Screening of Crude Drugs Used in Japanese Kampo Formulas for Autophagy-Mediated Cell Survival of the Human Hepatocellular Carcinoma Cell Line

The discovery of herbal drugs and natural compounds as inhibitors of SARS-CoV-2 infection in vitro

The emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic in 2019 has led to a global health crisis. Mutations of the SARS-CoV-2 genome have impeded the development of effective therapeutics and vaccines against SARS-CoV-2. Natural products are important for discovering therapeutics to treat the 2019 coronavirus disease (COVID-19). In the present study, we investigated the antiviral activity of herbal drug extracts from Polygala Root, Areca, and Quercus Bark and natural compounds derived from herbal drug such as baicalin and glabridin, with IC₅₀ values of 9.5 µg/ml, 1.2 µg/ml, 5.4 µg/ml, 8.8 µM, and 2.5 µM, respectively, against SARS CoV-2 infection in vitro. Certain herbal drug extracts and natural compounds were found to inhibit viral RNA levels and infectious titers of SARS-CoV-2 in a dose-dependent manner. Furthermore, viral protein analyses showed that herbal drug extracts and natural compounds effectively inhibited SARS-CoV-2 in the various entry treatments. Our study revealed that three herbal drugs are good candidates for further in vivo and clinical studies.

Steroidal Saponins Isolated from the Rhizome of Dioscorea tokoro Inhibit Cell Growth and Autophagy in Hepatocellular Carcinoma Cells

Our preliminary screening identified an extract from the rhizome of Dioscorea tokoro, which strongly suppressed the proliferation of HepG2 hepatocellular carcinoma cells and inhibited autophagy. This study aimed to isolate active compounds from the rhizome of D. tokoro that exert antiproliferative effects and inhibit autophagy. The bioassay-guided fractionation of the active fraction led to the isolation of two spirostan-type steroidal saponins, dioscin (1) and yamogenin 3-O-α-l-rhamnopyranosyl (1→4)-O-α-l-rhamnopyranosyl(1→2)-β-d-glucopyranoside (2), and the frostane-type steroidal saponin protodioscin (3) from the n-BuOH fraction. Furthermore, acid hydrolysis of 1 and 2 produced the aglycones diosgenin (4) and yamogenin (5), respectively. Compounds 1-5 suppressed proliferation of HepG2 cells. The analysis of structure-activity relationships indicated that the 25(R)-conformation, structures with a sugar moiety, and the spirostan-type aglycone moiety contributed to antiproliferative activity. Analysis of autophagy-related proteins demonstrated that 1-3 clearly increased the levels of both LC3-II and p62, implying that 1-3 deregulate the autophagic pathway by blocking autophagic flux, which results in p62 and LC3-II accumulation. In contrast, 1-3 did not significantly affect caspase-3 activation and PARP cleavage, suggesting that the antiproliferative activity of 1-3 occurred independently of caspase-3-mediated apoptosis. In summary, our study showed that 1-3, active compounds in the rhizome of D. tokoro, suppressed cell proliferation and autophagy, and might be potential agents for autophagy research and cancer chemoprevention.

Costunolide and dehydrocostuslactone from Saussurea lappa root inhibit autophagy in hepatocellular carcinoma cells

Autophagy is a catabolic process for degradation of intracellular components and plays an important role in the development and growth of cancer. Our preliminary screening confirmed that an extract from the root of Saussurea lappa remarkably suppressed the proliferation of HepG2 hepatocellular carcinoma cells and inhibited autophagy. In this study, we explored the effects of costunolide (CL) and dehydrocostuslactone (DCL), which are bioactive sesquiterpene lactones in this extract, on autophagy modulation in HepG2 cells. An analysis of autophagy-related proteins demonstrated that CL and DCL blocks the autophagy process that leads to the accumulation of microtubule-associated protein 1 light chain 3 (LC3) and SQSTM1/p62 (p62). LC3 turnover assays indicated that CL and DCL trigger autophagy inhibition by blocking the autophagic flux, thereby resulting in the accumulation of LC3-II and p62. These results are encouraging and warrant further study of CL and DCL for potential use as autophagy inhibiting agents for liver cancer therapy.

Arctigenin suppresses cell proliferation via autophagy inhibition in hepatocellular carcinoma cells

Autophagy is a catabolic process that degrades dysfunctional proteins and organelles and plays critical roles in cancer development. Our preliminary screening identified that extracts of the fruits of Arctium lappa and the fruits of Forsythia suspensa notably suppressed the proliferation of hepatocellular carcinoma HepG2 cells and downregulated the autophagy. In this study, we explored the effect of arctigenin (ARG), a bioactive lignan in both extracts, on cell proliferation and autophagy-related proteins in HepG2 cells. ARG inhibited the proliferation of HepG2 cells. Analysis of autophagy-related proteins demonstrated that ARG might block the autophagy that leads to sequestosome 1/p62 (p62) accumulation. The stage of inhibition in autophagy by ARG differed from those by the autophagy inhibitors 3-methyladenine (3-MA) or chloroquine (CQ). ARG could also inhibit starvation-induced autophagy. Further analysis of apoptosis-related proteins indicated that ARG did not affect caspase-3 activation and PARP cleavage, suggesting that the antiproliferative effect of ARG can occur independently of apoptosis. In summary, our study showed that ARG suppresses cell proliferation and inhibits autophagy, and might lead to the development of agents for autophagy research and cancer chemoprevention.

Starvation-induced autophagy via calcium-dependent TFEB dephosphorylation is suppressed by Shigyakusan

Kampo, a system of traditional Japanese therapy utilizing mixtures of herbal medicine, is widely accepted in the Japanese medical system. Kampo originated from traditional Chinese medicine, and was gradually adopted into a Japanese style. Although its effects on a variety of diseases are appreciated, the underlying mechanisms remain mostly unclear. Using a quantitative tf-LC3 system, we conducted a high-throughput screen of 128 kinds of Kampo to evaluate the effects on autophagy. The results revealed a suppressive effect of Shigyakusan/TJ-35 on autophagic activity. TJ-35 specifically suppressed dephosphorylation of ULK1 and TFEB, among several TORC1 substrates, in response to nutrient deprivation. TFEB was dephosphorylated by calcineurin in a Ca²⁺ dependent manner. Cytosolic Ca²⁺ concentration was increased in response to nutrient starvation, and TJ-35 suppressed this increase. Thus, TJ-35 prevents the starvation-induced Ca²⁺ increase, thereby suppressing induction of autophagy.