Genes affecting the cell cycle, growth, maintenance, and drug sensitivity are preferentially regulated by anti-HER2 antibody through phosphatidylinositol 3-kinase-AKT signaling

Plasma THBS1 as a predictive biomarker for poor prognosis and brain metastasis in patients with HER2-enriched breast cancer

BACKGROUND

Thrombospondin-1 (THBS1) is a secretory adhesive glycoprotein involved in the progression of multiple malignancies, including breast cancer. However, the clinical significance and prognostic role of plasma THBS1 in breast cancer have yet to be clarified.

METHODS

Plasma THBS1 levels in 627 breast cancer patients were analyzed by enzyme-linked immunosorbent assay. Bone marrow blood was drawn from the anterior/posterior superior iliac spine to detect the presence of disseminated tumor cells (DTCs). The effects of plasma THBS1 on the clinicopathological characteristics and survival prediction of breast cancer patients were explored.

RESULTS

Plasma THBS1 did not correlate with overall survival, breast cancer-specific survival (BCSS), and distant disease-free survival (DDFS) in the entire breast cancer cohort. Notably, HER2-enriched patients with high-plasma THBS1 levels had significantly shorter BCSS (P = 0.027) and DDFS (P = 0.011) than those with low levels. Multivariate analyses revealed that plasma THBS1 was an independent prognostic marker of BCSS (P = 0.026) and DDFS (P = 0.007) in HER2-enriched patients. THBS1 levels were 24% higher in positive DTC patients than in negative DTC patients (P = 0.031), and high levels were significantly associated with poor BCSS in positive DTC patients (HR 2.08, 95% CI 1.17-3.71; P = 0.019). Moreover, high-plasma THBS1 levels were specifically associated with an increased occurrence of brain metastasis in HER2-enriched patients (P = 0.041).

CONCLUSION

These findings suggest that plasma THBS1 may be serving as an unfavorable prognosis predictor for HER2-enriched breast cancer and justifies the need for further research.

Chromosomal Instability as Enabling Feature and Central Hallmark of Breast Cancer

Chromosomal instability (CIN) has become a topic of great interest in recent years, not only for its implications in cancer diagnosis and prognosis but also for its role as an enabling feature and central hallmark of cancer. CIN describes cell-to-cell variation in the number or structure of chromosomes in a tumor population. Although extensive research in recent decades has identified some associations between CIN with response to therapy, specific associations with other hallmarks of cancer have not been fully evidenced. Such associations place CIN as an enabling feature of the other hallmarks of cancer and highlight the importance of deepening its knowledge to improve the outcome in cancer. In addition, studies conducted to date have shown paradoxical findings about the implications of CIN for therapeutic response, with some studies showing associations between high CIN and better therapeutic response, and others showing the opposite: associations between high CIN and therapeutic resistance. This evidences the complex relationships between CIN with the prognosis and response to treatment in cancer. Considering the above, this review focuses on recent studies on the role of CIN in cancer, the cellular mechanisms leading to CIN, its relationship with other hallmarks of cancer, and the emerging therapeutic approaches that are being developed to target such instability, with a primary focus on breast cancer. Further understanding of the complexity of CIN and its association with other hallmarks of cancer could provide a better understanding of the cellular and molecular mechanisms involved in prognosis and response to treatment in cancer and potentially lead to new drug targets.

A Novel Mechanism Underlying the Inhibitory Effects of Trastuzumab on the Growth of HER2-Positive Breast Cancer Cells

To improve the efficacy of trastuzumab, it is essential to understand its mechanism of action. One of the significant issues that makes it difficult to determine the precise mechanism of trastuzumab action is the formation of various HER receptor dimers in HER2-positive breast cancer cells. So far, studies have focused on the role of HER2-HER3 heterodimers, and little is known regarding EGFR-HER2 heterodimers. Here, we study the role of trastuzumab on the cell signaling and cell proliferation mediated by EGFR-HER2 heterodimers in BT474 and SRBR3 cells. EGF stimulates the formation of both EGFR homodimer and EGFR-HER2 heterodimer. Trastuzumab only binds to HER2, not EGFR. Therefore, any effects of trastuzumab on EGF-induced activation of EGFR, HER2, and downstream signaling proteins, as well as cell proliferation, are through its effects on EGFR-HER2 heterodimers. We show that trastuzumab inhibits EGF-induced cell proliferation and cell cycle progression in BT474 and SKBR3 cells. Interestingly trastuzumab strongly inhibits EGF-induced Akt phosphorylation and slightly inhibits EGF-induced Erk activation, in both BT474 and SKBR3 cells. These data suggest the presence of a novel mechanism that allows trastuzumab to inhibit EGR-induced Akt activation and cell proliferation, without blocking EGF-induced EGFR-HER2 heterodimerization and activation. We show that trastuzumab inhibits EGF-induced lipid raft localization of the EGFR-HER2 heterodimer. Disruption of the lipid raft with MβCD blocks HER2-mediated AKT activation in a similar way to trastuzumab. MβCD and trastuzumab synergically inhibit AKT activation. We conclude that trastuzumab inhibits EGF-induced lipid raft localization of EGFR-HER2 heterodimer, which leads to the inhibition of Akt phosphorylation and cell proliferation, without blocking the formation and phosphorylation of the EGFR-HER2 heterodimer.

Human Blood Serum Inhibits Ductal Carcinoma Cells BT474 Growth and Modulates Effect of HER2 Inhibition

Trastuzumab, a HER2-targeted antibody, is widely used for targeted therapy of HER2-positive breast cancer (BC) patients; yet, not all of them respond to this treatment. We investigated here whether trastuzumab activity on the growth of HER2-overexpressing BT474 cells may interfere with human peripheral blood endogenous factors. Among 33 individual BC patient blood samples supplemented to the media, BT474 sensitivity to trastuzumab varied up to 14 times. In the absence of trastuzumab, human peripheral blood serum samples could inhibit growth of BT474, and this effect varied ~10 times for 50 individual samples. In turn, the epidermal growth factor (EGF) suppressed the trastuzumab effect on BT474 cell growth. Trastuzumab treatment increased the proportion of BT474 cells in the G0/G1 phases of cell cycle, while simultaneous addition of EGF decreased it, yet not to the control level. We used RNA sequencing profiling of gene expression to elucidate the molecular mechanisms involved in EGF- and human-sera-mediated attenuation of the trastuzumab effect on BT474 cell growth. Bioinformatic analysis of the molecular profiles suggested that trastuzumab acts similarly to the inhibition of PI3K/Akt/mTOR signaling axis, and the mechanism of EGF suppression of trastuzumab activity may be associated with parallel activation of PKC and transcriptional factors ETV1-ETV5.

A single-cell analysis of breast cancer cell lines to study tumour heterogeneity and drug response

Cancer cells within a tumour have heterogeneous phenotypes and exhibit dynamic plasticity. How to evaluate such heterogeneity and its impact on outcome and drug response is still unclear. Here, we transcriptionally profile 35,276 individual cells from 32 breast cancer cell lines to yield a single cell atlas. We find high degree of heterogeneity in the expression of biomarkers. We then train a deconvolution algorithm on the atlas to determine cell line composition from bulk gene expression profiles of tumour biopsies, thus enabling cell line-based patient stratification. Finally, we link results from large-scale in vitro drug screening in cell lines to the single cell data to computationally predict drug responses starting from single-cell profiles. We find that transcriptional heterogeneity enables cells with differential drug sensitivity to co-exist in the same population. Our work provides a framework to determine tumour heterogeneity in terms of cell line composition and drug response.

