Chemoresistant tumor cell lines display altered epidermal growth factor receptor and HER3 signaling and enhanced sensitivity to gefitinib

Deregulated signaling through the epidermal growth factor receptor (EGFR) is involved in chemoresistance. To identify the molecular determinants of sensitivity to the EGFR inhibitor gefitinib (Iressa, ZD1839) in chemoresistance, we compared the response of matched chemosensitive and chemoresistant glioma and ovarian cancer cell lines. We found that chemoresistant cell lines were 2- to 3-fold more sensitive to gefitinib growth-inhibitory effects, because of decreased proliferation rather than survival. Sensitivity to gefitinib correlated with overexpression and constitutive phosphorylation of HER2 and HER3, but not EGFR, altered HER ligand expression, and enhanced activation of EGF-triggered EGFR pathway. No activating mutations were found in EGFR. Gefitinib fully inhibited EGF-induced and constitutive Akt activation only in chemoresistant cells. In parallel, gefitinib downregulated constitutively phosphorylated HER2 and HER3, and activated GSK3beta with a concomitant degradation of cyclin D1. Ectopically overexpressed HER2 on its own was insufficient to sensitize chemonaive cells to gefitinib. pHER3 coimmunoprecipitated with p85-PI3K in chemoresistant cells and gefitinib dissociated these complexes. siRNA-mediated inhibition of HER3 decreased constitutive activation of Akt and sensitivity to gefitinib in chemoresistant cells. Our study indicates that in chemoresistant cells gefitinib inhibits both an enhanced EGF-triggered pathway and a constitutive HER3-mediated Akt activation, indicating that inhibition of HER3 together with that of EGFR could be relevant in chemorefractory tumors. Furthermore, in combination experiments gefitinib enhanced the effects of coadministered drugs more in chemoresistant than chemosensitive ovarian cancer cells. Combined treatment might be therapeutically beneficial in chemoresistant tumors from ovary and likely from other tissues.     

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.     

Chemosensitisation by manganese superoxide dismutase inhibition is caspase-9 dependent and involves extracellular signal-regulated kinase 1/2

Chemoresistance and therapeutic selectivity are major obstacles to successful chemotherapy of ovarian cancer. Manganese superoxide disumutase (MnSOD) is an important antioxidant enzyme responsible for the elimination of superoxide radicals. We reported here that MnSOD was significantly elevated in ovarian cancer cells and its overexpression was one of the mechanisms that increased resistance to apoptosis in cancer cells. Knockdown of MnSOD by small-interfering RNA (siRNA) led to an increase in superoxide generation and sensitisation of ovarian cancer cells to the two front-line anti-cancer agents doxorubicin and paclitaxel whose action involved free-radical generation. This synergistic effect was not observed in non-transformed ovarian surface epithelial cells. Furthermore, our results revealed that this combination at the cellular level augmented activation of caspase-3 and caspase-9, but not caspase-8, suggesting involvement of an intrinsic apoptotic pathway. Evaluation of signalling pathways showed that MnSOD siRNA enhanced doxorubicin- and paclitaxel-induced phosphorylation of extracellular signal-regulated kinase 1/2. Akt activation was not affected. These results identify a novel chemoresistance mechanism in ovarian cancer, and show that combination of drugs capable of suppressing MnSOD with conventional chemotherapeutic agents may provide a novel strategy with a superior therapeutic index and advantage for the treatment of refractory ovarian cancer.     

