Lapatinib acts on gastric cancer through both antiproliferative function and augmentation of trastuzumab-mediated antibody-dependent cellular cytotoxicity

Background

Trastuzumab has been recently approved for clinical use to treat HER2-expressing advanced gastric cancer, and anti-HER2-targeting therapy has become a promising option for gastric cancer. Lapatinib is a dual tyrosine kinase inhibitor targeting EGFR and HER2. The aim of the present study was to explore the utility of lapatinib for gastric cancer, with a particular focus on trastuzumab-mediated antibody-dependent cellular cytotoxicity (ADCC).

Methods

Nine gastric cancer cell lines were evaluated for the effects of lapatinib on the cell-surface accumulation of HER2 and analyzed for their additional effects on trastuzumab-mediated ADCC. Also, HER2 signaling with Western blot, proliferative function with the MTT assay, and apoptosis-inducing activity with 7ADD/Annexin-V were investigated when a panel of gastric cancer cell lines was treated with lapatinib.

Results

Lapatinib inhibited HER2 signaling and cell proliferation in the panel of gastric cancer cell lines. Lapatinib also induced the accumulation of HER2 on the cell surface, resulting in the enhancement of trastuzumab-mediated ADCC of gastric cancer.

Conclusions

Lapatinib exhibits inhibitory activity in gastric cancer cells, and the combination of lapatinib with trastuzumab may be a promising treatment strategy for gastric cancer patients.     

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.     

In vitro and in vivo evidence that a combination of lapatinib plus S‐1 is a promising treatment for pancreatic cancer

Lapatinib is a small molecule inhibitor of both HER2 and the epidermal growth factor receptor (EGFR). We investigated the effect of treatment with lapatinib alone or in combination with a fluoropyrimidine derivative S‐1 against pancreatic cancer. The HER2/EGFR expression in each of the four pancreatic cancer cell lines MiaPaca‐2, PANC‐1, Capan‐1 and Capan‐2 was measured by flow cytometry. The anti‐tumor effects of lapatinib (30 mg/kg) and/or S‐1 (10 mg/kg) were evaluated using female BALB/c nude mice xenografts generated using these four cell lines. Synergy between lapatinib and S‐1 was examined by median effect analysis in vitro. Resected pancreatic cancer tissues from 137 patients were immunohistochemically stained with anti‐human HER2 and EGFR antibodies. The administration of lapatinib as a single agent substantially suppressed tumor growth in vivo of all pancreatic cancer cell lines examined. A strong correlation was observed between HER2 expression and the anti‐tumor effect of lapatinib in vivo. Lapatinib synergized with S‐1 to inhibit the tumor growth of MiaPaca‐2 and PANC‐1 xenografts. When used as a single agent in vitro, lapatinib barely inhibit the cell growth of any cell line. However, lapatinib synergized with the anti‐tumor activity of the S‐1 components 5‐fluorouracil and 5‐chloro‐2,4‐dihydrogenase against all cell lines. Immunohistochemical staining demonstrated that 70% of the pancreatic cancers overexpressed HER2 and/or EGFR. Both lapatinib monotherapy and combined treatment with S‐1 may be promising treatments for patients with pancreatic cancers; the majority these cancers express lapatinib target molecules. (Cancer Sci 2009; 00: 000–000)     

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.     

The dual EGFR/HER‐2 tyrosine kinase inhibitor lapatinib sensitizes colon and gastric cancer cells to the irinotecan active metabolite SN‐38

