Amplified expression of the HER2/ERBB2 oncogene induces resistance to tumor necrosis factor alpha in NIH 3T3 cells

KAT6A amplifications are associated with shorter progression-free survival and overall survival in patients with endometrial serous carcinoma

Somatic copy number alterations (CNA) are common in endometrial serous carcinoma (ESC). We used the Tumor Cancer Genome Atlas Pan Cancer dataset (TCGA Pan Can) to explore the impact of somatic CNA and gene expression levels (mRNA) of cancer-related genes in ESC. Results were correlated with clinico-pathologic parameters such as age of onset, disease stage, progression-free survival (PFS) and overall survival (OS) (n = 108). 1,449 genes with recurrent somatic CNA were identified, observed in 10% or more tumor samples. Somatic CNA and mRNA expression levels were highly correlated (r> = 0.6) for 383 genes. Among these, 45 genes were classified in the Tier 1 category of Cancer Genome Census-Catalogue of Somatic Mutations in Cancer. Eighteen of 45 Tier 1 genes had highly correlated somatic CNA and mRNA expression levels including ARNT, PIK3CA, TBLXR1, ASXL1, EIF4A2, HOOK3, IKBKB, KAT6A, TCEA1, KAT6B, ERBB2, BRD4, KEAP1, PRKACA, DNM2, SMARCA4, AKT2, SS18L1. Our results are in agreement with previously reported somatic CNA for ERBB2, BRD4 and PIK3C in ESC. In addition, AKT2 (p = 0.002) and KAT6A (p = 0.015) amplifications were more frequent in tumor samples from younger patients (<60), and CEBPA (p = 0.028) and MYC (p = 0.023) amplifications were more common with advanced (stage III and IV) disease stage. Patients with tumors carrying KAT6A and MYC amplifications had shorter PFS and OS. The hazard ratio (HR) of KAT6A was 2.82 [95 CI 1.12-7.07] for PFS and 3.87 [95 CI 1.28-11.68] for OS. The HR of MYC was 2.25 [95 CI 1.05-4.81] and 2.62[95 CI 1.07-6.41] for PFS and OS, respectively.

First-in-human phase 0 study of 111In-CHX-A"-DTPA trastuzumab for HER2 tumor imaging

Introduction:

Tumors over-expressing the human epithelial receptor 2 (HER2) or exhibiting amplification or mutation of its proto-oncogene have a poorer prognosis. Using trastuzumab and/or other HER2 targeted therapies can increase overall survival in patients with HER2(+) tumors making it critical to accurately identify patients who may benefit. We report on a Phase 0 study of the imaging agent, ¹¹¹In-CHX-A”-DTPA trastuzumab, in patients with known HER2 status to evaluate its safety and biodistribution and to obtain preliminary data regarding its ability to provide an accurate, whole-body, non-invasive means to determine HER2 status.

Methods:

¹¹¹In-CHX-A”-DTPA trastuzumab was radiolabeled on-site and slowly infused into 11 patients who underwent single (n=5) or multiple (n=6) ɣ-camera (n=6) and/or SPECT (n=8) imaging sessions.

Results:

No safety issues were identified. Visual and semi-quantitative imaging data were concordant with tissue HER2 expression profiling in all but 1 patient. The biodistribution showed intense peak liver activity at the initial imaging timepoint (3.3h) and a single-phase clearance fit of the average time-activity curve (TAC) estimated t_1/2=46.9h (R²=0.97; 95%CI 41.8 to 53h). This was followed by high gastrointestinal (GI) tract activity peaking by 52h. Linear regression predicted GI clearance by 201.2h (R² =0.96; 95%CI 188.5 to 216.9h). Blood pool had lower activity with its maximum on the initial images. Non-linear regression fit projected a t_1/2=34.2h (R² =0.96; 95%CI 25.3 to 46.3h). Assuming linear whole-body clearance, linear regression projected complete elimination (x-intercept) at 256.5hr (R²=0.96; 95%CI 186.1 to 489.2h).

Conclusion:

¹¹¹In-CHX-A”-DTPA trastuzumab can be safely imaged in humans. The biodistribution allowed for visual and semiquantitative analysis with results concordant with tissue expression profiling in 10 of 11 patients. Advances in Knowledge and Implications for Patient Care Using readily available components and on-site radiolabeling ¹¹¹In-CHX-A”-DTPA trastuzumab SPECT imaging may provide an economical, non-invasive means to detect HER2 over-expression.

Significance of Serum Tumor Necrosis Factor-Alpha and its Combination with Her-2 Codon 655 Polymorphism in the Diagnosis and Prognosis of Breast Cancer

Purpose

The present study was conducted to clarify the diagnostic and prognostic significance of TNF-alpha and its combination with HER-2 Ile655Val SNP in breast cancer.

Methods

In this case-control study, 56 consecutive patients with primary breast cancer were prospectively evaluated. The control group consisted of 45 healthy women. Serum concentrations of TNF-alpha were measured by quantitative sandwich enzyme immunoassay (ELISA). HER-2 SNP was genotyped using the PCR-RFLP method.

Results

Serum TNF-alpha was significantly increased in patients compared to controls. ROC analysis indicated a cutoff point of 11.00 pg/mL to classify breast cancer patients (sensitivity, 86%; specificity, 71%). Elevated TNF-alpha levels were associated with larger, poorly differentiated, invasive and advanced-stage tumors, and >3 positive lymph nodes. Regarding HER-2 SNP, patients with Ile-Val and Val-Val genotypes had significant TNF-α elevation compared with homozygous Ile-Ile patients. In multivariate analysis, high serum TNF-alpha remained an independent prognostic factor of worse overall survival; its combination with Val-Val genotype predicted a worse prognosis than high TNF-alpha alone.

Conclusions

Serum TNF-a could be used clinically as a useful tumor marker for diagnosis, disease extent and outcome of breast cancer. The negative impact on survival seems to be enhanced through the interaction with HER-2 Ile655Val SNP.

Circulating and disseminated tumor cells: diagnostic tools and therapeutic targets in motion

Enumeration of circulating tumor cells (CTCs) in peripheral blood with the gold standard CellSearchTM has proven prognostic value for tumor recurrence and progression of metastatic disease. Therefore, the further molecular characterization of isolated CTCs might have clinical relevance as liquid biopsy for therapeutic decision-making and to monitor disease progression. The direct analysis of systemic cancer appears particularly important in view of the known disparity in expression of therapeutic targets as well as epithelial-to-mesenchymal transition (EMT)-based heterogeneity between primary and systemic tumor cells, which all substantially complicate monitoring and therapeutic targeting at present. Since CTCs are the potential precursor cells of metastasis, their in-depth molecular profiling should also provide a useful resource for target discovery. The present review will discuss the use of systemically spread cancer cells as liquid biopsy and focus on potential target antigens.

Developments in therapy with monoclonal antibodies and related proteins

Monoclonal antibody therapeutics have been approved for over 30 targets and diseases, most commonly cancer. Antibodies have become the new backbone of the pharmaceutical industry, which previously relied on small molecules. Compared with small molecules, monoclonal antibodies (mAbs) have exquisite target selectivity and hence less toxicity as a result of binding other targets. The clinical value of both mAbs and ligand traps has been proven. New applications of mAbs are being tested and mAbs have now been designed to target two (bi-specific, eg TNF-α and IL-17) or more targets simultaneously, augmenting their therapeutic potential. Because of space limitations and the wide ranging scope of this review there are regrettably, but inevitably, omissions and missing citations. We have chosen to highlight the first successes in inflammatory diseases and cancer, but a broader overview of approved mAbs and related molecules can be found in Table 1.

