Early and multifocal tumors in breast, salivary, harderian and epididymal tissues developed in MMTY-Neu transgenic mice

ErbB2 transgenic mice: a tool for investigation of the immune prevention and treatment of mammary carcinomas

The epidermal growth factor receptor belongs to a superfamily of receptor tyrosine kinases (RTK) that includes ErbB2. ErbB2 is involved in normal physiological processes, such as embryogenesis, cell proliferation, differentiation, adhesion motility, and apoptosis, while its malfunction or overexpression is responsible for development defects, diabetes, and cancer. The human ortholog of ErbB2 is referred as Her-2 (human ErbB2) while the rat ortholog is referred as neu (rat ErbB2). As ErbB2 is directly involved in carcinogenesis, mice transgenic for the rat neu oncogene allow straightforward assessment of the ability of drugs and vaccines to inhibit the progression of neu-driven cancer. Information from this model may provide indications on the efficacy of similar treatments in patients. This commentary provides key information regarding the use of these transgenic mouse models for evaluation of the efficacy of anti-tumor strategies.

Fast-tracked CTL: rapid induction of potent anti-tumor killer T cells in situ

Current strategies to elicit cytolytic T cell responses specific for tumor-associated or over-expressed self antigens rely on multiple immunizations and in vitro expansion schemes. Here we report the in vivo induction of activated tumor-specific CD8(+) CTL just 6 days after treatment with the IgM immune modulator B7-DC XAb. Antibody treatment of mice at the time of tumor challenge elicited potent CTL with a specificity that distinguished between MHC-compatible tumors. Remarkably, these effector cells were not generated by the extensive proliferation of naive CTL precursors, though their induction required CD4(+) T cell help and classical B7 costimulatory signals. Tumor targets were recognized and lysed in an MHC-restricted, perforin-dependent manner, indicating that these rapidly induced effectors resemble traditionally defined CTL, despite the finding that strong increases in the expression of the effector/memory marker CD44 and the activation marker CD69 were not elicited. These CTL were induced in animals bearing well-established tumors and resulted in anti-tumor protection, underscoring the therapeutic potential of this type of effector T cell population in cancer patients.

Sam68 haploinsufficiency delays onset of mammary tumorigenesis and metastasis

The Src-associated substrate in mitosis Sam68 is a KH type RNA-binding protein known to be a substrate of numerous tyrosine kinases, and often referred to as a STAR (signal transduction activator of RNA) protein. Herein, we observed that Sam68-null mice display mammary gland and the uterine development defects. Moreover, we report that Sam68 haploinsufficiency impedes mammary tumor onset in vivo driven by the potent mammary-targeted polyoma middle T-antigen (MMTV-PyMT) oncogene. The effect was cell autonomous as the Sam68 knockdown in PyMT-transformed cell lines also delayed tumorigenesis and metastasis formation in nude mice. Interestingly, tumor extracts isolated from PyMT/Sam68(+/-) mice compared with PyMT/Sam68(+/+) mice contained activated Src and FAK kinases. These findings suggest that Sam68 may be a modulator of tyrosine kinase activity in vivo and a signaling requirement for mammary tumorigenesis and metastasis.

Adenovirus vaccination against neu oncogene exerts long-term protection from tumorigenesis in BALB/neuT transgenic mice

The transforming rat HER2/neu oncogene (neu), when embedded in the genome of transgenic BALB/c (neuT) mice, provokes the development of an invasive carcinoma in each of their 10 mammary glands. We used the neuT mice model system to evaluate the immunization efficiency and the protective effect of intramuscular injection of adenovirus (Ad) and/or of DNA with electrostimulation (DNA+ES), both expressing the rat p185(neu) protein. A neu cDNA sequence, which exclusively contains codons preferred by highly expressed mammalian genes, was used in this study. This "optimized" cDNA displayed higher expression in cultured cells and greater cell-mediated response than the original gene when injected as DNA+ES. Ad expressing the optimized sequence (Ad5-neu.opt) induced a higher immune response, as measured by the frequency of IFN-gamma-secreting spleen cells and antibody titers. Different Ad/DNA combinations and immunization schedules confirmed the superiority of Ad5-neu.opt in inducing a strong Th1-skewed humoral and CD8(+) cell-mediated response. Two Ad5-neu.opt injections of 10(9) viral particles at week 10 and 12 were sufficient to induce the highest response, which persisted at detectable levels up to 33 weeks of age. Anti-Ad5 antibodies elicited by previous injections neutralized the effect of an additional Ad5-neu.opt immunization at week 19. A group, which received 3 injections of DNA+ES at week 23, 27 and 31, in addition to the 3 Ad injections at week 10, 12 and 19 showed an increased frequency of IFN-gamma(+), CD8(+) PBMC at week 25, which persisted at detectable levels till week 38. Ad5-neu.opt administration at 10 and 12 weeks of age had a significant impact on tumor progression. At 44 weeks, 40% of the mice were completely protected from tumors with a mean tumor of 3.8. In contrast, control mice developed 10 tumors and died by week 27. Vaccination blocked the tumor development at the atypical hyperplasia stage present at the time of treatment. Tumors developing at later times express reduced levels of rat p185(neu) protein.

Peptide vaccine given with a Toll-like receptor agonist is effective for the treatment and prevention of spontaneous breast tumors

Our goal is to develop peptide vaccines that stimulate tumor antigen-specific T-cell responses against frequently found cancers. Previous work has shown that to generate effective T-cell responses, peptides have to be administered in combination with strong adjuvants such as Toll-like receptor agonists. However, most animal tumor model systems used to study peptide vaccines were not truly representative of malignant diseases in humans because they solely used transplantable tumor lines, and instead of true tumor antigens, they used highly immunogenic foreign proteins. Here, we describe a peptide vaccination strategy, which is highly effective in delaying or preventing the occurrence of spontaneous breast tumors. Transgenic female BALB-neuT mice that carry the activated rat HER-2/neu oncogene were vaccinated with a synthetic peptide from the rat HER-2/neu gene product, which represents an epitope for CTLs in combination with a Toll-like receptor agonist adjuvant. Our results show that to obtain tumor antigen-specific CTL responses and antitumor effects, the vaccine had to be administered repetitively, or the function of CD4/CD25 T regulatory cells had to be blocked with anti-CD25 antibody therapy. Mice that were vaccinated with this approach remained tumor-free or were able to control spontaneous tumor growth and exhibited long-lasting CTL responses, not only against the immunizing peptide but also against other peptides derived from rat HER-2/neu product (i.e., epitope spreading). These results suggest that similar strategies should be followed for conducting clinical studies in patients.

