Autophagy is a highly conserved catabolic process observed in all eukaryotic cells to maintain homeostasis. The process of autophagy starts with initiation, followed by nucleation, maturation and degradation of intracellular content. Therefore, the progression of various diseases and drug resistance can be regulated by autophagy, including cancer. Several trials assessing the efficacy of different anticancer treatments focus on autophagy inhibition. Of these, chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) have garnered the most attention. Since CQ and its derivatives are the only autophagy inhibitors available in the clinic, several clinical trials currently use CQ or HCQ. However, due to drug resistance, the lack of effective and potent autophagy inhibitors hinders clinical application. Here, we identified a novel autophagy inhibitor Aradisiacrispin (AA), a natural bioactive triterpenoid saponin extracted from Ardisia pusilla.

In our study, we detected the effect of AA in combination with a chemotherapeutic drug, Cisplatin (Cis), on MCF- 7 and MDA-MB-231 breast cancer cells using an MTT assay. Surprisingly, we found that AA exerts synergistic cytotoxicity with Cisplatin in vitro against MCF-7 and MDA-MB-231 cells and significantly reduced viability in more than mono-therapy. Moreover, we further investigated the efficacy of AA in blocking autophagy using western blot analysis of autophagy markers, ATP assay, and the fluorescent imaging of the mCherry-GFP-LC3 probe. The co-localization of autophagosomes and lysosomes was analysed by fluorescent imaging. Interestingly our findings showed that AA reduced ATP levels and inhibited late-stage autophagy by blocking autophagosome-lysosome fusion

In conclusion, our study identified a natural autophagy inhibitor and discussed its potential in anti-cancer therapy. As a promising anti-cancer natural product, AA inhibits autophagy at a low dose, contributing to chemotherapy potency. On the other hand, AA, as a novel autophagy inhibitor, showed a significant effect on breast cancer cells either alone or with Cisplatin, which should be further studied for more findings. Moreover, many potential agents must be examined for their efficacy in clinical trials. To improve the effectiveness of a treatment approach, it is crucial to identify the patient population responses and determine the optimal combination of treatments. Finally, autophagy inhibitors are very effective when used alone or combined with chemotherapy, and it is crucial to address the new autophagy inhibitors, like AA, in clinical trials.