Abstract
Because the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor erlotinib and the multitargeted antifolate pemetrexed are registered in the treatment of second-line non-small-cell lung cancer (NSCLC), empirical combinations of these drugs are being tested. This study investigated molecular mechanisms underlying their combination in six NSCLC cell lines. Cells were characterized by heterogeneous expression of pemetrexed determinants, including thymidylate synthase (TS) and dihydrofolate reductase (DHFR), and mutations potentially affecting chemosensitivity. Pharmacological interaction was studied using the combination index (CI) method, whereas cell cycle, apoptosis induction, and EGFR, extracellular signal-regulated kinases 1 and 2, and Akt phosphorylation were studied by flow cytometry, fluorescence microscopy, and enzyme-linked immunosorbent assays. Reverse-transcriptase polymerase chain reaction (RT-PCR), Western blot, and activity assays were performed to assess whether erlotinib influenced TS. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assays demonstrated that EGFR and k-Ras mutations were related to erlotinib sensitivity, whereas TS and DHFR expression were related to pemetrexed sensitivity. Synergistic cytotoxicity was found in all cells, most pronounced with pemetrexed + erlotinib (24 h) → erlotinib (48 h) sequence (CI, 0.09-0.40), which was associated with a significant induction of apoptosis. Pemetrexed increased EGFR phosphorylation and reduced Akt phosphorylation, which was additionally reduced by drug combination (-70.6% in H1650). Erlotinib significantly reduced TS expression and activity, possibly via E2F-1 reduction, as detected by RT-PCR and Western blot, and the combination decreased TS in situ activity in all cells. Erlotinib and pemetrexed showed a strong synergism in NSCLC cells, regardless of their genetic characteristics. Induction of apoptosis, modulation of EGFR and Akt phosphorylation, and changes in the expression of critical genes involved in pemetrexed activity contribute to this synergistic interaction and support the clinical investigation of these markers.
Footnotes
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E.G. was supported by the L'Orèal-UNESCO Award for Women in Science 2007 (V Italian edition).
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This work was presented previously in abstract form: Giovannetti E, Smid K, Mey V, Tekle C, Nannizzi S, Del Tacca M, Rodriguez JA, Danesi R, Giaccone G, and Peters GJ (2007) Synergistic interaction between erlotinib and pemetrexed in non-small cell lung cancer (NSCLC) cells. 97th Annual Meeting American of the Association for Cancer Research; 2007 Apr 14-18; Los Angeles, CA. Abstract 4078, American Association for Cancer Research, Philadelphia, PA.
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ABBREVIATIONS: NSCLC, non-small-cell lung cancer; 5-FU, 5-fluorouracil; AI, apoptotic index; BCRP, breast cancer resistance protein; CI, combination index; DHFR, dihydrofolate reductase; EGFR, epidermal growth factor receptor; FA, fraction affected; FPGS, folyl-polyglutamate synthetase; GARFT, glycinamide ribonucleotide formyltransferase; MRPs, multidrug-related protein; PI3K, phosphatidylinositide 3-kinase; RFC, reduced folate carrier; TKI, tyrosine-kinase inhibitor; TS, thymidylate synthase; LY294002, (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride); ERK, extracellular signal-regulated kinase; RT-PCR, reverse-transcriptase polymerase chain reaction; DMEM, Dulbecco's modified Eagle's medium; FACS, fluorescence-activated cell sorting; TSER, tandem repeat sequence of the enhancer region of the thymidylate synthase promoter; MTHFR, methylenetetrahydrofolate reductase; γGH, γ-glutamyl hydrolase.
- Received October 3, 2007.
- Accepted January 10, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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