Randomized Phase II trial of paclitaxel and carboplatin followed by gemcitabine switch-maintenance therapy versus gemcitabine and carboplatin followed by gemcitabine continuation-maintenance therapy in previously untreated advanced non-small cell lung cancer.

BACKGROUND: In recent years, maintenance chemotherapy is increasingly being recognized as a new treatment strategy to improve the outcome of advanced non-small cell lung cancer (NSCLC). However, the optimal maintenance strategy is still controversial. Gemcitabine is a promising candidate for single-agent maintenance therapy because of little toxicity and good tolerability. We have conducted a randomized phase II study to evaluate the validity of single-agent maintenance chemotherapy of gemcitabine and to compare continuation- and switch-maintenance. METHODS: Chemonaïve patients with stage IIIB/IV NSCLC were randomly assigned 1:1 to either arm A or B. Patients received paclitaxel (200 mg/m2, day 1) plus carboplatin (AUC 6 mg/mL/min, day 1) every 3 weeks in arm A, or gemcitabine (1000 mg/m2, days 1 and 8) plus carboplatin (AUC 5 mg/mL/min, day1) every 3 weeks in arm B. Non-progressive patients following 3 cycles of induction chemotherapy received maintenance gemcitabine (1000 mg/m2, days 1 and 8) every 3 weeks. ( TRIAL REGISTRATION: UMIN000008252) RESULTS: The study was stopped because of delayed accrual at interim analysis. Of the randomly assigned 50 patients, 49 except for one in arm B were evaluable. Median progression-free survival (PFS) was 4.6 months for arm A vs. 3.5 months for arm B (HR = 1.03; 95% CI, 0.45-2.27; p = 0.95) and median overall survival (OS) was 15.0 months for arm A vs. 14.8 months for arm B (HR = 0.79; 95% CI, 0.40-1.51; p = 0.60), showing no difference between the two arms. The response rate, disease control rate, and the transit rate to maintenance phase were 36.0% (9/25), 64.0% (16/25), and 48% (12/25) for arm A vs. 16.7% (4/24), 50.0% (12/24), and 33% (8/24) for arm B, which were also statistically similar between the two arms (p = 0.13, p = 0.32, and p = 0.30, respectively). Both induction regimens were tolerable, except that more patients experienced peripheral neuropathy in arm A. Toxicities during the maintenance phase were also minimal. CONCLUSION: Survival and overall response were not significantly different between the two arms. Gemcitabine may be well-tolerable and feasible for maintenance therapy.

[Renal actinomycosis with pneumonia].

A 55-year-old man was hospitalized for pneumonia. His fever did not subside despite administration of antibiotics ; therefore, he was referred to our hospital. A chest radiograph and thoracic computed tomography showed multiple tubercles ; abdominal computed tomography (CT) showed left renal abscess. The patient's temperature fell after antibiotic administration, but inflammation reaction exacerbated. Abdominal CT showed inflammation spreading to the subcutaneous tissues. We considered renal resection, but the patient could not be administered general anesthesia because of low breathing function caused by pneumonia. We attempted open drainage and wedge resection of the left renal under local anesthesia ; but we were not able to identify the infectious bacteria. Four days later, the patient had blood poisoning and died because of deterioration of breathing function. Actinomyces was detected in the lungs and the kidneys by pathological examination.

Proatherogenic effect of interleukin-18 is exerted with high-fat diet, but not with normal diet in spontaneously hyperlipidemic mice.

AIM: It has been considered that interleukin (IL)-18, a T helper 1(Th1) type cytokine, has a promoting effect on atherosclerosis development. A previous mouse study demonstrated that short-term exogenous IL-18 promoted atherosclerosis through a Th1 type immune response; however, the serum IL-18 may have increased greatly beyond its physiological range, and the effect of increased serum IL-18 on atherosclerosis development has not been investigated under different conditions of dietary fat content. The purpose of this study was to reveal the effect of increased serum IL-18 within its physiological fluctuations on atherosclerosis development under different conditions of dietary fat content. METHODS: Spontaneously hyperlipidemic (SHL) mice were systemically supplied with IL-18 for 10 weeks by means of an in vivo gene transfer system with a high-fat diet containing 0.15% cholesterol or a normal diet. RESULTS: Serum IL-18 steadily elevated within its physiological fluctuations. An atherosclerotic lesion area in the aortic root significantly increased with a high-fat diet. Systemic cytokine balance shifted to a Th1-dominant state, and IL-12 mRNA in the arterial wall significantly increased with a high-fat diet; however, these findings were not observed with a normal diet. CONCLUSIONS: It was suggested that the proatherogenic effect of IL-18 is physiologically exerted exclusively with a high-fat diet through Th1 type immune responses, but not with a normal diet.

