Suppression of tumor growth in human gastric cancer with HER2 overexpression by an anti-HER2 antibody in a murine model

New modalities are necessary for the treatment of patients with unresectable gastric cancer. The aim of this study was to investigate whether or not anti-HER2 antibody could suppress the growth of human gastric cancer cells with HER2 overexpression in vitro and in vivo. Four human gastric cancer cell lines, NCI-N87, MKN-45P, Kato-III, and MKN-1, were used in this study. The suppression of cell proliferation in vitro and of subcutaneous tumor growth in a nude mouse model after treatment with trastuzumab was examined. The expression of HER2 protein was investigated by Western blot analysis. The effect of trastuzumab on the survival rate of nude mice with peritoneal dissemination was examined. Trastuzumab significantly reduced proliferative activity in NCI-N87, a HER2-overexpressing human gastric cancer cell line, in vitro. In the nude mouse model with transplanted subcutaneous tumor, trastuzumab significantly suppressed the tumor growth of NCI-N87 cells, and then HER2 expression was reduced. Trastuzumab improved the survival rate of mice with peritoneal dissemination of MKN-45P cells. Trastuzumab therapy is a potential candidate for a novel treatment of HER2-overexpressing gastric cancer.     

Antitumor activity of trastuzumab in combination with chemotherapy in human gastric cancer xenograft models

Purpose

To clarify the antitumor activity of trastuzumab and its potential as an effective treatment for gastric cancer patients.

Methods

Levels of HER2 expression in tumor tissues of gastric cancer cell lines were examined using immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and mRNA quantification. Efficacy of trastuzumab was examined as a single agent or in combination with chemotherapeutic agents widely used clinically for gastric cancers in HER2-overexpressing human gastric cancer xenograft models.

Results

Two of nine human gastric cancer xenograft models, NCI-N87 and 4-1ST, showed overexpression of HER2 mRNA and protein by IHC (HercepTest^®) and HER2 gene amplification by FISH (Pathvysion^®). HER2 protein showed potent staining in peripheral membranes, similar to the staining pattern of breast cancer. FISH scores were also comparable to those of breast cancer models. Trastuzumab as a single agent inhibited the tumor growth in both of the HER2-overexpressing models but not in the HER2-negative models, GXF97 and MKN-45. In any combination with capecitabine, cisplatin, irinotecan, docetaxel, or paclitaxel, trastuzumab showed more potent antitumor activity than the anticancer agents alone. A three-drug combination of capecitabine, cisplatin, and trastuzumab showed remarkable tumor growth inhibition. In NCI-N87 in vitro, trastuzumab showed direct antiproliferative activity according to cell count or crystal violet dying, and showed indirect antitumor activity such as antibody-dependent cellular cytotoxicity.

Conclusion

The antitumor activity of trastuzumab observed in human gastric cancer models warrants consideration of its use in clinical treatment regimens for human gastric cancer as a single agent or a combination drug with various chemotherapeutic agents.     

Growth inhibitory effects of trastuzumab and chemotherapeutic drugs in gastric cancer cell lines

The various treatments for advanced gastric cancer have limitations and induce only marginal survival benefit. HER-2/neu protein is overexpressed in several types of human cancers and its amplification is associated with poor prognosis. Recombinant humanized anti-HER-2/neu antibody (trastuzumab) not only inhibits the proliferation of HER-2/neu overexpressing tumor cells but also augments the cytotoxicity of concomitant chemotherapeutic agents in metastatic breast cancer. In this study, we evaluated the growth inhibitory effects of trastuzumab in gastric cancer cells. HER-2/neu protein was evaluated by immunohistochemical analysis in seven gastric cancer cell lines. MTT assay was performed to evaluate the growth inhibitory effects of trastuzumab and three chemotherapeutic agents, doxorubicin, cisplatin and paclitaxel, both alone and in combinations. The changes of cell cycle after trastuzumab treatment were analyzed by flow cytometry. Four of the cell lines, YCC-2 with strong positivity of HER-2/neu expression, NCI-N87 with moderate positivity, YCC-3 with weak positivity, and SK-BR-3 as a positive control, were selected. After in vitro MTT assay for 1-day and 5 consecutive days' treatment of trastuzumab at various concentrations, growth inhibition was not observed in any cancer cell lines. However, there was variable dose-dependent sensitivity to doxorubicin, cisplatin and paclitaxel. YCC-2 and SK-BR-3 cancer cells were more sensitive to three chemotherapeutic drugs, constantly (P<0.05). The combination of 5 consecutive days' treatment of trastuzumab with 1-day doxorubicin treatment showed significant growth inhibition only in YCC-2 and NCI-N87 gastric cancer cells. After 1-day trastuzumab treatment, the S-phase fraction was decreased by 52 and 70% in YCC-2 and SK-BR-3, respectively. In conclusion, the expressions of HER-2/neu protein in gastric cancer cells are variable, and concomitant treatments of trastuzumab with doxorubicin increase cytotoxicity. This suggests that trastuzumab-based biologic therapy with chemotherapeutic agents can be applied in gastric cancer treatment.     

