Anti-HER2 antibody trastuzumab inhibits CDK2-mediated NPAT and histone H4 expression via the PI3K pathway

Adavosertib Enhances Antitumor Activity of Trastuzumab Deruxtecan in HER2-Expressing Cancers

PURPOSE

Cyclin E (CCNE1) has been proposed as a biomarker of sensitivity to adavosertib, a Wee1 kinase inhibitor, and a mechanism of resistance to HER2-targeted therapy.

EXPERIMENTAL DESIGN

Copy number and genomic sequencing data from The Cancer Genome Atlas and MD Anderson Cancer Center databases were analyzed to assess ERBB2 and CCNE1 expression. Molecular characteristics of tumors and patient-derived xenografts (PDX) were assessed by next-generation sequencing, whole-exome sequencing, fluorescent in situ hybridization, and IHC. In vitro, CCNE1 was overexpressed or knocked down in HER2+ cell lines to evaluate drug combination efficacy. In vivo, NSG mice bearing PDXs were subjected to combinatorial therapy with various treatment regimens, followed by tumor growth assessment. Pharmacodynamic markers in PDXs were characterized by IHC and reverse-phase protein array.

RESULTS

Among several ERBB2-amplified cancers, CCNE1 co-amplification was identified (gastric 37%, endometroid 43%, and ovarian serous adenocarcinoma 41%). We hypothesized that adavosertib may enhance activity of HER2 antibody-drug conjugate trastuzumab deruxtecan (T-DXd). In vitro, sensitivity to T-DXd was decreased by cyclin E overexpression and increased by knockdown, and adavosertib was synergistic with topoisomerase I inhibitor DXd. In vivo, the T-DXd + adavosertib combination significantly increased γH2AX and antitumor activity in HER2 low, cyclin E amplified gastroesophageal cancer PDX models and prolonged event-free survival (EFS) in a HER2-overexpressing gastroesophageal cancer model. T-DXd + adavosertib treatment also increased EFS in other HER2-expressing tumor types, including a T-DXd-treated colon cancer model.

CONCLUSIONS

We provide rationale for combining T-DXd with adavosertib in HER2-expressing cancers, especially with co-occuring CCNE1 amplifications. See related commentary by Rolfo et al., p. 4317.

Decreased TMEM40 expression is associated with malignant behavior of cutaneous squamous cell carcinoma and inhibits tumor progression

Cutaneous squamous cell carcinoma (CSCC) is one of the most common types of skin cancer in humans worldwide. The identification and characterization of cancer-associated transmembrane proteins are important for understanding the molecular biology of CSCC. The aim of the present study was to evaluate the expression pattern of transmembrane protein 40 (TMEM40) in CSCC and its clinical significance. The underlying mechanisms were also examined. Reverse transcription-quantitative PCR, western blot and immunohistochemistry analysis were used to determine the relative expression of TMEM40 in CSCC cell lines and clinical tissue samples. The effect of TMEM40 gene silencing on cell proliferation was also evaluated using Cell Counting Kit-8 assays. Wound healing assays, flow cytometry and Transwell assays were used to explore the migration, cell cycle distribution/apoptosis and invasion of CSCC cells following TMEM40 silencing, respectively. In the present study, increased TMEM40 expression was observed in CSCC tissue samples, compared with normal skin, and TMEM40 expression was associated with large tumor size in patients with CSCC. In vitro functional assays indicated that TMEM40 was involved in the regulation of A431 and SCL1 cell growth through its effects on the cell cycle and apoptosis. Silencing TMEM40 in A431 and SCL1 cells resulted in cell cycle arrest at the G₀/G₁ phase and promoted apoptosis. In addition, migration and invasion were significantly inhibited following silencing of TMEM40 expression in CSCC cells. Taken together, the results of the present study indicated that reduced TMEM40 expression could inhibit CSCC development and that TMEM40 may represent a therapeutic target in CSCC.