Immunogenicity and safety of a DNA prime/adenovirus boost vaccine against rhesus CEA in nonhuman primates

Scaling up experimental protocols from rodents to humans is often not a straightforward procedure, and this particularly applies to cancer vaccines, where vaccination technology must be especially effective to overcome a variety of immune suppressive mechanisms. DNA electroporation (DNA-EP) and adenoviral vectors (Ad) have shown high potency and therapeutic efficacy for different antigens in several pre-clinical models. To evaluate the ability of DNA-EP and Ad to break tolerance to a self-antigen in large animals, we have cloned the CEA homologue (rhCEA) from rhesus monkeys (Macaca mulatta) colon tissue samples. rhCEA is a 705 aa protein and shares 78.9% homology to human CEA protein. Immunogenicity of rhCEA expressing vectors was tested in mice and subsequently in rhesus monkeys. To further increase the immunogenic potency of these vectors, a synthetic codon optimized rhCEA cDNA (rhCEAopt) was constructed. Genetic vaccination of rhesus monkeys was effective in breaking immune tolerance to rhCEA in all immunized animals, maintaining over time the elicited immune response, and most importantly, neither autoimmunity nor other side-effects were observed upon treatment. Our data confirm the efficacy of genetic cancer vaccines in large animals such as nonhuman primates and show that development of modified expression cassettes that result in increased potency of plasmid DNA and adenovirus may have a significant impact on vaccine development against malignancies expressing tumor associated antigens in patients.

Establishment and characterization of new mammary adenocarcinoma cell lines derived from double transgenic mice expressing GFP and neu oncogene

A new murine cell line, named GFPneu, was established from a mammary adenocarcinoma arising in double transgenic MMTVneu x CMV-GFP mice. Breast tumours develop in 100% of females after 2 months latency, as a result of the over-expression of the activated rat neu oncogene in the mammary glands. All tissues, and in particular the breast tumours, express the GFP protein. This cell line was tumorigenic when inoculated into nude mice and the derived tumours showed the same histological features as the primaries from which they were isolated. Their histopathology reproduces many characteristics of human breast adenocarcinomas, in particular their ability to metastasize. The GFP marker allows us to visualize the presence of lung metastases in fresh tissues immediately, to confirm the histopathology. From a lung metastatic fluorescent nodule, we derived a further cell line, named MTP-GFP, which we also characterized. These two cell lines could be useful to study the role played by the neu oncogene in the maintenance of the transformed phenotype, in the metastatic process, to test novel therapeutic strategies to inhibit primary tumour growth and to observe the generation of distant metastases.

Individual mouse analysis of the cellular immune response to tumor antigens in peripheral blood by intracellular staining for cytokines

Among the experimental animal models, mice remain the most widely used for the evaluation of immunotherapeutic strategies. Vaccines against parasites and viral antigens are commonly administered to the appropriate mouse strain which also allows testing of the therapeutic effect. Similarly, in mice transgenic for human tumor associated antigens (TAA), cancer vaccines must lead to breakage of immune tolerance to elicit a significant effect on the tumor. However, one of the major drawbacks in the monitoring of cellular immune responses induced by vaccination is that functional immunological assays require suppression of the animals to collect the spleen or lymph nodes for analysis. Here, we report the application of a rapid intracellular staining (ICS) method to quantify antigen-specific T cells responses in small volumes of murine blood. Genetic vaccination with plasmid DNA followed by electroporation (DNA-EP) and the use of adenoviral vectors (Ad) encoding CEA as a model target antigen were applied to different strains of mice. Optimal blood volume, number of lymphocytes, sensitivity and reproducibility of intracellular staining for IFN-gamma were determined both in non-tolerant/wild type mice as well as in tolerant CEA transgenic mice upon restimulation of PBMCs with CEA peptides. Groups of vaccinated mice were then sacrificed and PBMCs and splenocytes from individual animals were compared for intracytoplasmic detection of IFN-gamma and TNF-alpha. A significant correlation was observed between splenic and blood immune responses. Finally, the cellular immune response was followed over time in groups of vaccinated mice. The kinetics of IFN-gamma producing effectors were measured after priming and successive boosting with adenoviral vectors. We show that intracellular staining for mouse PBMCs is a rapid and simple method to measure antigen-specific immune responses. It does not require animal euthanasia and mirrors the response observed in lymphoid organs such as the spleen.

Activity of DNA vaccines encoding self or heterologous Her-2/neu in Her-2 or neu transgenic mice

To assess the efficacy of self versus heterologous ErbB-2 vaccines, the reactivity to human and rat ErbB-2 (Her-2 and neu, respectively) DNA vaccines were tested in normal, Her-2 or neu transgenic mice. When immunized with either Her-2 or neu DNA, normal BALB/c and C57BL/6 mice produced cross-reactive T cells, but only antigen specific antibodies. In Her-2 Tg mice, weak to no anti-Her-2 response was induced by either self Her-2 or heterologous neu DNA, demonstrating profound tolerance to Her-2 and the inability to induce anti-Her-2 immunity with either vaccine. In NeuT mice, vaccination with self neu but not heterologous Her-2 DNA induced anti-neu antibodies and delayed spontaneous tumorigenesis. Both neu and Her-2 DNA induced anti-neu T cell response, but depletion of CD8 T cells did not change the delay in tumorigenesis. Therefore, in NeuT mice, both self and heterologous DNA activated anti-neu T cells, although T cell response did not reach sufficient level to suppress spontaneous tumorigenesis. Rather, induction of anti-neu antibodies by self neu DNA is associated with the delay in spontaneous tumor growth. Overall, NeuT mice were more responsive to DNA vaccination than Her-2 Tg mice and this may be associated with the continuous production of neu by the 10 mammary glands undergoing tumor progression.