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。     

Comparison of 3D and 2D tumor models reveals enhanced HER2 activation in 3D associated with an increased response to trastuzumab

Three-dimensional (3D) cell culture techniques are frequently used to model alterations in tissue architecture critically important for tumor development. Here, we report on a detailed comparison of a spheroid model of human epidermal growth factor receptor (HER2) overexpressing cancer cells with the traditional monolayer culture. In 2D culture, HER2 and HER3 form heterodimers, whereas in multicellular spheroids HER2 homodimers are formed. These homodimers localize in membrane rafts, resulting in enhanced inhibition of the proliferation of cancer cells with trastuzumab (Herceptin), a monoclonal antibody specifically targeting HER2. Within the tumor spheroids, HER2 homodimerization leads to enhanced activation of HER2 and results in a switch in signaling pathways from phosphoinositide 3-kinase (PI3K) to mitogen-activated protein kinase (MAPK). Diminished PI3K signaling is accompanied by the activation of the integrin beta4/Rac1/PAK 2 signaling cascade. We propose that the described 3D culture system may better reflect some in vivo aspects of HER signaling and can be used to further improve the understanding of the molecular mechanisms of trastuzumab action. Furthermore, the described human multicellular tumor spheroids may allow identification of new targets for the treatment of HER2-positive breast cancer patients who currently benefit suboptimally from trastuzumab treatment.     

Targeting HER proteins in cancer therapy and the role of the non-target HER3

Members of the human epidermal growth factor receptor (HER) family have been of considerable interest in the cancer arena due to their potential to induce tumorigenesis when their signalling functions are deregulated. The constitutive activation of these proteins is seen in a number of different common cancer subtypes, and in particular EGFR and HER2 have become highly pursued targets for anti-cancer drug development. Clinical studies in a number of different cancers known to be driven by EGFR or HER2 show mixed results, and further mechanistic understanding of drug sensitivity and resistance is needed to realise the full potential of this treatment modality. Signalling in trans is a key feature of HER family signalling, and the activation of the PI3K/Akt pathway, so critically important in tumorigenesis, is driven predominantly through phosphorylation in trans of the kinase inactive member HER3. An increasing body of evidence shows that HER3 plays a critical role in EGFR- and HER2-driven tumours. In particular, HER3 lies upstream of a critically important tumorigenic signalling pathway with extensive ability for feedback and cross-talk signalling, and targeting approaches that fail to account for this important trans-target of EGFR and HER2 can be undermined by its resiliency and resourcefulness. Since HER3 is kinase inactive, it is not a direct target of kinase inhibitors and not presently an easily drugable target. This review presents the current evidence highlighting the role of HER3 in tumorigenesis and its role in mediating resistance to inhibitors of EGFR and HER2.     

HER2 signaling modulates the equilibrium between pro- and antiangiogenic factors via distinct pathways: implications for HER2-targeted antibody therapy

We determined the impact of HER2 signaling on two proangiogenic factors, vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8), and on an antiangiogenic factor, thrombospondin-1 (TSP-1). Re-expression of HER2 in MCF-7 and T-47D breast cancer cells that endogenously express low levels of HER2 resulted in elevated expression of VEGF and IL-8 and decreased expression of TSP-1. Inhibition of HER2 with a humanized anti-HER2 antibody (trastuzumab, or Herceptin) or a retrovirus-mediated small interfering RNA against HER2 (siHER2) decreased VEGF and IL-8 expression, but increased TSP-1 expression in BT474 breast cancer cells that express high levels of HER2. These in vitro results were further evaluated by treatment of BT474 xenografts in immunosuppressed mice with trastuzumab. Trastuzumab inhibited growth of BT474 xenografts and decreased microvascular density associated with downregulation of VEGF and IL-8 and with upregulation of TSP-1 expression. Inhibiting the PI3K-AKT pathway decreased VEGF and IL-8 expression. AKT1 overexpession increased VEGF and IL-8 expression, but did not increase TSP-1 expression. A p38 kinase inhibitor, SB203580, instead blocked TSP-1 expression and a p38 activator, MKK6, increased TSP-1 expression. Trastuzumab stimulated sustained p38 activation and SB203580 attenuated the TSP-1 upregulation induced by trastuzumab. HER2 signaling therefore influences the equilibrium between pro- and antiangiogenic factors via distinct signaling pathways. Trastuzumab inhibits angiogenesis and tumor growth, at least in part, through activation of the HER2-p38-TSP-1 pathway and inhibition of the HER2-PI3K-AKT-VEGF/IL-8 pathway.     