MicroRNAs in cancer drug resistance: Basic evidence and clinical applications

Development of drug resistance has considerably limited the efficacy of cancer treatments, including chemotherapy and targeted therapies. Hence, understanding the molecular mechanisms underpinning the innate or the acquired resistance to these therapies is critical to improve drug efficiency and clinical outcomes. Several studies have implicated microRNAs (miRNA) in this process. MiRNAs repress gene expression by specific binding to complementary sequences in the 3' region of target messenger RNAs (mRNAs), followed by target mRNA degradation or blocked translation. By targeting molecules specific to a particular pathway within tumor cells, the new generation of cancer treatment strategies has shown significant advantages over conventional chemotherapy. However, the long-term efficacy of targeted therapies often remains poor, because tumor cells develop resistance to such therapeutics. Targeted therapies often involve monoclonal antibodies (mAbs), such as those blocking the ErB/HER tyrosine kinases, epidermal growth factor receptor (cetuximab) and HER2 (trastuzumab), and those inhibiting vascular endothelial growth factor receptor signaling (e.g., bevacizumab). Even though these are among the most used agents in tumor medicine, clinical response to these drugs is reduced due to the emergence of drug resistance as a result of toxic effects in the tumor microenvironment. Research on different types of human cancers has revealed that aberrant expression of miRNAs promotes resistance to the aforementioned drugs. In this study, we review the mechanisms of tumor cell resistance to mAb therapies and the role of miRNAs therein. Emerging treatment strategies combine therapies using innovative miRNA mimics or antagonizers with conventional approaches to maximize outcomes of patients with cancer.

HER2 in Breast Cancer Stemness: A Negative Feedback Loop towards Trastuzumab Resistance

HER2 receptor tyrosine kinase that is overexpressed in approximately 20% of all breast cancers (BCs) is a poor prognosis factor and a precious target for BC therapy. Trastuzumab is approved by FDA to specifically target HER2 for treating HER2+ BC. However, about 60% of patients with HER2+ breast tumor develop de novo resistance to trastuzumab, partially due to the loss of expression of HER2 extracellular domain on their tumor cells. This is due to shedding/cleavage of HER2 by metalloproteinases (ADAMs and MMPs). HER2 shedding results in the accumulation of intracellular carboxyl-terminal HER2 (p95HER2), which is a common phenomenon in trastuzumab-resistant tumors and is suggested as a predictive marker for trastuzumab resistance. Up-regulation of the metalloproteinases is a poor prognosis factor and is commonly seen in mesenchymal-like cancer stem cells that are risen during epithelial to mesenchymal transition (EMT) of tumor cells. HER2 cleavage during EMT can explain why secondary metastatic tumors with high percentage of mesenchymal-like cancer stem cells are mostly resistant to trastuzumab but still sensitive to lapatinib. Importantly, many studies report HER2 interaction with oncogenic/stemness signaling pathways including TGF-β/Smad, Wnt/β-catenin, Notch, JAK/STAT and Hedgehog. HER2 overexpression promotes EMT and the emergence of cancer stem cell properties in BC. Increased expression and activation of metalloproteinases during EMT leads to proteolytic cleavage and shedding of HER2 receptor, which downregulates HER2 extracellular domain and eventually increases trastuzumab resistance. Here, we review the hypothesis that a negative feedback loop between HER2 and stemness signaling drives resistance of BC to trastuzumab.

The impact of concomitant genomic alterations on treatment outcome for trastuzumab therapy in HER2-positive gastric cancer