Tissue-specific sensitivity to AID expression in transgenic mouse models

Activation-induced cytidine deaminase (AID), an enzyme with homology to members of the APOBEC family, is involved in somatic hypermutation (SHM) of immunoglobulin (Ig) genes, either by direct deamination of DNA or by an indirect action through its putative RNA editing activity. AID is able to mutate both Ig-like reporter constructs and selected non-Ig genes in normal B cells and in other cells when ectopically overexpressed in mammalian cells and transgenic mice. However, in spite of the fact that in these transgenic animals AID activity was driven by an ubiquitous promoter, only T lymphomas and lung adenomas occurred. In the present work, we constructed three sets of transgenic mice in which AID was under the control of lck, HTLV-I and MMTV promoters, respectively. The lck/AID mice developed thymic lymphomas with variable but high efficiency, while no tumor was detected in HTLV-I/AID mice after two years of monitoring. Four MMTV/AID founder mice died with an atypical clinical picture, although no mammary tumor was found. These findings suggest that additional factors, present in thymocytes but not in other tissues or in lymphoid cells at different stages of differentiation, are needed for AID to fully manifest its tumorigenic potential in mouse. Alternatively, the display of full AID mutagenic and transforming activity could be related to the existence of physiologic DSBs which occur in both thymocytes and switching B cells.

p130Cas as a new regulator of mammary epithelial cell proliferation, survival, and HER2-neu oncogene-dependent breast tumorigenesis

To investigate the mechanisms through which p130Cas adaptor protein is linked to tumorigenesis, we generated mouse mammary tumor virus (MMTV)-p130Cas mice overexpressing p130Cas in the mammary gland. MMTVp130Cas transgenic mice are characterized by extensive mammary epithelial hyperplasia during development and pregnancy and by delayed involution at the end of lactation. These phenotypes are associated with activation of Src kinase, extracellular signal-regulated kinase 1/2, mitogen-activated protein kinase, and Akt pathways, leading to an increased rate of proliferation and a decreased apoptosis. A double-transgenic line derived from crossing MMTV-p130Cas with MMTV-HER2-Neu mice expressing the activated form of the HER2-Neu oncogene develops multifocal mammary tumors with a significantly shorter latency than the HER2-Neu parental strain alone. Mammary epithelial cells isolated from tumors of double-transgenic mice display increased tyrosine phosphorylation, c-Src, and Akt activation compared with cells derived from HER2-Neu tumors. In addition, p130Cas down-regulation by RNA interference increases apoptosis in HER2-Neu-expressing cells, indicating that p130Cas regulates cell survival. Consistently with the double-transgenic mice model, p130Cas is overexpressed in a significant subset of human breast cancers and high levels of p130Cas in association with HER2 expression correlate with elevated proliferation. These findings provide evidences for a role of p130Cas as a positive regulator of both proliferation and survival in normal and transformed mammary epithelial cells. Its overexpression contributes to HER2-Neu-induced breast tumorigenesis, thus identifying this protein as a putative target for clinical therapy.

Adenovirus as vehicle for anticancer genetic immunotherapy

Adenoviruses (Ads) are in the forefront of genetic immunization methods being developed against cancer. Their ability to elicit an effective immune response against tumor-associated antigens has been demonstrated in many model systems. Several clinical trials, which use Ad as vehicle for immunization, are already in progress. Preclinical studies have also demonstrated the efficacy of combining Ad-mediated immunization with adjuvants such as chemotherapeutic agents and cytokines. Issues related to sero-prevalence and safety of Ads, however, continue to pose a challenge and need to be addressed.

Vaccination for Treatment and Prevention of Cancer in Animal Models

Two approaches to immunological intervention in tumor-host interactions in mouse models are discussed in this review. The first is described with reference to experiments in which CD8(+) T lymphocytes are used to kill established transplantable tumors. Peptides and their optimal presentation by dendritic cells and intervention in immune regulatory mechanisms are the key issues for efficient induction of T-killer cell-mediated tumor eradication. The time frame of tumor therapy and the threat imposed by tumor growth in transplantable models and cancer patients require the induction of a robust T-cell reaction. Prevention of the progression of small preneoplastic lesions, on the other hand, requires the significant and prolonged immune protection sought in the second approach. This is based on antibody production and the coordinated activation of multiple low-avidity cell-mediated mechanisms elicited by DNA vaccination in genetically modified cancer-prone mice, transgenic for a mutant Her-2/neu growth factor receptor expressed at the plasma membrane surface of preneoplastic mammary gland epithelial cells. Vaccination with appropriate DNA formulations results in prolonged immune inhibition of the progression of preneoplastic mammary lesions but is ineffective against established tumors. The use of molecularly defined adjuvants and intervention in immune regulatory mechanisms are critical in both the elicitation of an effective T-cell mediated reaction required for tumor debulking in the first set of models and the induction by vaccination of a sustained immune memory able to prevent the expansion of preneoplastic lesions in genetically cancer-prone mice.

Nordihydroguaiaretic Acid (NDGA) Inhibits the IGF-1 and c-erbB2/HER2/neu Receptors and Suppresses Growth in Breast Cancer Cells

Nordihydroguaiaretic acid (NDGA) is a phenolic compound isolated from the creosote bush Larrea divaricatta that has anti-cancer activities both in vitro and in vivo. We can now attribute certain of these anti-cancer properties in breast cancer cells to the ability of NDGA to directly inhibit the function of two receptor tyrosine kinases (RTKs), the insulin-like growth factor receptor (IGF-1R) and the c-erbB2/HER2/neu (HER2/neu) receptor. In MCF-7 human breast cancer cells, low micromolar concentrations of NDGA inhibited activation of the IGF-1R, and downstream phosphorylation of both the Akt/PKB serine kinase and the pro-apoptotic protein BAD. In mouse MCNeuA cells, NDGA also inhibited ligand independent phosphorylation of HER2/neu. To study whether this inhibitory effect in cells was due to a direct action on these receptors, we studied the IGF-1-stimulated tyrosine kinase activity of isolated IGF-1R, which was inhibited by NDGA at 10 muM or less. NDGA was also effective at inhibiting autophosphorylation of the isolated HER2/neu receptor at similar concentrations. In addition, NDGA inhibited IGF-1 specific growth of cultured breast cancer cells with an IC50 of approximately 30 muM. NDGA treatment (intraperitoneal injection 3 times per week) also decreased the activity of the IGF-1R and the HER2/neu receptor in MCNeuA cells implanted into mice. This inhibition of RTK activity was associated with decreased growth rates of MCNeuA cells in vivo. These studies indicate that the anti-breast cancer properties of NDGA are related to the inhibition of two important RTKs. Agents of this class may therefore provide new insights into potential therapies for this disease.

