Pectin supplement significantly enhanced the anti-PD-1 efficacy in tumor-bearing mice humanized with gut microbiota from patients with colorectal cancer

Abstract

Background: Anti-PD-1-based immunotherapy has emerged as a promising therapy for several cancers. However, it only benefits a small subset of colorectal cancer (CRC) patients. Mounting data supports the pivotal role of gut microbiota in shaping immune system. Pectin, a widely consumed soluble fiber, has been reported to ameliorate the imbalance of gut microbiota. Therefore, we aimed to explore the effect and the underlying mechanisms of pectin in improving anti-PD-1 mAb efficacy. Methods: The C57BL/6 mice were treated with a broad-spectrum antibiotic (ATB) cocktail to depleted endogenous gut microbiota and subsequently humanized with feces from healthy controls or newly diagnosed CRC patients. The antitumor efficacies of anti-PD-1 mAb combined with or without pectin were assessed using these mice. Flow cytometry and immunohistochemistry (IHC) were conducted to investigate the tumor immune microenvironment after treatment. The gut microbiota profiles and short-chain fatty acids (SCFAs) levels were determined by 16S ribosomal RNA (16S rRNA) gene sequencing and gas chromatography-mass spectrometry (GC-MS), respectively. The effect of gut microbiota on anti-PD-1 mAb efficacy after pectin supplement was further tested by fecal microbiota transplantation (FMT). Results: The anti-PD-1 mAb efficacy was largely impaired in the mice humanized with feces from newly diagnosed CRC patients compared to those from healthy controls. However, pectin significantly enhanced the anti-PD-1 mAb efficacy in the tumor-bearing mice humanized with CRC patient gut microbiota. Flow cytometry and IHC analysis revealed increased T cell infiltration and activation in the tumor microenvironment of mice treated with anti-PD-1 mAb plus pectin. In vivo depletion of CD8 + T cells diminished the anti-tumor effect of anti-PD-1 mAb combined with pectin. 16S rRNA gene sequencing showed that pectin significantly increased gut microbial diversity and beneficially regulated microbial composition. In addition, we identified unique bacterial modules that were significantly enriched in the anti-PD-1 mAb + pectin group, which composed of butyrate-producing bacteria indicative of good response to immunotherapy. Meanwhile, GC-MS showed that pectin altered the level of SCFA butyrate. Furthermore, butyrate, a main product of dietary fiber in gut microbial fermentation, was found to be sufficient to promote T cells infiltration and thus enhance the efficacy of anti-PD-1 mAb. In addition, FMT demonstrated the effects of pectin were dependent on gut microbiota. Importantly, the beneficial effects of pectin were confirmed in the mice humanized with gut microbiota from patient with resistance to anti-PD-1 mAb. Conclusion: Pectin facilitated the anti-PD-1 mAb efficacy in CRC via regulating the T cell infiltration in the tumor microenvironment, which was potentially mediated by the metabolite butyrate.

Colorectal cancer and microbiota modulation for clinical use. A systematic review

“…172 Pectin is the fundamental metabolite of plant walls, and its fermentation serves as a source of energy for numerous microorganisms, producing metabolites with beneficial functions for our organism. 131, 173 Furthermore, pectin is currently used in numerous food additives, so its study is of great interest. 131, 174 In fact, it has been observed that pectin can be beneficial against several types of tumors such as CRC, breast and prostate cancer by halting tumor development.…”

“…131, 173 Furthermore, pectin is currently used in numerous food additives, so its study is of great interest. 131, 174 In fact, it has been observed that pectin can be beneficial against several types of tumors such as CRC, breast and prostate cancer by halting tumor development. 174 Its effect seems to be mediated through the increase of different SCFA-producing bacteria and in particular acetate, and the enhancement of the immune response through IFN-γ-producing TCD8+.…”

“…In addition, a transplantation of fecal microbiota from PD-1 refractory patients showed enhanced anti-tumor response in PD-1 and pectin-treated mice. 131…”

Natural Products with Activity against Lung Cancer: A Review Focusing on the Tumor Microenvironment

“…Pectin is a natural excellent macromolecule polymer with biocompatible and biodegradable properties that is used for targeted drug delivery [ 141 , 142 ]. Moreover, some experiments have shown that pectin has the ability to inhibit tumor growth in cancers [ 143 , 144 ]. Poly (vinyl pyrrolidone) (PVP) is used in the development of biomedical applications as a complexing agent or cross-linker with excellent biocompatibility and solubility characteristics.…”

The microbiome, gastrointestinal cancer, and immunotherapy

“…Additionally, FMT from these high fiber fed‐mice was enough to improve therapeutic response in a recipient MC38 tumor‐bearing mouse 25 . Another study found that pectin supplementation, a soluble fiber found in fruits and vegetables, could improve response to anti‐PD‐1 therapy in MC38‐bearing mice colonized with feces from human CRC patients 47 . Dietary pectin increased the abundance of several short‐chain fatty acid (SCFA)‐producing bacteria such as Erysipelotrichaceae , Ruminococcaceae , and Bifidobacteriaceae , as well as butyrate levels, illustrating how diet supplementation could rescue dysbiotic microbiota‐induced resistance 47 .…”