Trastuzumab inhibits the growth of human gastric cancer cell lines with HER2 amplification synergistically with cisplatin

HER2 has been found to be amplified in 10-20% of gastric cancers, and is correlated with poor outcome. The aims of this study were to recognize HER2 amplification in gastric cancer cell lines via fluorescence in situ hybridization and to evaluate the growth inhibitory effect of trastuzumab in HER2-amplified cell lines. To elucidate the mechanism of the growth inhibition, we performed cell cycle analysis and immunoblotting of downstream molecules. We also conducted drug interaction studies of trastuzumab with other chemotherapeutic agents. HER2 amplification was newly identified only in SNU-216 cells, and trastuzumab moderately inhibited the growth of SNU-216 cells and positive controls. Trastuzumab-mediated G1 arrest occurred with increased expression of p27(KIP1) and decreased cyclins. Phosphorylation of HER2 and downstream molecules, STAT3, AKT, and ERK, was also inhibited by trastuzumab. Treatment of SNU-216 cells with trastuzumab plus cisplatin resulted in a synergistic inhibitory effect, whereas treatment of SNU-216 cells with trastuzumab plus 5-FU, or trastuzumab plus oxaliplatin produced an additive effect. These results suggest that trastuzumab combined with chemotherapeutic agents can be active against gastric cancer with HER2 amplification.     

Trastuzumab-DM1 is highly effective in preclinical models of HER2-positive gastric cancer

Background

A novel antibody–drug conjugate (trastuzumab-DM1, T-DM1) is currently in clinical trials for patients with trastuzumab resistant HER2-positive breast cancer. Since no clinical data is available from gastric cancer, we studied T-DM1 on HER2-positive human gastric cancer cells and xenograft tumors.

Methods

Effects of T-DM1 were studied in four HER2-positive gastric cancer cell lines (N-87, OE-19, SNU-216 and MKN-7) in vitro. Xenograft tumors from N-87 and OE-19 were studied to determine the effect of T-DM1 in vivo.

Results

T-DM1 was found more effective than trastuzumab in N-87 and OE-19, and moderately effective in MKN-7 cells. On SNU-216 cells both trastuzumab and T-DM1 showed limited efficacy. In xenograft tumor experiments, complete pathological response was observed in all OE-19 xenografted mice and in half of the N-87 xenografted mice. The results were equally good irrespective of the tumor burden at therapy initiation, or preceding trastuzumab treatment. T-DM1 treatment showed direct effects (apoptotic cell death and aberrant mitosis) as well as it mediated antibody-dependent cellular cytotoxcity (ADCC).

Conclusions

T-DM1 showed a promising anti-tumor effect in HER2-positive gastric cancer cell lines in vitro and in vivo, even in tumors which had developed resistance to trastuzumab. T-DM1 therapy may warrant clinical trials for HER2-positive gastric cancer patients.     