Challenging a Misnomer? The Role of Inflammatory Pathways in Inflammatory Breast Cancer

Inflammatory breast cancer is a rare, yet highly aggressive form of breast cancer, which accounts for less than 5% of all locally advanced presentations. The clinical presentation of inflammatory breast cancer often differs significantly from that of noninflammatory breast cancer; however, immunohistochemistry reveals few, if any, distinguishing features. The more aggressive triple-negative and HER2-positive breast cancer subtypes are overrepresented in inflammatory breast cancer compared with noninflammatory breast cancer, with a poorer prognosis in response to conventional therapies. Despite its name, there remains some controversy regarding the role of inflammation in inflammatory breast cancer. This review summarises the current molecular evidence suggesting that inflammatory signaling pathways are upregulated in this disease, including NF-κB activation and excessive IL-6 production among others, which may provide an avenue for novel therapeutics. The role of the tumor microenvironment, through tumor-associated macrophages, infiltrating lymphocytes, and cancer stem cells is also discussed, suggesting that these tumor extrinsic factors may help account for the differences in behavior between inflammatory breast cancer and noninflammatory breast cancer. While there are various novel treatment strategies already underway in clinical trials, the need for further development of preclinical models of this rare but aggressive disease is paramount.

Tanapoxvirus lacking a neuregulin-like gene regresses human melanoma tumors in nude mice

Neuregulin (NRG), an epidermal growth factor is known to promote the growth of various cell types, including human melanoma cells through ErbB family of tyrosine kinases receptors. Tanapoxvirus (TPV)-encoded protein TPV-15L, a functional mimic of NRG, also acts through ErbB receptors. Here, we show that the TPV-15L protein promotes melanoma proliferation. TPV recombinant generated by deleting the 15L gene (TPVΔ15L) showed replication ability similar to that of wild-type TPV (wtTPV) in owl monkey kidney cells, human lung fibroblast (WI-38) cells, and human melanoma (SK-MEL-3) cells. However, a TPV recombinant with both 15L and the thymidine kinase (TK) gene 66R ablated (TPVΔ15LΔ66R) replicated less efficiently compared to TPVΔ15L and the parental virus. TPVΔ15L exhibited more robust tumor regression in the melanoma-bearing nude mice compared to other TPV recombinants. Our results indicate that deletion of TPV-15L gene product which facilitates the growth of human melanoma cells can be an effective strategy to enhance the oncolytic potential of TPV for the treatment of melanoma.

Tumor driven by gain-of-function HER2 H878Y mutant is highly sensitive to HER2 inhibitor

HER2, a well established oncogenic member of EGFR family, is among the most intensely investigated kinase drug targets. In contrast to hotspot mutations of EGFR, few mutations of HER2 locate in activation loop within kinase domain. We previously reported the molecular mechanism underlying hyper kinase activity of HER2^H878Y, a mutation located in activation loop. However, its tumorigenicity in vivo and relevant therapeutics remain to be determined. Here, we report for the first time that HER2^H878Y was tumorigenic in vivo in lung adenocarcinoma transgenic mouse model. Induced expression of HER2^H878Y in lung epithelial compartments resulted in formation of poorly differentiated lung adenocarcinoma with bronchioloalveolar carcinoma (BAC) features. Strikingly, we found that these tumors depended on continuous expression of HER2^H878Y for maintenance. Typical HER2 downstream signaling mediators, including PLCγ1, STAT5 and AKT, were hyperactivated in HER2^H878Y driven lung tumors. More importantly, administration of HKI-272, a tyrosine kinase inhibitor (TKI), efficiently shrank HER2^H878Y driven tumors in transgenic mouse model. Moreover, we found that combinational treatment with HKI272 and mTOR inhibitor, Rapamycin, showed a superior cytotoxicity to H878Y mutant transformed cells and enhanced activity to elicit apoptosis and inhibit growth in situ in tumorous area. Our work therefore showed that HER2^H878Y mutant was a reasonable drug target. Hence, our work supported the assessment of HKI-272/rapamycin treatment in clinical trials.

Breaching the Castle Walls: Hyaluronan Depletion as a Therapeutic Approach to Cancer Therapy

Hyaluronan (HA) has many functions in the extracellular milieu of normal and diseased tissues. Disease-associated HA accumulation has been shown to predict a worsened prognosis in cancer patients, with tumors having a high-extracellular HA content (HA-high) being more aggressive than their HA-low counterparts. HA-high tumor aggressiveness is derived from the specialized biomechanical and molecular properties of the HA-based assembly of HA binding proteins and the growth-promoting factors that accumulate in it. Biophysical characteristics of an HA-high tumor microenvironment include high tumor interstitial pressure, compression of tumor vasculature, and resulting tumor hypoxia. Within the tumor cell membrane, HA receptors, primarily CD44 and RHAMM, anchor the HA-high extracellular network. HA-CD44 association on the tumor cell surface enhances receptor tyrosine kinase activity to drive tumor progression and treatment resistance. Together, malignant cells in this HA-high matrix may evolve dependency on it for growth. This yields the hypothesis that depleting HA in HA-high tumors may be associated with a therapeutic benefit. A pegylated form of recombinant human hyaluronidase PH20 (PEGPH20) has been deployed as a potential cancer therapeutic in HA-high tumors. PEGPH20 can collapse this matrix by degrading the HA-assembled tumor extracellular framework, leading to tumor growth inhibition, preferentially in HA-high tumors. Enzymatic depletion of HA by PEGPH20 results in re-expansion of the tumor vasculature, reduction in tumor hypoxia, and increased penetration of therapeutic molecules into the tumor. Finally, HA-depletion results in reduced signaling via CD44/RHAMM. Taken together, HA-depletion strategies accomplish their antitumor effects by multiple mechanisms that include targeting both biophysical and molecular signaling pathways. Ongoing clinical trials are examining the potential of PEGPH20 in combination with partner therapeutics in several cancers.

Tumor-associated hyaluronan limits efficacy of monoclonal antibody therapy

Despite tremendous progress in cancer immunotherapy for solid tumors, clinical success of monoclonal antibody (mAb) therapy is often limited by poorly understood mechanisms associated with the tumor microenvironment (TME). Accumulation of hyaluronan (HA), a major component of the TME, occurs in many solid tumor types, and is associated with poor prognosis and treatment resistance in multiple malignancies. In this study, we describe that a physical barrier associated with high levels of HA (HA(high)) in the TME restricts antibody and immune cell access to tumors, suggesting a novel mechanism of in vivo resistance to mAb therapy. We determined that approximately 60% of HER2(3+) primary breast tumors and approximately 40% of EGFR(+) head and neck squamous cell carcinomas are HA(high), and hypothesized that HA(high) tumors may be refractory to mAb therapy. We found that the pericellular matrix produced by HA(high) tumor cells inhibited both natural killer (NK) immune cell access to tumor cells and antibody-dependent cell-mediated cytotoxicity (ADCC) in vitro. Depletion of HA by PEGPH20, a pegylated recombinant human PH20 hyaluronidase, resulted in increased NK cell access to HA(high) tumor cells, and greatly enhanced trastuzumab- or cetuximab-dependent ADCC in vitro. Furthermore, PEGPH20 treatment enhanced trastuzumab and NK cell access to HA(high) tumors, resulting in enhanced trastuzumab- and NK cell-mediated tumor growth inhibition in vivo. These results suggest that HA(high) matrix in vivo may form a barrier inhibiting access of both mAb and NK cells, and that PEGPH20 treatment in combination with anticancer mAbs may be an effective adjunctive therapy for HA(high) tumors.