The loss of PIN1 deregulates cyclin E and sensitizes mouse embryo fibroblasts to genomic instability

During the G0/G1-S phase transition, the timely synthesis and degradation of key regulatory proteins is required for normal cell cycle progression. Two of these proteins, c-Myc and cyclin E, are recognized by the Cdc4 E3 ligase of the Skp1/Cul1/Rbx1 (SCF) complex. SCF(Cdc4) binds to a similar phosphodegron sequence in c-Myc and cyclin E proteins resulting in ubiquitylation and degradation of both proteins via the 26 S proteosome. Since the prolyl isomerase Pin1 binds the c-Myc phosphodegron and participates in regulation of c-Myc turnover, we hypothesized that Pin1 would bind to and regulate cyclin E turnover in a similar manner. Here we show that Pin1 regulates the turnover of cyclin E in mouse embryo fibroblasts. Pin1 binds to the cyclin E-Cdk2 complex in a manner that depends on Ser384 of cyclin E, which is phosphorylated by Cdk2. The absence of Pin1 results in an increased steady-state level of cyclin E and stalling of the cells in the G1/S phase of the cell cycle. The cellular changes that result from the loss of Pin1 predispose Pin1 null mouse embryo fibroblasts to undergo more rapid genomic instability when immortalized by conditional inactivation of p53 and sensitizes these cells to more aggressive Ras-dependent transformation and tumorigenesis.

Wnt pathway is involved in pleomorphic adenomas induced by overexpression of PLAG1 in transgenic mice

Pleomorphic adenoma gene 1 (PLAG1) was found frequently rearranged and activated in human salivary gland pleomorphic adenomas. It encodes a developmentally regulated transcription factor. Ectopic overexpression of PLAG1 has been proposed to play a crucial role in tumorigenesis of salivary gland pleomorphic adenomas. It was reported that PLAG1 can activate the transcription of insulin-like growth factor 2 (IGF2), functioning as a protooncogene. In this report, we show that the salivary gland tumors developed in PLAG1 transgenic mice share major histopathologic features with human pleomorphic adenomas. It was found that beta-catenin, the key component of Wnt signaling pathway, was upregulated at transcriptional level in tumors developed in 3 independent transgenic mouse lines. Immunohistochemical staining revealed that expression of beta-catenin as well as c-myc, downstream of beta-catenin in Wnt signaling pathway, was highly upregulated with overexpression of PLAG1 transgene in tumor and normal transgenic salivary gland tissues. Moreover, we found that PLAG1 can activate the transcription of mouse but not human beta-catenin in the 3T3 cells cotransfected with reporter constructs. Sequence analysis shows there are 4 PLAG1 consensus binding sites in mouse beta-catenin promoter region but not in human. Our findings provide the first in vivo evidence for the oncogenic activity of PLAG1 in pleomorphic adenoma tumorigenesis, reveal a valued animal model for human salivary gland tumors and suggest that Wnt signaling pathway may also contribute to the development of pleomorphic adenomas in transgenic mice.

T cell-mediated delay of spontaneous mammary tumor onset: increased efficacy with in vivo versus in vitro activation

Peripheral tolerance to shared Ags expressed on both tumors and normal self-tissues presents a major barrier to T cell-based immunotherapy as a treatment for cancer. To assess the activity of tumor-specific T cells against spontaneously arising carcinomas in the context of shared Ag expression, we developed a model system whereby an identified tumor Ag, tumor ERK (tERK), is expressed transgenically on both normal mammary tissue and spontaneous mammary carcinomas. Transfer of in vitro-activated, tERK-specific DUC18 T cells delayed spontaneous tumor development in tERK-expressing mice when T cells were given before the development of palpable carcinomas. However, antitumor activity mediated by in vitro-activated DUC18 T cells, as measured by responsiveness against a transplanted tERK-expressing fibrosarcoma challenge, was lost within days of transfer. This loss was due to expression of tERK as a self-Ag on normal tissues and was independent of the presence of mammary tumors. In contrast, transferred naive DUC18 T cells maintained a long-term protective function in tERK-expressing mice. Ten-fold fewer naive T cells activated in vivo were able to replicate the delay in spontaneous tumor development achieved by in vitro-activated T cells. These results are in contrast to our earlier studies using transplanted tumors alone, in which in vitro-activated DUC18 T cells were more efficacious than naive DUC18 T cells and highlight the need to perform tumor studies in the presence of tumor Ag expression on normal self-tissue.

Xenogeneic immunization in mice using HER2 DNA delivered by an adenoviral vector

The protective efficacy of xenogeneic vaccination with DNA encoding the HER2 oncogene was evaluated in BALB/c mice transgenic for the transforming form of the neu oncogene, which spontaneously develops carcinomas in all mammary glands. Intramuscular injection of either plasmid DNA followed by electrical stimulation (pVIJ-HER2 with ES) or an adenoviral vector (Ad5-HER2), both expressing the HER2 oncogene, was tested. Immunization using pVIJ-HER2 with ES elicited a cell-mediated response that was much lower than that elicited by the immunization with Ad5-HER2, as measured by the frequency of IFN-gamma-secreting spleen cells. The dominant T-cell epitope of the HER2 protein product (p185) in the BALB/c (H-2(d)) genetic background was identified. While the T-cell response elicited was only partially crossreactive with the corresponding rat epitopes because of sequence variations (89% similarity), a cytotoxic T-lymphocyte activity against the rat immunodominant epitope was also evident. The Ad5-HER2 vaccination induced also antibodies against p185, which crossreacted with the rat protein homolog. Both T- and B-cell responses slowly declined with time. Vaccination with Ad5-HER2 at 6 and 9 weeks of age delayed incidence and reduced multiplicity of tumors in neu transgenic mice.