Trastuzumab Mechanism of Action; 20 Years of Research to Unravel a Dilemma

Trastuzumab as a first HER2-targeted therapy for the treatment of HER2-positive breast cancer patients was introduced in 1998. Although trastuzumab has opened a new avenue to treat patients with HER2-positive breast cancer and other types of cancer, some patients are not responsive or become resistant to this treatment. So far, several mechanisms have been suggested for the mode of action of trastuzumab; however, the findings regarding these mechanisms are controversial. In this review, we aimed to provide a detailed insight into the various mechanisms of action of trastuzumab.

Association of Sperm-Associated Antigen 5 and Treatment Response in Patients With Estrogen Receptor-Positive Breast Cancer

Importance

There is no proven test that can guide the optimal treatment, either endocrine therapy or chemotherapy, for estrogen receptor-positive breast cancer.

Objective

To investigate the associations of sperm-associated antigen 5 (SPAG5) transcript and SPAG5 protein expressions with treatment response in systemic therapy for estrogen receptor-positive breast cancer.

Design, Settings, and Participants

This retrospective cohort study included patients with estrogen receptor-positive breast cancer who received 5 years of adjuvant endocrine therapy with or without neoadjuvant anthracycline-based combination chemotherapy (NACT) derived from 11 cohorts from December 1, 1986, to November 28, 2019. The associations of SPAG5 transcript and SPAG5 protein expression with pathological complete response to NACT were evaluated, as was the association of SPAG5 mRNA expression with response to neoadjuvant endocrine therapy. The associations of distal relapse-free survival with SPAG5 transcript or SPAG5 protein expressions were analyzed. Data were analyzed from September 9, 2015, to November 28, 2019.

Main Outcomes and Measures

The primary outcomes were breast cancer-specific survival, distal relapse-free survival, pathological complete response, and clinical response. Outcomes were examined using Kaplan-Meier, multivariable logistic, and Cox regression models.

Results

This study included 12 720 women aged 24 to 78 years (mean [SD] age, 58.46 [12.45] years) with estrogen receptor-positive breast cancer, including 1073 women with SPAG5 transcript expression and 361 women with SPAG5 protein expression of locally advanced disease stage IIA through IIIC. Women with SPAG5 transcript and SPAG5 protein expressions achieved higher pathological complete response compared with those without SPAG5 transcript or SPAG5 protein expressions (transcript: odds ratio, 2.45 [95% CI, 1.71-3.51]; P < .001; protein: odds ratio, 7.32 [95% CI, 3.33-16.22]; P < .001). Adding adjuvant anthracycline chemotherapy to adjuvant endocrine therapy for SPAG5 mRNA expression in estrogen receptor-positive breast cancer was associated with prolonged 5-year distal relapse-free survival in patients without lymph node involvement (hazard ratio, 0.34 [95% CI, 0.14-0.87]; P = .03) and patients with lymph node involvement (hazard ratio, 0.35 [95% CI, 0.18-0.68]; P = .002) compared with receiving 5-year endocrine therapy alone. Mean (SD) SPAG5 transcript was found to be downregulated after 2 weeks of neoadjuvant endocrine therapy compared with pretreatment levels in 68 of 92 patients (74%) (0.23 [0.18] vs 0.34 [0.24]; P < .001).

Conclusions and Relevance

These findings suggest that SPAG5 transcript and SPAG5 protein expressions could be used to guide the optimal therapies for estrogen receptor-positive breast cancer. Retrospective and prospective clinical trials are warranted.

Overcoming trastuzumab resistance in HER2-positive breast cancer using combination therapy

Human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) comprises around 20-30% of all BC subtypes and is correlated with poor prognosis. For many years, trastuzumab, a monoclonal antibody, has been used to inhibit the HER2 activity. Though, the main resistance to trastuzumab has challenged the use of this drug in the management of HER2-positive BC. Therefore, the determination of resistance mechanisms and the incorporation of new agents may lead to the development of a better blockade of the HER family receptor signaling. During the last few years, some therapeutic drugs have been developed for treating patients with trastuzumab-resistant HER2-positive BC that have more effective influences in the management of this condition. In this regard, the present study aimed at reviewing the mechanisms of trastuzumab resistance and the innovative therapies that have been investigated in trastuzumab-resistant HER2-positive BC subjects.

Targeting tumor cells with antibodies enhances anti-tumor immunity

Tumor-targeting antibodies were initially defined as a group of therapeutic monoclonal antibodies (mAb) that recognize tumor-specific membrane proteins, block cell signaling, and induce tumor-killing through Fc-driven innate immune responses. However, in the past decade, ample evidence has shown that tumor-targeting mAb (TTmAb) eradicates tumor cells via activation of cytotoxic T cells (CTLs). In this review, we specifically focus on how TTmAbs induce adaptive anti-tumor immunity and its potential in combination therapy with immune cytokines, checkpoint blockade, radiation, and enzyme-targeted small molecule drugs. Exploring the mechanisms of these preclinical studies and retrospective clinical data will significantly benefit the development of highly efficient and specific TTmAb-oriented anti-tumor remedies.

Phosphorylated Akt1 in Human Breast Cancer Measured by Direct Sandwich Enzyme-Linked Immunosorbent Assay: Correlation with Clinicopathological Features and Tumor VEGF-Signaling System Component Levels

Protein kinase B (Akt) plays a major role in the regulation of breast cancer growth, survival, hormone, drug and radiosensitivity, but the clinical value of its expression and activation in human tumors is unclear. Activated Akt1 (pAkt1) expression was quantified in a series of 46 breast cancer and adjacent mammary gland samples by a direct Path-Scan™ PhosphoAkt1 (Ser473) sandwich ELISA kit. VEGF, sVEGFR1 and sVEGFR2 levels were measured simultaneously by standard ELISA kits. Forty-nine percent of the tumors had an increased pAkt1 level as compared to adjacent tissue. pAkt1 levels were significantly higher in stage IIb than in stage I-IIa tumors. The frequency of pAkt1 elevation was positively associated with tumor size and malignancy grade. pAkt1 was also twice as frequently increased in PgR-negative as in PgR-positive tumors, while its mean level was significantly higher in ER-positive than in ER-negative tumors. VEGF, sVEGFR1 and sVEGFR2 were increased in 73–85% of the tumors, but no associations with most clinicobiological factors and pAkt1 level were found. In conclusion, activation of Akt1 is not associated with VEGF signaling protein expression in breast cancer but is related to tumor size, grade of malignancy, and steroid receptor status.

Combination therapeutics in complex diseases

The biological redundancies in molecular networks of complex diseases limit the efficacy of many single drug therapies. Combination therapeutics, as a common therapeutic method, involve pharmacological intervention using several drugs that interact with multiple targets in the molecular networks of diseases and may achieve better efficacy and/or less toxicity than monotherapy in practice. The development of combination therapeutics is complicated by several critical issues, including identifying multiple targets, targeting strategies and the drug combination. This review summarizes the current achievements in combination therapeutics, with a particular emphasis on the efforts to develop combination therapeutics for complex diseases.

Enhancing tumor-targeting monoclonal antibodies therapy by PARP inhibitors

Monoclonal antibodies (mAbs) have become a successful therapeutic approach in cancer. However, some patients do not achieve long-term clinical benefit and most mAbs only exert modest effects as monotherapies. Therefore, combinations with chemotherapy are currently being investigated. Emerging studies have shown a synergistic therapeutic effect of PARP inhibitors and mAbs in cancer. PARP enzymes catalytically cleave β-NAD⁺ and transfer the ADP-ribose moiety to acceptor proteins, modifying their function. In here, we update recent data about the therapeutic effect of the combination of PARP inhibitors with mAbs in cancer treatment and discuss the molecular mechanisms involved in this synergy.

Basal Protein Expression Is Associated With Worse Outcome and Trastuzamab Resistance in HER2+ Invasive Breast Cancer

BACKGROUND

We investigated the effect of basal protein expression on trastuzamab response in patients with HER2-positive (HER2(+)) breast cancer who received trastuzamab (T) and in HER2(+) breast cancer cell lines.