Identification of therapeutic targets in ovarian cancer through active tyrosine kinase profiling

The activation status of a set of pro-oncogenic tyrosine kinases in ovarian cancer patient samples was analyzed to define potential therapeutic targets. Frequent activation of HER family receptor tyrosine kinases, especially HER2, was observed. Studies in ovarian cancer cell lines confirmed the activation of HER2. Moreover, knockdown of HER2 caused a strong inhibition of their proliferation. Analyses of the action of agents that target HER2 indicated that the antibody drug conjugate trastuzumab-emtansine (T-DM1) caused a substantial antitumoral effect in vivo and in vitro, and potentiated the action of drugs used in the therapy of ovarian cancer. T-DM1 provoked cell cycle arrest in mitosis, and caused the appearance of aberrant mitotic spindles in cells treated with the drug. Biochemical experiments confirmed accumulation of the mitotic markers phospho-Histone H3 and phospho-BUBR1 in cells treated with the drug. Prolonged treatment of ovarian cancer cells with T-DM1 provoked the appearance of multinucleated cells which later led to cell death. Together, these data indicate that HER2 represents an important oncogene in ovarian cancer, and suggest that targeting this tyrosine kinase with T-DM1 may be therapeutically effective, especially in ovarian tumors with high content of HER2.     

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.     

SV40 T/t-common polypeptide enhances the sensitivity of HER2-overexpressing human cancer cells to anticancer drugs cisplatin and doxorubicin

HER2-overexpressing cancer cells are resistant to cisplatin (CDDP) and doxorubicin (DXR). Here we report that SV40 T/t-common polypeptide could specifically sensitize HER2-overexpressing cancer cells to CDDP and DXR and specifically enhance CDDP- or DXR-induced apoptosis in these cells. This activity of T/t-common may be attributed to its ability to inhibit Bcl-2 and Bcl-XL and to suppress ERK activity in CDDP- or DXR-treated HER2-overexpressing cancer cells. T/t-common could enhance the antitumor activity of DXR on HER2-overexpressing ovarian tumor in NOD/SCID mice, suggesting that combination therapy using T/t-common and chemotherapeutic agents may provide a new approach for treating HER2-overexpressing cancers.     

Protein levels and gene expressions of the epidermal growth factor receptors, HER1, HER2, HER3 and HER4 in benign and malignant ovarian tumors

The epidermal growth factor receptors, HER1, HER2, HER3 and HER4 play a key role in the growth of malignant tumors. The receptors of the EGF receptor family are not cancer-specific proteins since these receptors are expressed to some extent in both normal and benign tissue, but this is not elucidated in detail in ovarian tissue. High tumor-to-normal-tissue concentration ratios would be favorable for molecular targeted anti-cancer treatment. The primary aim of the study was to analyze the potential differential protein content and gene expression of the four receptors in benign and malignant ovarian tumors. Tissue from 207 patients (101 malignant, 19 borderline, 64 benign ovarian tumors and 23 normal ovaries) were analyzed by quantitative ELISA for HER1-HER4 protein concentrations and by real-time PCR for HER1-HER4 gene expression. HER2 was also analyzed by immunohistochemistry. The HER2-4 receptor protein content and the median gene expression level was significantly higher in ovarian cancer patients compared to patients with benign ovarian tumors and normal ovaries (p<0.0000001). The protein content of the HER1 receptor was significantly lower in ovarian cancer compared to borderline tumors (p=0.012), benign ovarian tumors (p=0.049) and to normal ovaries (p=0.000069). A sound correlation between the protein levels and gene expressions was documented. In conclusion, decreased concentration of HER1 protein and increased HER2, HER3 and HER4 protein concentration were observed, as also elevated HER2-HER4 gene expression levels in ovarian cancer patients with barely any overlap of the HER3 and HER4 expression in malignant ovarian tumors compared to benign ovarian tissues.     