Adaptive Immune Responses and HER2/neu Positive Breast Cancer

Oncogenic signaling, such as HER2/neu signaling, has been shown to play major role for tumorigenesis in a subset of breast cancer patients. The use of anti-HER2/neu antibody has not only revealed the mechanisms for HER2/neu signaling but also shown a therapeutic advantage of its blockade. Indeed, the use of trastuzumab has greatly improved the treatment of HER2-positive breast cancer. Although this therapy has been used in the clinic for over twenty years, recent data is still uncovering new mechanisms by which this antibody exerts its anti-tumor activity. In addition to an improved understanding of the molecular mechanisms by which this therapy inhibits growth of tumor cells, the discovery that anti-HE2/neu therapy initiates and requires the adaptive immune system is one of these new mechanisms. The presence of anti-HER2/neu initiated adaptive immunity gives credence to efforts targeted at stimulating the immune system in treating HER2 positive breast cancer. This review focuses on the role of the inflammatory response in HER2 positive breast cancer with particular emphasis on trastuzumab therapy.

The tanapoxvirus 15L protein is a virus-encoded neuregulin that promotes viral replication in human endothelial cells

Studies on large double-stranded DNA (dsDNA) viruses such as poxviruses have been helpful in identifying a number of viral and cellular growth factors that contribute to our broad understanding of virus-host interaction. Orthopoxviruses and leporipoxviruses are among the most studied viruses in this aspect. However, tanapoxvirus (TPV), a member of the genus Yatapoxvirus, still remains largely unexplored, as the only known hosts for this virus are humans and monkeys. Here, we describe the initial characterization of an epidermal growth factor (EGF)-like growth factor mimicking human neuregulin from TPV, expressed by the TPV-15L gene. Assays using a baculovirus-expressed and tagged TPV-15L protein demonstrated the ability to phosphorylate neuregulin receptors. Neuregulins represent a large family of EGF-like growth factors that play important roles in embryonic endocardium development, Schwann and oligodendrocyte survival and differentiation, localized acetylcholine receptor expression at the neuromuscular junction, and epithelial morphogenesis. Interestingly, certain neuregulin molecules are able to target specific tissues through interactions with heparin sulfate proteoglycans via an immunoglobulin (Ig)-like domain. Analyses of TPV-15L revealed no Ig-like domain, but it retains the ability to bind heparin and phosphorylate neuregulin receptors, providing compelling evidence that TPV-15L is a functional mimetic of neuregulin. TPV-15L knockout virus experiments demonstrate that the virus replicates in human umbilical vein endothelial cells less efficiently than wild-type TPV-Kenya, indicating that this is a nonessential protein for virus viability but can serve a stimulatory role for replication in some cultured cells. However, the precise role of this protein in host-virus interaction still remains to be deduced.

Novel anti-HER2 monoclonal antibodies: synergy and antagonism with tumor necrosis factor-α

Background

One-third of breast cancers display amplifications of the ERBB2 gene encoding the HER2 kinase receptor. Trastuzumab, a humanized antibody directed against an epitope on subdomain IV of the extracellular domain of HER2 is used for therapy of HER2-overexpressing mammary tumors. However, many tumors are either natively resistant or acquire resistance against Trastuzumab. Antibodies directed to different epitopes on the extracellular domain of HER2 are promising candidates for replacement or combinatorial therapy. For example, Pertuzumab that binds to subdomain II of HER2 extracellular domain and inhibits receptor dimerization is under clinical trial. Alternative antibodies directed to novel HER2 epitopes may serve as additional tools for breast cancer therapy. Our aim was to generate novel anti-HER2 monoclonal antibodies inhibiting the growth of breast cancer cells, either alone or in combination with tumor necrosis factor-α (TNF-α).

Methods

Mice were immunized against SK-BR-3 cells and recombinant HER2 extracellular domain protein to produce monoclonal antibodies. Anti-HER2 antibodies were characterized with breast cancer cell lines using immunofluorescence, flow cytometry, immunoprecipitation, western blot techniques. Antibody epitopes were localized using plasmids encoding recombinant HER2 protein variants. Antibodies, either alone or in combination with TNF-α, were tested for their effects on breast cancer cell proliferation.

Results

We produced five new anti-HER2 monoclonal antibodies, all directed against conformational epitope or epitopes restricted to the native form of the extracellular domain. When tested alone, some antibodies inhibited modestly but significantly the growth of SK-BR-3, BT-474 and MDA-MB-361 cells displaying ERBB2 amplification. They had no detectable effect on MCF-7 and T47D cells lacking ERBB2 amplification. When tested in combination with TNF-α, antibodies acted synergistically on SK-BR-3 cells, but antagonistically on BT-474 cells. A representative anti-HER2 antibody inhibited Akt and ERK1/2 phosphorylation leading to cyclin D1 accumulation and growth arrest in SK-BR-3 cells, independently from TNF-α.

Conclusions

Novel antibodies against extracellular domain of HER2 may serve as potent anti-cancer bioactive molecules. Cell-dependent synergy and antagonism between anti-HER2 antibodies and TNF-α provide evidence for a complex interplay between HER2 and TNF-α signaling pathways. Such complexity may drastically affect the outcome of HER2-directed therapeutic interventions.

Transactivation of ErbB-2 induced by tumor necrosis factor alpha promotes NF-kappaB activation and breast cancer cell proliferation

Tumor necrosis factor alpha (TNFalpha) is a pleiotropic cytokine which, acting locally, induces tumor growth. Accumulating evidence, including our findings, showed that TNFalpha is mitogenic in breast cancer cells in vitro and in vivo. In the present study, we explored TNFalpha involvement on highly aggressive ErbB-2-overexpressing breast cancer cells. We found that TNFalpha induces ErbB-2 phosphorylation in mouse breast cancer C4HD cells and in the human breast cancer cell lines SK-BR-3 and BT-474. ErbB-2 phosphorylation at Tyr877 residue was mediated by TNFalpha-induced c-Src activation. Moreover, TNFalpha promoted ErbB-2/ErbB-3 heterocomplex formation, Akt activation and NF-kappaB transcriptional activation. Inhibition of ErbB-2 by addition of AG825, an epidermal growth factor receptor/ErbB-2-tyrosine kinase inhibitor, or knockdown of ErbB-2 by RNA interference strategy, blocked TNFalpha-induced NF-kappaB activation and proliferation. However, the humanized monoclonal antibody anti-ErbB-2 Herceptin could not inhibit TNFalpha ability to promote breast cancer growth. Interestingly, our work disclosed that TNFalpha is able to transactivate ErbB-2 and use it as an obligatory downstream signaling molecule in the generation of mitogenic signals. As TNFalpha has been shown to be present in the tumor microenvironment of a significant proportion of human infiltrating breast cancers, our findings would have clinical implication in ErbB-2-positive breast cancer treatment.

