Abstract
Autophagy is a cellular bulk degradation pathway implicated in various diseases. Inhibition of autophagy has been regarded as a new therapeutic strategy for cancer treatment, especially in combination with chemotherapy. In our study, we identified two natural compounds, dauricine (DAC) and daurisoline (DAS), as two potent autophagy blockers through a high-content screening. DAC and DAS are alkaloids isolated from traditional Chinese medicine Rhizoma Menispermi. We systematically examined the effects of DAC and DAS on autophagy function in HeLa cells and found that DAC and DAS induced massive formation of autophagic vacuoles and lipidation of LC3. The accumulation of autophagic vacuoles and LC3 lipidation are due to blockage of autophagosome maturation as evidenced by interrupted colocalization of autophagsosome and lysosome, increased GFP-LC3/RFP-LC3 ratio and accumulation of autophagic substrate p62. Moreover, DAC and DAS impaired lysosomal function, as indicated by reduced lysosomal protease activity and increased lysosomal pH values. Importantly, we showed that DAC and DAS strongly inhibited the lysosome V-type ATPase activity. For the therapeutic potential, we found that DAC and DAS blocked the campothecin (CPT)-induced protective autophagy in HeLa cells, and dramatically sensitized the multiple cancer cells to CPT-induced cell death. In conclusion, our result shows that DAC and DAS are autophagy inhibitors which inhibit the lysosomal degradation of auophagic vacuoles, and sensitize the CPT-induced cancer cell death. The study implies the therapeutic potential of DAC and DAS in the treatment of cancers in combination of chemotherapy by inhibiting autophagy.
Highlights
Dauricine (C38H44N2O6) (DAC) and daurisoline (C37H42N2O6) (DAS) are two isoquinoline alkaloids isolated from Chinese herbal medicine Rhizoma Menispermi which has been used in the decoction to treat various diseases including cancers
The high content screening identified dauricine (DAC) and daurisoline (DAS) as DAC and DAS inhibit the fusion of autophagosome and lysosome in HeLa cell Autophagosome clearance depends on its fusion with lysosome
The accumulation of autophagic vacuoles (AVs) is not a sufficient evidence to indicate the enhancement of autophagy, it could be resulted from the blockage of autophagic degradation
Summary
Dauricine (C38H44N2O6) (DAC) and daurisoline (C37H42N2O6) (DAS) are two isoquinoline alkaloids isolated from Chinese herbal medicine Rhizoma Menispermi which has been used in the decoction to treat various diseases including cancers. DAC and DAS have been reported to show potential pharmacological efficacy in many diseases, such as focal ischemia/reperfusion injury [1, 2], arrhythmia [3, 4], and platelet aggregation [5, 6] via suppressing NF-κB pathway [7], antagonizing potassium and calcium channel [8, 9], and inhibiting thromboxane A2 (TXA2) function [10]. DAC has been reported to inhibit the proliferation of tumor cells, such as urinary tract tumor cell www.impactjournals.com/oncotarget [11] and colon cell [12], which revealed a new potential therapeutic direction for the two compounds. In recent years, increasing evidence strongly suggests that autophagy is fundamentally elevated in cancer tissue regardless of Akt/ mTOR signal activation [21,22,23], indicating that autophagy has been induced mostly as a protective mechanism in cancer cells. Besides the wellknown autophagy inhibitors, other candidates from natural compounds may be found to facilitate cancer therapy
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