AKT inhibition relieves feedback suppression of receptor tyrosine kinase expression and activity

Activation of the PI3K-AKT pathway in tumors is modulated by negative feedback, including mTORC1-mediated inhibition of upstream signaling. We now show that AKT inhibition induces the expression and phosphorylation of multiple receptor tyrosine kinases (RTKs). In a wide spectrum of tumor types, inhibition of AKT induces a conserved set of RTKs, including HER3, IGF-1R, and insulin receptor. This is in part due to mTORC1 inhibition and in part secondary to a FOXO-dependent activation of receptor expression. PI3K-AKT inhibitors relieve this feedback and activate RTK signaling; this may attenuate their antitumor activity. Consistent with this model, we find that, in tumors in which AKT suppresses HER3 expression, combined inhibition of AKT and HER kinase activity is more effective than either alone.     

Adjuvant therapy of breast cancer

The treatment of early-stage breast cancer includes the use of chemotherapeutic and hormonal agents. Both chemotherapy and hormonal therapy have been shown by large, randomized trials to offer a survival advantage. The most commonly used chemotherapeutic agents used in the United States are doxorubicin and cyclophosphamide (AC). However, 3 studies have suggested that there may be an advantage in the use of taxanes in the adjuvant treatment of breast cancer. Furthermore the use of dose dense chemotherapy, incorporating AC and paclitaxel, has shown very promising results. It is well established that tamoxifen, a selective estrogen receptor modulator (SERM), improves overall survival (OS) in women with hormone receptor (HR) positive breast cancer. However, the results from large multicenter, randomized trials, suggest the potential superiority of aromatase inhibitors, compared to tamoxifen or an advantage of sequencing tamoxifen followed by an aromatase inhibitor (AI). The role of ovarian suppression is still being investigated in patients who have received prior chemotherapy. Newer agents, such as the monoclonal antibody against the HER2/neu receptor, trastuzumab, are now being studied as adjuvant therapy in early-stage breast cancer. In the next few years, with the completion of several large randomized trials, we will be able to answer several questions, including the optimal way of incorporating AIs into adjuvant therapy, the long-term sequella of using trastuzumab in the adjuvant treatment of breast cancer and the role of ovarian suppression combined with an aromatse inhibitor in premenopausal women with breast cancer.     

HER2/HER3 heterodimers and p21 expression are capable of predicting adjuvant trastuzumab response in HER2+ breast cancer

Human epidermal growth factor receptor 2 (HER2) plays an important role in breast cancer progression and provides predictive information for response to targeted therapy including trastuzumab although this is limited. Downstream pathways, such as PI3K/Akt, are associated with HER2/HER3 heterodimerization promoting survival and proliferation amongst cancer cells. Thus, patient outcome and trastuzumab therapy effectiveness might be further characterised by HER2/HER3 dimerisation and its signalling pathways. HER2/HER3 dimerisation status was assessed, using chromogenic in situ Proximity Ligation Assay, in two breast cancer series: early stage primary breast cancer, including 224 HER2+ patients that were not submitted to trastuzumab, and HER2+ breast cancer where patients were treated with adjuvant trastuzumab (n = 143). Levels of biomarkers including PI3K, pAKT, ER, PgR, HER3, BCL2, p53, PTEN and p21 were measured using immunohistochemistry. Levels of HER2/HER3 heterodimers were compared with biomarker expression and patient outcome. An association between high levels of HER2/HER3 dimerisation and absence of hormone receptors, ER and PgR, was observed. We further show for the first time the presence of HER2/HER3 heterodimers and the loss of p21 expression in HER2+ breast cancer predicts a significantly poorer outcome when submitted to adjuvant trastuzumab. Breast cancer patients that reveal high levels of HER2/HER3 dimerisation and loss of p21 are associated with poor survival prognosis in patients with HER2+ breast cancer treated with adjuvant trastuzumab. Further quantification analysis of HER dimer/ligand complexes and downstream signalling pathways will begin to unravel the complex associations with patient outcome and its relationship with sensitivity to targeted treatment.     