Members of the human epidermal receptor (HER) family are frequently associated with aggressive disease and poor prognosis in multiple malignancies. Lapatinib is a dual tyrosine kinase inhibitor targeting the epidermal growth factor receptor (EGFR) and HER‐2. This study evaluated the therapeutic potential of lapatinib, alone and in combination with SN‐38, the active metabolite of irinotecan (CPT‐11), in colon and gastric cancer cell lines. Concentration‐dependent antiproliferative effects of both lapatinib and SN‐38 were observed in all colon and gastric cancer cell lines tested but varied significantly between individual cell lines (lapatinib range 0.08–11.7 μM; SN‐38 range 3.6–256 nM). Lapatinib potently inhibited the growth of a HER‐2 overexpressing gastric cancer cell line and demonstrated moderate activity in gastric and colon cancer cells with detectable HER‐2 expression. The combination of lapatinib and SN‐38 interacted synergistically to inhibit cell proliferation in all colon and gastric cancer cell lines tested. Cotreatment with lapatinib and SN‐38 also resulted in enhanced cell cycle arrest and the induction of apoptosis with subsequent cellular pharmacokinetic analysis demonstrating that lapatinib promoted the increased intracellular accumulation and retention of SN‐38 when compared to SN‐38 treatment alone. Finally, the combination of lapatinib and CPT‐11 demonstrated synergistic antitumor efficacy in the LoVo colon cancer mouse xenograft model with no apparent increase in toxicity compared to CPT‐11 monotherapy. These results provide compelling preclinical rationale indicating lapatinib to be a potentially efficacious chemotherapeutic combination partner for irinotecan in the treatment of gastrointestinal carcinomas. © 2009 UICC     

Preclinical antitumor activity of the novel heat shock protein 90 inhibitor CH5164840 against human epidermal growth factor receptor 2 (HER2)-overexpressing cancers

Heat shock protein 90 (Hsp90), a molecular chaperone that plays a significant role in the stability and maturation of client proteins, including oncogenic targets for cell transformation, proliferation, and survival, is an attractive target for cancer therapy. We identified the novel Hsp90 inhibitor, CH5164840, and investigated its induction of oncogenic client protein degradation, antiproliferative activity, and apoptosis against an NCI-N87 gastric cancer cell line and a BT-474 breast cancer cell line. Interestingly, CH5164840 demonstrated tumor selectivity both in vitro and in vivo, binding to tumor Hsp90 (which forms active multiple chaperone complexes) in vitro, and being distributed effectively to tumors in a mouse model, which, taken together, supports the decreased levels of phosphorylated Akt by CH5164840 that we observed in tumor tissues, but not in normal tissues. As well as being well tolerated, the oral administration of CH5164840 exhibited potent antitumor efficacy with regression in NCI-N87 and BT-474 tumor xenograft models. In addition, CH5164840 significantly enhanced antitumor efficacy against gastric and breast cancer models when combined with the human epidermal growth factor receptor 2 (HER2)-targeted agents, trastuzumab and lapatinib. These data demonstrate the potent antitumor efficacy of CH5164840 when administered alone, and its significant combination efficacy when combined with trastuzumab or lapatinib, supporting the clinical development of CH5164840 as an Hsp90 inhibitor for combination therapy with HER2-targeted agents against HER2-overexpressing tumors.     

Activity of lapatinib a novel HER2 and EGFR dual kinase inhibitor in human endometrial cancer cells

In this study, we explore the therapeutic potential of lapatinib a selective inhibitor of both the EGFR and HER2 tyrosine kinases for the treatment of endometrial cancer. The effect of lapatinib on tumour cell growth and receptor activation was studied in a panel of human endometrial cancer cell lines. Candidate molecular markers predicting sensitivity were assessed by baseline gene expression profiling, ELISA, and western blot analyses. Multiple drug effect/combination index (CI) isobologram analysis was used to study the interactions between chemotherapeutic drugs and lapatinib. Concentration-dependent anti-proliferative effects of lapatinib were seen in all endometrial cancer cell lines tested, but varied significantly between individual cell lines (IC(50) range: 0.052-10.9 micromol). HER2 overexpression or increased expression of EGFR was significantly associated with in vitro sensitivity (P=0.024 or 0.011, respectively). Lapatinib exerts growth inhibition in a PTEN-independent manner. Sensitive cell lines also exhibited increased expression of EGFR ligands or HER3. In contrast, lapatinib-resistant cell lines exhibited high androgen receptor (AR) levels or epithelial-to-mesenchymal transition (post-EMT) features. In endometrial cancer cells, at a wide range of clinically achievable drug concentrations, additive and synergistic interactions were observed for lapatinib plus carboplatin, paclitaxel, docetaxel, and doxorubicin. These observations provide a clear biologic rational to test lapatinib as a single agent or in combination with chemotherapy in endometrial cancer with HER2 overexpression. Expression of EGFR, its ligands, HER3, AR, and post-EMT markers warrant further evaluation to help define patients with HER2-nonoverexpressing endometrial cancer most likely to benefit from lapatinib.     