Overexpression of SOCS3 exhibits preclinical antitumor activity against malignant pleural mesothelioma.

Malignant pleural mesothelioma (MPM) is an aggressive tumor with poor prognosis for which an effective therapy remains to be established. Our study investigated the therapeutic potential of the suppressor of cytokine signaling 3 (SOCS3), an endogenous inhibitor of intracellular signaling pathways, for treatment of MPM. We infected MPM cells (H226, EHMES-1, MESO-1 and MESO-4) with an adenovirus-expressing SOCS3 (AdSOCS3) to examine the effect of SOCS3 overexpression on MPM cells. SOCS3 overexpression reduced MPM proliferation and induced apoptosis and partial G0/G1 arrest. SOCS3 also inhibited the proliferation of MPM cells via multiple signaling pathways including Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3), extracellular signal-regulated kinase (ERK), focal adhesion kinase (FAK) and p53 pathways. Notably, AdSOCS3 treatment inhibited tumor growth in an MPM pleural xenograft model. These findings demonstrate that overexpression of SOCS3 has a potent antitumor effect against MPM both in vitro and in vivo and indicate the potential for clinical use of SOCS3 for MPM treatment.

High frequencies of less differentiated and more proliferative WT1-specific CD8+ T cells in bone marrow in tumor-bearing patients: an important role of bone marrow as a secondary lymphoid organ.

In tumor-bearing patients, tumor-associated antigen (TAA)-specific CTLs are spontaneously induced as a result of immune response to TAAs and play an important role in anti-tumor immunity. Wilms' tumor gene 1 (WT1) is overexpressed in various types of tumor and WT1 protein is a promising pan-TAA because of its high immunogenicity. In this study, to clarify the immune response to the WT1 antigen, WT1-specific CD8(+) T cells that were spontaneously induced in patients with solid tumor were comparatively analyzed in both bone marrow (BM) and peripheral blood (PB). WT1-specific CD8(+) T cells more frequently existed in BM than in PB, whereas frequencies of naïve (CCR7(+) CD45RA(+)), central memory (CCR7(+) CD45RA-), effector-memory (CCR7- CD45RA(-)), and effector (CCR7- CD45RA(+)) subsets were not significantly different between BM and PB. However, analysis of these subsets for the expression of CD57 and CD28, which were associated with differentiation, revealed that effector-memory and effector subsets of the WT1-specific CD8(+) T cells in BM had less differentiated phenotypes and more proliferative potential than those in PB. Furthermore, CD107a/b functional assay for WT1 peptide-specific cytotoxic potential and carboxyfluorescein diacetate succinimidyl ester dilution assay for WT1 peptide-specific proliferation also showed that WT1-specific CD8(+) T cells in BM were less cytotoxic and more proliferative in response to WT1 peptide than those in PB. These results implied that BM played an important role as a secondary lymphoid organ in tumor-bearing patients. Preferential residence of WT1-specific CD8(+) T cells in BM could be, at least in part, explained by higher expression of chemokine receptor CCR5, whose ligand was expressed on BM fibroblasts on the WT1-specific CD8(+) T cells in BM, compared to those in PB. These results should provide us with an insight into WT1-specific immune response in tumor-bearing patients and give us an idea of enhancement of clinical response in WT1 protein-targeted immunotherapy.

A phase II study directed by a clinical pathway for carboplatin and weekly paclitaxel in previously untreated patients with unresectable non-small cell lung cancer.

The objective of this phase II study was to evaluate the efficacy and safety of carboplatin and weekly paclitaxel in previously untreated patients with unresectable non-small cell lung cancer. In addition, the clinical pathway intensified the management of chemotherapy including the assessment of efficacy, safety and implementation of treatment and patient education. Patients received paclitaxel at a dose of 70 mg/m(2) on days 1, 8 and 15 and carboplatin (area under the curve of 6) on day 1 and every 28th day thereafter. Fifty-eight patients were enrolled. A median of 3 cycles (range 1-6) were administered. Twenty-eight cases showed objective responses (48.2%), including 2 complete (3.4%) and 26 partial responses (44.8%; 95% confidence interval 35.4-61.1). The median survival time was 663 days, and the 1-year survival rate was 59.9%. Nineteen patients (32.8%) had grade 3, and 4 patients (6.9%) had grade 4 neutropenia. Nine patients (15.5%) experienced > or =3 grade nonhematological toxicities. There were no treatment-related deaths due to this study. Carboplatin and weekly paclitaxel combination chemotherapy might be an alternative treatment selection in patients with unresectable non-small cell lung cancer.