The cannabinoid delta(9)-tetrahydrocannabinol inhibits RAS-MAPK and PI3K-AKT survival signalling and induces BAD-mediated apoptosis in colorectal cancer cells

Deregulation of cell survival pathways and resistance to apoptosis are widely accepted to be fundamental aspects of tumorigenesis. As in many tumours, the aberrant growth and survival of colorectal tumour cells is dependent upon a small number of highly activated signalling pathways, the inhibition of which elicits potent growth inhibitory or apoptotic responses in tumour cells. Accordingly, there is considerable interest in therapeutics that can modulate survival signalling pathways and target cancer cells for death. There is emerging evidence that cannabinoids, especially Delta(9)-tetrahydrocannabinol (THC), may represent novel anticancer agents, due to their ability to regulate signalling pathways critical for cell growth and survival. Here, we report that CB1 and CB2 cannabinoid receptors are expressed in human colorectal adenoma and carcinoma cells, and show for the first time that THC induces apoptosis in colorectal cancer cells. THC-induced apoptosis was rescued by pharmacological blockade of the CB1, but not CB2, cannabinoid receptor. Importantly, THC treatment resulted in CB1-mediated inhibition of both RAS-MAPK/ERK and PI3K-AKT survival signalling cascades; two key cell survival pathways frequently deregulated in colorectal tumours. The inhibition of ERK and AKT activity by THC was accompanied by activation of the proapoptotic BCL-2 family member BAD. Reduction of BAD protein expression by RNA interference rescued colorectal cancer cells from THC-induced apoptosis. These data suggest an important role for CB1 receptors and BAD in the regulation of apoptosis in colorectal cancer cells. The use of THC, or selective targeting of the CB1 receptor, may represent a novel strategy for colorectal cancer therapy.     

HER2/neu antisense targeting of human breast carcinoma

Overexpression of the HER2/neu oncogene is observed in approximately 30% of human breast carcinoma specimens. HER2/neu overexpression is a negative prognostic factor in breast cancer patients. Cancer cells that overexpress HER2/neu may also be less sensitive to chemotherapy. In order to further define mechanisms by which HER2/neu overexpression drives neoplastic cell growth and chemoresistance, antisense oligonucleotides (ODNs) have been utilized to selectively down-regulate HER2/neu expression in human breast cancer cells. Such antisense ODNs suppress HER2/neu mRNA and protein levels in a dose-dependent, sequence-specific manner. Down-regulation of HER2/neu expression in HER2/neu overexpressing breast cancer cells inhibits cell cycle progression in G0/G1 and results in apoptotic cell death. In tissue culture studies, combined treatment of HER2/ neu overexpressing breast cancer cells with HER2/neu antisense ODNs and conventional chemotherapeutic agents results in synergistic inhibition of cancer cell growth and activation of apoptotic cell death mechanisms. These studies have been extended to demonstrate synergistic antitumor effects following systemic treatment with antisense ODNs plus doxorubicin in nude mice bearing human breast carcinoma xenografts. Collectively these findings demonstrate that HER2/neu overexpression stimulates anti-apoptotic cell survival mechanisms and suggest that HER2/neu antisense ODNs may be of use in cancer therapeutics.     