Vaccination by genetically modified dendritic cells expressing a truncated neu oncogene prevents development of breast cancer in transgenic mice

Dendritic cells (DCs) are powerful antigen-presenting cells that process antigens and present peptide epitopes in the context of the major histocompatibility complex molecules to generate immune responses. DCs are being studied as potential anticancer vaccines because of their ability to present antigens to naive T cells and to stimulate the expansion of antigen-specific T-cell populations. We investigated an antitumor vaccination using DCs modified by transfer of a nonsignaling neu oncogene, a homologue of human HER-2/neu, in a transgenic model of breast cancer. BALB-neuT mice develop breast cancers as a consequence of mammary gland-specific expression of an activated neu oncogene. We vaccinated BALB-neuT mice with bone marrow-derived DCs transduced with Ad.Neu, a recombinant adenovirus expressing a truncated neu oncoprotein. The vaccine stimulated the production of specific anti-neu antibodies, enhanced interferon-gamma expression by T cells, and prevented or delayed the onset of mammary carcinomas in the mice. Over 65% of vaccinated mice remained tumor free at 28 weeks of age, whereas all of the mice in the control groups developed tumors. When challenged with a neu-expressing breast cancer cell line, vaccinated tumor-free animals had delayed tumor growth compared with controls. The antitumor effect of the vaccine was specific for expression of neu. Studies showed that CD4+ T cells were required in order to generate antitumor immunity. Importantly, the effectiveness of the vaccine was not diminished by preexisting immunity to adenovirus, whereas the protection afforded by vaccination that used direct injection of Ad.Neu was markedly reduced in mice with anti-adenovirus antibody titers. DCs modified by recombinant adenoviruses expressing tumor-associated antigens may provide an effective antitumor vaccination strategy.

Anti–HER-2/neu Immune Responses Are Induced before the Development of Clinical Tumors but Declined following Tumorigenesis in HER-2/neu Transgenic Mice

HER-2/neu oncogene products have been implicated as a potential target of T cell-mediated immune responses to HER-2/neu-induced tumors. Using HER-2/neu transgenic mice (oncomice), we investigated whether, and if so how, anti-HER-2/neu immune responses are induced and modulated in these oncomice from birth to tumor initiation. Female oncomice carrying the activated HER-2/neu oncogene displayed apparent hyperplasia in mammary glands at 10 weeks of age and developed mammary carcinomas around an average age of 26 weeks. Unfractionated spleen cells from 10- to 15-week-old oncomice that were cultured without any exogenous stimuli exhibited cytotoxicity against the F31 tumor cell line established from an HER-2/neu-induced mammary carcinoma mass. The final antitumor effectors were a macrophage lineage of cells. However, this effector population was activated, depending on the stimulation of oncomouse CD4(+) T cells with oncomouse-derived antigen-presenting cell (APC) alone or with wild-type mouse APC in the presence of F31 membrane fractions, suggesting the presence of HER-2/neu-primed CD4(+) T cells and HER-2/neu-presenting APC in 10- to 15-week-old oncomice. These antitumor cytotoxic responses were detected at approximately 5 weeks of age and peaked at age 10 to 15 weeks. However, the responses then declined at tumor-bearing stages in which the expression of target proteins could progressively increase. This resulted from the dysfunction of CD4(+) T cells but not of APC or effector macrophages. These results indicate that an anti-HER-2/neu CD4(+) T cell-mediated immune response was generated at the pretumorigenic stage but did not prevent tumorigenesis and declined after the development of clinical tumors.

Lymphatic drainage imaging of breast cancer in mice by micro-magnetic resonance lymphangiography using a nano-size paramagnetic contrast agent

BACKGROUND

The presence of lymph node metastases is an important factor in breast cancer patient prognosis. Therefore, the precise identification of sentinel lymph nodes in these patients is critical. Improving current magnetic resonance (MR) imaging methods using a newly synthesized nano-size paramagnetic molecule, G6, as a contrast agent, provides an attractive means toward attaining this goal.

METHODS

A four-dimensional method of micro-MR lymphangiography using G6 (9 nm/240 kd) was developed to visualize the lymphatic ducts and lymph nodes draining mouse mammary tumors over time. The ability of micro-MR lymphangiography with the G6 contrast agent to visualize lymphatic drainage of normal mouse mammary tissue was compared with that of the conventional MR contrast agent, Gd-[DTPA]-dimeglumine (<1 kd). Lymphatic drainage in spontaneous and xenografted breast tumor models was visualized using the G6 contrast agent.

RESULTS

Draining lymphatic ducts and lymph nodes were clearly visualized in the mammary tissue of normal mice and in spontaneous and xenografted breast tumor models after a direct mammary gland or peritumoral injection of G6. Gd-[DTPA]-dime-glumine, by contrast, failed to depict lymphatic flow from the mammary tissue in normal mice using the same method. Micro-MR lymphangiography using the G6 contrast agent revealed the absence of filling in the metastatic foci of affected lymph nodes.

CONCLUSIONS

The superior temporal and spatial resolution of micro-MR lymphangiography using the contrast agent G6 may facilitate the study of tumor lymphatic drainage and lymphatic metastasis in both experimental animals and clinical medicine. In addition, this may be a powerful new method for sentinel lymph node localization in human breast cancer.

