Chemotherapy-induced Release Of GM-CSF:A Potentially Novel Mechanism Of Drug Resistance In KRAS-mutated Colorectal Cancer

Colorectal cancer(CRC)is the most common malignant gastrointestinal cancer in clinic.The incidence and mortality of the colorectal carcinoma have been increasing significantly in recent years,and its occurrence and development are a complex process involving multiple pathways and large amounts of factors.The resistance of colorectal cancer cells to chemotherapeutic drugs represents one of the main causes for the failure of clinical chemotherapy for colorectal cancer,as well as the recurrence,migration,invasion,or progression of colorectal cancer.Current chemotherapy regimens commonly used for colorectal cancer include the m FOLFOX6 regimen(Oxaliplatin + leucovorin + 5-fluorouracil)and the FOLFIRI regimen(Irinotecan + leucovorin + 5-fluorouracil),of which 5-fluorouracil(5-FU)is a first-line chemotherapeutic drug for the treatment of colorectal cancer.5-Fluorouracil is a derivative of fluorine substituted uracil at the 5’ end,which interferes with DNA and RNA synthesis and exerts a biological anticancer effect.5-FU as a single and combination drug is still the first-line treatment of gastrointestinal cancer.However,it is not clear why the drug resistance occurs,accounting for the low overall responses of colorectal cancer.KRAS is a proto-oncogene protein that plays an essential role in the development of normal tissues,and KRAS mutation is a key step in the initiation of many cancers.Studies have shown that KRAS has a high frequency of mutation in malignant and refractory diseases such as leukemia,colorectal cancer,pancreatic cancer,and lung cancer.KRAS mutation is indication of poor efficacy in the treatment of colorectal cancer with the targeted drugs panitumumab and cetuximab.A large number of studies have shown that cetuximab has a significant effect on KRAS wild-type colon cancer patients,while the mutant-type of patients have a shorter progression-free survival and a poorer prognosis.Intriguingly,there is intimate correlation of KRAS status with the follow-up of patients receiving chemotherapy.Further investigations indicate that,compared with those harboring G12 mutations,patients with G13 D mutation have a poorer prognosis.The underlying mechanisms,however,remain elusive.Granulocyte macrophage colony stimulating factor(GM-CSF)is a hematopoietic cell growth factor with multiple immunomodulatory activities,which has an important role in promoting cell proliferation and differentiation regulation.Which also can promote cell differentiation and maturation at different stages of bone marrow development.Our previous stidues showed that GM-CSF plays a tumor-promoting role in CRC development.In this study,we sought to determine the relationship between chemotherapy,KRAS and tumor microenvironment(TME)as well as the underlying mechanisms.Based on in vitro and in vivo experiments,we found that 5-FU stimulation potently induced GM-CSF release by mutant KRAS-harboring colon cancer cell lines,while those with wild-type KRAS could not.Subsequently,we confirmed a causal relationship between KRAS status and the above effects.Knockdown of KRAS render significant repression of 5-FU-elicited GM-CSF expression.5-FU triggered KRAS G13 Dharboring CRC cell line to release large amounts of GM-CSF,while the cell line with KRAS G12 D was not.Finally,MAPK/ERK and NF-κB signalling pathways were verified to be involved in this process.Taken together,considering the putative tumor-promoting function of GM-CSF in many types of cancer including CRC,it is reasonable that the effect of 5-FU-elicited GM-CSF release by CRC cell line with KRAS G13 D may account for the poor prognosis of patients with KRAS G13 D.