曲妥珠单抗联合氟尿嘧啶或顺铂治疗胃癌的实验研究

目的：探讨曲妥珠单抗（Herceptin,HCP）联合氟尿嘧啶（5-FU）或顺铂（PDD）治疗胃癌的效果及机制。方法：采用流式细胞检查确定胃癌细胞株的HER-2/neu（HER2）表达情况,并测定药物对细胞周期的影响;以MTT法评价药物的细胞毒性作用;以Westernblot法分析药物对HER2-PI3K-AKT信号转导的影响;以RT-PCR分析药物对靶蛋白酶mRNA的影响。结果：HCP单抗可增强化疗药对HER2阳性细胞的毒性作用。先予5-FU后予HCP单抗、先HCP单抗和PDD联合再序贯使用HCP单抗的方案效果最佳,但先予HCP单抗再和5-FU联合可拮抗5-FU的化疗效果。HCP单抗单用或与化疗药联用均可抑制AKT的磷酸化,HCP单抗与PDD同时使用可抑制NF-κB的核移位;HCP单抗不能增强5-FU对胸苷酸合成酶（TS）mRNA表达的抑制,但可使PDD上调的核苷酸切除修复交叉互补基因（ERCC1）mRNA恢复至正常水平;联合方案对细胞周期的改变影响明显。结论：HCP单抗更适于与PDD联合用于HER2阳性胃癌的治疗,HCP单抗与PDD同时使用再序贯使用HCP单抗的给药方法可能是最佳联合模式;而HCP单抗与5-FU联合则要注意正确的用药次序,以免减弱5-FU的化疗效果。     

Inhibition of doxorubicin-induced HER3-PI3K-AKT signalling enhances apoptosis of ovarian cancer cells

Resistance to chemotherapy is a serious problem for the successful treatment of ovarian cancer patients but signalling pathways that contribute to this chemoinsensitivity are largely unknown. We demonstrate that the chemotherapeutic drug doxorubicin induces activation of the HER3-PI3K-AKT signalling cascade in ovarian cancer cells. We further show that the induction of this anti-apoptotic signalling pathway is based on upregulated expression of HER3 ligands, their shedding by the metalloprotease ADAM17, and is dependent on the HER2 receptor. The doxorubicin-mediated activation of this important survival cascade can be blocked by the kinase inhibitors lapatinib or erlotinib as well as by the therapeutic monoclonal antibody trastuzumab. Inhibition of the doxorubicin-induced activation of HER3-PI3K-AKT signalling significantly increased apoptosis of ovarian cancer cells. Besides doxorubicin, treatment of cells with cisplatin resulted in activation of the HER3 receptor whereas other chemotherapeutics did not show this effect. The increase in HER3 phosphorylation was detected in well-established ovarian cancer cell lines which originate from patients previously treated with these chemotherapeutic drugs. Based on these results, we postulate that activation of the HER3-PI3K-AKT cascade represents a major mechanism of chemoresistance in ovarian cancer.     

PTEN低表达增加胃癌曲妥珠单抗的耐药性

目的:明确PTEN活性和胃癌曲妥珠单抗耐药性的关系。方法:用Western blot方法检测胃腺癌细胞株中HER2蛋白、PTEN蛋白、PI3K蛋白、AKT蛋白的表达;用CCK-8方法检测曲妥珠单抗对HER2阳性/PTEN野生型NCI-N87细胞的生长抑制作用;构建PTEN siRNA载体并将其PTEN siRNA载体感染HER2阳性/PTEN野生型NCI-N87细胞,建立稳定表达PTEN siRNA的细胞株N87-PD和阴性对照N87-NC,用Western blot验证其表达水平;同时用CCK-8验证曲妥珠单抗对各组细胞生长的影响。结果:Western blot结果显示,NCI-N87细胞的HER2表达水平高于MNK-7细胞。CCK-8检测表明,随着药物浓度的增加,细胞存活率持续呈下降趋势。三种siRNA中以siRNA-1对PTEN mRNA的干扰效果最优,选择siRNA-1进行后续实验。实时定量PCR法测定最终病毒滴度为1.56×109/ml（siRNA-1）和1.62×109/ml（NC）。PTEN siRNA对NCI-N87细胞的PTEN蛋白表达有明显的下调作用且N87-PD细胞中磷酸化AKT蛋白水平显著高于对照组细胞N87-NC;曲妥珠单抗作用72h后,CCK-8测定N87-NC细胞存活率显著下降,而N87-PD细胞存活率与阴性对照组细胞无显著差异。结论:PTEN低表达增加胃癌曲妥珠单抗的耐药性。     