Concordant morphologic and gene expression data show that a vaccine halts HER-2/neu preneoplastic lesions

While much experimental data shows that vaccination efficiently inhibits a subsequent challenge by a transplantable tumor, its ability to inhibit the progress of autochthonous preneoplastic lesions is virtually unknown. In this article, we show that a combined DNA and cell vaccine persistently inhibits such lesions in a murine HER-2/neu mammary carcinogenesis model. At 10 weeks of age, all of the ten mammary gland samples from HER-2/neu-transgenic mice displayed foci of hyperplasia that progressed to invasive tumors. Vaccination with plasmids coding for the transmembrane and extracellular domain of rat p185neu followed by a boost with rp185neu+ allogeneic cells secreting IFN-gamma kept 48% of mice tumor free. At 22 weeks, their mammary glands were indistinguishable from those of 10-week-old untreated mice. Furthermore, the transcription patterns of the two sets of glands coincided. Of the 12,000 genes analyzed, 17 were differentially expressed and related to the antibody response. The use of B cell knockout mice as well as the concordance of morphologic and gene expression data demonstrated that the Ab response is the main mechanism facilitating tumor growth arrest. This finding suggests that a new way can be found to secure the immunologic control of the progression of HER-2/neu preneoplastic lesions.

Inactivation of p53 tumor suppressor gene acts synergistically with c-neu oncogene in salivary gland tumorigenesis

Transgenic mice expressing specific oncogenes usually develop tumors in a stochastic fashion suggesting that tumor progression is a multi-step process. To gain further understanding of the interactions between oncogenes and tumor suppressor genes during tumorigenesis, we have crossed a transgenic strain (TG.NK) carrying an activated c-neu oncogene driven by the MMTV enhancer/promoter with p53-deficient mice. c-neu transgenic mice have stochastic breast tumor formation and normal appearing salivary glands. However, c-neu mice heterozygous for a p53 deletion develop parotid gland tumors and loose their wild type p53 allele. c-neu mice with a homozygous p53 deletion have increased rates of parotid tumor onset suggesting that inactivation of p53 is required and sufficient for parotid gland transformation in the presence of activated c-neu. In contrast to the dramatic effect of p53 in parotid gland transformation, p53 loss has little effect on the rate or stochastic appearance of mammary tumors. In addition, p53 loss was accompanied by the down regulation of p21 in parotid gland tumors but not breast tumors. The parotid gland tumors were aneuploid and demonstrated increased levels of Cyclin D1 expression. These observations suggest that in c-neu transgenic mice, p53 alterations have differential tissue effects and may be influenced by the tissue specific expression of genes influencing p53 activity.

Loss of p21WAF1/CIP1 accelerates Ras oncogenesis in a transgenic/knockout mammary cancer model

Upregulation of the cyclin-dependent kinase inhibitor p21WAF1/CIP1 and subsequent cell growth arrest or senescence is one mechanism by which normal cells are believed to respond to stress induced by the constitutively activated GTPase Ras. We hypothesize that in the absence of p21, the onset of Ras-dependent oncogenesis is accelerated. To test this hypothesis, we crossed MMTV/v-Ha-ras transgenic mice into a p21-deficient background. By 63 days of age, all 8 ras/p21-/- mice developed either malignant (mammary and/or salivary adenocarcinomas) or benign (Harderian hyperplasia) tumors. In contrast, by the same age, only one out of nine of the ras/p21+/+ mice developed a tumor. Furthermore, by 94 days of age, half of the ras/p21-/- mice, but none of the ras/p21+/+ mice, developed mammary tumors. p21-deficiency also accelerated the development of salivary (T50=66 days for ras/p21-/- vs T50=136 days for ras/p21+/+) and Harderian (T50=52 days for ras/p21-/- vs T50>221 days for ras/p21+/+) tumors. Furthermore, two out of the eight ras/p21-/- mice had metastatic lesions, one in its lungs, the other in its abdomen. None of the nine ras/p21+/+ mice had metastatic lesions. By 4 months of age, the mammary tumor multiplicity was 10-fold greater in ras/p21-/- (average 3.40 tumors/mouse) than in ras/p21+/+ (average 0.33 tumor/mouse) mice. However, once the tumors appeared, their growth rate, apoptosis level, and mitotic index were not affected by the loss of p21, suggesting that loss of p21 is critical in early but not late events of Ras oncogenesis. Altogether, the results show that tumor onset in MMTV/v-Ha-ras mice is p21-dependent with loss of p21 associated with earlier tumor appearance and increased tumor multiplicity and aggressiveness.

Submandibular gland adenocarcinoma of intercalated duct origin in Smgb-Tag mice

A line of transgenic mice that develops submandibular gland adenocarcinoma of intercalated duct origin was established. In these mice, the oncogene SV40 T antigen (Tag) is expressed from the neonatal submandibular gland secretory protein b (Smgb) gene promoter. This hybrid gene directs expression of the oncoprotein to neonatal submandibular gland proacinar and terminal tubule cells and to intercalated ducts of the adult gland. Transgene expression resulted in duct luminal cell hyperplasia as early as 20 to 30 days postnatally, which progressed to dysplasia by 3 to 4 months of age. Marked dysplasia and in situ carcinoma were evident at 4 to 6 months of age. All histologic changes were more pronounced in males. Submandibular gland adenocarcinoma developed stochastically in more than half of the adult male mice by 12 months of age (average age: 10.8 months, range: 6 to 13.5 months). Tag expression persisted in in situ carcinoma and all tumors. Using a combination of immunocytochemical and ultrastructural criteria, submandibular gland dysplasia and tumors were found to originate from intercalated ducts. The dysplastic ducts and adenocarcinoma in Smgb-Tag mice were morphologically similar to previously reported Tag-induced dysplasias of striated ducts and granular convoluted tubules and a Tag-induced adenocarcinoma of striated duct origin. These findings demonstrate that salivary gland dysplasias and tumors of similar histologic appearance can arise from distinct differentiated cell types. Analysis of the molecular changes accompanying tumor formation in Smgb-Tag mice could increase knowledge of human salivary gland tumorigenesis.

Mammary gland neoplasia: insights from transgenic mouse models

Current theories of breast cancer progression have been greatly influenced by the development and refinement of mouse transgenic and gene targeting technologies. Early transgenic mouse models confirmed the involvement of oncogenes, previously implicated in human breast cancer, by establishing a causal relationship between overexpression or activation of these genes and mammary tumorigenesis. More recently, the importance of genes located at sites of loss of heterozygosity in human breast cancer have been examined in mice by their targeted disruption via homologous recombination. The union of these two approaches allows the generation of complex animal models that more accurately reflect the multistep nature of human breast cancer. This review will examine how the study of transgenic mice has increased our understanding of the molecular events responsible for oncogenic transformation of the mammary gland. BioEssays 22:554-563, 2000.