PATIENTS AND METHODS

Expression of cytokeratin (CK) 5/6, CK14, and epidermal growth factor receptor (EGFR) was evaluated after immunohistochemical staining in paraffin-embedded tissue of 97 patients with stage I to III HER2(+) breast cancer treated with chemotherapy/T. Groups with and without basal protein expression were compared with respect to clinicopathologic parameters and survival. We treated 4 cell lines (2 basal-HER2 [HCC1569, HCC1954] and 2 nonbasal HER2 [BT474, SKBR3]) each with vehicle, T 20 μg/mL, paclitaxel 0.01 μM (P), and T with P (T + P). Cell viability was assessed and HER2 pathway suppression was compared between groups using immunoblot analysis. Mammosphere formation was used to assess breast cancer stem cell properties.

RESULTS

EGFR expression was significantly associated with cancer-specific survival (CSS) (P = .05). CK5/6 expression strongly correlated with overall and disease-free survival, and CSS (P = .03, P = .04, and P = .03, respectively). Statistical significance was maintained for EGFR and CK5/6 after adjustment for covariates. CK14 was not associated with survival. All cell lines expressed similar levels of HER2. T and P alone inhibited proliferation of nonbasal cell lines; T + P had an additive cytotoxic effect. Basal cells were resistant to T, P inhibited proliferation, but T + P had no additive cytotoxic effect on cell growth in basal cells. Immunoblot analysis showed a significant decrease in phosphorylated Akt levels after treatment with T or T + P in nonbasal cells but not in basal cells. Akt blockade suppressed growth of basal and nonbasal HER2(+) cells. Furthermore, basal HER2 cell lines had increased mammosphere formation, which suggests increased stem cell properties compared with nonbasal HER2 cell lines.

CONCLUSION

CK5/6 and EGFR expression are predictive of worse prognosis in HER2(+) breast cancer patients treated with T. Basal HER2 breast cancer cell lines are resistant to trastuzamab, which is mediated through the Akt pathway; AKT inhibition abrogates this resistance. Basal HER2 cell lines also have increased stem cell properties, which might play a role in the resistance pathway.

Lewis y enhances CAM-DR in ovarian cancer cells by activating the FAK signaling pathway and upregulating Bcl-2/Bcl-XL expression

Oligosaccharides on the surface of adhesion molecules may contribute to the process of CAM-DR. To investigate the role of the Lewis y antigen in this process, we established a cell adhesion model mediated by the integrin α5β1-FN interaction in the ovarian cancer cell line, RMG-1-hFUT, which highly expresses Lewis y by transfection with α1,2-fucosyltransferase into RMG-1 cells. Our results indicate that the rates of carboplatin-induced apoptosis and necrosis are reduced in FN-adhered tumor cells, and carboplatin resistance is significantly decreased in the presence of anti-Lewis y antibody. CAM-DR in tumor cells has been correlated with elevated expression of the nuclear anti-apoptotic proteins Bcl-2 and Bcl-XL. Lewis y promotes the expression of the Bcl-2 and Bcl-XL genes by activating the focal adhesion kinase signaling pathway and accelerating their transcription. Thus, Lewis y leads to inhibition of apoptosis and enhancement of CAM-DR by activation of the FAK signaling pathway and upregulation of Bcl-2/Bcl-XL expression in ovarian cancer cell lines.

Integrative transcriptome-wide analyses reveal critical HER2-regulated mRNAs and lincRNAs in HER2+ breast cancer

Breast cancer is a major health problem affecting millions of women worldwide. Over 200,000 new cases are diagnosed annually in the USA, with approximately 40,000 of these cases resulting in death. HER2-positive (HER2+) breast tumors, representing 20-30 % of early-stage breast cancer diagnoses, are characterized by the amplification of the HER2 gene. However, the critical genes and pathways that become affected by HER2 amplification in humans are yet to be specifically identified. Furthermore, it is yet to be determined if HER2 amplification also affects the expression of long intervening non-coding (linc)RNAs, which are involved in the epigenetic regulation of gene expression. We examined changes in gene expression by next generation RNA sequencing in human tumors pre- and post- HER2 inhibition by trastuzumab in vivo, and changes in gene expression in response to HER2 knock down in cell culture models. We integrated our results with gene expression analysis of HER2+ tumors vs matched normal tissue from The Cancer Genome Atlas. The integrative analyses of these datasets led to the identification of a small set of mRNAs, and the associated biological pathways that become deregulated by HER2 amplification. Furthermore, our analyses identified three lincRNAs that become deregulated in response to HER2 amplification both in vitro and in vivo. Our results should provide the foundation for functional studies of these candidate mRNAs and lincRNAs to further our understanding of how HER2 amplification results in tumorigenesis. Also, the identified lincRNAs could potentially open the door for future RNA-based biomarkers and therapeutics in HER2+ breast cancer.

Poly (ADP-ribose) polymerase inhibition enhances trastuzumab antitumour activity in HER2 overexpressing breast cancer

AIM

Poly (ADP-ribose) polymerase (PARP) inhibitors have shown promising results in Breast Cancer (BRCA) deficient breast cancer, but not in molecularly unselected patient populations. Two lines of research in this field are needed: the identification of novel subsets of patients that could potentially benefit from PARP inhibitors and the discovery of suitable targeted therapies for combination strategies.

METHODS

We tested PARP inhibition, alone or combined with the anti-HER2 antibody trastuzumab on HER2+ breast cancer. We used two PARP inhibitors in clinical development, olaparib and rucaparib, as well as genetic downmodulation of PARP-1 for in vitro studies. DNA damage was studied by the formation of γH2AX foci and comet assay. Finally, the in vivo anti-tumour effect of olaparib and trastuzumab was examined in nude mice subcutaneously implanted with BT474 cells.

RESULTS

In a panel of four HER2 overexpressing breast cancer cell lines, both olaparib and rucaparib significantly decreased cell growth and enhanced anti-tumour effects of trastuzumab. Cells exposed to olaparib and trastuzumab had greater DNA damage than cells exposed to each agent alone. Mechanistic exploratory assays showed that trastuzumab downmodulated the homologous recombination protein proliferating cell nuclear antigen (PCNA). Combination treatment in the BT474 xenograft model resulted in enhanced growth inhibition, reduced tumour cell proliferation, and increased DNA damage and apoptosis.

CONCLUSION

Taken together, our results show that PARP inhibition has antitumour effects and increases trastuzumab activity in HER2 overexpressing breast cancer. These findings make this novel combination a promising strategy for clinical development.

SPAG5 upregulation predicts poor prognosis in cervical cancer patients and alters sensitivity to taxol treatment via the mTOR signaling pathway

Previously, we found that sperm-associated antigen 5 (SPAG5) was upregulated in pelvic lymph node metastasis–positive cervical cancer. The aim of this study is to examine the role of SPAG5 in the proliferation and tumorigenicity of cervical cancer and its clinical significance in tumor progression. In our study, SPAG5 expression in cervical cancer patients was detected using quantitative real-time polymerase chain reaction, western blotting, and immunohistochemistry; cervical cancer cell function with downregulated SPAG5 in vitro was explored using tetrazolium assay, flow cytometry, and colony formation and Transwell assays. SPAG5 was upregulated in tumor tissue compared with paired adjacent noncancerous tissues; SPAG5 upregulation in tumor tissues indicated poor disease-free survival, which was also an independent prognostic indicator for cervical cancer patients. In vitro study demonstrated that SPAG5 downregulation inhibited cell proliferation and growth significantly by G2/M arrest and induction of apoptosis, and hindered cell migration and invasion. Under SPAG5 downregulation, the sensitivity of cervical cancer cells differed according to taxol dose, which correlated with mammalian target of rapamycin (mTOR) signaling pathway activity. In general, SPAG5 upregulation relates to poor prognosis in cervical cancer patients, and SPAG5 is a regulator of mTOR activity during taxol treatment in cervical cancer.

