Autophagy Inhibition Promotes Bevacizumab-induced Apoptosis and Proliferation Inhibition in Colorectal Cancer Cells

Aim: Anti-VEGF therapy plays an important role in the treatment of malignant tumors, especially metastatic malignant tumors. However, resistance and an inefficient response to anti-VEGF therapy exist. The current study aimed to investigate whether autophagy plays a part in the anti-tumor effect of bevacizumab in colorectal cancer cells. Methods: VEGF-A expression was measured by immunohistochemical methods. Cell viability and cell apoptosis were detected using 3-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) and flow cytometry. Autophagy was assessed by a western blot, fluorescence microscopy and transmission electron microscopy. HIF-1α was measured using a western blot. A xenograft tumor model of colorectal cancer was constructed to determine the efficacy of the treatment of bevacizumab and chloroquine. Results: VEGF-A protein was upregulated in colorectal cancer tissue. Anti-VEGF (bevacizumab) inhibited cell viability and induced apoptosis. Moreover, bevacizumab induced autophagy. The inhibition of autophagy by chloroquine or by small interfering RNA promoted bevacizumab-induced apoptosis and proliferation inhibition. Further study showed that bevacizumab treatment significantly augmented HIF-1α. Furthermore, cells pretreated with YC-1, a HIF-1α inhibitor, displayed significantly attenuated bevacizumab-induced autophagy. Finally, a combinatory treatment of bevacizumab and chloroquine synergistically inhibited tumor growth in a xenograft tumor model of colorectal cancer cells. Conclusions: Our results showed that the inhibition of autophagy promoted the anti-tumor effect of bevacizumab and may offer a promising therapeutic strategy for colorectal cancer.