Role of gut microbiome in the outcome of cancer immunotherapy

Revealing the therapeutic properties of gut microbiota: transforming cancer immunotherapy from basic to clinical approaches

The immune system plays a pivotal role in the battle against cancer, serving as a formidable guardian in the ongoing fight against malignant cells. To combat these malignant cells, immunotherapy has emerged as a prevalent approach leveraging antibodies and peptides such as anti-PD-1, anti-PD-L1, and anti-CTLA-4 to inhibit immune checkpoints and activate T lymphocytes. The optimization of gut microbiota plays a significant role in modulating the defense system in the body. This study explores the potential of certain gut-resident bacteria to amplify the impact of immunotherapy. Contemporary antibiotic treatments, which can impair gut flora, may diminish the efficacy of immune checkpoint blockers. Conversely, probiotics or fecal microbiota transplantation can help re-establish intestinal microflora equilibrium. Additionally, the gut microbiome has been implicated in various strategies to counteract immune resistance, thereby enhancing the success of cancer immunotherapy. This paper also acknowledges cutting-edge technologies such as nanotechnology, CAR-T therapy, ACT therapy, and oncolytic viruses in modulating gut microbiota. Thus, an exhaustive review of literature was performed to uncover the elusive link that could potentiate the gut microbiome's role in augmenting the success of cancer immunotherapy.

Microbiota-Host-Irinotecan Axis: A New Insight Toward Irinotecan Chemotherapy

Irinotecan (CPT11) and its active metabolite ethyl-10-hydroxy-camptothecin (SN38) are broad-spectrum cytotoxic anticancer agents. Both cause cell death in rapidly dividing cells (e.g., cancer cells, epithelial cells, hematopoietic cells) and commensal bacteria. Therefore, CPT11 can induce a series of toxic side-effects, of which the most conspicuous is gastrointestinal toxicity (nausea, vomiting, diarrhea). Studies have shown that the gut microbiota modulates the host response to chemotherapeutic drugs. Targeting the gut microbiota influences the efficacy and toxicity of CPT11 chemotherapy through three key mechanisms: microbial ecocline, catalysis of microbial enzymes, and immunoregulation. This review summarizes and explores how the gut microbiota participates in CPT11 metabolism and mediates host immune dynamics to affect the toxicity and efficacy of CPT11 chemotherapy, thus introducing a new concept that is called "microbiota-host-irinotecan axis". Also, we emphasize the utilization of bacterial β-glucuronidase-specific inhibitor, dietary interventions, probiotics and strain-engineered interventions as emergent microbiota-targeting strategies for the purpose of improving CPT11 chemotherapy efficiency and alleviating toxicity.

Pathogenic mitochondrial dysfunction and metabolic abnormalities

Herein we trace links between biochemical pathways, pathogenesis, and metabolic diseases to set the stage for new therapeutic advances. Cellular and acellular microorganisms including bacteria and viruses are primary pathogenic drivers that cause disease. Missing from this statement are subcellular compartments, importantly mitochondria, which can be pathogenic by themselves, also serving as key metabolic disease intermediaries. The breakdown of food molecules provides chemical energy to power cellular processes, with mitochondria as powerhouses and ATP as the principal energy carrying molecule. Most animal cell ATP is produced by mitochondrial synthase; its central role in metabolism has been known for >80 years. Metabolic disorders involving many organ systems are prevalent in all age groups. Progressive pathogenic mitochondrial dysfunction is a hallmark of genetic mitochondrial diseases, the most common phenotypic expression of inherited metabolic disorders. Confluent genetic, metabolic, and mitochondrial axes surface in diabetes, heart failure, neurodegenerative disease, and even in the ongoing coronavirus pandemic.

Corticosteroid administration for cancer-related indications is an unfavorable prognostic factor in solid cancer patients receiving immune checkpoint inhibitor treatment

OBJECTIVE

Immunotherapies targeting immune checkpoints have achieved encouraging survival benefits in patients with various solid cancers. Corticosteroids are frequently administrated for cancer/non-cancer related indications and immune-related adverse events (irAEs). This study aimed to clarify the prognostic significance of corticosteroid administration in solid cancer patients receiving immune checkpoint inhibitor (ICI) treatment.

METHOD

First, a meta-analysis was performed using the literatures searched from PubMed, Cochrane Library, Web of Science, Embase, and Clinicaltrials.gov before January 2021. The Hazard ratios (HRs) coupled with 95% confidence intervals (CIs) were used to evaluate the correlation of corticosteroid administration with overall survival (OS) and progression-free survival (PFS). Then, a retrospective analysis enrolling 118 ICI-treated cancer patients was performed for validation, among which 26 patients received corticosteroids for cancer-related indications.

RESULT

In the meta-analysis, corticosteroid administration for cancer-related indications was significantly correlated with worse PFS (HR = 1.735(1.381-2.180)) and OS (HR = 1.936(1.587-2.361)) of the ICI-treated patients. However, corticosteroid administration for non-cancer-related indications and irAEs was unrelated with PFS (non-cancer-related indications: HR = 0.830(0.645-1.067); irAEs: HR = 1.302(0.628-2.696)) and OS (non-cancer-related indications: HR = 0.786(0.512-1.206); irAEs: HR = 1.107(0.832-1.474)) of the ICI-treated patients. The following retrospective analysis identified corticosteroid administration for cancer-related indications was an independent unfavorable predictor for PFS (P = 0.006) and OS (P = 0.044) of the ICI-treated patients. The subgroup analysis based on non-small cell lung cancer (NSCLC) demonstrated the similar results (P = 0.002 for PFS and P = 0.047 for OS).

CONCLUSION

Our study demonstrated corticosteroid administration for cancer-related indications is an unfavorable prognostic factor in solid cancer patients receiving ICI treatment. Therefore, careful selection of corticosteroid-treated patients for ICI therapy is quite necessary in individualized clinical management.