Investigating the resistance mechanism of 5-fluorouracil in colorectal cancer based on surface markers of cancer stemness and cytokine level: A pre-clinical study

Background: Colorectal cancer (CRC) is the deadliest malignancy in the world. The first-line chemotherapy used for CRC is 5-fluorouracil (5-FU). 5-FU completely eradicates rapidly proliferating and terminally differentiated tumor cells but fails to target cancer stem cells (CSCs). As a result, the tumor may shrink temporarily, but remnant CSC multiplies and forms a tumor again more aggressively. The recurrence and resistance lead to metastasis. Methodology: CRC was induced in 12 Sprague-Dawley (RPCP/IAEC/2019-20/R2) rats by 1,2 dimethyl hydrazine. Later, animals were treated with 5-FU for 7 weeks at a 10 mg/kg dose by the subcutaneous route. At the end of treatment, half population was sacrificed (6), whereas the remaining half (6) was left without treatment of 5-FU for 5 weeks and then sacrificed. Parameters such as body weight, complete blood count (CBC), immune cell subset (CD4, CD8, and NK cells), colon length to weight index, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-a) level, occult blood in stool, tumor multiplicity, and liver metastasis were estimated. In addition, the dissected colon was fixed in formalin and sent to the histology lab for hematoxylin-eosin staining and immunohistochemistry at both intervals. Results: All blood and tissue-based markers have shown significant differences (p < 0.05) between the animals sacrificed at the end of the 27(th) week and the end of the 32(nd) week for 5-FU treatment. Conclusion: It can be concluded that 5-FU up-regulates inflammatory cytokines and cell surface markers of CSC that promote CRC stemness via the Wnt/beta-catenin pathway. Also, involvement of Nf-kappa B, fibronectin, MMP-9, and RANKL leads to tumorigenesis, disease aggressiveness, metastasis, and resistance.