title: Effects of pemetrexed, gefitinib, and their combination on human colorectal cancer cells.
abstract: OBJECTIVE
  The study investigated the effects of pemetrexed, gefitinib, and their combination on human colorectal cancer cells.
  
  
  METHODS
  Six human colorectal cancer cells were exposed to pemetrexed, gefitinib, and their combination. Antitumor effects were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Thymidylate synthase (TS) mRNA expression and EGFR mutation were studied by real-time RT-PCR and DNA sequence determination. Pharmacological interaction was studied using the combination index method. Cell cycle distribution and apoptosis were determined by flow cytometry. Activity assay was performed to assess the effects of drugs on TS activity, and Western blot was performed to assess the protein expression of pEGFR, pAKT, and pERK 1/2.
  
  
  RESULTS
  Six colorectal cancer cells are all sensitive to pemetrexed, and TS gene expression of cells was negatively related to pemetrexed sensitivity. The cytotoxic synergism was observed in concurrent pemetrexed combined with gefitinib and sequential pemetrexed followed by gefitinib. The combination of pemetrexed and gefitinib modulated cell cycle and induced apoptosis. Pemetrexed combined with gefitinib decreased TS mRNA expression and in situ activity. Pemetrexed induced an EGFR-mediated activation of the phosphatidylinositol 3-kinase/AKT and ERK pathway, which was inhibited by gefitinib.
  
  
  CONCLUSIONS
  Pemetrexed is a promising agent, and pemetrexed combined with gefitinib has a significantly synergistic effect on colorectal cancer cells, which seems to present a strategy of pemetrexed combined with EGFR-TKIs in colorectal cancer treatment.
authors: Guanzhong
authors: G
authors: Zhang
authors: Xiaodong
authors: X
authors: Xie
authors: Tianyi
authors: T
authors: Liu
authors: Jihua
authors: J
authors: Yang
authors: Shunchang
authors: S
authors: Jiao
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000473:pathology; D004357:Drug Synergism; D066246:ErbB Receptors / Q000235:genetics*; D005434:Flow Cytometry; D000077156:Gefitinib; D015972:Gene Expression Regulation, Neoplastic; D005971:Glutamates / Q000008:administration & dosage; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives; D006801:Humans; D009154:Mutation; D000068437:Pemetrexed; D011799:Quinazolines / Q000008:administration & dosage; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013940:Thymidylate Synthase / Q000235:genetics*
chemical_list: D005971:Glutamates; D011799:Quinazolines; D012333:RNA, Messenger; D000068437:Pemetrexed; D006147:Guanine; D013940:Thymidylate Synthase; D066246:ErbB Receptors; D000077156:Gefitinib