Akiko Uchida

Emergence of epidermal growth factor receptor T790M mutation during chronic exposure to gefitinib in a non-small cell lung cancer cell line

The epidermal growth factor receptor (EGFR)-specific tyrosine kinase inhibitor gefitinib may provide dramatic clinical responses in some patients with pulmonary adenocarcinoma carrying activating mutations of the EGFR. However, prolonged administration of gefitinib may eventually induce acquired resistance in such patients. To gain insight into the mechanisms of this phenomenon, we placed PC-9, a cell line derived from pulmonary adenocarcinoma that has a 15-bp deletion in EGFR exon 19, under the continuous selective pressure of low levels of gefitinib without any mutagen, and established a subline that was able to grow in the presence of 2 micromol/L of gefitinib (designated RPC-9). In this cell line, about half of the reverse transcription-PCR products from mutated EGFR also carried an additional mutation (T790M). In keeping with the proposed role of T790M in abrogating gefitinib binding with EGFR, gefitinib-treated RPC-9 hardly displayed any decrease in the constitutive phosphorylation of EGFR, Akt, or Erk1/2 unlike in PC-9 cells. Interestingly, transfection of the EGFR carrying only a 15-bp deletion reversed the resistance to gefitinib in RPC-9 cells. Thus, the balance of expression levels between gefitinib-sensitive or gefitinib-resistant EGFR may govern the response to gefitinib in lung cancer.

Activation of downstream epidermal growth factor receptor (EGFR) signaling provides gefitinib-resistance in cells carrying EGFR mutation

Patients with pulmonary adenocarcinoma carrying the epidermal growth factor receptor (EGFR) mutation tend to display dramatic clinical response to treatment with the EGFR tyrosine kinase inhibitor gefitinib. Unfortunately, in many cases the cancer cells eventually acquire resistance, and this limits the duration of efficacy. To gain insight into these acquired resistance mechanisms, we first prepared HEK293T cell line stably transfected with either wild‐type (WT) or mutant (L858R) EGFR, and then expressed oncogenic K‐Ras12V mutant in the latter transfectant. Although 293T cells expressing wild‐type EGFR did not show any growth inhibition by gefitinib treatment similarly to the non‐transfected cells, the cells expressing the EGFR‐L858R were exquisitely sensitive. Consistently, phospho‐Akt levels were decreased in response to gefitinib in cells expressing EGFR‐L858R but not in cells with EGFR‐WT. In contrast, 293T cells expressing both EGFR‐L858R and oncogenic K‐Ras were able to proliferate even in the presence of high concentration of gefitinib probably by inducing Erk1/2 activation. We also expressed K‐Ras12V in the gefitinib‐sensitive pulmonary adenocarcinoma cell line PC‐9, which harbors an in‐frame deletion in the EGFR gene. The activated K‐Ras inhibited the effects of gefitinib treatment on cell growth, cell death induction and levels of phospho‐Akt, as well as phospho‐Erk. These data indicate that activated Ras could substitute most of the upstream EGFR signal, and are consistent with the hypothesis that mutational activation of targets immediately downstream from the EGFR could induce the secondary resistance to gefitinib in patients with lung cancer carrying EGFR mutation. (Cancer Sci 2007; 98: 357–363)

A requirement of FancL and FancD2 monoubiquitination in DNA repair

The rare hereditary disorder Fanconi anemia (FA) can be caused by mutations in components of the FA core complex (FancA/B/C/E/F/G/L/M), a key regulator FancD2, the breast cancer susceptibility protein BRCA2/FancD1, or the newly identified FancJ/BRIP1 helicase. By performing yeast two‐hybrid (Y2H) screens using N‐terminal chicken (ch) FancD2 as a bait, we have identified chFancL, the likely ubiquitin E3 ligase subunit of the FA core complex. We also found that ectopically expressed FancD2 and FancL co‐immunoprecipitated in 293T cells, and this interaction was dependent on the PHD domain of FancL. FANCL‐disrupted chicken DT40 cells displayed defects in both FancD2 monoubiquitination and focus formation. Importantly, cell lines lacking the FANCL or FANCD2 genes, or carrying a “knock‐in” mutation of the FancD2 monoubiquitination site (where the Lys 563 residue is changed to Arg), displayed quantitatively identical defects in the repair of I‐SceI‐induced chromosomal breaks by homologous recombination (HR). These data establish the role of FANCL and FancD2 monoubiquitination in HR repair.