Trastuzumab and lapatinib modulation of HER2 tyrosine/threonine phosphorylation and cell signaling

Cell surface transmembrane signaling receptors EGFR, HER3, and HER4 are activated by ligand-binding-mediated dimerization and phosphorylation. In contrast, HER2 amplification promotes signaling by increasing homo/heterodimerization and ligand binding. Trastuzumab or lapatinib therapy of HER2 amplicon-positive breast cancer cells induces growth inhibition and intracellular growth pathway signaling modulation. The mechanism(s) by which trastuzumab, an IgG1 humanized antibody, induces modification of cell signaling upon binding to an extracellular determinant on a ligand-less ??receptor?? membrane protein remains unexplained. Using immune detection methodology comprised of antibodies detecting three distinct domains of HER and five tyrosine/threonine phosphorylation sites, the effects of trastuzumab and lapatinib were defined during steady state growth inhibition. Here, we show that lapatinib markedly reduces HER2 tyrosine phosphorylation, while in contrast, no change in tyrosine phosphate levels is detected during trastuzumab-mediated cell growth inhibition. As trastuzumab treatment does not change either the steady state HER2 protein levels or HER2 mRNA, these findings argue against an antibody-dependent alteration in internalization kinetics. We further show a sequenced relationship between lapatinib-induced blockage of phosphorylation (6?C8?h) and induction of delayed cell death (5?C6?days), while trastuzumab-treated cells showed no evidence of cell death up to 9?days. Taken together, these results demonstrate that inhibition of HER2 phosphorylation by lapatinib is sufficient to induce apoptosis while trastuzumab binding to the extracellular HER2 domain may function by sterically modulating the detection of phosphate moieties by cytoplasmic signal transducers. This investigation also detected a 20?kD protein, which is down-regulated by lapatinib, further demonstrating the complexity of this signal transduction system.     

The growth inhibitory effect of lapatinib, a dual inhibitor of EGFR and HER2 tyrosine kinase, in gastric cancer cell lines

HER2 overexpression is observed in 5-25% of gastric cancers. Lapatinib is a dual inhibitor of the epidermal growth factor receptor and HER2 tyrosine kinase. We examined the antitumor effect of lapatinib in gastric cancer cell lines. Lapatinib induced selective and potent growth inhibition in two HER2-amplified gastric cancer cell lines (SNU-216 and NCI-N87). Lapatinib inhibited the phosphorylation of HER2, EGFR and downstream signaling proteins, resulting in G1 arrest in both cell lines with down-regulation of cMyc and induction of p27kip1. Lapatinib also induced apoptosis in NCI-N87 which has high HER2 amplification ratio. Lapatinib combined with 5-fluorouracil, cisplatin, oxaliplatin or paclitaxel showed an additive or synergistic effect. These results provide a rationale for the future clinical trials of lapatinib combined with cytotoxic drugs in the treatment of HER2-positive gastric cancer.     

Combination of novel HER2‐targeting antibody 1E11 with trastuzumab shows synergistic antitumor activity in HER2‐positive gastric cancer

The synergistic interaction of two antibodies targeting the same protein could be developed as an effective anti‐cancer therapy. Human epidermal growth factor receptor 2 (HER2) is overexpressed in 20–25% of breast and gastric cancer patients, and HER2‐targeted antibody therapy using trastuzumab is effective in many of these patients. Nonetheless, improving therapeutic efficacy and patient survival is important, particularly in patients with HER2‐positive gastric cancer. Here, we describe the development of 1E11, a HER2‐targeted humanized monoclonal antibody showing increased efficacy in a highly synergistic manner in combination with trastuzumab in the HER2‐overexpressing gastric cancer cell lines NCI‐N87 and OE‐19. The two antibodies bind to sub‐domain IV of the receptor, but have non‐overlapping epitopes, allowing them to simultaneously bind HER2. Treatment with 1E11 alone induced apoptosis in HER2‐positive cancer cells, and this effect was enhanced by combination treatment with trastuzumab. Combination treatment with 1E11 and trastuzumab reduced the levels of total HER2 protein and those of aberrant HER2 signaling molecules including phosphorylated HER3 and EGFR. The synergistic antitumor activity of 1E11 in combination with trastuzumab indicates that it could be a novel potent therapeutic antibody for the treatment of HER2‐overexpressing gastric cancers.     