Many cytokines are very useful therapeutic targets in disease

Cytokines are a large family of more than 100 small proteins that function as short-range mediators involved in essentially all biological processes. They have been found to be important rate-limiting signals, and it is now known that blocking some cytokines, e.g., TNF-alpha, and cytokine receptors, such as human EGFR 1 (HER1) or HER2, yields effective therapeutics that address unmet needs. This Review Series surveys three chronic inflammatory disease areas and two forms of cancer and discusses the important role of cytokines and their receptors in these disease processes. Their role as potential therapeutic targets is also highlighted.

Signal integration: a framework for understanding the efficacy of therapeutics targeting the human EGFR family

The human EGFR (HER) family is essential for communication between many epithelial cancer cell types and the tumor microenvironment. Therapeutics targeting the HER family have demonstrated clinical success in the treatment of diverse epithelial cancers. Here we propose that the success of HER family-targeted monoclonal antibodies in cancer results from their ability to interfere with HER family consolidation of signals initiated by a multitude of other receptor systems. Ligand/receptor systems that initiate these signals include cytokine receptors, chemokine receptors, TLRs, GPCRs, and integrins. We further extrapolate that improvements in cancer therapeutics targeting the HER family are likely to incorporate mechanisms that block or reverse stromal support of malignant progression by isolating the HER family from autocrine and stromal influences.

Herceptin

The biology of the human epidermal growth factor (EGF) receptor-2 (HER2) has been reviewed numerous times and provides an excellent example for developing a targeted cancer therapeutic. Herceptin, the FDA-approved therapeutic monoclonal antibody against HER2, has been used to treat over 150,000 women with breast cancer. However, the developmental history of Herceptin, the key events within the program that created pivotal decision points, and the reasons why decisions were made to pursue the monoclonal antibody approach have never been adequately described. The history of Herceptin is reviewed in a way which allows the experience to be shared for the purposes of understanding the drug discovery and development process. It is the objective of this review to describe the pivotal events and explain why critical decisions were made that resulted in the first therapeutic to successfully target tyrosine kinases in cancer. New approaches and future prospects for therapeutics targeting the HER family are also discussed.

Ajoene inhibits both primary tumor growth and metastasis of B16/BL6 melanoma cells in C57BL/6 mice

Ajoene is an organosulphur compound derived from garlic with important effects on several membrane-associated processes such as platelet aggregation, as well as being cytotoxic for tumor cell lines in vitro. In the present study, we investigated the effect of ajoene on different cell types in vitro, as well as its inhibitory effects on both primary tumors and metastasis in a mouse model. We found ajoene to inhibit tumor cell growth in vitro, but also to inhibit strongly metastasis to lung in the B16/BL6 melanoma tumor model in C57BL/6 mice. As far as we are aware, this is the first report of the anti-metastatic effect of ajoene. Ajoene also inhibited tumor-endothelial cell adhesion, as well as the in vivo TNF-alpha response to lipopolysaccharide. Possible mechanisms of its antitumoral activity are discussed in the light of these results.

The immunocytokine scFv23/TNF sensitizes HER-2/neu–overexpressing SKBR-3 cells to tumor necrosis factor (TNF) via up-regulation of TNF receptor-1

Overexpression of HER-2/neu confers cellular resistance to tumor necrosis factor (TNF)-mediated cytotoxicity to SKBR-3 breast cancer cell lines. To understand the correlation between HER-2/neu expression and TNF resistance, we examined the unique signaling pathways associated with the cytotoxic effects of the immunocytokine scFv23/TNF, recombinant single-chain antibody fusion constructs containing TNF and targeting HER-2/neu, in TNF-resistant SKBR-3-LP cells. We found that treatment of HER-2/neu-overexpressing SKBR-3-LP cells with scFv23/TNF resulted in a 5- to 7-fold higher level of TNF receptor-1 expression 48 hours after exposure. In addition, treatment of SKBR-3-LP cells with scFv23/TNF resulted in down-regulation of Akt phosphorylation and induced apoptosis through cleavage of caspase-8, caspase-3, and poly(ADP-ribose) polymerase. ScFv23/TNF-induced cytotoxicity was inhibited by blocking of the binding of the TNF component of scFv23/TNF to TNF receptor-1 and was dependent on activation of caspase-8 and caspase-3. These results indicate that the immunocytokine scFv23/TNF sensitizes TNF-resistant HER-2/neu-overexpressing SKBR-3-LP cells to TNF-induced apoptosis via the overexpression of TNF receptor-1 and suggest that the overexpression of TNF receptor-1 plays a crucial role in TNF sensitivity in HER-2/neu-overexpressing cancer cells. ScFv23/TNF targeting the HER-2/neu may be an effective cytotoxic agent against HER-2/neu-overexpressing cancer cells, which are inherently resistant to TNF.

Tyrosine kinases in disease: overview of kinase inhibitors as therapeutic agents and current drugs in clinical trials

Tyrosine kinases, first described as oncogenes, have been shown to play a role in normal cellular processes. Aberrations in tyrosine kinase activity lead to disease states. For fifteen years it has been postulated that the inhibition of tyrosine kinases may have therapeutic utility and the design and testing of inhibitors have been major focuses of research and development in both academic institutions and pharmaceutical companies. While early research focused on developing chemical entities that mimic phosphotyrosine, later research has focused on developing competitive adenosine triphosphate (ATP) inhibitors with various levels of selectivity on kinase targets. This review focuses on a discussion of tyrosine kinases thought to be important in disease, including platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), vascular endothelial cell growth factor (VEGF), epidermal growth factor (EGF) receptors, HER-2 and Src. In addition, the classes of inhibitors designed to affect these targets and that have overcome research and development challenges and entered clinical trials are discussed. These include isoxazole, quinazoline, substituted pyrimidines and indolinone compounds, all of which are in clinical trials or near clinical development by SUGEN, Zeneca, Novartis, Pfizer and Parke-Davis. A summary of the chemistry and activity of these agents is provided.

Caspase-8-Dependent HER-2 Cleavage in Response to Tumor Necrosis Factor α Stimulation Is Counteracted by Nuclear Factor κB through c-FLIP-L Expression

The oncoprotein HER-2/neu is a prosurvival factor, and its overexpression has been correlated with poor prognosis in patients with breast cancer. We report that HER-2 is a new substrate for caspase-8 and that tumor necrosis factor alpha (TNF-alpha) stimulation leads to an early caspase-8-dependent HER-2 cleavage in MCF7 A/Z breast adenocarcinoma cells defective for nuclear factor kappaB (NFkappaB) activation. We show that the antiapoptotic transcription factor NFkappaB counteracts this cleavage through induction of the caspase-8 inhibitor c-FLIP. Our results also demonstrate that this HER-2 cleavage contributes to the TNF-alpha-induced apoptosis pathway because ectopic expression of an uncleavable HER-2 protects NFkappaB-defective cells against TNF-alpha-mediated cell death. Therefore, we propose an original model in which NFkappaB exerts a new antiapoptotic function by counteracting TNF-alpha-triggered cleavage of the HER-2 survival factor.