Signal transduction in mammary tumorigenesis: a transgenic perspective

A number of genes have been implicated in breast cancer development, yet few have been demonstrated to play causative roles in mammary tumor formation. The advent of transgenic mouse and embryonic stem cell technologies now permits manipulation of the mouse genome in such a way as to temporally and spatially control a gene product's expression. Thus, the basic researcher now can directly assess the involvement of particular genes in tumorigenesis and disease progression and, in the process, to develop mouse models of human genetic disease. The utility of such technologies is emphasized in transgenic mice expressing genes thought to play important roles in the initiation and progression of mammary carcinomas. As these transgenic strains have been the subject of several reviews, here we focus on two mouse mammary tumor models, Polyomavirus middle T antigen and the Neu/ErbB-2 receptor tyrosine kinase, which are most amenable to study specific signaling pathways in process of mammary tumorigenesis.

Tyrosine kinase signalling in breast cancer: tyrosine kinase-mediated signal transduction in transgenic mouse models of human breast cancer

The ability of growth factors and their cognate receptors to induce mammary epithelial proliferation and differentiation is dependent on their ability to activate a number of specific signal transduction pathways. Aberrant expression of specific receptor tyrosine kinases (RTKs) has been implicated in the genesis of a significant proportion of sporadic human breast cancers. Indeed, mammary epithelial expression of activated RTKs such as ErbB2/neu in transgenic mice has resulted in the efficient induction of metastatic mammary tumours. Although it is clear from these studies that activation these growth factor receptor signalling cascades are directly involved in mammary tumour progression, the precise interaction of each of these signalling pathways in mammary tumourigenesis and metastasis remains to be elucidated. The present review focuses on the role of several specific signalling pathways that have been implicated as important components in RTK-mediated signal transduction. In particular, it focuses on two well characterized transgenic breast cancer models that carry the polyomavirus middle T(PyV mT) and neu oncogenes.

The role of the epidermal growth factor receptor family in mammary tumorigenesis and metastasis

A number of receptor systems have been implicated to play an important role in the development and progression of many human cancers. The epidermal growth factor (EGF) receptor tyrosine kinase family has been found to consistently play a leading role in tumor progression. Indeed, in human breast cancer cases the prognosis of a patient is inversely correlated with the overexpression and/or amplification of this receptor family. Furthermore, downstream signaling components such as the Src kinases, PI3'K, and the Ras pathway display evidence of deregulation that can accelerate tumor progression. The transgenic mouse system has been ideal in elucidating the biological significance of this receptor family in mammary tumorigenesis. Molecular events involved in mammary tumorigenesis such as ligand binding, receptor dimerization, and the activation of downstream pathways have been addressed using this system. Although there are many molecular steps that appear to drive each stage of tumor development, the EGF receptor family appears to play a causal role in the progression to a transformed phenotype.

Retrovirus-mediated IL-4 gene therapy in spontaneous adenocarcinomas from MMTV-neu transgenic mice

Gene therapy approaches to the treatment of experimental cancer are usually based on established neoplastic cell lines which are manipulated in vitro and subsequently transplanted in host animals. However, the relevance of these artificial models to the biology and therapy of human tumors is uncertain. We have previously validated an experimental model based on MMTV-neu transgenic mice in which breast tumors arise spontaneously in 100% of animals and have many features in common with their human counterpart, including the involvement of the neu oncogene and the ability to metastatize. In this article we report the effect of intratumoral, retrovirus-mediated, IL-4 expression on the growth of breast tumors arising in these mice. The size of IL-4 inoculated tumors on the right side was significantly smaller than that of controlateral untreated tumors, suggesting a local effect of IL-4. In addition, the non-injected tumors on the left side of treated animals were significantly smaller than those arising in control transgenic mice, suggesting that IL-4 can also inhibit tumor growth systemically. These findings suggest that IL-4 gene transfer can significantly reduce the growth rate of spontaneously arising breast tumors and that immune-based gene therapy could efficiently complement other approaches based on different mechanisms, such as suicide gene transfer or antisense technology.

Development of hyperplasias, preneoplasias, and mammary tumors in MMTV-c-erbB-2 and MMTV-TGFalpha transgenic rats

Human cDNAs corresponding to two epidermal growth factor-related products that are overexpressed in human breast cancers, that for c-erbB-2 (HER-2) and for transforming growth factor alpha (TGFalpha), have been cloned downstream of the mouse mammary tumor virus (MMTV) long terminal repeat promoter and injected into the pronucleus of fertilized oocytes of Sprague-Dawley rats to produce transgenic offspring. Expression of the transgenic mRNAs is not detectable in mammary tissue from virgin transgenic rats but is detected in mammary tissue from certain lines of mid-pregnant transgenic rats. When two such lines of either type of transgenic rat are subjected to repeated cycles of pregnancy and lactation, they produce, primarily in the mammary glands, extensive pathologies, whereas virgin transgenic rats produce no such abnormalities. Multiparous transgenic female offspring from c-erbB-2-expressing lines develop a variety of focal hyperplastic and benign lesions that resemble lesions commonly found in human breasts. These lesions include lobular and ductal hyperplasia, fibroadenoma, cystic expansions, and papillary adenomas. More malignant lesions, including ductal carcinoma in situ and carcinoma, also develop stochastically at low frequency. The mammary glands of transgenic females invariably fail to involute fully after lactation. Similar phenotypes are observed in female MMTV-TGFalpha transgenic rats. In addition, multiparous TGFalpha-expressing female transgenics frequently develop severe pregnancy-dependent lactating hyperplasias as well as residual lobules of hyperplastic secretory epithelium and genuine lactating adenomas after weaning. These transgenic rat models confirm the conclusions reached in transgenic mice that overexpression of the c-erbB-2 and TGFalpha genes predisposes the mammary gland to stochastic tumor development.