曲妥珠单抗联合放疗对HER2高表达胃癌细胞的协同杀伤作用

目的:研究曲妥珠单抗联合放疗对人类表皮生长因子受体2（HER2）高表达胃癌细胞NCI-N87的协同杀伤作用。方法:应用细胞增殖与毒性检测（CCK-8）法筛选曲妥珠单抗杀伤胃癌细胞的IC20浓度;将NCI-N87分为对照组与加药组,两组依次给予照射剂量不同的X线（0 Gy、2 Gy、4 Gy、6 Gy、8 Gy）,应用克隆形成实验分析两者的杀伤作用;凋亡实验分4组:对照、曲妥珠单抗、2 Gy照射、2 Gy照射+曲妥珠单抗,流式细胞仪用于测定凋亡率。结果:IC20为10 μg/ml。与单纯放疗相比,曲妥珠单抗与放疗同时作用可明显降低细胞存活率,差异具有统计学意义（P＜0.05）。凋亡率为对照（3.80±0.26）%、曲妥珠单抗（4.84±0.14）%、2 Gy照射（6.83±0.17）%、联合组（13.60±0.35）%,曲妥珠单抗或照射组均可增加NCI-N87细胞凋亡率,其中凋亡率在联合组中最高（P＜0.05）。结论:曲妥珠单抗和放疗可协同杀伤HER2高表达的胃癌细胞。     

Pharmacologic synergy between dual phosphoinositide-3-kinase and mammalian target of rapamycin inhibition and 5-fluorouracil in PIK3CA mutant gastric cancer cells

Phosphoinositide-3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitors are an emerging class of anti-cancer agents. Here, we tested the hypothesis that the dual PI3K/mTOR inhibitor, PI103, could synergize with the chemotherapeutic agent, 5-fluorouracil (5-FU) by inhibiting E2F1, thymidylate synthase (TS) and enhancing DNA damage. Drug combination effects were assessed in gastric cancer cells using the median-effect equation. The specific effects of inhibition of E2F1 and PIK3CA were examined by siRNA, and mTOR by rapamycin exposure. Protein expression and apoptosis pre- and post-treatment was measured using standard methods. PI103 and 5-FU was synergistic in 3/5 gastric cancer cell lines tested. Synergy was associated with PI3KCA mutation, reduced TS and E2F1 protein levels, increased H2AX phosphorylation and apoptosis. E2F1 siRNA enhanced sensitivity to 5-FU only in cells displaying synergy. Excess thymidine exposure converted synergism to antagonism in all cells. Inhibition of PI3K and mTOR alone enhanced 5-FU cytotoxicity in only 2/3 cell lines that displayed synergy each. In AGS cells, PI3K inhibition alone enhanced 5-FU sensitivity as much as dual PI3K/mTOR inhibition. In HGC27 cells, dual inhibition increased 5-FU sensitivity more than single PI3K or mTOR inhibition. Combined PI103 and 5-FU treatment reduced in vivo tumor growth more than treatment with single agents. PI3K/mTOR inhibitors can enhance 5-FU cytotoxicity in vitro and in vivo, especially in PIK3CA mutant tumor cells. Dual, rather than single, PI3K/mTOR inhibitors may combine better with 5-FU due to cellular heterogeneity in sensitivity to PI3K and mTOR inhibition.     