Clinical benefit from trastuzumab and other anti-human epidermal growth factor receptor-2 (HER2) therapies in patients with HER2-positive gastric cancer (GC) remains limited by primary or acquired resistance. We aimed to investigate the impact of concomitant molecular alterations to HER2 amplification on the clinical outcome of trastuzumab-treated patients. Using immunohistochemistry (IHC), copy number variations (CNVs), and Ion Ampliseq Cancer Panel, we analyzed the status of concomitant alterations in 50 HER2-positive advanced GC patients treated with trastuzumab in combination with other chemotherapeutic agents. The percentage of tumor samples with at least one concomitant alteration was 40% as assessed by IHC, 16% by CNVs, and 64% by Ampliseq sequencing. Median progression-free survival (PFS) was 8.0 months (95% confidence interval, 4.8-11.3). Patients were divided into two subgroups according to PFS values with a cutoff point of 8 months; results show that concomitant genomic alterations do not correlate with trastuzumab response. However, CNVs of CCNE1 significantly correlated (p < 0.05) with a shorter survival time. Our findings indicate that additional alterations implemented for prediction of clinical benefit from HER2-targeting agents in GC remained unclear. Further studies will be needed to elucidate the role of each specific biomarker and to optimize therapeutic approaches.

Pertuzumab in combination with trastuzumab and docetaxel for HER2-positive metastatic breast cancer

Overexpression of HER2 - found in approximately 15-20% of all breast cancers - is a negative prognostic factor. Although trastuzumab significantly improves the prognosis of HER2-positive breast cancer, half of the patients with metastatic breast cancer experience disease progression within 1 year. Pertuzumab is a novel HER2-targeted humanized monoclonal antibody that binds to the dimerization domain of HER2 and acts synergically with trastuzumab in inhibiting tumor progression. The CLEOPATRA trial demonstrated that adding pertuzumab to trastuzumab plus docetaxel significantly prolonged progression-free survival and overall survival without increasing severe adverse events. Conclusively, pertuzumab was approved by the US FDA in June 2012 for use in combination with trastuzumab and docetaxel for the treatment of patients with HER2-positive metastatic breast cancer. Furthermore, various clinical trials to evaluate the efficacy and safety of pertuzumab combined with other cytotoxic agents are ongoing at present. Thus, pertuzumab has been becoming important for the treatment of patients with HER2-positive metastatic breast cancer.

Nek2 and Plk4: prognostic markers, drivers of breast tumorigenesis and drug resistance

The Nek2 and Plk4 kinases serve as crucial regulators of mitotic processes such as the centrosome duplication cycle and spindle assembly. Deregulation of these processes can trigger chromosome instability and aneuploidy, which are hallmarks of many solid tumors, including breast cancer. Emerging data from the literature illustrated various functions of Nek2 in breast cancer models, with compelling evidence of its prognostic value in breast tumors. The two kinases control distinct steps in the centrosome-centriole cycle and their dysregulation lead to centrosome amplification, marked by the presence of more than two centrosomes within the cell. We found single or composite overexpression of these kinases in breast tumor samples, regardless of subtype, which strongly associated with poor prognosis. Interestingly, in a panel of established cell lines, both kinases are highly expressed in Her2-positive breast cancer cells exhibiting centrosome amplification and trastuzumab resistance. In summary, it appears that Nek2 and Plk4 might synergize to promote breast tumorigenesis and may also be involved in tamoxifen and trastuzumab resistance.

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.

Functional coupling of transcription factor HiNF-P and histone H4 gene expression during pre- and post-natal mouse development

Transcription factor Histone Nuclear Factor P (HiNF-P; gene symbol Hinfp) mediates cell cycle control of histone H4 gene expression to support the packaging of newly replicated DNA as chromatin. The HiNF-P/p220(NPAT) complex controls multiple H4 genes in established human cell lines and is critical for cell proliferation. The mouse Hinfp(LacZ) null allele causes early embryonic lethality due to a blastocyst defect. However, neither Hinfp function nor its temporal expression relative to histone H4 genes during fetal development has been explored. Here, we establish that expression of Hinfp is biologically coupled with expression of twelve functional mouse H4 genes during pre- and post-natal tissue-development. Both Hinfp and H4 genes are robustly expressed at multiple embryonic (E) days (from E5.5 to E15.5), coincident with ubiquitous LacZ staining driven by the Hinfp promoter. Five highly expressed mouse H4 genes (Hist1h4d, Histh4f, Hist1h4m and Hist2h4) account for >90% of total histone H4 mRNA throughout development. Post-natal expression of H4 genes in mice is most evident in lung, spleen, thymus and intestine, and with few exceptions (e.g., adult liver) correlates with Hinfp gene expression. Histone H4 gene expression decreases butHinfp levels remain constitutive upon cell growth inhibition in culture. The in vivo co-expression of Hinfp and histone H4 genes is consistent with the biological function of Hinfp as a principal transcriptional regulator of histone H4 gene expression during mouse development.