Tetraspanin CD9 negatively regulates lipopolysaccharide-induced macrophage activation and lung inflammation.

Tetraspanins facilitate the formation of multiple molecular complexes at specialized membrane microdomains and regulate cell activation and motility. In the present study, the role of tetraspanin CD9 in LPS-induced macrophage activation and lung inflammation was investigated in vitro and in vivo. When CD9 function was ablated with mAb treatment, small interfering RNA transfection, or gene knockout in RAW264.7 cells or bone marrow-derived macrophages, these macrophages produced larger amounts of TNF-alpha, matrix metalloproteinase-2, and -9 upon stimulation with LPS in vitro, when compared with control cells. Sucrose gradient analysis revealed that CD9 partly colocalized with the LPS-induced signaling mediator, CD14, at low-density light membrane fractions. In CD9 knockout macrophages, CD14 expression, CD14 and TLR4 localization into the lipid raft, and their complex formation were increased whereas IkappaBalpha expression was decreased when compared with wild-type cells, suggesting that CD9 prevents the formation of LPS receptor complex. Finally, deletion of CD9 in mice enhanced macrophage infiltration and TNF-alpha production in the lung after intranasal administration of LPS in vivo, when compared with wild-type mice. These results suggest that macrophage CD9 negatively regulates LPS response at lipid-enriched membrane microdomains.

Combined mobilization and stimulation of tumor-infiltrating dendritic cells and natural killer cells with Flt3 ligand and IL-18 in vivo induces systemic antitumor immunity.

It was hypothesized that if dendritic cells (DC) could be efficiently manipulated in vivo, this might enable functional maturation and retention of their potent functions and might represent a more promising approach in DC immunotherapy. The present study focused on the modulation of DC in tumor microenvironment using Fms-like thyrosine kinase 3 ligand (Flt3L) combined with interferon-gamma-inducing factor (IL-18). Tumor-inoculated mice were treated with in vivo electroporation (IVE) of expression plasmids carrying complementary DNA of Flt3L. As a combination therapy, mice in the other group were treated with intra-tumoral injection of adenoviral vector carrying IL-18 gene (Ad.IL-18). Significant antitumor effect was observed in mice treated with Ad.IL-18 alone when compared with that of control (P < 0.01). Complete eradication was observed more frequently (100%versus 33%: P < 0.05) in the mice treated with Flt3L and Ad.IL-18 when compared with the mice treated with Ad.IL-18 alone. In un-injected distant tumor, significant antitumor responses were observed only in the mice treated with combination therapy. Lymphoid cells in lymph nodes of mice treated with combination therapy showed significant cytolytic activity against inoculated tumor cells and YAC-1 cells when compared with the lymphoid cells in other groups. In the tumor microenvironment, combination therapy resulted in the recruitment of mobilized DC into the tumor bed, although Flt3L-IVE alone had an effect in the peri-tumoral area. Tumor-infiltrating DC in mice treated with combination therapy showed higher CD86 expression and more potent allogeneic T-cell stimulatory capacity. These results may suggest that local expression of IL-18 combined with in vivo DC mobilization with Flt3L is clinically applicable as a new strategy of DC immunotherapy.

Double deficiency of tetraspanins CD9 and CD81 alters cell motility and protease production of macrophages and causes chronic obstructive pulmonary disease-like phenotype in mice.