Lapatinib, a preventive/therapeutic agent against mammary cancer, suppresses RTK-mediated signaling through multiple signaling pathways

Activation of receptor tyrosine kinases (RTK) plays a key role in the prognosis of mammary cancer. Lapatinib is a small molecule dual RTK inhibitor that targets epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2). Identifying the protein targets involved in the effects of lapatinib and other RTK inhibitors might help determine why preventive efficacy varies. In this study, female Sprague-Dawley rats were given methylnitrosourea (MNU) by intravenous injection resulting in the development of multiple estrogen receptor-positive tumors. Treatment with lapatinib beginning 5 days after MNU was highly effective in preventing cancer development. In addition, we treated rats with palpable mammary tumors with lapatinib daily. In these tumor-bearing animals, treatment continued for 42 days and therapeutic results were obtained. Some rats bearing cancers were treated for 5 days, and the resulting lesions were examined for biomarker modulation. Lapatinib effectively suppressed the abundance of HER2, phosphorylated HER2 (Tyr1221/1222), and phosphorylated EGFR (Tyr1173, Tyr1110) compared with tumors from untreated rats. Protein array analyses allowed parallel determination of the effect of lapatinib on the relative levels of protein phosphorylation and proteins associated with apoptosis. These results combined with immunoreactivity data indicated that, in addition to EGFR and HER2, lapatinib treatment was associated with changes in a number of other signaling molecules, including IGF-1R, Akt, and downstream targets such as GSK3, p27, p53, and cyclin D1 presumably leading to impaired proliferation, apoptosis, or cell-cycle arrest.     

Lapatinib sensitivities of two novel trastuzumab-resistant HER2 gene-amplified gastric cancer cell lines

Background

Trastuzumab (Tmab) resistance is a major clinical problem to be resolved in patients with HER2-positive gastric cancers. However, in contrast to the situation for HER2-positive breast cancer lines, the Tmab-resistant gastric cancer preclinical models that are needed to develop a new therapy to overcome this problem are not yet available.

Methods

We developed three new cell lines from HER2 gene-amplified gastric cancer cell lines (GLM-1, GLM-4, NCI N-87) by a new in vivo selection method consisting of the repeated culture of small residual peritoneal metastasis but not subcutaneous tumor after Tmab treatment. We then evaluated the anti-tumor efficacy of lapatinib for these Tmab-resistant cells.

Results

We successfully isolated two Tmab-resistant cell lines (GLM1-HerR2(3), GLM4-HerR2) among the three tested cell lines. These resistant cells differed from the parental cells in their flat morphology and rapid growth in vitro, but HER2, P95HER2 expression, and Tmab binding were essentially the same for the parental and resistant cells. MUC4 expression was up- or downregulated depending on the cell line. These resistant cells were still sensitive to lapatinib, similar to the parental cells, in vitro. This growth inhibition of the Tmab-resistant cells by lapatinib was due to both G1 cell-cycle arrest and apoptosis induction via effective blockade of the PI3K/Akt and MAPK pathways. A preclinical study confirmed that the Tmab-resistant tumors are significantly susceptible to lapatinib.

Conclusion

These results suggest that lapatinib has antitumor activity against the Tmab-resistant gastric cancer cell lines, and that these cell lines are useful for understanding the mechanism of Tmab resistance and for developing a new molecular therapy for Tmab-resistant HER2-positive gastric cancers.     