Current status of anti-human epidermal growth factor receptor 2 therapies: predicting and overcoming herceptin resistance

Human epidermal growth factor receptor 2-overexpressing (HER2+) breast cancer occurs in 20% to 25% of cases and is associated with poor prognosis. Trastuzumab (Herceptin; Genentech, South San Francisco, CA) is a monoclonal antibody targeting the HER2 extracellular domain that has been shown to significantly reduce relapse rates. However, some patients with HER2+ tumors do not respond to Herceptin, and 60% to 85% of patients with HER2+ metastatic breast cancer acquire resistance within a short time period. In this review, we discuss proposed mechanisms of action of trastuzumab and trastuzumab resistance and various drugs that have been developed to overcome drug resistance. We introduce the basal molecular subtype as a predictor of increased risk in HER2+ breast cancer and a possible alternative cause of drug resistance.

Overexpression of high mobility group box 1 and 2 is associated with the progression and angiogenesis of human bladder carcinoma

High mobility group box 1 (HMGB1) and HMGB2 overexpression has been observed in several human tumor types, and is involved in cancer progression and prognosis. However, the clinicopathological significance of HMGB1 and HMGB2 expression in bladder carcinoma (BCa), particularly the involvement of these proteins in angiogenesis, remains unclear. In the present study, immunohistochemistry and real-time polymerase chain reaction (PCR) of HMGB1 and HMGB2 in 64 BCa patients revealed that HMGB1 and HMGB2 were overexpressed in BCa tissues compared with normal tissues, and were correlated with tumor clinical stage and pathological grade. In addition, correlation analysis of vascular endothelial growth factor (VEGF) and microvessel density (MVD) counts indicated that the overexpression of HMGB1 and HMGB2 was also correlated with angiogenesis. We conclude that HMGB proteins act as key regulators in the progression and angiogenesis of bladder carcinoma, and serve as potential diagnostic and therapeutic targets.

Modulation of MicroRNA-194 and cell migration by HER2-targeting trastuzumab in breast cancer

Trastuzumab, a humanized monoclonal antibody directed against the extracellular domain of the HER2 oncoprotein, can effectively target HER2-positive breast cancer through several mechanisms. Although the effects of trastuzumab on cancer cell proliferation, angiogenesis and apoptosis have been investigated in depth, the effect of trastuzumab on microRNA (miRNA) has not been extensively studied. We have performed miRNA microarray profiling before and after trastuzumab treatment in SKBr3 and BT474 human breast cancer cells that overexpress HER2. We found that trastuzumab treatment of SKBr3 cells significantly decreased five miRNAs and increased three others, whereas treatment of BT474 cells significantly decreased two miRNAs and increased nine. The only change in miRNA expression observed in both cell lines following trastuzumab treatment was upregulation of miRNA-194 (miR-194) that was further validated in vitro and in vivo. Forced expression of miR-194 in breast cancer cells that overexpress HER2 produced no effect on apoptosis, modest inhibition of proliferation, significant inhibition of cell migration/invasion in vitro and significant inhibition of xenograft growth in vivo. Conversely, knockdown of miR-194 promoted cell migration. Increased miR-194 expression markedly reduced levels of the cytoskeletal protein talin2 and specifically inhibited luciferase reporter activity of a talin2 wild-type 3'-untranslated region, but not that of a mutant reporter, indicating that talin2 is a direct downstream target of miR-194. Trastuzumab treatment inhibited breast cancer cell migration and reduced talin2 expression in vitro and in vivo. Knockdown of talin2 inhibited cell migration/invasion. Knockdown of trastuzumab-induced miR-194 expression with a miR-194 inhibitor compromised trastuzumab-inhibited cell migration in HER2-overexpressing breast cancer cells. Consequently, trastuzumab treatment upregulates miR-194 expression and may exert its cell migration-inhibitory effect through miR-194-mediated downregulation of cytoskeleton protein talin2 in HER2-overexpressing human breast cancer cells.

Intrinsic and acquired resistance to HER2-targeted therapies in HER2 gene-amplified breast cancer: mechanisms and clinical implications

Approximately 25% of human breast cancers overexpress the HER2 (ErbB2) proto-oncogene, which confers a more aggressive tumor phenotype and associates with a poor prognosis in patients with this disease. Two approved therapies targeting HER2, the monoclonal antibody trastuzumab and the tyrosine kinase inhibitor lapatinib, are clinically active against this type of breast cancer. However, a significant fraction of patients with HER2+ breast cancer treated with these agents eventually relapse or develop progressive disease. This suggests that tumors acquire or possess intrinsic mechanisms of resistance that allow escape from HER2 inhibition. This review focuses on mechanisms of intrinsic and/or acquired resistance to HER2-targeted therapies that have been identified in preclinical and clinical studies. These mechanisms involve alterations to HER2 itself, coexpression or acquisition of bypass signaling through other receptor or intracellular signaling pathways, defects in mechanisms of cell cycle regulation or apoptosis, and host factors that may modulate drug response. Emerging clinical evidence already suggests that combinations of therapies targeting HER2 as well as these resistance pathways will be effective in overcoming or preventing resistance.

Defining the molecular response to trastuzumab, pertuzumab and combination therapy in ovarian cancer

BACKGROUND

Trastuzumab and pertuzumab target the Human Epidermal growth factor Receptor 2 (HER2). Combination therapy has been shown to provide enhanced antitumour activity; however, the downstream signalling to explain how these drugs mediate their response is not clearly understood.

METHODS

Transcriptome profiling was performed after 4 days of trastuzumab, pertuzumab and combination treatment in human ovarian cancer in vivo. Signalling pathways identified were validated and investigated in primary ovarian xenografts at the protein level and across a timeseries.

RESULTS

A greater number and variety of genes were differentially expressed by the combination of antibody therapies compared with either treatment alone. Protein levels of cyclin-dependent kinase inhibitors p21 and p27 were increased in response to both agents and further by the combination; pERK signalling was inhibited by all treatments; but only pertuzumab inhibited pAkt signalling. The expression of proliferation, apoptosis, cell division and cell-cycle markers was distinct in a panel of primary ovarian cancer xenografts, suggesting the heterogeneity of response in ovarian cancer and a need to establish predictive biomarkers.

CONCLUSION

This first comprehensive study of the molecular response to trastuzumab, pertuzumab and combined therapy in vivo highlights both common and distinct downstream effects to agents used alone or in combination, suggesting that complementary pathways may be involved.

Array-based pharmacogenomics of molecular-targeted therapies in oncology

The advent of microarrays over the past decade has transformed the way genome-wide studies are designed and conducted, leading to an unprecedented speed of acquisition and amount of new knowledge. Microarray data have led to the identification of molecular subclasses of solid tumors characterized by distinct oncogenic pathways, as well as the development of multigene prognostic or predictive models equivalent or superior to those of established clinical parameters. In the field of molecular-targeted therapy for cancer, in particular, the application of array-based methodologies has enabled the identification of molecular targets with 'key' roles in neoplastic transformation or tumor progression and the subsequent development of targeted agents, which are most likely to be active in the specific molecular setting. Herein, we present a summary of the main applications of whole-genome expression microarrays in the field of molecular-targeted therapies for solid tumors and we discuss their potential in the clinical setting. An emphasis is given on deciphering the molecular mechanisms of drug action, identifying novel therapeutic targets and suitable agents to target them with, and discovering molecular markers/signatures that predict response to therapy or optimal drug dose for each patient.