Cyclin E amplification/overexpression is a mechanism of trastuzumab resistance in HER2+ breast cancer patients

Clinical benefits from trastuzumab and other anti-HER2 therapies in patients with HER2 amplified breast cancer remain limited by primary or acquired resistance. To identify potential mechanisms of resistance, we established trastuzumab-resistant HER2 amplified breast cancer cells by chronic exposure to trastuzumab treatment. Genomewide copy-number variation analyses of the resistant cells compared with parental cells revealed a focal amplification of genomic DNA containing the cyclin E gene. In a cohort of 34 HER2(+) patients treated with trastuzumab-based therapy, we found that cyclin E amplification/overexpression was associated with a worse clinical benefit (33.3% compared with 87.5%, P < 0.02) and a lower progression-free survival (6 mo vs. 14 mo, P < 0.002) compared with nonoverexpressing cyclin E tumors. To dissect the potential role of cyclin E in trastuzumab resistance, we studied the effects of cyclin E overexpression and cyclin E suppression. Cyclin E overexpression resulted in resistance to trastuzumab both in vitro and in vivo. Inhibition of cyclin E activity in cyclin E-amplified trastuzumab resistant clones, either by knockdown of cyclin E expression or treatment with cyclin-dependent kinase 2 (CDK2) inhibitors, led to a dramatic decrease in proliferation and enhanced apoptosis. In vivo, CDK2 inhibition significantly reduced tumor growth of trastuzumab-resistant xenografts. Our findings point to a causative role for cyclin E overexpression and the consequent increase in CDK2 activity in trastuzumab resistance and suggest that treatment with CDK2 inhibitors may be a valid strategy in patients with breast tumors with HER2 and cyclin E coamplification/overexpression.

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.

A novel interaction between HER2/neu and cyclin E in breast cancer

HER2/neu (HER2) and cyclin E are important prognostic indicators in breast cancer. Since both are involved in cell cycle regulation we investigated whether there was a direct interaction between the two. HER2 and cyclin E expression levels were determined in 395 breast cancer patients. Patients with HER2-overexpression and high levels of cyclin E had decreased 5-year disease-specific survival compared with low levels of cyclin E (14% versus 89%, P < .0001) In vitro studies were performed in which HER2-mediated activity in HER2-overexpressing breast cancer cell lines was downregulated by transfection with HER2 siRNA or treatment with trastuzumab. Cyclin E expression levels were determined, and functional effects investigated using kinase assays, MTT assays to assess cell viability as a marker of proliferation, and FACS analysis to determine cell cycle profiles. Decreased HER2-mediated signaling resulted in decreased expression of cyclin E, particularly the low molecular weight (LMW) isoforms. Decreased HER2 and LMW cyclin E expression had functional effects, including decreased cyclin E-associated kinase activity and decreased proliferation, due to increased apoptosis and an increased accumulation of cells in the G1 phase. In vivo studies performed in a HER2-overexpressing breast cancer xenograft model confirmed the effects of trastuzumab on cyclin E expression. Given the relationship between HER2 and cyclin E, in vitro clonogenic assays were performed to assess combination therapy targeting both proteins. Isobologram analysis showed a synergistic interaction between the two agents (trastuzumab targeting HER2 and roscovitine targeting cyclin E). Taken together, these studies demonstrate that HER2-mediated signaling effects LMW cyclin E expression, which in turn effects cell cycle regulation. LMW cyclin E has prognostic and predictive roles in HER2-overexpressing breast cancer, warranting further study of its potential as a therapeutic target.