Regulation of HER-2 oncogene expression by cyclooxygenase-2 and prostaglandin E2

The oncoprotein HER-2/neu is a prosurvival factor and its overexpression has been correlated with adverse prognosis in breast cancers. High levels of the cyclooxygenase-2 (COX-2), a proinflammatory and antiapoptotic enzyme, were detected in HER-2-positive tumors and this observation was linked to an HER-2-mediated induction of COX-2 gene transcription. Here, we report that COX-2 expression, and synthesis of its major enzymatic product, PGE2, leads in turn to an enhanced HER-2 expression. Moreover, COX-2 enzymatic inhibition dramatically reduced HER-2 protein levels, efficiently increased the cancer cells sensitility to chemotherapeutic treatment and acted in synergy with HER-2 inhibitor, trastuzumab. Therefore, we propose an original model where HER-2 and COX-2 transcriptionally regulate each other in a positive loop.

Mechanism of action of anti-HER2 monoclonal antibodies

The search for new methods of treating cancer, combined with advances in our understanding of carcinogenesis, molecular biology and technology, has resulted in the development of novel biologic agents with proven clinical efficacy. One such agent is trastuzumab (Herceptin), a humanized monoclonal antibody that targets the human epidermal growth factor receptor-2 (HER2). HER2 is a member of a family of receptors that interact with each other and various ligands to stimulate various intracellular signal transduction pathways involved in cell growth control. HER2 is overexpressed in 20%-30% of women with breast cancer and is associated with aggressive tumor characteristics and poor prognosis. Trastuzumab is the first humanized monoclonal antibody to be approved for therapeutic use and the first oncogene-targeted treatment with proven survival benefit in women with HER2-positive metastatic breast cancer. However, its mechanism of action has not been fully characterized and appears to be complex. This paper reviews current knowledge of the mechanism of action of trastuzumab, including HER2 protein downregulation, prevention of HER2-containing heterodimer formation, initiation of G1 arrest and induction of p27, prevention of HER2 cleavage, inhibition of angiogenesis, and induction of immune mechanisms. The significance of these mechanisms for selection of concomitant chemotherapy is also considered.

Her-2/neu and breast cancer

Breast cancer is the most common malignancy in women in the United States in the year 2000. The proto-oncogene Her-2/neu (c-erb-B2) has become an increasingly important prognostic and predictive factor in breast cancer. Overexpression/amplification of the Her-2/neu has been associated with a worse outcome in patients with breast cancer. Herceptin, a "humanized" murine monoclonal antibody directed against the extracellular domain of the Her-2/neu protein, is being used to treat breast cancer that overexpresses Her-2/neu. The status of Her-2/neu in the tumor has become a critical factor in the management strategy of a breast cancer patient. The objective of this article is to provide a comprehensive review of all aspects of Her-2/neu in breast cancer, including biology, prognostic and predictive value, targeted Herceptin therapy, and the laboratory testing of Her-2/neu.

Expression of herstatin, an autoinhibitor of HER-2/neu, inhibits transactivation of HER-3 by HER-2 and blocks EGF activation of the EGF receptor

The four members of the EGF receptor family are capable of homomeric as well as heteromeric interactions. HER-2/neu (erbB-2) dominates as the preferred coreceptor that amplifies mitogenic signaling. An alternative HER-2/neu product, herstatin, consists of a segment of the ectodomain of p185HER-2 and an intron-encoded C-terminus. Recombinant herstatin was found to bind with nM affinity and inhibit p185HER-2. To further examine the impact on receptor activity, herstatin was expressed with various receptor tyrosine kinases. In CHO cells that overexpressed HER-2, herstatin caused a sevenfold inhibition of colony formation that corresponded to a reduction in the tyrosine phosphorylation of p185HER-2. Herstatin also prevented HER-2 mediated transactivation of the kinase impaired HER-3 as reflected in transphosphorylation of HER-3 and heteromers between HER-2 and HER-3. In EGF receptor-overexpressing cells, EGF induction of receptor dimerization and tyrosine phosphorylation were reduced more than 90%, and receptor down-regulation as well as colony formation were also suppressed by coexpression with herstatin. Inhibition was selective for the EGF receptor family since herstatin expression did not reduce tyrosine phosphorylation mediated by the FGF receptor-2 or by insulin-like growth factor -1. Herstatin bound to the EGF receptor as well as to p185HER-2 in pull-down assays suggesting that complex formation may be involved in receptor inhibition. Our findings indicate that herstatin has the capability to negatively regulate combinations of interactions between group I receptor tyrosine kinases that confer synergistic growth signals.

Local intratumoral tumor necrosis factor-alpha and systemic IFN-alpha 2b in patients with locally advanced prostate cancer

To examine tolerability and activity of local, intratumoral tumor necrosis factor-alpha (TNF-alpha) and systemic interferon-alpha2b (IFN-alpha2b) in locally advanced, hormone-resistant prostate cancer (LA-HRPC), 10 patients with LA-HRPC (T4N x M0, n = 3, T4N x M1, n = 5; T4N1M1, n = 2) were treated with recombinant TNF-alpha injected locally into prostate tumor tissue at 4-week intervals (maximum of four cycles) combined with intermittent subcutaneous (s.c.) administration of 5 x 10(6) IU IFN-alpha2b. Twenty-nine TNF-alpha cycles were administered. Despite significant TNF-alpha leakage into the systemic circulation 2 h after intraprostatic application (from a mean of 9 to a mean of 416 pg/ml; p = 0.0034), TNF-alpha (and IFN-alpha2b) was well tolerated (WHO grade 1-2 toxicity), possibly because of its rapid neutralization by increasing soluble 55-kDa and 75-kDa TNF receptor levels in the serum (mean increase 268% and 91%, respectively) at the same time. TNF-alpha induced prostate tumor cell necrosis in all patients, leading to a significant reduction of prostate volume in 9 of 10 cases (mean 38%; p = 0.0025). The significant short-term increase of prostate-specific antigen (PSA) (mean 65%; p < 0.001), tissue polypeptide-specific antigen (TPS) (mean 85%; p = 0.001), and possibly interleukin-8 (IL-8) (mean 2687%; p < 0.009) serum levels within 4 h after TNF-alpha confirmed the cytotoxic effect in vivo. In the long term, serum PSA levels dropped by 18%-87%, reaching the nadir value 7 weeks after baseline. Objective responses of metastases were not seen. Intraprostatic administration of TNF-alpha is feasible at a tolerable toxicity in patients with LA-HRPC and, thus, may be a new treatment option for these patients.

Overexpression of ErbB2 in cancer and ErbB2-targeting strategies

This past decade has witnessed the remarkable advances in the understanding of the role of the erbB2 gene in cancers and the stunning progress in developing targeted therapies for erbB2-overexpressing cancers. Activation of the ErbB2 receptor signaling pathways can enhance various metastasis-associated properties that lead to an increase of cancer metastasis. Additionally, ErbB2 overexpression confers therapeutic resistance via receptor-mediated antiapoptotic signals. To limit these disastrous effects of the overexpressed ErbB2, various ErbB2-blocking strategies have been developed in the laboratories and several have been tested in clinical trials or approved as therapies for ErbB2 overexpressing cancers. In this article, we will discuss the detrimental effects of the erbB2 gene in cancers, with a focus on breast cancer. We will also outline ErbB2-targeting strategies as potential therapies for ErbB2-overexpressing cancers. Progress in understanding the molecular biology of ErbB2 and in molecular-based treatment of ErbB2-overexpressing tumors will bring great benefits to cancer patients.