Mechanisms of Trastuzumab resistance in ErbB2-driven breast cancer and newer opportunities to overcome therapy resistance

The Human Epidermal Growth Factor Receptor 2 (Her2, ErbB2 or Neu) is overexpressed in about 20 – 25% of breast cancers and is causally linked to oncogenesis, providing opportunities for targeted therapy. Trastuzumab (Herceptin^™, Genentech Inc, San Francisco, CA), a humanized monoclonal antibody against ErbB2, is a successful example of this concept and has vastly improved the response to treatment and overall survival in a majority of ErbB2+ breast cancer patients. However, lack of response in some patients as well as relapse during the course of therapy in others, continue to challenge researchers and clinicians alike towards a better understanding of the fundamental mechanisms of Trastuzumab action and resistance to treatment. The exact in vivo mechanism of action of Trastuzumab remains enigmatic, given its direct effects on the ErbB2 signaling pathway as well as indirect contributions from the immune system, by virtue of the ability of Trastuzumab to elicit Antibody-Dependent Cellular Cytotoxicity. Consequently, multiple mechanisms of resistance have been proposed. We present here a comprehensive review of our current understanding of the mechanisms, both of Trastuzumab action and clinical resistance to Trastuzumab-based therapies. We also review newer strategies (based on ErbB2 receptor biology) that are being explored to overcome resistance to Trastuzumab therapy.

The role of p27(Kip1) in dasatinib-enhanced paclitaxel cytotoxicity in human ovarian cancer cells

BACKGROUND

Less than 50% of ovarian cancers respond to paclitaxel. Effective strategies are needed to enhance paclitaxel sensitivity.

METHODS

A library of silencing RNAs (siRNAs) was used to identify kinases that regulate paclitaxel sensitivity in human ovarian cancer SKOv3 cells. The effect of dasatinib, an inhibitor of Src and Abl kinases, on paclitaxel sensitivity was measured in ovarian cancer cells and HEY xenografts. The roles of p27(Kip1), Bcl-2, and Cdk1 in apoptosis induced by dasatinib and paclitaxel were assessed using a terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, siRNA knockdown of gene expression, transfection with Bcl-2 and Cdk1 expression vectors, and flow cytometry. All statistical tests were two-sided.

RESULTS

Src family and Abl kinases were identified as modulators of paclitaxel sensitivity in SKOv3 cells. The siRNA knockdown of Src, Fyn, or Abl1 enhanced paclitaxel-mediated growth inhibition in ovarian cancer cells compared with a control siRNA. HEY cells treated with dasatinib plus paclitaxel formed fewer colonies than did cells treated with either agent alone. Treatment of HEY xenograft-bearing mice with dasatinib plus paclitaxel inhibited tumor growth more than treatment with either agent alone (average tumor volume per mouse, dasatinib + paclitaxel vs paclitaxel: 0.28 vs. 0.81 cm3, difference = 0.53 cm3, 95% confidence interval [CI] = 0.44 to 0.62 cm3, P = .014); dasatinib + paclitaxel vs. dasatinib: 0.28 vs. 0.55 cm3, difference = 0.27 cm3, 95% CI = 0.21 to 0.33 cm3, P = .035). Combined treatment induced more TUNEL-positive apoptotic cells than did either agent alone. The siRNA knockdown of p27(Kip1) decreased dasatinib- and paclitaxel-induced apoptosis compared with a negative control siRNA (sub-G1 fraction, control siRNA vs. p27(Kip1) siRNA: 42.5% vs. 20.1%, difference = 22.4%, 95% CI = 20.1% to 24.7%, P = .017). Studies with forced expression and siRNA knockdown of Bcl-2 and Cdk1 suggest that dasatinib-mediated induction of p27(Kip1) enhanced paclitaxel-induced apoptosis by negatively regulating Bcl-2 and Cdk1 expression.

CONCLUSION

Inhibition of Src family and Abl kinases with either siRNAs or dasatinib enhances paclitaxel sensitivity of ovarian cancer cells through p27(Kip1)-mediated suppression of Bcl-2 and Cdk1 expression.

Targeting chromosomal instability and tumour heterogeneity in HER2-positive breast cancer

Chromosomal instability (CIN) is a common cause of tumour heterogeneity and poor prognosis in solid tumours and describes cell-cell variation in chromosome structure or number across a tumour population. In this article we consider evidence suggesting that CIN may be targeted and may influence response to distinct chemotherapy regimens, using HER2-positive breast cancer as an example. Pre-clinical models have indicated a role for HER2 signalling in initiating CIN and defective cell-cycle control, and evidence suggests that HER2-targeting may attenuate this process. Anthracyclines and platinum agents may target tumours with distinct patterns of karyotypic complexity, whereas taxanes may have preferential activity in tumours with relative chromosomal stability. A greater understanding of karyotypic complexity and identification of methods to directly examine and target CIN may support novel strategies to improve outcome in cancer.

Induction of MUC5AC mucin by conjugated bile acids in the esophagus involves the phosphatidylinositol 3-kinase/protein kinase C/activator protein-1 pathway

BACKGROUND

Bile reflux contributes to the development of esophageal injury and neoplasia. The mucin 5AC (MUC5AC) is absent in the normal squamous epithelium of the esophagus but is strongly expressed in Barrett esophagus (BE). The objective of this study was to determine whether and how bile acids influence the expression of MUC5AC in the esophagus.

METHODS

MUC5AC expression was studied by immunohistochemistry and immunoblotting in human tissues, in tissues from a rat model of BE, and in SKGT-4 cultured esophageal epithelial cells. MUC5AC transcription was studied by real-time polymerase chain reaction and transient transfection assays.

RESULTS

MUC5AC was absent from normal squamous epithelium but was present in 100% of Barrett specimens and in 61.5% of human esophageal adenocarcinoma tissues that were examined. MUC5AC protein expression was induced to a greater degree by conjugated bile acids than by unconjugated bile acids, and this occurred at the transcriptional level. In the rat reflux model, MUC5AC mucin was expressed abundantly in tissues of BE stimulated by duodenoesophageal reflux. Conjugated bile acids induced AKT phosphorylation in SKGT-4 cells but had no effect on extracellular signal-regulated protein kinases 1 and 2, c-Jun N-terminal kinase, or protein-38 kinase phosphorylation. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and a dominant-negative protein kinase C (AKT) construct prevented the induction of MUC5AC by conjugated bile acids. Transactivation of AP-1 by conjugated bile acids coincided with MUC5AC induction, and cotransfection with a dominant-negative activator protein-1 (AP-1) vector decreased MUC5AC transcription and its induction.

CONCLUSIONS

Conjugated bile acids in the bile refluxate contribute to MUC5AC induction in the esophagus. This occurs at the level of transcription and involves activation of the PI3K/AKT/AP-1 pathway.

Dasatinib induces autophagic cell death in human ovarian cancer

BACKGROUND

Dasatinib, an inhibitor of Src/Abl family kinases, can inhibit tumor growth of several solid tumors. However, the effect and mechanism of action of dasatinib in human ovarian cancer cells remains unknown.

METHODS

Dasatinib-induced autophagy was determined by acridine orange staining, punctate localization of GFP-LC3, LC3 protein blotting, and electron microscopy. Significance of beclin 1, AKT, and Bcl-2 in dasatinib-induced autophagy and growth inhibition was assayed by small interfering RNA (siRNA) silencing and/or overexpression of the gene of interest.

RESULTS

Dasatinib inhibited cell growth by inducing little apoptosis, but substantial autophagy in SKOv3 and HEY ovarian cancer cells. In vivo studies showed dasatinib inhibited tumor growth and induced both autophagy and apoptosis in a HEY xenograft model. Knockdown of beclin 1 and Atg12 expression with their respective siRNAs diminished dasatinib-induced autophagy, whereas knockdown of p27Kip1 with specific siRNAs did not. Small hairpin RNA knockdown of beclin 1 expression reduced dasatinib-induced autophagy and growth inhibition. Dasatinib reduced the phosphorylation of AKT, mTOR, p70S6K, and S6 kinase expression. Constitutive expression of AKT1 and AKT2 inhibited dasatinib-induced autophagy in both HEY and SKOv3 cells. Dasatinib also reduced Bcl-2 expression and activity. Overexpression of Bcl-2 partially prevented dasatinib-induced autophagy.

