High-throughput screening for natural compound-based autophagy modulators reveals novel chemotherapeutic mode of action for arzanol

Abstract

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.

lncRNA SNHG26 promoted the growth, metastasis, and cisplatin resistance of tongue squamous cell carcinoma through PGK1/Akt/mTOR signal pathway

“…Mounting evidence shows that apoptosis and autophagy are closely linked to tumor chemotherapy resistance. 47 , 48 , 49 , 50 Herein, the findings showed that SNHG26 did not affect apoptosis and autophagy of TSCC cells. SNHG26 could indirectly increase cisplatin resistance of tongue cancer by enhancing its proliferative capacity.…”

Arzanol, a natural phloroglucinol α‐pyrone, protects HaCaT keratinocytes against H2O2‐induced oxidative stress, counteracting cytotoxicity, reactive oxygen species generation, apoptosis, and mitochondrial depolarization

“…According to our results, previous studies showed no cytotoxic effects of arzanol in peripheral blood mononuclear cells, obtained from healthy adult donors (Bauer et al, 2011), immortalized Vero cell line, and differentiated CaCo‐2 cells (Rosa et al, 2011), as a model of the intestinal epithelium. Conversely, the phloroglucinol showed the ability to decrease viability in cancer cells as epithelial cancer cell lines (A549, RT‐112, HeLa, CaCo‐2) and B16F10 melanoma cells (Bauer et al, 2011; Deitersen et al, 2021; Rosa et al, 2017), indicating its selective cytotoxicity versus tumoral cells, maybe interacting with targets of the cell proliferation and survival signaling pathways (Rosa et al, 2017).…”

“…Several secondary metabolites, such as phloroglucinols, acetophenones, pyrones, and sesquiterpenes, isolated from the aerial parts of this subspecies, exhibited antiinflammatory (Appendino et al, 2007;Bauer et al, 2011) and antioxidant activity in several models of oxidative stress (Rosa et al, 2007(Rosa et al, , 2011(Rosa et al, , 2017. Among them, the naturally prenylated pyrone-phloroglucinol heterodimer arzanol (Figure 1) showed anti-inflammatory, anticancer, antimicrobial, and antioxidant activities (Appendino et al, 2007;Deitersen et al, 2021;Del Gaudio et al, 2018;Mammino, 2017;Rosa et al, 2007Rosa et al, , 2017Taglialatela-Scafati et al, 2013). The antiinflammatory activity was explained by the inhibition of the activation of inflammatory transcription nuclear factor ƙB (NFκB) and the release of pro-inflammatory cytokines in lipopolysaccharide (LPS)-stimulated primary monocytes (Appendino et al, 2007).…”

Regulated cell death (RCD) in cancer: key pathways and targeted therapies

“… 256 Arzanol, as a novel compound, was observed to induce the accumulation of p62 and inhibit autophagy, thus improving the sensitivity of bladder cancer RT-112 cells to cisplatin. 257 Autophinib, as a VPS34 inhibitor, could inhibit p62 degradation via suppression of starvation- or Rapamycin-triggered autophagy by targeting VPS34 in MCF7-LC3 cells. 258 A dual inhibitor of both Hsp90 and late-autophagy, DCZ5248, promoted the LC3-II transformation and upregulated p62 level to inhibit colon cancer HCT116 cell late-autophagy.…”