Effects of prebiotic supplement on gut microbiota, drug bioavailability, and adverse effects in patients with colorectal cancer at different primary tumor locations receiving chemotherapy: study protocol for a randomized clinical trial

Colorectal cancer (CRC) is a common malignant tumor of the gastrointestinal tract that seriously affects the health of the digestive system. And the development of this tumor is a complex and multi-step process, from small dysplastic lesions of normal colorectal mucosa, through adenomatous polyps, to carcinoma in situ [1]. Based on location, CRC can be classified into left-sided CRC (LSCRC) and right-sided CC (RSCC). RSCC is defined as any tumor occurring in the cecum, ascending colon, hepatic flexure, or first two thirds of the transverse colon, while the LSCRC is defined as any tumor occurring in the latter one third of the transverse colon, splenic flexure, descending colon, sigmoid colon and rectum [2]. Worldwide, colorectal cancer (CRC) has become the third-ranked cancer in incidence and the second-ranked in mortality. It is estimated that 935,000 people died of CRC in 2020 according to the 2020 Global Cancer Statistics [3]. Lacking of physical activity, obesity, and diet were all independent factors related to the risk of CRC [4]. Some studies suggest that factors causing the imbalance of intestinal flora may also be significant to the carcinogenesis of CRC [5, 6]. Besides, different primary tumor locations differ in incidence, pathogenesis, clinical characteristics, survival prognosis, molecular biological characteristics, and gut microbiota [7]. Several studies have demonstrated that patients with LSCRC had a significantly better prognosis compared with those with RSCC [8‐11].

Increasing evidence supports the character of intestinal flora in the pathogenesis and treatment of CRC. Fusobacterium nucleatum adheres, invades, and induces carcinogenic and inflammatory responses via its unique FadA adhesion to activate the growth of CRC cells [12]. Other than the direct effect of specific bacteria on partial tissues, the broader bacterial community may regulate the risk and progression of CRC via competitive rejection and other mechanisms. Gut microbiota-dependent short-chain fatty acids (SCFAs) generation fermented from dietary fiber exert protection against colorectal tumorigenesis in rodents [13].

At present, cytotoxic drugs are generally applied for postoperative adjuvant therapy or advanced CRC patients, usually accompanied by a series of adverse effects (such as constipation, diarrhea, nausea, and bone marrow suppression) and individual differences in drug efficacy [14, 15]. In recent years, with the rise of “pharmacomicrobiomics,” the significance of the intestinal flora in regulating the host response to chemotherapeutic drugs is increasingly recognized [16]. Intestinal flora can modulate the anti-tumor activity of chemotherapy drugs [17]. The killing effectiveness of 5-Fu on CRC can be enhanced by bacterial-derived urolithin A [18]. Importantly, proteobacteria can promote the deglycosylation of capecitabine [19]. Moreover, some studies have reported that probiotics/prebiotics can reduce the adverse effects of chemotherapy. Lactobacillus casei variety rhamnosus plays a preventive role in FOLFOX-related intestinal mucositis in CRC-bearing mice [20]. In CRC patients, L. rhamnosus GG consumption reduced the incidence of 5-FU-induced severe diarrhea and abdominal discomfort compared with guar gum fiber [21]. Lu et al. found that synbiotics (containing a variety of probiotics and prebiotic ingredients) can help relieve postoperative chemotherapy-related adverse effects, further improving the quality of life (QoL) in CRC patients [22]. Furthermore, accumulating evidence demonstrated that prebiotics, such as non-digestible oligosaccharides, can reverse chemotherapy-induced intestinal dysbiosis through selective colonization of the probiotic bacteria [23]. In Peng’s trials, compared to those who received enteral nutrition therapy alone, surgical patients supplied with prebiotics experienced shorter durations of hospital stay and had reduced levels of inflammatory cytokines [24]. Hence, targeting the gut microbiota in clinical practice to modulate the efficacy and toxicity of chemotherapeutic drugs has a promising future.

Although there have been some reports on the effects of microecologics on modulating intestinal flora and reducing adverse effects in patients with CRC during chemotherapy, they are still very limited. Through our current knowledge, using microecologics to interfere with the bioavailability of chemotherapeutic agents in a microbiota-dependent manner has not been reported, as well as differences in the intervention effect of prebiotics on the intestinal flora of CRC patients at different primary tumor locations.

