Purpose5-Fluorouracil (5-Fu) is used as a conventional chemotherapy drug in chemotherapy for patients with advanced colorectal cancer, but many patients still suffer from treatment failure due to 5-Fu resistance. Emerging observations revealed the important role of chemokine (C-X-C motif) ligand 13 (CXCL-13) in tumor microenvironment and its relationship with prognosis in patients with colorectal cancer. This study is designed to reveal the important role of CXCL-13 in causing colorectal cancer resistance to 5-Fu.Materials and MethodsCXCL-13 levels of patient's serum or cell culture supernatants were measured separately by enzyme-linked immunosorbent assay. In cell assays, cell viability is detected by Cell Counting Kit-8. Therefore, the recombinant human CXCL-13 was used to simulate its high expression in cells while its antibody and siRNA were used to reduce CXCL-13 expression in cells.ResultsIn this study, we demonstrated that CXCL-13 is associated with 5-Fu resistance by culture medium exchange experiments and cytokine arrays of colorectal cancer resistant and nonresistant cells. Clinical studies showed that CXCL-13 is highly expressed in the serum of 5-Fu–resistant patients. High levels of serum CXCL-13 also predict a worse clinical outcome. The addition of recombinant CXCL-13 cytokine resulted in 5-Fu resistance, while its antibody overcame 5-Fu resistance, and knockdown of CXCL-13 expression by siRNA also reduced 5-Fu resistance, which can be saved by added recombination CXCL-13.ConclusionThese results not only identify a CXCL-13 mediated 5-Fu resistance mechanism but also provide a novel target for 5-Fu–resistant colorectal cancer in prevention and treatment strategies.

5-Fluorouracil (5-Fu) is the first-line chemotherapeutic option for colorectal cancer. However, its efficacy is inhibited by drug resistance. Cytokines play an important role in tumor drug resistance, even though their mechanisms are largely unknown. Using a cytokine array, we established that tissue inhibitor metalloproteinase 2 (TIMP-2) is highly expressed in 5-Fu resistant colorectal cancer patients. Analysis of samples from 84 patients showed that elevated TIMP-2 expression levels in colorectal patients were correlated with poor prognostic outcomes. In a 5-Fu-resistant patient-derived xenograft (PDX) model, TIMP-2 was also found to be highly expressed. We established an autocrine mechanism through which elevated TIMP-2 protein levels sustained colorectal cancer cell resistance to 5-Fu by constitutively activating the ERK/MAPK signaling pathway. Inhibition of TIMP-2 using an anti-TIMP-2 antibody or ERK/MAPK inhibition by U0126 suppressed TIMP-2 mediated 5-Fu-resistance in CRC patients. In conclusion, a novel TIMP-2-ERK/MAPK mediated 5-Fu resistance mechanism is involved in colorectal cancer. Therefore, targeting TIMP-2 or ERK/MAPK may provide a new strategy to overcome 5-Fu resistance in colorectal cancer chemotherapy.

BRAF ^V600E -mutant metastatic colorectal cancer (mCRC) is associated with poor prognosis. The combination of anti-BRAF/anti-EGFR (encorafenib/cetuximab) treatment for patients with BRAF ^V600E -mutant mCRC improves clinical benefits; unfortunately, inevitable acquired resistance limits the treatment outcome, and the mechanism has not been validated. Here, we discovered that monoacylglycerol O-acyltransferase 3–mediated (MOGAT3-mediated) diacylglycerol (DAG) accumulation contributed to acquired resistance to encorafenib/cetuximab by dissecting a BRAF ^V600E -mutant mCRC patient–derived xenograft (PDX) model exposed to encorafenib/cetuximab administration. Mechanistically, the upregulated MOGAT3 promoted DAG synthesis and reduced fatty acid oxidation–promoting DAG accumulation and activated PKCα/CRAF/MEK/ERK signaling, driving acquired resistance. Resistance-induced hypoxia promoted MOGAT3 transcriptional elevation; simultaneously, MOGAT3-mediated DAG accumulation increased HIF1A expression at the translation level through PKCα/CRAF/eIF4E activation, strengthening the resistance status. Intriguingly, reducing intratumoral DAG with fenofibrate or PF-06471553 restored the antitumor efficacy of encorafenib/cetuximab in resistant BRAF ^V600E -mutant mCRC, which interrupted PKCα/CRAF/MEK/ERK signaling. These findings reveal the critical role of the metabolite DAG as a modulator of encorafenib/cetuximab efficacy in BRAF ^V600E -mutant mCRC, suggesting that fenofibrate might prove beneficial for resistant BRAF ^V600E -mutant mCRC patients.