Epidermal Growth Factor Receptor Mutation Status and Adjuvant Chemotherapy With Uracil-Tegafur for Adenocarcinoma of the Lung

PURPOSE Adjuvant chemotherapy with uracil-tegafur has been demonstrated to prolong survival among patients with resected lung adenocarcinomas. Epidermal growth factor receptor (EGFR) mutations have been reported to be present in lung adenocarcinomas. The present study evaluated whether the EGFR status could be used as a biologic predictor of the outcome of adjuvant chemotherapy with uracil-tegafur. PATIENTS AND METHODS The EGFR mutational status of 187 patients with resected lung adenocarcinomas was determined using a polymerase chain reaction-based assay for EGFR exons 19 and 21; the results were then correlated with the effect of adjuvant uracil-tegafur chemotherapy on survival. The antiproliferative effect of fluorouracil (FU) on adenocarcinoma cell lines with EGFR wild-type or mutant type status was examined by measuring the inhibitory concentrations at 50% (IC(50)s). RESULTS Among the 187 patients, 68 received uracil-tegafur as adjuvant chemotherapy, and 119 were not treated with any chemotherapeutic agents. EGFR mutations were present in 79 patients (43%). Overall, the adjuvant chemotherapy with uracil-tegafur significantly prolonged survival compared with the control group (hazard ratio = 0.38; P = .005). The survival benefit of adjuvant chemotherapy with uracil-tegafur was also examined after stratifying the patients according to EGFR mutation status. Adjuvant chemotherapy significantly prolonged survival among patients with EGFR wild-type tumors (hazard ratio = 0.34; P = .013) but not among patients with EGFR mutant tumors. In an in vitro experiment, the IC(50)s of EGFR mutant cells to FU were higher than those of wild-type cells, indicating that EGFR wild-type cells are more sensitive to FU than mutant cells. CONCLUSION EGFR status influenced the effect of adjuvant chemotherapy with uracil-tegafur. Adjuvant chemotherapy could be customized based on EGFR status.

The Epidermal Growth Factor Receptor D761Y Mutation and Effect of Tyrosine Kinase Inhibitor

To the Editor: We read with great interest the November 1, 2006 article by Balak et al. ([1][1]) reporting that the epidermal growth factor receptor ( EGFR ) D761Y mutation was a “novel secondary mutation” that appeared in a metastatic brain lesion after the acquisition of gefitinib resistance.

APL during Gefitinib Treatment for Non–Small-Cell Lung Cancer

To the Editor: Gefitinib is an orally active inhibitor of tyrosine kinase epidermal growth factor,1 with clinical effectiveness in the control of non–small-cell lung cancer. We describe 3 patients ...

The Effect of Gefitinib on B-RAF Mutant Non-small Cell Lung Cancer and Transfectants

We previously reported one patient with squamous cell carcinoma of the lung that showed the long-term effect to gefitinib with complete response. In the present report, we examine the epidermal growth factor receptor (EGFR) and K-RAS, HER2, and B-RAF mutations in this patient to find a B-RAF exon11 mutation, resulting in a substitution of valine by phenylalanine at codon 470 (V470F) as a novel type of B-RAF mutation in human cancers. In addition, the fluorescence in situ hybridization analysis for EGFR showed the high polysomy status. B-RAF is a nonreceptor serine/threonine kinase whose kinase domain has a structure similar to other protein kinases, including EGFR members. Of interest, the B-RAF V470F mutation corresponds to a position similar to the EGFR G719X mutation located on the phosphate binding (P)-loop of EGFR that clamps ATP into the catalytic cleft. This observation suggests that gefitinib may have an anti-cancer effect on B-RAF mutant tumors. Indeed, previous reports demonstrated that H1666 cells harboring B-RAF G465V mutations showed sensitivity to gefitinib, inhibiting phosphorylation of ERK1/2. We examined the effect of gefitinib on transient transfectants of the B-RAF mutant, but no drastic inhibition of ERK1/2 phosphorylation that was one of the downstream molecules of B-RAF was induced by gefitinib. In summary, we found a novel B-RAF V470F mutation in lung squamous cell carcinoma that showed response to gefitinib. However, our in vitro investigation did not explain the response observed in this particular patient. Further investigation is necessary to elucidate the mechanism of tumor sensitivity to EGFR tyrosine kinase inhibitors.