CD9 and CD81 are closely related tetraspanins that regulate cell motility and signaling by facilitating the organization of multimolecular membrane complexes, including integrins. We show that CD9 and CD81 are down-regulated in smoking-related inflammatory response of a macrophage line, RAW264.7. When functions of CD9 and CD81 were ablated with monoclonal antibody treatment, small interfering RNA transfection, or gene knock-out, macrophages were less motile and produced larger amounts of matrix metalloproteinase (MMP)-2 and MMP-9 than control cells in vitro. In line with this, CD9/CD81 double-knock-out mice spontaneously developed pulmonary emphysema, a major pathological component of chronic obstructive pulmonary disease (COPD). The mutant lung contained an increased number of alveolar macrophages with elevated activities of MMP-2 and MMP-9 and progressively displayed enlarged airspace and disruption of elastic fibers in the alveoli. Secretory cell metaplasia, a finding similar to goblet cell metaplasia in cigarette smokers, was also observed in the epithelium of terminal bronchioles. With aging, the double-knockout mice showed extrapulmonary phenotypes, including weight loss, kyphosis, and osteopenia. These results suggest that the tetraspanins CD9 and CD81 regulate cell motility and protease production of macrophages and that their dysfunction may underlie the progression of COPD.

Megakaryocyte potentiating factor as a tumor marker of malignant pleural mesothelioma: evaluation in comparison with mesothelin.

PURPOSE: An early and reliable blood test is one deficiency in diagnosis of malignant pleural mesothelioma (MPM). Megakaryocyte potentiating factor (MPF) and mesothelin variants (MSLN), members of the mesothelin gene family, have been studied as candidate serum markers for MPM. We developed a novel enzyme-linked immunosorbent assay (ELISA) system to compare the diagnostic efficacy of MPF and MSLN in MPM and control groups. EXPERIMENTAL DESIGN: MPF and MSLN were assayed with ELISA in 27 consecutive MPM patients and 129 controls including patients with lung cancer and asymptomatic asbestos-exposed subjects. RESULTS: Statistically significant elevation of serum MPF and MSLN levels was noted in MPM patients in comparison with every control group. The area under the receiver operating characteristic curve (AUC) was calculated for differentiation of MPM and lung cancer, healthy asbestos-exposed subjects, and healthy adults. While the AUC for serum MPF was 0.879, cut-off=19.1ng/ml (sensitivity=74.1%, specificity=90.4%), the AUC for serum MSLN was 0.713, cut-off=93.5ng/ml (sensitivity=59.3%, specificity=86.2%). Comparison between AUC for MPF and MSLN values shows that MPF is significantly superior to MSLN (p=0.025). Finally, there was a significant correlation between MPF and MSLN values for MPM (Pearson's correlation coefficient=0.77; p<0.001). CONCLUSIONS: These findings suggest that diagnostic value of MPF for MPM was better than that of MSLN although both markers showed almost equal specificity for MPM.

Gefitinib-sensitive EGFR lacking residues 746-750 exhibits hypophosphorylation at tyrosine residue 1045, hypoubiquitination, and impaired endocytosis.

Gefitinib-sensitive nonsmall cell lung cancers (NSCLC) are characterized by somatic mutations in the kinase domain of epidermal growth factor receptor (EGFR). The mutant EGFR forms are reported to mediate characteristic signal transduction pathways that are different from those mediated by the wild-type EGFR and are involved in transformation in vivo. We have examined signal transduction pathways initiated from a frequently identified gefitinib-sensitizing mutant EGFR lacking residues 746-750 by employing a mouse fibroblast cell line that is free of endogenous EGFR and transiently transfected COS-7 cells. Upon EGF stimulation, the deletion-mutant EGFR mediated prolonged downstream signals. The analysis of the phosphotyrosine patterns of the receptor revealed that the deletion-mutant EGFR lacked phosphorylation at tyrosine residue 1045, which is the major binding site of Cbl. The EGF-induced endocytosis of the deletion-mutant EGFR was impaired. The ubiquitination and downregulation of the deletion-mutant EGFR were also reduced. On the other hand, another mutant, EGFR, possessing a L858R substitution, exhibited phosphorylation at 1045 and its downstream signalings were not prolonged. These data suggest that the signal transduction pathways initiated from these mutant forms are different, and that impaired endocytosis might be responsible for the prolonged signals mediated by the deletion-mutant EGFR.

Short-term gefitinib treatment brought about a long-term regression of bronchioloalveolar carcinoma without EGFR gene alterations: a case report.

