Autophagy is an intracellular recycling pathway with implications for intracellular homeostasis and cell survival. Its pharmacological modulation can aid
chemotherapy by sensitizing
cancer cells toward approved drugs and overcoming chemoresistance. Recent translational data on autophagy modulators show promising results in reducing
tumor growth and
metastasis, but also reveal a need for more specific compounds and novel lead structures. Here, we searched for such autophagy-modulating compounds in a flow cytometry-based high-throughput screening of an in-house natural compound library. We successfully identified novel inducers and inhibitors of the autophagic pathway. Among these, we identified
arzanol as an autophagy-modulating
drug that causes the accumulation of ATG16L1-positive structures, while it also induces the accumulation of lipidated LC3. Surprisingly, we observed a reduction of the size of autophagosomes compared to the bafilomycin control and a pronounced accumulation of p62/SQSTM1 in response to
arzanol treatment in HeLa cells. We, therefore, speculate that
arzanol acts both as an inducer of early autophagosome biogenesis and as an inhibitor of later autophagy events. We further show that
arzanol is able to sensitize RT-112
bladder cancer cells towards
cisplatin (CDDP). Its anticancer activity was confirmed in monotherapy against both CDDP-sensitive and -resistant
bladder cancer cells. We classified
arzanol as a novel mitotoxin that induces the fragmentation of mitochondria, and we identified a series of targets for
arzanol that involve
proteins of the class of mitochondria-associated
quinone-binding
oxidoreductases. Collectively, our results suggest
arzanol as a valuable tool for autophagy research and as a lead compound for
drug development in
cancer therapy.