CONCLUSIONS

Dasatinib induces autophagic cell death in ovarian cancer that partially depends on beclin 1, AKT, and Bcl-2. These results may have implications for clinical use of dasatinib.

HER2-positive male breast cancer: an update

Although rare, male breast cancer (MBC) remains a substantial cause for morbidity and mortality in men. Based on age frequency distribution, age-specific incidence rate pattern, and prognostic factor profiles, MBC is considered similar to postmenopausal breast cancer (BC). Compared with female BC (FBC), MBC cases are more often hormonal receptor (estrogen receptor/progesterone receptor [ER/PR]) positive and human epidermal growth factor receptor 2 (HER2) negative. Treatment of MBC patients follows the same indications as female postmenopausal with surgery, systemic therapy, and radiotherapy. To date, ER/PR and HER2 status provides baseline predictive information used in selecting optimal adjuvant/neoadjuvant therapy and in the selection of therapy for recurrent or metastatic disease. HER2 represents a very interesting molecular target and a number of compounds (trastuzumab [Herceptin®; F. Hoffmann-La Roche, Basel, Switzerland] and lapatinib [Tykerb®, GlaxoSmithKline, London, UK]) are currently under clinical evaluation. Particularly, trastuzumab, a monoclonal antibody which selectively binds the extracellular domain of HER2, has become an important therapeutic agent for women with HER2-positive (HER2+) BC. Currently, data regarding the use of trastuzumab in MBC patients is limited and only few case reports exist. In all cases, MBC patients received trastuzumab concomitantly with other drugs and no severe toxicity above grade 3 was observed. However, MBC patients that would be candidate for trastuzumab therapy (ie, HER2+/ER+ or HER2+/ER- MBCs) represent only a very small percentage of MBC cases. This is noteworthy, when taking into account that trastuzumab is an important and expensive component of systemic BC therapy. Since there is no data supporting the fact that response to therapy is different for men or women, we concluded that systemic therapy in MBC should be considered on the same basis as for FBC. Particularly in male patients, trastuzumab should be considered exclusively for advanced disease or high-risk HER2+ early BCs. On the other hand, lapatinib (Tykerb), a novel oral dual tyrosine kinase inhibitor that targets both HER2 and epidermal growth factor receptor, may represent an interesting and promising therapeutic agent for trastuzumab-resistant MBC patients.

Overexpression of high-mobility group box 2 is associated with tumor aggressiveness and prognosis of hepatocellular carcinoma

PURPOSE

We investigated the expression of high-mobility group box 2 (HMGB2) in patients with hepatocellular carcinoma (HCC) and its clinical effects with underlying mechanisms.

EXPERIMENTAL DESIGN

HMGB2 mRNA levels were measured in 334 HCC patients by real-time reverse transcription-PCR and HMGB2 protein levels in 173 HCC patients by immunohistochemical studies. The HMGB2 expression level was measured by Western blotting for three HCC cell lines. To clarify the precise role of HMGB2 on cell proliferation, we did in vitro analysis with expression vectors and small interfering RNAs.

RESULTS

HMGB2 mRNA and protein expression were significantly higher in HCC than in noncancerous surrounding tissues (P < 0.0001) and showed a positive correlation (ρ = 0.35, P < 0.001). HMGB2 overexpression was significantly correlated with shorter overall survival time, both at mRNA (P = 0.0054) and protein level (P = 0.023). Moreover, HMGB2 mRNA level was an independent prognostic factor for overall survival in a multivariate analysis (P = 0.0037). HMGB2 knockdown by small interfering RNAs decreased cell proliferation, and overexpression of HMGB2 by expression vectors diminished cisplatin- and etoposide-induced cell death.

CONCLUSIONS

Our clinical and in vitro data suggest that HMGB2 plays a significant role in tumor development and prognosis of HCC. These results can partly be explained by altered cell proliferations by HMGB2 associated with the antiapoptotic pathway.

The therapeutic effect of anti-HER2/neu antibody depends on both innate and adaptive immunity

Anti-HER2/neu antibody therapy is reported to mediate tumor regression by interrupting oncogenic signals and/or inducing FcR-mediated cytotoxicity. Here, we demonstrate that the mechanisms of tumor regression by this therapy also require the adaptive immune response. Activation of innate immunity and T cells, initiated by antibody treatment, was necessary. Intriguingly, the addition of chemotherapeutic drugs, although capable of enhancing the reduction of tumor burden, could abrogate antibody-initiated immunity leading to decreased resistance to rechallenge or earlier relapse. Increased influx of both innate and adaptive immune cells into the tumor microenvironment by a selected immunotherapy further enhanced subsequent antibody-induced immunity, leading to increased tumor eradication and resistance to rechallenge. This study proposes a model and strategy for anti-HER2/neu antibody-mediated tumor clearance.

Comparative Membranome expression analysis in primary tumors and derived cell lines

Despite the wide use of cell lines in cancer research, the extent to which their surface properties correspond to those of primary tumors is poorly characterized. The present study addresses this problem from a transcriptional standpoint, analyzing the expression of membrane protein genes--the Membranome--in primary tumors and immortalized in-vitro cultured tumor cells. 409 human samples, deriving from ten independent studies, were analyzed. These comprise normal tissues, primary tumors and tumor derived cell lines deriving from eight different tissues: brain, breast, colon, kidney, leukemia, lung, melanoma, and ovary. We demonstrated that the Membranome has greater power than the remainder of the transcriptome when used as input for the automatic classification of tumor samples. This feature is maintained in tumor derived cell lines. In most cases primary tumors show maximal similarity in Membranome expression with cell lines of same tissue origin. Differences in Membranome expression between tumors and cell lines were analyzed also at the pathway level and biological themes were identified that were differentially regulated in the two settings. Moreover, by including normal samples in the analysis, we quantified the degree to which cell lines retain the Membranome up- and down-regulations observed in primary tumors with respect to their normal counterparts. We showed that most of the Membranome up-regulations observed in primary tumors are lost in the in-vitro cultured cells. Conversely, the majority of Membranome genes down-regulated upon tumor transformation maintain lower expression levels also in the cell lines. This study points towards a central role of Membranome genes in the definition of the tumor phenotype. The comparative analysis of primary tumors and cell lines identifies the limits of cell lines as a model for the study of cancer-related processes mediated by the cell surface. Results presented allow for a more rational use of the cell lines as a model of cancer.

Understanding the mechanisms behind trastuzumab therapy for human epidermal growth factor receptor 2-positive breast cancer

PURPOSE

Targeted therapy with the humanized monoclonal antibody trastuzumab has become a mainstay for human epidermal growth factor receptor 2 (HER2) -positive breast cancer (BC). The mechanisms of action of trastuzumab have not been fully elucidated, and data available to date are reviewed here. The impact of the mechanisms of action on clinical benefit also is discussed.

METHODS

An extensive literature review of trastuzumab and proposed mechanisms of action was performed.

RESULTS

At least five potential extracellular and intracellular antitumor mechanisms of trastuzumab have been identified in the preclinical setting. These include activation of antibody-dependent cellular cytotoxicity, inhibition of extracellular domain cleavage, abrogation of intracellular signaling, reduction of angiogenesis, and decreased DNA repair. These effects lead to tumor cell stasis and/or death. Clinical benefit from trastuzumab-based therapy in both early and advanced BC has been demonstrated. The benefit of trastuzumab use beyond progression has also been shown, which indicates the need for continuous suppression of the HER2 pathway. Targeting both HER2, with various approaches, and other pathways may enhance the clinical benefit observed with trastuzumab and overcome potential resistance. Novel combinations include pertuzumab (a HER2 dimerization inhibitor), lapatinib (a HER1/HER2 tyrosine kinase inhibitor), bevacizumab (an antiangiogenic agent), tanespimycin (a heat shock protein inhibitor), antiestrogen therapies, and an antibody-drug conjugate (trastuzumab-DM1).