Roles of BIM induction and survivin downregulation in lapatinib-induced apoptosis in breast cancer cells with HER2 amplification

Lapatinib, a dual tyrosine kinase inhibitor of the epidermal growth factor receptor and human epidermal growth factor receptor 2 (HER2), is clinically active in patients with breast cancer positive for HER2 amplification. The mechanism of this anti-tumor action has remained unclear, however. We have now investigated the effects of lapatinib in HER2 amplification-positive breast cancer cells with or without an activating PIK3CA mutation. Lapatinib induced apoptosis in association with upregulation of the pro-apoptotic protein Bcl-2 interacting mediator of cell death (BIM) through inhibition of the MEK-ERK signaling pathway in breast cancer cells with HER2 amplification. RNA interference (RNAi)-mediated depletion of BIM inhibited lapatinib-induced apoptosis, implicating BIM induction in this process. The pro-apoptotic effect of lapatinib was less pronounced in cells with a PIK3CA mutation than in those without one. Lapatinib failed to inhibit AKT phosphorylation in PIK3CA mutant cells, likely because of hyperactivation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway by the mutation. Depletion of PIK3CA (a catalytic subunit of PI3K) revealed that survivin expression is regulated by the PI3K pathway in these cells, suggesting that insufficient inhibition of PI3K-survivin signaling is responsible for the limited pro-apoptotic effect of lapatinib in HER2 amplification-positive cells with a PIK3CA mutation. Consistent with this notion, depletion of survivin by RNAi or treatment with a PI3K inhibitor markedly increased the level of apoptosis in PIK3CA mutant cells treated with lapatinib. Our results thus suggest that inhibition of both PI3K-survivin and MEK-ERK-BIM pathways is required for effective induction of apoptosis in breast cancer cells with HER2 amplification.     

Inhibition of the mTOR/S6K signal is necessary to enhance fluorouracil-induced apoptosis in gastric cancer cells with HER2 amplification

The purpose of this study was to explore the effect of trastuzumab in enhancing the activity of chemotherapeutic agents and the molecular basis of this effect. Two gastric cancer cell types with HER2 amplification, one sensitive (NCI?N87) and one insensitive (MKN-7) to trastuzumab, were tested for the effects of trastuzumab on cell growth and cell signaling using MTS assay and western blotting, respectively. Interaction between trastuzumab and chemotherapeutic agents (fluorouracil, doxorubicin, cisplatin and paclitaxel) was evaluated by the combination index (CI). Fluorouracil-induced apoptosis was evaluated using western blot for poly (ADP-ribose) polymerase (PARP). Trastuzumab decreased phosphorylation of S6K, showed synergistic effect with fluorouracil or doxorubicin, and increased fluorouracil-induced apoptosis in NCI-N87 cells, but not in MKN-7 cells. While the mTOR inhibitor everolimus enhanced fluorouracil-induced apoptosis in both HER2-amplified cell lines, this was not the case in the gastric cancer cell lines without HER2 amplification. Consistently, while the EGFR/HER2 inhibitor Cl-387,785 inhibited cell growth of MKN-7, this growth inhibition did not accompany decrease in phosphorylation of S6K, and the compound did not enhance fluorouracil-induced apoptosis. In summary, inhibition of the mTOR/S6K signal may be a key molecular event in enhancing fluorouracil-induced apoptosis specifically in gastric cancer cells with HER2 amplification. mTOR inhibitors may therefore be attractive alternative drugs in gastric cancers with HER2 amplification regardless of their sensitivity to trastuzumab.     