The tyrosine kinase inhibitor (TKI) of the epidermal growth factor receptor (EGFR) gefitinib has beneficial effect in some patients with refractory advanced non-small cell lung cancer (NSCLC). However, the majority of responders eventually develop acquired resistance during the course of prolonged continuous treatment. Here we present a case of 76-year-old Japanese female, who had never smoked, with poor performance status from bronchioloalveolar carcinoma (BAC), in whom a brief initial 5-week administration of gefitinib resulted in dramatic antitumor effects that lasted approximately 8.5 months after cessation of the treatment. Furthermore, the relapsed tumor later regressed again by re-treatment with the TKI. She survived 26 months since she first took gefitinib. Unexpectedly, neither sensitizing mutations for EGFR-TKIs nor increased copy numbers were detected in EGFR gene of her BAC cells. This case suggests that, in some patients with NSCLC, even short-term administration of gefitinib may bring about clinical benefits and disease response comparable to the standard long-term daily dosing schedule. Short-term use of gefitinib will also be able to minimize the expensive medical cost of the TKI. The potential role of short-term or pulse-dose therapy with EGFR-TKIs should be clarified in further prospective studies. Moreover, it is urgent to develop better strategies by which we could distinguish responders to the TKIs from nonresponders among patients who do not have any EGFR gene alterations.

Overexpression of PIAS3 suppresses cell growth and restores the drug sensitivity of human lung cancer cells in association with PI3-K/Akt inactivation.

Constitutively activated signal transducers and activators of transcription (STAT) are reported to cause uncontrolled transmission of growth signals. In this study, we analyzed the roles of an inhibitor of STAT, protein inhibitor of activated STAT (PIAS) 3, in the development of lung cancer. Treatment with an inhibitor of phosphatidylinositol 3-kinase, LY294002, retarded the growth of human lung cancer cells and rendered them more sensitive to chemotherapeutic agents. However, the inhibition of JAK/STAT by AG490 significantly suppressed cell growth but did not increase drug sensitivity at all. Overexpression of PIAS3 not only significantly inhibited cell growth but also rendered cancer cells up to 12.0-fold more sensitive to the above drugs, which was associated with the suppression of Akt phosphorylation. Inhibition of PIAS3 with small interfering RNA, nevertheless, led cancer cells to accelerate cell proliferation, deteriorate chemosensitivity, and augment Akt phosphorylation. Although the overexpression of suppressors of cytokine signaling 3 in cancer cells also inhibited cell growth and STAT3 phosphorylation, it neither increased sensitivity to chemotherapeutic drugs nor affected the phosphorylation of Akt. These results indicate that PIAS3 may be an attractive candidate for targeting the JAK/STAT and PI3-K/Akt signaling pathways in cancer treatment.

Absence of CD9 enhances adhesion-dependent morphologic differentiation, survival, and matrix metalloproteinase-2 production in small cell lung cancer cells.

While adhering to extracellular matrix proteins in vitro and in vivo, small cell lung cancer (SCLC) cells frequently show morphologic differentiation and are protected from apoptosis. Integrin beta(1)-mediated protein phosphorylation is suggested to be an essential signaling event in these processes. CD9 is an almost ubiquitously expressed tetraspanin protein that suppresses tumor progression by regulating cell motility and signaling through complex formation with beta(1) integrins. We reported previously that, among tetraspanins, CD9 is selectively absent in most SCLC cells and that ectopic expression of CD9 suppresses their motility. Here, we show that the ectopic expression of CD9 suppressed neurite-like process outgrowth and promoted apoptotic death of SCLC cells that were adherent to fibronectin in serum-starved conditions. This correlated with attenuation of adhesion-dependent phosphorylation of Akt but not that of focal adhesion kinase or c-Jun NH(2)-terminal kinase. Treatment of CD9(-) parent cells with a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, inhibited process outgrowth and survival, suggesting that PI3K/Akt signaling is required for the morphologic change and cell survival. Production of matrix metalloproteinase (MMP)-2 was likewise suppressed in the CD9 transfectants and in LY294002-treated parent cells. These results suggest that the absence of CD9 in SCLC cells may contribute to postadhesive morphologic differentiation, survival, and MMP-2 production via PI3K/Akt pathway.

The extracellular domain of p185(c-neu) induces density-dependent inhibition of cell growth in malignant mesothelioma cells and reduces growth of mesothelioma in vivo.

