Relationship Between Gut Commensal Bacteria And Response To Neoadjuvant Chemoradiotherapy In Locally Advanced Rectal Cancer

Purples:Colorectal cancer(CRC)is one of the most common cancers.Globally,CRC ranked third in incidence and second in mortality in 2020.The proportion of rectal cancer accounting for CRC in China is higher than that in Western countries.While most patients have developed into Locally Advanced Rectal Cancer(LARC)at initial diagnosis.Thus,neoadjuvant chemoradiotherapy(n CRT)has become the standard treatment method for LARC at present.Studies have shown that concurrent chemoradiotherapy can change the gut bacterial structure of LARC patients,and it is different among patients with different responses to n CRT.Gut commensal bacteria in LARC patients may reverse the response to n CRT.Therefore,this study aims to explore the relationship between the structure of gut commensal bacteria and the response to n CRT in LARC patients.Methods:In this study,fecal samples from 35 LARC patients who received n CRT and 14 healthy adult donors were retrospectively collected for 16 S r RNA sequencing.Recruited patients were divided into Sensitive group(TRG 0 ～ 1,n = 12)and Resistant group(TRG 2 ～ 3,n = 23)according to pathological tumor regression grade(AJCC 8.0)after radical surgery.16 S r RNA sequencing method was used for analyzing bacterial structure in feces,and then bioinformatics analysis was performed to compare difference between two groups of LARC patients.Partial least squares discriminant analysis(PLS-DA),weighted Uni Frac distance and unweighted Uni Frac distance were used to calculate β-diversities among groups.By Wilcox test,species with significant differences among different groups were identified(P < 0.05,FDR < 1).Linear discriminant analysis(LDA)Effect Size(LEf Se)analysis was used to identify the strains that significantly affected sample division and had symbolic significance.Finally,species network diagrams were used to further explain the formation mechanism of phenotypic differences between samples.Results:In this study,it was found that there were significant differences in gut bacterial structure between Sensitive group and Resistant group before concurrent chemoradiotherapy,presenting a higher abundance of butyrate-producing bacteria in feces of Sensitive group,whereas a higher abundance of colorectal cancer-facilitated bacteria in feces of Resistant group.n CRT can differentially change the gut bacterial structure of LARC patients.After treatment,the relative abundance of butyrateproducing bacteria and Bifidobacterium in Sensitive group is significantly higher than that in Resistant group.During n CRT,β-diversities of the two groups were significantly decreased compared with their baseline,but bacterial structures of two groups was remodeled differentially.Combined with the results of LEf Se analysis,different marker bacteria appeared in Resistant group at different stages of treatment,indicating that the gut bacterial structure of Resistant group was constantly evolving with the increase of the dose of n CRT.Intriguingly,the relative abundance of Akkermansia muciniphila in feces of Resistant group was significantly increased in this study,but bacteria function network analysis revealed that Akkermansia muciniphila was functionally counteracted against tumorigenic bacteria,such as Escherichia and Bacteroides.Akkermansia muciniphila is a critical member of probiotics,and this highlighted a potential of Akkermansia muciniphila in improving LARC response to n CRT.In the future,Akkermansia muciniphila may become one of the key therapeutic targets of LARC.Conclusion:Generally,responses of LARC patients to n CRT correlate with their gut bacterial structures.n CRT can remodel the gut bacterial structure of LARC patients,and this remodeling effect is different between Sensitive group and Resistant group as the dose of chemoradiotherapy increases.This indicates that gut commensal bacteria undergo different evolution paths during this process.In this context,the natural bacterial structure in gut appears to impact the response of LARC patients to chemoradiotherapy greatly.Therefore,the management of gut bacterial structure may become a strategy to improve the efficacy of n CRT in LARC patients.