Novel anticancer targets: revisiting ERBB2 and discovering ERBB3

Aberrant receptor expression or functioning of the epidermal growth factor receptor (Erbb) family plays a crucial part in the development and evolution of cancer. Inhibiting the signalling activity of individual receptors in this family has advanced the treatment of a range of human cancers. In this Review we re-evaluate the role of two important family members, ERBB2 (also known as HER2) and ERBB3 (also known as HER3), and explore the mechanisms of action and preclinical and clinical data for new therapies that target signalling through these pivotal receptors. These new therapies include tyrosine kinase inhibitors, antibody-chemotherapy conjugates, heat-shock protein inhibitors and antibodies that interfere with the formation of ERBB2-ERBB3 dimers.

Single-chain antibody/activated BID chimeric protein effectively suppresses HER2-positive tumor growth

BH3-interacting domain death agonist (BID) is a crucial element in death signaling pathways and is recognized as an intracellular link connecting the intrinsic mitochondrial apoptotic and extrinsic death receptor-mediated apoptotic pathways. Herein, we describe experiments conducted with a fusion protein, which was generated by fusing a human epidermal growth factor receptor-2 (HER2)-specific single-chain antibody with domain II of Pseudomonas exotoxin A and the truncated active BID (tBID). These experiments extend our previous work on several other immuno-proapoptotic proteins. Specifically, by excluding cells with undetectable HER2, we showed that the secreted immuno-tBID molecule selectively recognized and killed HER2-overexpressing tumor cells in vitro by attacking their mitochondria and inducing their apoptotic death. This apoptosis could only be inhibited partially by caspase pan-inhibitor zVAD and mitochondrial protector TAT-BH4. Subsequently, we transferred the immuno-tbid gene into BALB/c athymic mice bearing HER2-positive tumors together with other immuno-proapoptotic proteins using i.m. injections of liposome-encapsulated vectors. The expression of the immuno-tbid gene suppressed tumor growth and prolonged animal survival significantly. We also shortened the translocation domain of Pseudomonas exotoxin A II to only 10-amino acid sequence, which were crucial for furin cleavage. The new recombinant molecule retained the translocation efficiency and the ability of specific killing HER2-positive tumor cells. Our data showed that, compared with the toxins employed before, the chimeric immuno-tBID molecule can not only specifically recognize HER2-positive tumor cells but also certainly induce apoptosis even in the presence of zVAD and TAT-BH4, thereby suggesting an alternative approach to treating HER2/neu-positive tumors.

Cutaneous vasculitis in breast cancer treated with chemotherapy

A patient from the University of California Los Angeles Medical Center who developed cutaneous vasculitis during the course of treatment for metastatic breast cancer is presented (status: post-lumpectomy and radiation therapy). Since the onset of vasculitis occurred during the course of therapy for the neoplasm, it was difficult to differentiate between drug-induced vasculitis and paraneoplastic vasculitis. The patient had been exposed to medications including gabapentin, methimazole, trastuzumab, fulvestrant, and letrozole - which could cause endothelial cell toxicity. Drug-induced small vessel vasculitis usually attacks the skin or subcutaneous parts of the skin. In cancer therapy, there have been case reports that hormonal drugs such as estrogen receptor antagonists, aromatase inhibitors, and epidermal growth factor receptor (EGFR) inhibitors can induce cutaneous vasculitis. On the other hand, paraneoplastic syndromes manifested as cutaneous vasculitis have been documented, possibly mediated by unknown immunological mechanisms associated with the tumor such as formation of immune complexes, direct antibody-mediated effects on endothelial cells, or direct effects of tumor cells on the vascular wall. Some patients with drug-induced cutaneous vasculitis have antineutrophil cytoplasm antibodies (ANCA) directed to one or more neutrophil cytoplasm antigens - the most common being granule protein myeloperoxidase (MPO), human leukocyte elastase (HLE), cathepsin G and lactoferrin. Some patients also have antibodies against histones and antiphospholipid. Serologic testing and measurements suggest an influence of therapy on vasculitis, yet the lack of sensitivity and specificity for a biomarker in endothelial injury indicate the need to search and evaluate new markers for improved predictive value of the tests, and to provide guidance in therapy.