Induction of neuropilin-1 and vascular endothelial growth factor by epidermal growth factor in human gastric cancer cells

The epidermal growth factor receptor (EGF-R) pathway plays a pivotal role in the progression of human gastric cancer. The angiogenic factor vascular endothelial growth factor (VEGF) has been shown to be induced by EGF in various cancer cell lines. Neuropilin-1 (NRP-1) acts as a coreceptor for VEGF-165 and increases its affinity for VEGF receptor 2 (VEGFR-2) in endothelial cells. Furthermore, NRP-1 has been found to be expressed by tumour cells and has been shown to enhance tumour angiogenesis and growth in preclinical models. We examined the expression of NRP-1 mRNA and EGF-R protein in seven human gastric cancer cell lines. NRP-1 expression was expressed in five of seven cell lines, and EGF-R expression closely mirrored NRP-1 expression. Moreover, in EGF-R-positive NCI-N87 and ST-2 cells, EGF induced both NRP-1 and VEGF mRNA expression. C225, a monoclonal antibody to EGF-R, blocked EGF-induced NRP-1 and VEGF expression in NCI-N87 cells in a dose-dependent manner. The treatment of NCI-N87 cells with EGF resulted in increases in phosphorylation of Erk1/2, Akt, and P38. Blockade of the Erk, phosphatidylinositol-3 kinase/Akt, or P38 pathways in this cell line prevented EGF induction of NRP-1 and VEGF. These results suggest that regulation of NRP-1 expression in human gastric cancer is intimately associated with the EGF/EGF-R system. Activation of EGF-R might contribute to gastric cancer angiogenesis by a mechanism that involves upregulation of VEGF and NRP-1 expression via multiple signalling pathways.     

Lapatinib inhibits receptor phosphorylation and cell growth and enhances antibody-dependent cellular cytotoxicity of EGFR- and HER2-overexpressing esophageal cancer cell lines

Lapatinib is a dual tyrosine kinase inhibitor of the EGFR and HER2 tyrosine kinase domains. EGFR is expressed in 33.3% and HER2 in 30.3% of esophageal squamous cell carcinomas (ESCCs). To explore the potential utility of Lapatinib for therapy of ESCC patients, we evaluated the effect of Lapatinib on a panel of ESCC cell lines. EGFR and HER2 expression by the cell lines was established, and the effects of Lapatinib on inhibition of the phosphorylation of HER2, antiproliferative effect, apoptosis-inducing activity and accumulation of HER2 and EGFR on cell surface were evaluated. Additionally, the combined effect of Lapatinib together with Herceptin or Cetuximab on cell-mediated cytotoxicity was evaluated. Lapatinib inhibited HER2 phosphorylation in HER2-overexpressing, HER2 gene amplification positive ESCC cell line. Lapatinib also inhibited cell proliferation, induced apoptosis and caused the surface accumulation of HER2 and EGFR in ESCC cell lines. Addition of Lapatinib increased Herceptin-mediated antibody-dependent cell-mediated cytotoxicity by 15-25% with three ESCC target cell lines. Similarly, Cetuximab-mediated antibody-dependent cell-mediated cytotoxicity also increased by 15-30% in two ESCC cell lines on addition of Lapatinib. Cumulatively, the data indicate that Lapatinib has activity in EGFR- and/or HER2-expressing ESCC cells, and the combination therapy of Lapatinib and Cetuximab/Herceptin is a promising strategy in ESCC.     

An anti-HER2 antibody conjugated with monomethyl auristatin E is highly effective in HER2-positive human gastric cancer

Antibody-drug conjugate (ADC) is a novel class of therapeutics for cancer target therapy. This study assessed antitumor activity of ADC with an antimitotic agent, monomethyl auristatin E (MMAE) and a humanized monoclonal anti-HER2 antibody, hertuzumab, in gastric cancer. The efficacy of hertuzumab-MC-Val-Cit-PAB-MMAE (hertuzumab-vcMMAE) on human epidermal growth factor receptor 2 (HER2) positive human gastric cancer cells, NCI-N87, was evaluated in vitro and in vivo. The cytotoxicity of hertuzumab was significantly enhanced after conjugation with MMAE. Compared to trastuzumab, hertuzumab had a higher affinity to HER2 and had more potent antibody-dependent cell-mediated cytotoxicity (ADCC) activity in vitro. After conjugation with MMAE, the binding specificity for HER2 was not affected. Furthermore, the internalization of hertuzumab-vcMMAE in HER2 positive gastric cancer cells was verified. Although the conjugation of hertuzumab and MMAE decreased the ADCC effect, the overall cytotoxicity was dramatically increased in HER2 positive gastric cancer cells. In vitro data on this hertuzumab-vcMMAE has exerted much stronger antitumor activity compared to trastuzumab-DM1 in HER2 positive gastric cancer cells. A single administration of hertuzumab-vcMMAE at 5 or 10 mg/kg showed high potency and a sustained tumor inhibitory effect on NCI-N87 xenografts in mice. In conclusion, hertuzumab-vcMMAE conjugate is a highly effective anti-HER2 targeted therapy for HER2-positive gastric cancer.     