EGFR is involved in the density-dependent inhibition of cell growth, while coexpression of EGFR with erbB2 can render normal cells transformed. In this study, we have examined the effect of a species of p185 that contains the transmembrane domain and the extracellular domain of p185(c-neu), on growth properties of a human malignant mesothelioma cell line that coexpresses EGFR and erbB2. The ectodomain form of p185(c-neu) enhanced density-dependent inhibition of cell growth and we found that p21 induction appeared to be responsible for this inhibitory effect. Previously, the extracellular domain species was shown to suppress the transforming abilities of EGFR and p185(c-neu/erbB2) in a dominant-negative manner. The ability of this subdomain to affect tumor growth is significant, as it reduced in vivo tumor growth. Unexpectedly, we found that the domain did not abrogate all of EGFR functions. We noted that EGFR-induced density-dependent inhibition of cell growth was retained. Tyrosine kinase inhibitors of EGFR did not cause density-dependent inhibition of cell growth of malignant mesothelioma cells. Therefore, simultaneously inhibiting the malignant phenotype and inducing density-dependent inhibition of cell growth in malignant mesothelioma cells by the extracellular domain of p185(c-neu) may represent an important therapeutic advance.

[Clinical efficacy of TS-1 in refractory bone recurrence of a postoperative squamous lung cancer patient].

BACKGROUND: We need more effective treatments for refractory non-small cell lung cancer. CASE: A 61-year-old man had a recurrence in the left ninth rib invading the chestwall 4 years after resection of squamous cell lung cancer. The metastatic lesion grew larger even after 3 different regimens of systemic chemotherapy and local irradiation. Then he started to receive 120 mg of TS-1 daily for 28 days followed by 14 days of rest (1 course). A partial response was achieved after 2 courses of the treatment and continued for 6 weeks. Doses of oxycodone hydrochloride could be reduced to one-sixth of the initial dose according to tumor regression. CONCLUSION: This is the first report to show the effectiveness of TS-1 for a refractory recurrence of lung cancer to the bone.

A phase I/II trial of a WT1 (Wilms' tumor gene) peptide vaccine in patients with solid malignancy: safety assessment based on the phase I data.

OBJECTIVE: We conducted a phase I study to investigate the safety of a weekly WT1 tumor vaccine therapy in patients with solid tumors that had been refractory to all other anti-cancer therapies. METHODS: Skin-test-negative patients were intradermally injected weekly for 12 weeks with 3.0 mg of an HLA-A*2402-restricted modified 9-mer WT1 peptide emulsified in Montanide ISA51 adjuvant. We estimated the Bayesian posterior probability of the occurrence of grade 3 or 4 toxicity when receiving the weekly WT1 vaccination. This analysis provided the basis for making a decision to terminate the phase I study and switch to phase II. Moreover, we performed an exploratory assessment of the anti-tumor effects of WT1 treatment. RESULTS: Ten patients received 114 vaccinations with WT1 on a weekly schedule. No grade 3 or 4 toxicities were observed. Based on the Bayesian approach, it was highly likely that the probability of grade 3 or 4 toxicity was below 20% (the posterior probability = 0.914). Fifteen grade 2 and two grade 1 toxicities were observed; all of these incidents, however, were determined by the Independent Data and Safety Monitoring Committee to be unrelated to the WT1 treatment. One patient exhibited a partial response; five additional patients had stable disease while receiving weekly WT1 treatment. CONCLUSION: This paper confirms that the potential toxicities of the treatment schedule of weekly WT1 vaccination are acceptable and suggested a potential anti-tumor effect. Consequently, we validated the decision to continue to the phase II trial.

The gefitinib-sensitizing mutant epidermal growth factor receptor enables transformation of a mouse fibroblast cell line.

A specific inhibitor of the Epidermal Growth Factor Receptor (EGFR), Gefitinib, displays significant antitumor effects against non-small cell lung cancers (NSCLC) that express EGFR with mutations in their tyrosine kinase domain. Although previous reports have already demonstrated that oncogenic transformation can be induced by some mutant EGFR forms, the precise differences between mutant and wild-type EGFR in terms of mechanisms of transformation have not been fully elucidated. We show here that a murine fibroblast cell line, NR6 becomes transformed by an expression level of the mutant EGFR form lacking E746-A750 that is far less than that needed with transfected wild-type EGFR. However, the mutant EGFR was unable to transform NR6 in a ligand-independent manner, as was seen with the wild-type EGFR. The consequent biological features after transformation, including DNA synthesis or cell cycle progression and biochemical characteristics such as MAPK activation mediated by the mutant EGFR are comparable and equivalent to those mediated by wild-type EGFR. These data suggest that the mutant EGFR possesses greater ligand-dependent transformation when compared with wild-type EGFR, although the exact mechanisms to account for this characteristic remain to be defined.