Breast cancer related proteins are present in saliva and are modulated secondary to ductal carcinoma in situ of the breast

OBJECTIVE

The objective of this study was to determine if protein-by-products secondary to cancer related oncogenes appear in the saliva of breast cancer patients.

METHODS

Three pooled (n = 10 subjects/pool) stimulated whole saliva specimens from women were analyzed. One pooled specimen was from healthy women, another pooled specimen from women diagnosed with a benign breast tumor and the other one pooled specimen was from women diagnosed with ductal carcinoma in situ (DCIS). Differential expression of proteins was measured by isotopically tagging proteins in the tumor groups and comparing them to the healthy control group. Experimentally, saliva from each of the pooled samples was trypsinized and the peptide digests labeled with the appropriate iTRAQ reagent. Labeled peptides from each of the digests were combined and analyzed by reverse phase (C18) capillary chromatography on an Applied Biosystems QStar LC-MS/MS mass spectrometer equipped with an LC-Packings HPLC.

RESULTS

The results of the salivary analyses in this population of patients yielded approximately 130 proteins in the saliva specimens. Forty-nine proteins were differentially expressed between the healthy control pool and the benign and cancer patient groups.

CONCLUSIONS

The study suggests that saliva is a fluid suffused with solubilized by-products of oncogenic expression and that these proteins may be modulated secondary to DCIS. Additionally, there may be salivary protein profiles that are unique to both DCIS and fibroadenoma tumors.

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.

Combinatorial RNAi for quantitative protein network analysis

The elucidation of cross-talk events between intersecting signaling pathways is one main challenge in biological research. The complexity of protein networks, composed of different pathways, requires novel strategies and techniques to reveal relevant interrelations. Here, we established a combinatorial RNAi strategy for systematic single, double, and triple knockdown, and we measured the residual mRNAs and proteins quantitatively by quantitative real-time PCR and reverse-phase protein arrays, respectively, as a prerequisite for data analysis. Our results show that the parallel knockdown of at least three different genes is feasible while keeping both untargeted silencing and cytotoxicity low. The technique was validated by investigating the interplay of tyrosine kinase receptor ErbB2 and its downstream targets Akt-1 and MEK1 in cell invasion. This experimental approach combines multiple gene knockdown with a subsequent quantitative validation of reduced protein expression and is a major advancement toward the analysis of signaling pathways in systems biology.

relocating job wise? A mathematical model separates quantitatively the cytostatic and cytotoxic effects of a HER2 tyrosine kinase inhibitor

BACKGROUND

Oncogene signaling is known to deregulate cell proliferation resulting in uncontrolled growth and cellular transformation. Gene amplification and/or somatic mutations of the HER2/Neu (ErbB2) proto-oncogene occur in approximately 20% of breast cancers. A therapeutic strategy that has been used to block HER2 function is the small molecule tyrosine kinase inhibitor lapatinib. Using human mammary epithelial cells that overexpress HER2, we determined the anti-proliferative effect of lapatinib through measuring the total cell number and analyzing the cell cycle distribution. A mathematical model was used to interpret the experimental data.

RESULTS

The model suggests that lapatinib acts as expected by slowing the transition through G1 phase. However, the experimental data indicated a previously unreported late cytotoxic effect, which was incorporated into the model. Both effects depend on the dosage of the drug, which shows saturation kinetics.

CONCLUSION

The model separates quantitatively the cytostatic and cytotoxic effects of lapatinib and may have implications for preclinical studies with other anti-oncogene therapies.