Molecular mechanisms underlying ErbB2/HER2 action in breast cancer

Overexpression of ErbB2, a receptor-like tyrosine kinase, is shared by several types of human carcinomas. In breast tumors the extent of overexpression has a prognostic value, thus identifying the oncoprotein as a target for therapeutic strategies. Already, antibodies to ErbB2 are used in combination with chemotherapy in the treatment of metastasizing breast cancer. The mechanisms underlying the oncogenic action of ErbB2 involve a complex network in which ErbB2 acts as a ligand-less signaling subunit of three other receptors that directly bind a large repertoire of stroma-derived growth factors. The major partners of ErbB2 in carcinomas are ErbB1 (also called EGFR) and ErbB3, a kinase-defective receptor whose potent mitogenic action is activated in the context of heterodimeric complexes. Why ErbB2-containing heterodimers are relatively oncopotent is a function of a number of processes. Apparently, these heterodimers evade normal inactivation processes, by decreasing the rate of ligand dissociation, internalizing relatively slowly and avoiding the degradative pathway by returning to the cell surface. On the other hand, the heterodimers strongly recruit survival and mitogenic pathways such as the mitogen-activated protein kinases and the phosphatidylinositol 3-kinase. Hyper-activated signaling through the ErbB-signaling network results in dysregulation of the cell cycle homeostatic machinery, with upregulation of active cyclin-D/CDK complexes. Recent data indicate that cell cycle regulators are also linked to chemoresistance in ErbB2-dependent breast carcinoma. Together with D-type cyclins, it seems that the CDK inhibitor p21waf1 plays an important role in evasion from apoptosis. These recent findings herald a preliminary understanding of the output layer which connects elevated ErbB-signaling to oncogenesis and chemoresistance.

Cell death induced by TNF or serum starvation is independent of ErbB receptor signaling in MCF-7 breast carcinoma cells

The ErbB receptor tyrosine kinase family consists of the epidermal growth factor (EGF) receptor (ErbB1) and three related receptors (ErbB2, ErbB3, ErbB4). Their intrinsic tyrosine kinases can be activated by receptor-dimerization induced by numerous ligands or overexpression. ErbB receptors are frequently overexpressed in breast cancer, and their overexpression is associated with protection from apoptosis. To directly assess their role in apoptosis sensitivity of breast cancer cells, we established MCF-7 breast carcinoma cell lines overexpressing each ErbB receptor alone or in all possible pairs. Overexpression of ErbB1, ErbB2 and ErbB4 receptors was enough to activate them as judged by their phosphorylation, whereas co-expression of other ErbB receptors was necessary for the phosphorylation of the ErbB3. Surprisingly, overexpression of the ErbB receptors even when combined with treatment with their ligands (EGF, transforming growth factor alpha, betacellulin, neuregulins) failed to protect the MCF-7 cells from cell death induced by either tumor necrosis factor (TNF) or serum starvation. During starvation TGF-alpha, however, increased the cell size of the ErbB1 overexpressing cell line, and neuregulin1-beta1 increased that of all cell lines. In conclusion, our data does not support the role of ErbB receptors in the regulation of cell death induced by TNF or serum starvation, and the observed association in breast cancer may be due to other concomitant changes.

HER-2/neu blocks tumor necrosis factor-induced apoptosis via the Akt/NF-kappaB pathway

Overexpression of HER-2/neu correlates with poor survival of breast and ovarian cancer patients and induces resistance to tumor necrosis factor (TNF), which causes cancer cells to escape from host immune defenses. The mechanism of HER-2/neu-induced TNF resistance is unknown. Here we report that HER-2/neu activates Akt and NF-kappaB without extracellular stimulation. Blocking of the Akt pathway by a dominant-negative Akt sensitizes the HER-2/neu-overexpressing cells to TNF-induced apoptosis and inhibits IkappaB kinases, IkappaB phosphorylation, and NF-kappaB activation. Our results suggested that HER-2/neu constitutively activates the Akt/NF-kappaB anti-apoptotic cascade to confer resistance to TNF on cancer cells and reduce host defenses against neoplasia.

The ets protein PEA3 suppresses HER-2/neu overexpression and inhibits tumorigenesis

Because HER-2/neu overexpression is important in cancer development, we looked for a method of suppressing the cell transformation mediated by HER-2/neu overexpression. We have identified that the DNA-binding protein PEA3, which is encoded by a previously isolated gene of the ets family, specifically targeted a DNA sequence on the HER-2/neu promoter and downregulated the promoter activity. Expression of PEA3 resulted in preferential inhibition of cell growth and tumor development of HER-2/neu-overexpressing cancer cells. This is a new approach to targeting HER-2/neu overexpression and also provides a rationale to the design for repressors of diseases caused by overexpression of pathogenic genes.

TNF-induced signaling in apoptosis

Out of the almost 17 members of the TNF superfamily, TNF is probably the most potent inducer of apoptosis. TNF activates both cell-survival and cell-death mechanisms simultaneously. Activation of NF-kB-dependent genes regulates the survival and proliferative effects pf TNF, whereas activation of caspases regulates the apoptotic effects. TNF-induced apoptosis is mediated primarily through the activation of type I receptors, the death domain of which recruits more than a dozen different signaling proteins, which together are considered part of an apoptotic cascade. This cascade does not, however, account for the role of reactive oxygen intermediates, ceramide, phospholipases, and serine proteases which are also implicated in TNF-induced apoptosis. This cascade also does not explain how type II TNF receptors which lack the death domain, induce apoptosis. Nevertheless, this review of apoptosis signaling will be limited to those proteins that makeup the cascade.

Biologic effects of heregulin/neu differentiation factor on normal and malignant human breast and ovarian epithelial cells

The heregulins are a family of ligands with ability to induce phosphorylation of the p185HER-2/neu receptor. Various investigators have reported a variety of responses of mouse and human breast and ovarian cells to this family of ligands including growth stimulation, growth inhibition, apoptosis and induction of differentiation in cells expressing the HER-2/neu receptor. Some of the disparity in the literature has been attributed to variations in the cell lines studied, ligand dose applied, methodologies utilized or model system evaluated (i.e. in vitro or in vivo). To evaluate the effects of heregulin on normal and malignant human breast and ovarian epithelial cells expressing known levels of the HER-2/neu receptor, this report presents the use of several different assays, performed both in vitro and in vivo, in vitro proliferation assays, direct cell counts, clonogenicity under anchorage-dependent and anchorage-independent conditions, as well as the in vivo effects of heregulin on human cells growing in nude mice to address heregulin activity. Using a total of five different biologic assays in nine different cell lines, across two different epithelia and over a one log heregulin dose range, we obtained results that clearly indicate a growth-stimulatory role for this ligand in human breast and ovarian epithelial cells. We find no evidence that heregulin has any growth-inhibitory effects in human epithelial cells. We also quantitated the amount of each member of the type I receptor tyrosine kinase family (RTK I, i.e. HER-1, HER-2, HER-3 and HER-4) in the cell lines employed and correlated this to their respective heregulin responses. These data demonstrate that HER-2/neu overexpression itself affects the expression of other RTK I members and that cells expressing the highest levels of HER-2/neu have the greatest response to HRG.