顺铂等化疗药物对胃癌细胞株端粒酶活性的调节作用

目的：研究常用化疗药物对SGC－7901人胃癌细胞株端粒酶活性的调节作用,探讨端料酶作为化疗敏感性指标的可行性。方法：选择顺铂、丝裂霉素C、阿霉素及5－氟尿嘧啶和甲酰四氢叶酸处理胃癌细胞,采用半定量TRAP－银染法检测药物处理前后的端粒酶活性,流式细胞学检测细胞周期和细胞凋亡。结果：顺铂、丝裂霉素C和阿霉素在诱导SGC－7901细胞凋亡的同时,下调端粒酶活性,且抑制作用呈时间依赖关系,5－氟尿嘧啶和甲酰四氢叶酸对端粒酶活性无明显抑制作用。结论：观测细胞株端粒酶的活性变化可作为化疗药物敏感性的指标,可合理选择新的化疗药物。     

顺铂等化疗药物对胃癌细胞端粒酶活性的影响

目的：探讨端粒酶作为化疗敏感性指标的可行性。方法：选择IC50剂量的顺铂，丝裂霉素C，阿霉素及5－氟脲嘧啶和甲酰四氢叶酸处理胃癌细胞，采用半定量TRAP－银染法检测药物处理前后胃癌细胞端粒酶活性。并应用流式细胞学检测细胞周期和细胞凋亡率。结果：顺铂，丝裂霉素C和阿霉素在诱导两细胞凋亡的同时，下调端粒酶活性，且其抑制作用呈时间依赖关系；5－氟脲嘧啶和甲酰四氢叶酸对胃癌细胞端粒酶活性无明显抑制作用，结论：化疗前后细胞端粒酶活性的变化，可作为化疗敏感性指标。     

The HER2 amplicon includes several genes required for the growth and survival of HER2 positive breast cancer cells

About 20% of breast cancers are characterized by amplification and overexpression of the HER2 oncogene. Although significant progress has been achieved for treating such patients with HER2 inhibitor trastuzumab, more than half of the patients respond poorly or become resistant to the treatment. Since the HER2 amplicon at 17q12 contains multiple genes, we have systematically explored the role of the HER2 co-amplified genes in breast cancer cell growth and their relation to trastuzumab resistance. We integrated aCGH data of the HER2 amplicon from 71 HER2 positive breast tumors and 10 cell lines with systematic functional RNA interference analysis of 23 core amplicon genes with several phenotypic endpoints in a panel of trastuzumab responding and non-responding HER2 positive breast cancer cells. Silencing of HER2 caused a greater growth arrest and apoptosis in the responding compared to the non-responding cell lines, indicating that the resistant cells are inherently less dependent on the HER2 pathway. Several other genes in the amplicon also showed a more pronounced effect when silenced; indicating that expression of HER2 co-amplified genes may be needed to sustain the growth of breast cancer cells. Importantly, co-silencing of STARD3, GRB7, PSMD3 and PERLD1 together with HER2 led to an additive inhibition of cell viability as well as induced apoptosis. These studies indicate that breast cancer cells may become addicted to the amplification of several genes that reside in the HER2 amplicon. The simultaneous targeting of these genes may increase the efficacy of the anti-HER2 therapies and possibly also counteract trastuzumab resistance. The observed additive effects seem to culminate to both apoptosis and cell proliferation pathways indicating that these pathways may be interesting targets for combinatorial treatment of HER2+ breast cancers.     

Heregulin induces resistance to lapatinib‐mediated growth inhibition of HER2‐amplified cancer cells

Human epidermal growth factor receptor 2 (HER2) amplification occurs in approximately 20% of gastric and gastroesophageal junction cancers in the United States and European Union. Lapatinib, a dual HER2 and epidermal growth factor receptor tyrosine kinase inhibitor, has demonstrated clinical efficacy in HER2‐amplified cancer cells. However, several studies have shown that some cytokines can mediate resistance to lapatinib using their receptor tyrosine kinase (RTK) pathways. One of these, Heregulin1 (HRG1), can confer resistance to lapatinib‐mediated growth inhibition in HER2‐amplified breast cancer cells, but the underlying mechanisms remain unknown. Here, we investigated whether and how HRG1 causes resistance to lapatinib in gastric and gastroesophageal junction cancers in vitro. HER2‐amplified gastric and gastroesophageal junction cancer cell lines were highly sensitive to lapatinib. Exposure to HRG1 together with lapatinib rescued cells from lapatinib‐induced cell cycle arrest and apoptosis. Downregulation of HER3 with siRNA in the presence of HRG1 re‐sensitized HER2‐amplified cancer cells to lapatinib. Immunoblotting analysis indicated that HRG1 re‐activated HER3 and AKT in the presence of lapatinib, which persisted for at least 72 h. Activation of HER3 and downstream AKT was mediated by residual activity of HER2. HRG1‐mediated resistance could be reduced by PI3K/mTOR inhibitors or by complete inhibition of HER2. Thus, we conclude that HRG1 mediates resistance to lapatinib through HER3 and AKT activation, and that this depends on residual HER2 activity. Lapatinib in combination with anti‐PI3K therapies or more potent HER2 inhibitors would improve the efficacy and avoid the emergence of resistant cells.     

