Low-Dose Chemotherapy Preferentially Shapes the Ileal Microbiome and Augments the Response to Immune Checkpoint Blockade by Activating AIM2 Inflammasome in Ileal Epithelial Cells.

Intervention of the gut microbiome is a promising adjuvant strategy in cancer immunotherapy. Chemotherapeutic agents are recognized for their substantial impacts on the gut microbiome, yet their therapeutic potential as microbiome modulators remains uncertain, due to the complexity of microbiome-host-drug interactions. Here, it is showed that low-dose chemotherapy preferentially shapes the ileal microbiome to augment the extraintestinal immune response to anti-programmed death-1 (anti-PD-1) therapy without causing intestinal toxicity. Mechanistically, low-dose chemotherapy causes DNA damage restricted to highly-proliferative ileal epithelial cells, resulting in the accumulation of cytosolic dsDNA and the activation of the absent in melanoma 2 (AIM2) inflammasome. AIM2-dependent IL-18 secretion triggers the interplay between proximal Th1 cells and Paneth cells in ileal crypts, impairing the local antimicrobial host defense and resulting in ileal microbiome change. Intestinal epithelium-specific knockout of AIM2 in mice significantly attenuates CPT-11-caused IL-18 secretion, Paneth cell dysfunction, and ileal microbiome alteration. Moreover, AIM2 deficiency in mice or antibiotic microbial depletion attenuates chemotherapy-augmented antitumor responses to anti-PD1 therapy. Collectively, these findings provide mechanistic insights into how chemotherapy-induced genomic stress is transduced to gut microbiome change and support the rationale of applying low-dose chemotherapy as a promising adjuvant strategy in cancer immunotherapy with minimal toxicity.

A RIPK3-independent role of MLKL in suppressing parthanatos promotes immune evasion in hepatocellular carcinoma.

Mixed lineage kinase domain-like (MLKL) is widely accepted as an executioner of necroptosis, in which MLKL mediates necroptotic signaling and triggers cell death in a receptor-interacting protein kinase 3 (RIPK3)-dependent manner. Recently, it is increasingly noted that RIPK3 is intrinsically silenced in hepatocytes, raising a question about the role of MLKL in hepatocellular carcinoma (HCC). This study reports a previously unrecognized role of MLKL in regulating parthanatos, a programmed cell death distinct from necroptosis. In HCC cells with intrinsic RIPK3 deficiency, knockout of MLKL impedes the orthotopic tumor growth, activates the anti-tumor immune response and enhances the therapeutic effect of immune checkpoint blockade in syngeneic HCC tumor models. Mechanistically, MLKL is required for maintaining the endoplasmic reticulum (ER)-mitochondrial Mg2+ dynamics in HCC cells. MLKL deficiency restricts ER Mg2+ release and mitochondrial Mg2+ uptake, leading to ER dysfunction and mitochondrial oxidative stress, which together confer increased susceptibility to metabolic stress-induced parthanatos. Importantly, pharmacological inhibition of poly(ADP-ribose) polymerase to block parthanatos restores the tumor growth and immune evasion in MLKL-knockout HCC tumors. Together, our data demonstrate a new RIPK3-independent role of MLKL in regulating parthanatos and highlight the role of MLKL in facilitating immune evasion in HCC.

Harnessing Genomic Stress for Antitumor Immunity.

Significance: Genomic instability, a hallmark of cancer, renders cancer cells susceptible to genomic stress from both endogenous and exogenous origins, resulting in the increased tendency to accrue DNA damage, chromosomal instability, or aberrant DNA localization. Apart from the cell autonomous tumor-promoting effects, genomic stress in cancer cells could have a profound impact on the tumor microenvironment. Recent Advances: Recently, it is increasingly appreciated that harnessing genomic stress could provide a promising strategy to revive antitumor immunity, and thereby offer new therapeutic opportunities in cancer treatment. Critical Issues: Genomic stress is closely intertwined with antitumor immunity via mechanisms involving the direct crosstalk with DNA damage response components, upregulation of immune-stimulatory/inhibitory ligands, release of damage-associated molecular patterns, increase of neoantigen repertoire, and activation of DNA sensing pathways. A better understanding of these mechanisms will provide molecular basis for exploiting the genomic stress to boost antitumor immunity. Future Directions: Future research should pay attention to the heterogeneity between individual cancers in the genomic instability and the associated immune response, and how to balance the toxicity and benefit by specifying the types, potency, and treatment sequence of genomic stress inducer in therapeutic practice. Antioxid. Redox Signal. 34, 1128-1150.

Effects of gut microbiota and time of treatment on tissue levels of green tea polyphenols in mice.

The previous studies have shown that tea polyphenols are metabolized by gut microbiota. This study investigated the effect of gut microbiota on the bioavailability, tissue levels, and degradation of tea polyphenols. Mice were treated with antibiotics (ampicillin/sulfamethoxazole/trimethoprim) in drinking water and the control mice received water for 11 days, and they were given an AIN93M diet enriched with 0.32% of Polyphenon E. The levels of catechins and their metabolites (if present) in the serum, liver, urine, and fecal samples were determined by high-performance liquid chromatography. The results showed that treatment with antibiotics significantly increased the levels of the major polyphenol, (-)-epigallocatechin-3-gallate (EGCG), in serum and liver samples. Antibiotics also raised the levels of some catechins in urine and fecal samples but decreased the levels of their metabolites. These results suggest that antibiotics eliminated gut microbes and increased the bioavailabilities of these tea catechins. In a second study, mice were given different concentrations of green tea infusions as the drinking fluid. The plasma levels of EGCG and (-)-epicatechin-3-gallate (ECG) at day 112 were significantly lower than those at day 5. The urine levels of EGCG and ECG increased in the first 4 or 5 days, and then decreased to much lower levels at day 23 and beyond. In contrast, the levels of (-)-epigallocatechin and (-)-epicatechin showed a trend of increase during the 112-day experiment, likely owing to microbial hydrolysis of EGCG and ECG. Both sets of experiments support the idea that the degradation of EGCG and ECG by gut microbiota decreases their bioavailabilities. © 2018 BioFactors, 2018.