Tumor necrosis factor receptor and Fas signaling mechanisms

Four members of the tumor necrosis factor (TNF) ligand family, TNF-alpha, LT-alpha, LT-beta, and LIGHT, interact with four receptors of the TNF/nerve growth factor family, the p55 TNF receptor (CD120a), the p75 TNF receptor (CD120b), the lymphotoxin beta receptor (LT beta R), and herpes virus entry mediator (HVEM) to control a wide range of innate and adaptive immune response functions. Of these, the most thoroughly studied are cell death induction and regulation of the inflammatory process. Fas/Apo1 (CD95), a receptor of the TNF receptor family activated by a distinct ligand, induces death in cells through mechanisms shared with CD120a. The last four years have seen a proliferation in knowledge of the proteins participating in the signaling by the TNF system and CD95. The downstream signaling molecules identified so far--caspases, phospholipases, the three known mitogen activated protein (MAP) kinase pathways, and the NF-kappa B activation cascade--mediate the effects of other inducers as well. However, the molecules that initiate these signaling events, including the death domain- and TNF receptor associated factor (TRAF) domain-containing adapter proteins and the signaling enzymes associated with them, are largely unique to the TNF/nerve growth factor receptor family.

Differential regulation of IL-6 promoter activity in a human ovarian-tumor cell line transfected with various p53 mutants: involvement of AP-1

In human ovarian carcinomas, the p53 tumor-suppressor gene is frequently mutated. Interleukin-6 (IL-6) in these tumors is known to stimulate tumor-cell proliferation. In order to evaluate the effect of several p53 phenotypes on the IL-6 promoter activity, the human ovarian wild-type (wt)-p53 cell line A2780 was stably transfected with an empty plasmid (CMV) or (m)-175-, m-248- or m-273-p53. Electrophoretic mobility-shift assays revealed differences in activator protein-1 (AP-1) DNA-binding activity in the various clones. The CMV and m-273 clone had comparable amounts of AP-1. The m-175 clone displayed the least and m-248 the most pronounced AP-1 binding. Supershift analysis of AP-1/DNA complexes with antibodies against the AP-1 sub-units, c-Fos, FosB, Fra-1, Fra-2, c-Jun, JunB, and JunD, revealed that the AP-1/DNA complexes in the various clones had different compositions. Fra proteins were basically present only in m-175 and m-248 AP-1. IL-6-promoter activity was evaluated in the presence and absence of the AP-1 binding site which showed that the m-175-transfected clone has a transcriptional suppressing AP-1, whereas the CMV and the m-273 clones have an activating AP-1. Exposure of the p53 clones to tumor-necrosis factor-alpha (TNF-alpha) clearly altered the AP-1/DNA complex composition. IL-6-promoter activity was enhanced by TNF-alpha irrespective of the presence of an AP-1 binding site, while the degree of activation differed in the various clones, being most pronounced in the m-175 and m-248 clones. The results demonstrate that the basic and activated IL-6-promoter activity is differently regulated in the various p53 clones, possibly due to alterations in the AP-1 composition.

Differential expression and translocation of protein tyrosine phosphatase 1B-related proteins in ME-180 tumor cells expressing apoptotic sensitivity and resistance to tumor necrosis factor: potential interaction with epidermal growth factor receptor

Tumor necrosis factor (TNF)-induced apoptosis can be inhibited by overexpression of specific tyrosine kinases or activation of tyrosine kinase cascades, suggesting potential antagonism between apoptotic and tyrosine kinase signaling processes. In this report, the effects of TNF on EGF receptor tyrosine phosphorylation in ME-180 cell variants selected for apoptotic sensitivity (Sen) or resistance (Res) to TNF, previously shown to differentially express EGFr, were examined. Prior to the onset of apoptosis, TNF caused a significant reduction in the level of EGFr tyrosine phosphorylation in Sen cells but mediated only limited suppression of EGFr tyrosine phosphorylation in apoptotically resistant Res cells. In vitro incubation of cellular membranes with TNF derived from Sen cells stimulated a resident protein tyrosine phosphatase (PTP) activity which was able to dephosphorylate EGFr or tyrosine phosphopeptides mimicking an EGFr autophosphorylation site. In membrane preparations, PTPIB complexed with tyrosine phosphorylated EGFr and this association was disrupted by TNF through an apparent stimulation of PTP activity and turnover of phosphotyrosine. Intrinsic enzymatic activity of PTP1B was 2-3-fold higher in Sen versus Res cell lysates and a family of PTP1B-related proteins with altered C-termini was found to be highly expressed in Sen cells but absent or expressed at reduced levels in Res cells. Cytoplasmic extracts of Sen cells contained PTP1B-like proteins and TNF incubation resulted in the time dependent accumulation of PTP1B-like proteins in Sen cells but did not effect these proteins in Res cells. Together, these results suggest that specific changes in expression and subcellular distribution of phosphotyrosine modulatory proteins may play a role in conveying intrinsic apoptotic sensitivity to TNF in some tumor cell types.

A sandwich type acridinium-linked immunosorbent assay (ALISA) detects soluble ErbB1 (sErbB1) in normal human sera

The epidermal growth factor receptor (ErbB1) is overexpressed in various human tumor-derived cell lines and neoplasms, where it is believed that receptor dysregulation plays a role in oncogenic transformation and tumor progression. In addition to the ErbB1 holoreceptor, numerous studies demonstrate that cells synthesize soluble or secreted forms of ErbB1, i.e., sErbB1. Overexpression of ErbB1 in a variety of tumors has led us to hypothesize that sErbB levels also may be altered during oncogenesis, tumor progression, and/or metastasis; and that these molecules may be useful tumor biomarkers. To address this hypothesis we have developed an acridinium-linked immunosorbent assay (ALISA) specific for the extracellular domain of ErbB1 that can be used to quantify the levels of sErbB1 molecules in body fluids and conditioned culture media. This assay can also detect full-length ErbB1 in cell and tissue extracts. Our ALISA is characterized by high sensitivity (intra-assay LLD < 1 fmol/ml), a broad linear range (approximately 1 to 4000 fmol/ml), and good reproducibility (CVs < 10%). Specificity experiments show that this ALISA detects p170 ErbB1 and soluble forms of ErbB1 that embody extracellular subdomains I through IV, but not forms of sErbB1 lacking subdomain IV. Our ALISA does not detect full-length ErbB2, ErbB3, or ErbB4; or p105 soluble ErbB2. We report that serum sErbB1 levels of healthy women (median = 3716 fmol/ml), ranging in age from 43 to 76 years, differ significantly from those of healthy men (median = 24,512 fmol/ml), ranging in age from 25 to 79 years. Additional analyses do not indicate that serum sErbB1 levels change with age in either healthy men or women. Immunoprecipitation experiments show that monoclonal antibodies specific for extracellular epitopes of ErbB1 completely neutralize the detection of sErbB1 in normal human sera by ALISA. Finally, we show by immunoprecipitation and Western immunoblot analyses with monoclonal antibodies specific for the extracellular domain of ErbB1 that normal human female and male sera contain a approximately 110-kDa protein. We conclude that our ALISA is measuring the relative levels of this p110 sErbB1 analog in normal human sera. Our ALISA, therefore, should be useful for measuring the levels of ErbB1 and sErbB1 molecules in tumor biopsy specimens and body fluids, respectively, and for determining whether sErbB1, like ErbB1, is a useful tumor biomarker.