CONCLUSION

Trastuzumab is the foundation of care for patients with HER2-positive BC. Emerging data from studies of other targeted agents may provide alternative treatment combinations to maximize the clinical benefit from trastuzumab and prevent or delay resistance. The continued development of trastuzumab highlights promising treatment approaches for the future.

Comparative expression pathway analysis of human and canine mammary tumors

BACKGROUND

Spontaneous tumors in dog have been demonstrated to share many features with their human counterparts, including relevant molecular targets, histological appearance, genetics, biological behavior and response to conventional treatments. Mammary tumors in dog therefore provide an attractive alternative to more classical mouse models, such as transgenics or xenografts, where the tumour is artificially induced. To assess the extent to which dog tumors represent clinically significant human phenotypes, we performed the first genome-wide comparative analysis of transcriptional changes occurring in mammary tumors of the two species, with particular focus on the molecular pathways involved.

RESULTS

We analyzed human and dog gene expression data derived from both tumor and normal mammary samples. By analyzing the expression levels of about ten thousand dog/human orthologous genes we observed a significant overlap of genes deregulated in the mammary tumor samples, as compared to their normal counterparts. Pathway analysis of gene expression data revealed a great degree of similarity in the perturbation of many cancer-related pathways, including the 'PI3K/AKT', 'KRAS', 'PTEN', 'WNT-beta catenin' and 'MAPK cascade'. Moreover, we show that the transcriptional relationships between different gene signatures observed in human breast cancer are largely maintained in the canine model, suggesting a close interspecies similarity in the network of cancer signalling circuitries.

CONCLUSION

Our data confirm and further strengthen the value of the canine mammary cancer model and open up new perspectives for the evaluation of novel cancer therapeutics and the development of prognostic and diagnostic biomarkers to be used in clinical studies.

Mechanisms of drug combinations: interaction and network perspectives

Understanding the molecular mechanisms underlying synergistic, potentiative and antagonistic effects of drug combinations could facilitate the discovery of novel efficacious combinations and multi-targeted agents. In this article, we describe an extensive investigation of the published literature on drug combinations for which the combination effect has been evaluated by rigorous analysis methods and for which relevant molecular interaction profiles of the drugs involved are available. Analysis of the 117 drug combinations identified reveals general and specific modes of action, and highlights the potential value of molecular interaction profiles in the discovery of novel multicomponent therapies.

Overcoming resistance to tyrosine kinase inhibitors: lessons learned from cancer cells treated with EGFR antagonists

Tyrosine kinase inhibitors (TKIs) are effective anti-cancer therapies but resistance to these agents eventually develops. Several models of resistance to TKIs have been studied including resistance to EGFR inhibitors. Recent studies in EGFR-dependent A431 cells found upregulation of the IGF1R pathway as a mechanism to overcome blockade of EGFR. This was associated with amplification of IGF1R signaling and recovery of downstream PI3K-AKT activation. This work adds to a growing body of cell lines in culture that have provided insights into mechanisms of resistance that can be interrogated in primary tumors in patients. In this review, these model systems and their applicability to human cancers, as well as strategies to identify and overcome resistance to TKIs, are discussed.

Specific blockade of VEGF and HER2 pathways results in greater growth inhibition of breast cancer xenografts that overexpress HER2

We have previously reported that breast cancer cells which overexpress HER2 produce higher levels of VEGF than cells with low levels of HER2. This study tested the hypothesis that dual targeting of the VEGF (with VEGF-Trap) and HER2 (with trastuzumab) pathways would result in greater growth inhibition of HER2-overexpressing breast cancer xenografts than either agent alone. In this study we found that human and murine endothelial cells expressed high levels of VEGF receptors (VEGFR1, VEGFR2, & VEGFR3). VEGF-Trap decreased levels of secreted VEGF derived from both human and murine cells and effectively blocked VEGF-induced tyrosine phosphorylation of VEGFR2. VEGF-Trap as a single treatment inhibited tumor microvessel density (MVD), tumor vasculature, cell proliferation and tumor growth of BT474 xenografts in a dose-dependent manner from 2.5 mg/kg to 25 mg/kg. VEGF-Trap decreased levels of both human VEGF and PlGF protein in vivo. Trastuzumab as a single agent effectively inhibited BT474 tumor growth in a dose-dependent manner, associated with a decrease in human VEGF, tumor MVD and tumor cell proliferation. Treatment with a combination of VEGF-Trap (2.5-10 mg/kg) and trastuzumab (1 mg/kg) produced significantly greater inhibition of BT474 tumor growth than either individual agent, associated with greater inhibition of tumor MVD and tumor cell proliferation. Thus, VEGF-Trap in combination with trastuzumab produces superior growth inhibition of tumor xenografts which overexpress HER2, which may result from inhibition of both tumor angiogenesis and proliferation. Similar mechanisms may contribute to the clinical anti-tumor activity of trastuzumab in combination with inhibitors of VEGF signaling pathway in women with breast cancers which overexpress HER2.

Roles of human epidermal growth factor receptor 2, c-jun NH2-terminal kinase, phosphoinositide 3-kinase, and p70 S6 kinase pathways in regulation of cyclin G2 expression in human breast cancer cells

The CCNG2 gene that encodes the unconventional cyclin G2 was one of the few genes up-regulated on anti-human epidermal growth factor receptor 2 (HER2) antibody-mediated inhibition of HER2 signaling. The purpose of this study was to explore how HER2 signaling modulates cyclin G2 expression and the effect of elevated cyclin G2 on breast cancer cell growth. Treatment of breast cancer cells that overexpress HER2 (BT474, SKBr3, and MDAMB453) with the anti-HER2 antibody trastuzumab or its precursor 4D5 markedly up-regulated cyclin G2 mRNA in vitro and in vivo, as shown by real-time PCR. Immunoblot and immunofluorescence analysis with specific antibodies against cyclin G2 showed that anti-HER2 antibody significantly increased cyclin G2 protein expression and translocated the protein to the nucleus. Trastuzumab was not able to induce cyclin G2 expression in cells weakly expressing HER2 (MCF7) or in cells that had developed resistance to trastuzumab. Enforced expression of HER2 in T47D and MDAMB435 breast cancer cells reduced cyclin G2 levels. Collectively, these data suggest that HER2-mediated signaling negatively regulates cyclin G2 expression. Inhibition of phosphoinositide 3-kinase (LY294002), c-jun NH(2)-terminal kinase (SP600125), and mammalian target of rapamycin (mTOR)/p70 S6 kinase (p70S6K; rapamycin) increased cyclin G2 expression. In contrast, treatment with inhibitors of p38 mitogen-activated protein kinase (SB203580), mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 (U0126), or phospholipase Cgamma (U73122) did not affect cyclin G2 expression. Anti-HER2 antibody in combination with LY294002, rapamycin, or SP600125 induced greater cyclin G2 expression than either agent alone. Ectopic expression of cyclin G2 inhibited cyclin-dependent kinase 2 activity, Rb phosphorylation, cell cycle progression, and cellular proliferation without affecting p27(Kip1) expression. Thus, cyclin G2 expression is modulated by HER2 signaling through multiple pathways including phosphoinositide 3-kinase, c-jun NH(2)-terminal kinase, and mTOR signaling. The negative effects of cyclin G2 on cell cycle and cell proliferation, which occur without altering p27(Kip1) levels, may contribute to the ability of trastuzumab to inhibit breast cancer cell growth.