Xylooligosaccharide (XOS) is a mixture of oligosaccharides consist of 2–9 xylose units connected by β-1,4-glycosidic bonds [25, 26], which can scape digestion by host enzymes in the small intestine and enter the large intestine directly, and served as major substrates for gut bacterial growth. XOS can be utilized by beneficial bacteria first in the intestine, enriching bifidobacteria and lactobacillus, and inhibiting the proliferation of harmful bacteria such as E. coli and Salmonella enteritidis to reduce the production of harmful substances [27, 28]. The proliferation effect of XOS on bifidobacteria is about 20 times that of other functional oligosaccharides, with higher selectivity [29]. XOS can facilitate the generation of SCFAs such as acetic acid, propionic acid, and butyric acid [30], as well as other organic acids such as lactic acid, succinate, formic acid, isobutyric acid, and isohexanoic acid [31], which play important roles in preventing various intestinal diseases. XOS was found to increase the moisture content of stool and improve constipation [32]. In addition, XOS have a strong ability to adsorb pathogens, thereby preventing diarrhea [33]. Evidence from in vitro and animal research indicates that XOS play roles in inhibiting the secretion of inflammatory cytokines and have an effect on anti-inflammatory and anti-tumor [34, 35]. Chronic toxicology studies on XOS show that it is safe and reliable with no toxicity in humans, dogs, rodents, and other animals [36‐38].

Firstly, this study aims to explore the difference of tumor microbiota and the different gut microbiota changes during treatment between LSCRC and RSCC. Moreover, another goal of the trial is to investigate the effect of XOS on (i) increasing the bioavailability of cytotoxic drug, (ii) reducing the adverse effects of chemotherapy, and (iii) improving the QoL of CRC patients by modifying gut microbiota.

CRC is one of the most prevalent cancers worldwide. Postoperative adjuvant chemotherapy for CRC is a helpful attempt in recent years. However, the adverse effects during chemotherapy and the inter-individual variation in drug efficacy are still relatively big problems. Moreover, the different primary tumor locations may result in differences in intestinal flora composition and prognosis. Efforts to find a kind of safe food with therapeutic effect and to evaluate its impact on patients with CRC at different primary tumor locations are critical. Studies have revealed the vital part of intestinal flora in the progression and treatment of CRC [5, 12, 46], and the concept of “pharmacomicrobiomics” is increasingly recognized [47]. Targeting intestinal flora, therefore, may modulate the efficacy and adverse effect of chemotherapy.

Both animal and human studies provide strong evidence that microecologics play essential roles in preventing chemotherapy-induced mucositis [48]. Bowen et.al. [49] have revealed the effects of VSL#3, a mixture of Lactobacilli, bifidobacteria, and streptococcus, on preventing diarrhea following chemotherapy with irinotecan in rats. Synbiotics have significantly reduced the occurrence of severe lymphopenia and diarrhea and increased levels of Bifidobacterium and Lactobacillus species and concentrations of SCFAs in esophageal cancer patients undergoing neoadjuvant chemotherapy [50]. Dietary supplementation of prebiotics (oligofructose and inulin) can enhance the efficacy of six cytotoxic drugs and prolong the lifespan of rodents with transplantable malignant tumors [51, 52]. XOS is a mixture of oligosaccharides which can be considered as a prebiotic [53]. XOS can modulate the diversity of intestinal flora, effectively multiply favorable bacteria such as bifidobacteria, and produce beneficial metabolites including SCFAs [54]. In addition, it has been reported that XOS are beneficial to type 2 diabetes mellitus [55], diarrhea [33], and constipation [32]. However, so far, there is no study evaluating the role of XOS consumption on the intestinal flora in patients with CRC.

This study will reveal the potential benefits of prebiotic for improving the gut microbiota composition, alleviating the adverse effects, and improving the efficacy of chemotherapy in patients with CRC. In addition, our study will provide data on the different distribution of tumor microbiota and the different changes of gut microbiota during treatment in LSCRC and RSCC, which may provide novel insights into personalized cancer treatment strategies based on primary tumor locations and gut microbiota in the future.

This trial was registered at ClinicalTrials.gov, and this article is based on the 2nd version of the protocol published in September 2021. It was not submitted earlier to be published due to changes in the study status. The recruitments have begun beginning of June 2021, and due to the COVID-19 pandemic, the patient inclusions were delayed to resume by October 2022. The final inclusion will be terminated 1 March 2023.

A second version of this protocol was conveyed in regard to the post-treatment visit (visit 2).