Enhanced sensitivity to tumor necrosis factor-alpha in doxorubicin-resistant tumor cell lines due to down-regulated c-erbB2

We have studied the relationship between tumor necrosis factor (TNF)-sensitivity and doxorubicin-resistance in our doxorubicin-resistant cell line panel consisting of the parental cell line GLC4 plus GLC4-Adr2x and GLC4-Adr350x with respective resistance factors of 2 and 350 compared with GLC4. At the highest dose of 1000 ng/ml TNF, GLC4 was almost completely resistant to TNF, whereas 37% and 68% growth inhibition was observed in GLC4-Adr2x and GLC4-Adr350x, respectively. Sensitivity to TNF appeared to correlate inversely with the expression and gene copies of topoisomerase IIalpha in these cell lines. The gene encoding for c-erbB2 is in the proximity of the topoisomerase IIalpha gene and its product is a known cause for TNF-resistance. We found that our doxorubicin-resistant cell lines with decreased topoisomerase IIalpha gene copies have a simultaneous decrease in c-erbB2 gene copies, probably due to linkage between these 2 genes. This reduced number of c-erbB2 gene copies resulted in decreased c-erbB2 expression and subsequently in increased sensitivity to TNF. Additionally, we tried to establish some of the mechanisms associated with TNF-resistance in GLC4 related to c-erbB2 overexpression. There was no difference in TNF-receptor-1 expression between the cell lines. Compared with the TNF-sensitive GLC4-Adr350x, GLC4 appeared to have a decreased activation of NF-kappaB after exposure to TNF that might indicate a reduced TNF-receptor function. In GLC4, increased Bcl-2 expression was found, a protein described to confer TNF-resistance. Moreover, it was demonstrated that combining TNF with the poly-ADP-ribose polymerase (PARP) inhibitors 6-aminonicotinamide and 3-aminobenzamide did not affect TNF-sensitivity in GLC4 and GLC4-Adr350x, excluding a pivotal role of PARP in TNF-resistance in these cell lines. In conclusion, our data show that doxorubicin-resistant tumor cell lines with decreased topoisomerase IIalpha gene copies can become sensitive to TNF due to loss of c-erbB2 gene copies. We also found that several mechanisms associated with c-erbB2 overexpressing contribute to TNF-resistance in GLC4.

Ras signaling in tumor necrosis factor-induced apoptosis

Tumor necrosis factor (TNF) exerts cytotoxicity on many types of tumor cells but not on normal cells. The molecular events leading to cell death triggered by TNF are still poorly understood. Our previous studies have shown that enforced expression of an activated H-ras oncogene converted non-tumorigenic, TNF-resistant C3H 10T1/2 fibroblasts into tumorigenic cells that also became very sensitive to TNF-induced apoptosis. This finding suggested that Ras activation may play a role in TNF-induced apoptosis. In this study we investigated whether Ras activation is an obligatory step in TNF-induced apoptosis. Introduction of two different molecular antagonists of Ras, the rap1A tumor suppressor gene or the dominant-negative rasN17 gene, into H-ras-transformed 10TEJ cells inhibited TNF-induced apoptosis. Similar results were obtained with L929 cells, a fibroblast cell line sensitive to TNF-induced apoptosis, which does not have a ras mutation. While Ras is constitutively activated in TNF-sensitive 10TEJ cells, TNF treatment increased Ras-bound GTP in TNF-sensitive L929 cells but not in TNF-resistant 10T1/2 cells. Moreover, RasN17 expression blocked TNF-induced Ras-GTP formation in L929 cells. These results demonstrate that Ras activation is required for TNF-induced apoptosis in mouse fibroblasts.

Activation of the insulin-like growth factor-I receptor inhibits tumor necrosis factor-induced cell death

The effect of insulin-like growth factor (IGF) on tumor necrosis factor (TNF)-induced cell killing was determined for mouse BALB/c3T3 fibroblasts in vitro. Cells maintained in 0.5% fetal bovine serum (FBS) were killed by TNF within 6 h in a concentration-dependent manner, an effect that was prevented by IGF-I. TNF-induced cytotoxicity of 3T3 cells that overexpress the human IGF-I receptor (p6 cells) was prevented by IGF-I alone in the absence of serum. TNF-induced cell death was associated with the morphologic features of apoptosis and the release of low-molecular-weight DNA, both of which were prevented by IGF-I. Neither epidermal growth factor (EGF) nor platelet-derived growth factor (PDGF) protected p6 cells from TNF-induced apoptosis. The specific protective action of the IGF-I receptor was demonstrated further by the marked sensitivity to TNF of embryo fibroblasts derived from mice with targeted disruption of the IGF-I receptor (R-cells) but not of fibroblasts derived from wild-type littermates or R-cells transfected with the cDNA for the human IGF-I receptor. Cycloheximide or actinomycin D markedly reduced the protection offered by IGF-I. IGF-I protection of BALB/c3T3 cells persisted for up to 5 days in the presence of PDGF and EGF, whereas IGF-I lost its effectiveness after 2 days in the absence of growth factors. IGF-I did not prevent TNF-induced release of arachidonic acid. The results demonstrate a specific role for the IGF-I receptor in the protection against TNF cytotoxicity. This action of the IGF-I receptor is mediated by protective cytosolic proteins that exhibit a high rate of turnover and whose levels are regulated principally by factors within serum other than IGF-I.

Activation of epidermal growth factor receptor tyrosine phosphorylation by tumor necrosis factor correlates with loss of cytotoxic activity

TNF induces cytotoxicity in human tumor cells through a receptor-mediated process with unknown signaling characteristics. Evidence suggests that overexpression of transmembrane growth factor receptors with intrinsic tyrosine kinase activity may suppress the antiproliferative or cytotoxic activity of TNF, suggesting antagonism between these two signaling pathways in tumor cells. To investigate TNF cytotoxic signal transduction, ME-180 cervical carcinoma cell variants were isolated that expressed complete cytotoxic sensitivity (ME-180S) or resistance (ME-180R) to TNF but identical levels of p55 TNF receptor expression. ME-180R cells expressed threefold higher EGFR than the ME-180S cell line and TNF treatment stimulated EGFR tyrosine phosphorylation only in resistant cells. Activation of tyrosine phosphorylation in ME-180R cells was TNF concentration dependent and maximally stimulated (three- to-five-fold) after 10-15 minutes of treatment. Other tyrosine phosphoproteins were not affected by TNF incubation demonstrating specific TNF-stimulated tyrosine phosphomodulation of EGFR. Pretreatment with the tyrosine kinase inhibitor tryphostin before incubation with TNF resulted in partial reversal of TNF cytotoxic resistance in ME-180R cells and enhanced TNF responsiveness in ME-180S cells, suggesting a "protective" role for tyrosine phosphorylation in TNF-induced cytotoxicity. Together these results demonstrate that TNF-mediated tyrosine phosphorylation is differentially regulated in sensitive and resistant tumor cells and may play a critical role in the cytotoxic signaling process through differential expression or regulation of tyrosine protein kinases and phosphatases.