Molecular basis for sensitivity and acquired resistance to gefitinib in HER2-overexpressing human gastric cancer cell lines derived from liver metastasis

Gastric cancer metastasised to the liver was found to overexpress HER2 at a significantly higher incidence than primary gastric cancers. The purpose of the present study was to investigate the possibility of molecular therapy targeting HER2 overexpression in gastric cancer liver metastasis. We developed three new HER2-overexpressing gastric cancer cell lines (GLM-1, GLM-2, GLM-4) without epidermal growth factor receptor (EGFR) mutations derived from such liver metastasis, two of which had HER2 gene amplifications. All these GLM series of cell lines were highly sensitive to gefitinib in vitro, a specific inhibitor of EGFR tyrosine kinase (Iressa) rather than anti-HER2 antibody trastuzumab (Herceptin), whereas most of the HER2 low-expressing counterparts were not. In these HER2-overexpressing GLM series, protein kinase B (Akt), but not extracellular signal-regulated kinase 1/2 (ERK1/2), was constitutively phosphorylated, and gefitinib efficiently inhibited this Akt phosphorylation, induced strong apoptosis in vitro and exhibited antitumour activity in tumour xenografts in nude mice. This gefitinib-mediated antitumour effect in xenograft was significantly potentiated by trastuzumab treatment. On the other hand, gefitinib-resistant cells (GLM-1R) exhibited increased EGFR expression, followed by constitutive activation of mitogen-activated protein kinase (MAPK) pathway. These results suggest that the antitumour effect of gefitinib is due to the effective inhibition of HER2-driven constitutive activation of phosphatidylinositol-3-kinase (PI3K)/Akt pathway, and that the acquired resistance to gefitinib is due to the constitutive activation of Ras/MAPK pathway in compensation for PI3K/Akt pathway. Gastric cancer liver metastasis with HER2 overexpression would be a potential molecular target for gefitinib and trastuzumab.     

HER2/PI-3K/Akt activation leads to a multidrug resistance in human breast adenocarcinoma cells

Growth factor receptor-mediated signal transduction has been implicated in conferring resistance to conventional chemotherapy on cancer cells. In this study, we delineated a pathway that involves HER2/PI-3K/Akt in mediating multidrug resistance in human breast cancer cells. We found that the cell lines that express both HER2 and HER3 appear to have a higher phosphorylation level of Akt (activated Akt). Transfection of HER2 in MCF7 breast cancer cells that express HER3 caused a phosphoinoside-3 kinase (PI-3K)-dependent activation of Akt, and was associated with an increased resistance of the cells to multiple chemotherapeutic agents (paclitaxel, doxorubicin, 5-fluorouracil, etoposide, and camptothecin). Selective inhibition of PI-3K or Akt activity with their respective dominant-negative expression vectors sensitized the cells to the induction of apoptosis by the chemotherapeutic agents. We further demonstrated that MCF7 cells expressing a constitutively active Akt, in which the phospholipid-interactive PH domain of Akt was replaced by a farnesylation sequence for constitutive membrane anchorage (DeltaPH-Akt1-farn), showed a similar increased resistance to the chemotherapeutic agents. Our results suggest that activation of Akt1 by HER2/PI-3K plays an important role in conferring a broad-spectrum chemoresistance on breast cancer cells and that Akt may therefore be a novel molecular target for therapies that would improve the outcome of patients with breast cancer.