Synergistic antitumor effect of the anti-ErbB2 antibodies trastuzumab and H2-18 on trastuzumab-resistant gastric cancer cells

Trastuzumab resistance is a severe problem in the treatment of ErbB2-amplified cancer. Although trastuzumab plus pertuzumab is able to partly overcome trastuzumab resistance in ErbB2-overexpressing cancer, its antitumor efficacy remains limited. The present study investigated the antitumor activity of the combination of trastuzumab with H2-18, which is an antibody targetinsg ErbB2 domain I. Cell proliferation and inhibition experiments indicated that H2-18 and trastuzumab synergistically inhibited the proliferation of both the trastuzumab-sensitive gastric cancer cell line, NCI-N87 and the trastuzumab-resistant gastric cancer cell line, NCI-N87-TraRT. Furthermore, H2-18 plus trastuzumab inhibited the growth of NCI-N87-TraRT cells more effectively than trastuzumab plus pertuzumab, both in vitro and in vivo. Compared with trastuzumab plus pertuzumab, H2-18 plus trastuzumab had a potent ability to inhibit NCI-N87-TraRT cells to form colonies. Notably, H2-18 plus trastuzumab was more effective in inducing cell death than trastuzumab plus pertuzumab. The in vivo studies demonstrated that H2-18 plus trastuzumab effectively inhibited the growth of both NCI-N87 and NCI-N87-TraRT xenograft tumors. Further experiments revealed that in NCI-N87-TraRT cells, H2-18 plus trastuzumab was comparable to trastuzumab plus pertuzumab in the inhibition of phosphorylated (p-)HER3, p-AKT and p-ERK. However, compared with trastuzumab plus pertuzumab, H2-18 plus trastuzumab effectively activated ROS production and the phosphorylation of JNK and c-jun in NCI-N87-TraRT cells. Therefore, the superior antitumor efficacy of H2-18 plus trastuzumab over trastuzumab plus pertuzumab may be mainly attributable to the potent cell death-inducing activity. In addition, the in vitro and in vivo antitumor effect of the combination of H2-18, trastuzumab and pertuzumab were further investigated. The results revealed that H2-18 plus trastuzumab plus pertuzumab exhibited a maximal antitumor effect among all the anti-ErbB2 monoclonal antibody combinations tested. In summary, H2-18 plus trastuzumab may have potential as an effective strategy to overcome the resistance to trastuzumab in ErbB2-amplified gastric cancer cell lines.     

Lapatinib, a dual inhibitor of EGFR and HER2, has synergistic effects with 5-fluorouracil on esophageal carcinoma

Epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) amplification occurs in over 30% of esophageal carcinomas. Combination therapies with EGFR and HER2-targeting agents and cytotoxic agents are considered a potential therapeutic option for esophageal cancer. We evaluated the antitumor effects of lapatinib, a dual tyrosine kinase inhibitor which simultaneously inhibits EGFR and HER2, 5-fluorouracil (5-Fu) alone and in combination on esophageal cancer cells. The antiproliferative activity of lapatinib, 5-Fu and lapatinib plus 5-Fu was measured by MTT assay and the combination index (CI) values were calculated. Additionally, cell cycle distribution of lapatinib alone and the combination with 5-Fu were detected by flow cytometry analysis. Annexin?V-FITC and propidium iodide stain were used for analyzing the apoptotic cells after cells were treated with either agent alone or in combination. The EGFR and HER2 activated signaling pathways were monitored by western blotting. The combination of lapatinib and 5-Fu synergistically inhibited cell proliferation and exhibited an enhanced proapoptotic effect on esophageal cancer cells. The potentiation effect of combined treatment was associated with downregulation of EGFR and HER2 signaling pathways because data from western blot analysis showed that lapatinib in combination with 5-Fu markedly reduced the phosphorylation of EGFR and HER2, and inhibited the activation of downstream signaling molecules, such as AKT and ERK. A significant G1 arrest was also observed in cell cycle analysis after exposing cells to lapatinib, however, combination with 5-Fu did not enhance G1 arrest. These results indicate that the combination of the lapatinib and 5-Fu is a promising treatment option for esophageal carcinoma with HER2 amplification.     

Quercetin‐3‐methyl ether inhibits lapatinib‐sensitive and ‐resistant breast cancer cell growth by inducing G2/M arrest and apoptosis

Lapatinib, an oral, small‐molecule, reversible inhibitor of both EGFR and HER2, is highly active in HER2 positive breast cancer as a single agent and in combination with other therapeutics. However, resistance against lapatinib is an unresolved problem in clinical oncology. Recently, interest in the use of natural compounds to prevent or treat cancers has gained increasing interest because of presumed low toxicity. Quercetin‐3‐methyl ether, a naturally occurring compound present in various plants, has potent anticancer activity. Here, we found that quercetin‐3‐methyl ether caused a significant growth inhibition of lapatinib‐sensitive and ‐resistant breast cancer cells. Western blot data showed that quercetin‐3‐methyl ether had no effect on Akt or ERKs signaling in resistant cells. However, quercetin‐3‐methyl ether caused a pronounced G₂/M block mainly through the Chk1‐Cdc25c‐cyclin B1/Cdk1 pathway in lapatinib‐sensitive and ‐resistant cells. In contrast, lapatinib produced an accumulation of cells in the G₁ phase mediated through cyclin D1, but only in lapatinib‐sensitive cells. Moreover, quercetin‐3‐methyl ether induced significant apoptosis, accompanied with increased levels of cleaved caspase 3, caspase 7, and poly(ADP‐ribose) polymerase (PARP) in both cell lines. Overall, these results suggested that quercetin‐3‐methyl ether might be a novel and promising therapeutic agent in lapatinib‐sensitive or ‐resistant breast cancer patients. © 2011 Wiley Periodicals, Inc.     

Drug Insight: intracellular inhibitors of HER2--clinical development of lapatinib in breast cancer

Targeting the human epidermal growth factor receptor type 2 (HER2) in breast cancer patients whose tumors overexpress HER2 has been clearly demonstrated to be effective in clinical trials with the monoclonal antibody trastuzumab. Not all patients, however, respond to trastuzumab therapy. Lapatinib is an oral receptor tyrosine kinase inhibitor that targets HER2 and the EGFR. Preclinical data reveal that lapatinib has activity in trastuzumab-resistant cell lines as well as synergistic activity with trastuzumab. In a pivotal phase III trial, a combination of lapatinib and capecitabine significantly decreased the risk of disease progression relative to capecitabine alone in women with HER2-positive advanced or metastatic breast cancer previously treated with anthracyclines, taxanes, and trastuzumab. Other trials are evaluating lapatinib in inflammatory breast cancer--for which encouraging data have been reported--in combination with hormone therapy, in combination with trastuzumab, and as an adjunct to adjuvant therapy for early-stage disease. Notably, lapatinib has not been associated with serious or symptomatic cardiotoxicity in clinical trials. It can cross the blood-brain barrier and might therefore have a role in preventing central-nervous-system progression. These features make lapatinib an ideal agent to evaluate more fully in HER2-positive metastatic and early-stage breast 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.