Rapamycin together with herceptin significantly increased anti-tumor efficacy compared to either alone in ErbB2 over expressing breast cancer cells

The objective of this study was to assess the anti-tumor efficacy of rapamycin alone or in combination with herceptin in breast cancer. A total of 20 human breast cancer lines were examined for expression of various receptor tyrosine kinases and activation of their down stream signaling molecules, as well as for their invasion and colony forming ability. The ErbB2 and PI3 kinase pathway inhibitors were tested for the inhibition on breast cancer cell growth and tumor development. Seven of the 20 lines displayed an elevated level of ErbB2, others had varying level of EGF, IGF-1 or insulin receptor. Over 30% of the lines also had constitutive activation of Akt and MAP kinase. The lines displayed a wide range of colony forming and invasion ability. The PI3 kinase pathway inhibitors LY294002 and rapamycin inhibited the colony forming ability of all of the lines with the ErbB2 overexpressing lines having a higher sensitivity. A similar trend was observed for inhibition of invasion by LY294002. Rapamycin alone and additively together with herceptin inhibited the breast cancer cell growth especially in ErbB2 overexpressing cells. Rapamycin and herceptin synergistically inhibited tumor growth and endpoint tumor load in a xenograft model using a MCF-7 subline and in a MMTV-ErbB2 transgenic model. Rapamycin and herceptin significantly reduced the level of cyclin D1 and D3 and increased the cleavage of caspase 3 suggesting an increased apoptosis. Our results suggest that rapamycin together with herceptin has an enhanced anti-cancer effect and could be developed as an improved therapeutic regimen for breast cancer.

Motexafin gadolinium modulates levels of phosphorylated Akt and synergizes with inhibitors of Akt phosphorylation

Motexafin gadolinium (MGd, Xcytrin) is a tumor-selective expanded porphyrin that targets oxidative stress-related proteins. MGd treatment of the follicular lymphoma-derived cell line HF-1 resulted in growth suppression and apoptosis whereas MGd treatment of the Burkitt's lymphoma-derived cell line Ramos resulted in growth suppression but not apoptosis. Because phosphorylation status of Akt/protein kinase B is regulated by oxidative stress, we monitored total and phosphorylated Akt (pAkt) in MGd-treated HF-1 and Ramos cells. Levels of pAkt increased within 30 minutes after MGd treatment of HF-1 but after 4 hours began to show a progressive decline to below baseline levels before cells underwent apoptosis. In MGd-treated Ramos cells, pAkt increased approximately 2-fold within 4 hours and remained persistently elevated. Because pAkt activates survival pathways, we determined if MGd-induced cell death could be enhanced by inhibiting phosphorylation of Akt. The addition of specific inhibitors of Akt phosphorylation (Akt inhibitor 1 or SH-5) reduced pAkt levels in MGd-treated HF-1 and Ramos cells and synergistically enhanced MGd-induced cell death. MGd was also evaluated in combination with celecoxib, an inhibitor of Akt phosphorylation, or docetaxel, a microtubule inhibitor that can decrease Akt phosphorylation. The combination of MGd/celecoxib or MGd/docetaxel resulted in decreased Akt phosphorylation and in synergistic cytotoxicity compared with either agent alone. These data point to a potential protective role for pAkt in MGd-induced apoptosis and suggest that MGd activity may be enhanced by combining it with agents that inhibit Akt phosphorylation.

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.

Effects of HER2-binding affibody molecules on intracellular signaling pathways

BACKGROUND

HER2, which is overexpressed in 25-30% of human breast cancers, is a tyrosine kinase receptor critical for the signal transduction network that regulates proliferation, migration and apoptosis of cells.

METHOD

We report the effects of two novel HER2-binding affibody molecules (Affibody), (ZHER2:4)2 and ZHER2:342, on intracellular signal transduction pathways (Erk1/2, Akt and PLCgamma1) using quantitative immunoblotting techniques and their biological effects in cell culture. The clinically approved antibody trastuzumab (Herceptin) was used as reference substance.

RESULTS

Our data showed that, although all substances target HER2, the effects on the receptor and signaling molecules differed. For example, HER2 phosphorylation was induced by trastuzumab and (ZHER2:4)2 but inhibited by ZHER2:342. The effects these substances had on signal transduction correlated to some degree with changes in growth and migration, e.g. (ZHER2:4)2 stimulated phosphorylation of Erk1/2 and PLCgamma1, as well as growth and migration, while ZHER2:342 did not. ZHER2:342 even inhibited phosphorylation of PLCgamma1 and migration.

CONCLUSION

Our data suggest that ZHER2:342 is a promising small agent (7 kDa) that may be used as an alternative, or complement, to trastuzumab. If radiolabelled, it can hopefully also be used for HER2 imaging and radionuclide therapy.

EGFR enhances Survivin expression through the phosphoinositide 3 (PI-3) kinase signaling pathway

The ErbB family of receptor tyrosine kinases includes the epidermal growth factor receptor (EGFR), p185/neu/c-erbB2, ErbB3, and ErbB4. Many of these receptors are overexpressed or amplified in various forms of cancers. Previous studies have indicated that activation of erbB molecules contributes to malignant transformation both by promoting cell proliferation through the mitogen-activated protein kinase (MAP kinase) signaling pathway and by preventing apoptosis through the Phosphoinositide 3 kinase (PI-3 kinase) pathway. Disabling erbB receptors converts malignant cells that were resistant to cell death caused by irradiation to cells that are sensitive to apoptosis. Here, we report that an activated form of EGFR can elevate the levels of Survivin, a member of the Inhibitor of Apoptosis Protein (IAP) family implicated in mitotic checkpoint control. Conversely, inactivation of the ErbB receptors reduces the expression levels of Survivin. Furthermore, we found that upregulation of Survivin by EGFR is dependent on the PI-3 kinase pathway but not on the MAP kinase pathway. Indeed, inhibition of PI-3 kinase can diminish Survivin at both the mRNA and the protein levels. Combined with previous findings that Survivin plays a role in control of chromosome segregation and that it is overexpressed in various cancers, our results suggest that EGFR may cause transformation by directly affecting mitosis and increasing chromosome instability.

Synergistic tumoricidal effect between celecoxib and adenoviral-mediated delivery of mda-7 in human breast cancer cells

BACKGROUND

Celecoxib, a selective cyclooxygenase 2 (COX-2) inhibitor, blocks growth and promotes apoptosis in breast cancer cells. The PI3K/Akt pathway is important in cell survival, and COX-2 and Akt might promote growth via a positive feedback loop. We have shown that adenoviral delivery of mda-7 (Ad-mda7) in breast cancer down-regulates Akt. We hypothesized that combining Ad-mda7 and celecoxib could mediate tumor suppression in COX-2 overexpressing breast cancer cells.

METHODS

Two COX-2 overexpressing human breast cancer cell lines (Her-18 and MDA-MB-436) were treated with celecoxib (20 micromol/L and 50 micromol/L) and Ad-mda7 (multiplicity of infection, 1000 and 2000 viral particles/cell). Adenovirus encoding the luciferase gene was used as a control. We assessed proliferation, cell cycle, apoptosis, prostaglandin E2 production, and changes in protein expression. Statistical analysis was performed by using the Student t test.

RESULTS

Regardless of HER-2/neu status, cell growth was markedly inhibited by celecoxib, Ad-mda7, and the combination compared with controls. Celecoxib + Ad-mda7 showed a greater than additive increase in cell death compared with either monotherapy (P < .05) and resulted in cell cycle block and apoptosis (P < .05). Both cell lines showed decreased prostaglandin E2 production after combination treatment compared with controls (P < .05), with decreased expression of COX-2, Akt, and phosphorylated Akt (P < .05).

CONCLUSIONS

Enhanced antitumor activity is achieved in breast cancer by combining celecoxib and Ad-mda7 regardless of HER-2/neu status. This occurs through inhibition of COX-2 expression and down-regulation of Akt. Combining Ad-mda7 with COX-2 inhibition provides a novel method of treatment in breast cancer.