results indicated that Tet triggered an LC3-independent autophagy in DU145 cells. Alkalizing lysosome with chloroquine enhanced Tet-induced cell death. The results of the present study indicated that detection of autophagy in tumor cells may assist in selecting lysosome inhibitors for chemotherapy treatment in prostate cancer.