ErbB3 expression and dimerization with EGFR influence pancreatic cancer cell sensitivity to erlotinib

Abnormal expression and signaling of ErbB receptors has been implicated in multiple epithelial malignancies, including pancreatic cancer. Erlotinib, an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), has been recently approved for pancreatic cancer treatment, but there are no reliable predictors of patient response. Expression of additional ErbB receptors seems to influence tumor response to EGFR-targeted therapy. We analyzed the influence of ErbB3 expression on pancreatic cancer cell response to erlotinib treatment. Proliferation assays of five human pancreatic cancer cell lines were performed following treatment with erlotinib. Expression and phosphorylation profiles of ErbB receptors and downstream adaptor protein (Akt, ERK1/2, STAT3, mTOR) were evaluated following stimulation with EGF or neuregulin-beta. The formation of EGFR homodimers and EGFR-ErbB3 heterodimers, necessary to enable ErbB3 downstream signaling, was demonstrated by chemical cross-linking assays. The effects of RNA inhibition of ErbB3 on sensitivity to erlotinib treatment were evaluated in AsPC-1 pancreatic cancer cells. Erlotinib inhibited Akt phosphorylation and proliferation of all the ErbB3-expressing cell lines but did not affect mTOR activation. Cross-linking studies confirmed the presence of EGFR-ErbB3 heterodimers in pancreatic cancer cells. Only the ErbB3-deficient MIA PaCa-2 cells displayed persistent Akt activation and ongoing proliferation in spite of erlotinib treatment. siRNA-mediated inhibition of ErbB3 expression in AsPC-1 cells resulted in acquired resistance to erlotinib treatment. Pancreatic cancer cells which lack ErbB3 do not display activation of the ErbB3-PI3K-Akt cascade induced by EGFR/ErbB3 heterodimers and become less critically dependent on EGFR signaling and therefore resistant to erlotinib. Pancreatic cancer expression of ErbB3 may be useful for EGFR-targeted therapy patient selection.     

Targeting HER3 with miR-450b-3p suppresses breast cancer cells proliferation

In breast cancer cells, heterodimerization of HER2 and HER3 plays important and dominant roles in the functionality and transformation of HER-mediated pathways, in particular the PI3K/Akt survival pathway. HER3 was considered as a major signaling hub in HER2-amplified cancers. Inhibition of HER3 expression may therefore represent a rational therapeutic approach to breast cancers where HER2/HER3-mediated signaling plays a role in tumorigenesis and progression. miRNAs exerts important roles in regulating gene expressions by binding to and repressing target mRNAs. Here we reported that miRNA-450b-3p inhibits HER3 expression by directly targeting 3′ UTR of HER3 mRNA and represses the downstream signal transductions of HER family. Overexpression of miRNA-450b-3p in SKBR3 cells inhibits cells clonogenic potential and enhances their sensitivity to trastuzumab, a monoclonal antibody that binds to the HER2 receptor, or doxorubicin through repressing proliferative signal pathways mediated by HER3/HER2/PI3K/AKT. Furthermore, we found that breast cancer patients with tumors that demonstrating upregulated HER3 (>2-fold) and downregulated miR-450b-3p (>2-fold) expressions compared with the paired adjacent non-tumorous tissues showed significantly poorer overall survival (P < 0.05). Our study identified miRNA-450b-3p as a new tumor repressor and also provided some evidences suggesting that downregulation of miR-450b-3p expression with concurrent overexpression of HER3 may serve as a prognostic biomarker for poor overall survival in breast cancer patients.     

The inhibitory effect of norepinephrine on the migration of ES-2 ovarian carcinoma cells involves a Rap1-dependent pathway

Our previous studies have shown that norepinephrine induces the migratory activity of human PC-3 prostate, SW 480 colon and MDA-MB-468 breast carcinoma cells. In contrast to these results, we show here that human ES-2 ovarian carcinoma cells have a reduced migratory activity after norepinephrine treatment. This inhibitory effect is possibly mediated by a cAMP-dependent activation of the small GTPase Rap1 via Epac. Furthermore, a key signalling event of the promigratory effect of norepinephrine in the above mentioned carcinoma cells is the activation of phospholipase C enzymes. In ES-2 cells, this part of the signalling cascade is constitutively active.