Elevated expression of activated forms of Neu/ErbB-2 and ErbB-3 are involved in the induction of mammary tumors in transgenic mice: implications for human breast cancer

To assess the importance of Neu activation during mammary tumorigenesis, altered receptors harboring in-frame deletions within the extracellular domain were expressed in transgenic mice. Females from several independent lines develop multiple mammary tumors that frequently metastasize to the lung. Tumor progression in these strains was associated with elevated levels of tyrosine-phosphorylated Neu and ErbB-3. Consistent with these observations, a survey of primary human breast tumors revealed frequent co-expression of both erbB-2 and erbB-3 transcripts. The ability of altered Neu receptors to induce mammary tumorigenesis in transgenic mice prompted us to examine whether similar mutations occurred in ErbB-2 during human breast cancer progression. Interestingly, an alternatively spliced form of erbB-2, closely resembling spontaneous activated forms of neu, was detected in human breast tumors. The ErbB-2 receptor encoded by this novel transcript harbors an in-frame deletion of 16 amino acids in the extracellular domain and can transform Rat-1 fibroblasts. Together, these observations argue that co-expression of ErbB-2 and ErbB-3 may play a critical role in the induction of human breast tumors, and raise the possibility that activating mutations in the ErbB-2 receptor may also contribute to this process.

Interleukin 12-mediated prevention of spontaneous mammary adenocarcinomas in two lines of Her-2/neu transgenic mice

The ability of interleukin (IL)-12 to prevent tumors when administered to individuals with a genetic risk of cancer was studied in two lines of transgenic mice expressing rat HER-2/neu oncogene in the mammary gland. Female BALB/c (H-2(d)) mice carrying the activated HER-2/ neu oncogene show no morphological abnormalities of the mammary gland until 3 wk of age. They then progress through atypical hyperplasia to in situ lobular carcinoma and at 33 wk of age all 10 mammary glands display invasive carcinomas. Adult FVB mice (H-2(q)) carrying the HER-2/neu protooncogene develop mammary carcinomas with a longer latency (38-49 wk) and a lower multiplicity (mean of 2.6 tumors/mice). Treatment with IL-12 (5 daily intraperitoneal injections, 1 wk on, 3 wk off; the first course with 50 ng IL-12/day, the second with 100 ng IL-12/day) begun at 2 wk of age in BALB/c mice and at 21 wk of age in FVB mice markedly delayed tumor onset and reduced tumor multiplicity. Analogous results were obtained in immunocompetent and permanently CD8(+) T lymphocyte-depleted mice. In both transgenic lines, tumor inhibition was associated with mammary infiltration of reactive cells, production of cytokines and inducible nitric oxide synthase, and reduction in microvessel number, in combination with a high degree of hemorrhagic necrosis.

Establishment and characterization of a new mammary adenocarcinoma cell line derived from MMTV neu transgenic mice

A new murine cell line, named MG1361, was established from mammary adenocarcinomas arising in a MMTV-neu transgenic mouse lineage where breast tumors develop in 100% of females, due to the overexpression of the activated rat neu oncogene in the mammary gland. The MG1361 cell line shows an epithelial-like morphology, has a poor plating efficiency, low clonogenic capacity, and a doubling time of 23.8 hours. Karyotype and flow cytometry analysis revealed a hypotetraploid number of chromosomes, whereas cell cycle analysis showed 31.2% of cells to be in the G1 phase, 21.4% in S and 47.4% in G2 + M. This cell line maintains a high level of neu expression in vitro. The MG1361 cell line was tumorigenic when inoculated in immunodeficient (nude) mice and the derived tumors showed the same histological features as the primary tumors from which they were isolated. MG1361 cells were positive for specific ER and PgR binding which was competed by tamoxifen, making this cell line useful for the evaluation of endocrine therapy. Moreover, they were sensitive to etoposide treatment, suggesting that they could be a model for the study of chemotherapy-induced apoptosis. As the tumors arising in MMTV-neu transgenic mice have many features in common with human mammary adenocarcinomas (Sacco et al., Gene Therapy 1995; 2: 493-497), this cell line can be utilized to perform basic studies on the role of the neu oncogene in the maintenance of the transformed phenotype, and to test novel protocols of therapeutic strategies.

The insulin receptor content is increased in breast cancers initiated by three different oncogenes in transgenic mice

The Insulin Receptor (IR) is a potential oncogene for mammary epithelial cells since its content is increased in most human breast cancer specimens, and both ligand-dependent malignant transformation and ligand-dependent enhanced growth occurs in cultured breast cells overexpressing the IR. To better understand whether the IR plays a role in mammary carcinogenesis which is independent of other initiation factors, we measured IR content in transgenic mouse models of breast cancer induced by 3 known oncogenes (Wnt-1, Neu, and Ret). Insulin receptor content was measured by a specific radioimmunoassay. In normal mammary gland tissues IR content was 14.6 +/- 1.4 ng/mg of protein (mean +/- SEM, n = 6). In the 3 cancers IR content was elevated (Neu = 36.1 +/- 4.6, n = 8, p < 0.002; Wnt-1 = 38.3 +/- 2.6, n = 13, p < 0.001; and Ret = 53.6 +/- 7.1, n = 7, p < 0.001). These data indicate that IR overexpression, in addition to being a potential oncogene, is increased in mouse tumors initiated by other oncogenes, and therefore may also play a supportive role in the growth of breast cancers.

Identification of a specific DNA region required for enhanced transcription of HER2/neu in the MDA-MB453 breast cancer cell line

Overexpression and/or amplification of the HER2/neu gene has been shown in roughly 30% of breast cancer patients. Increased levels of HER2/neu mRNA in some breast cancer cell lines is partially caused by increased gene transcription. In MDA-MB453 human breast cancer cells, an activated trans-acting factor is involved in the increased transcription of HER2/neu by mediating its effects through a specific DNA region in the HER2/neu promoter. A methylation interference experiment showed a novel sequence for protein-DNA interactions. Three polypeptides of approximately 110, 70, and 35 kD interact with this DNA element. This region of the human HER2/neu promoter is highly conserved in the rat and mouse promoters and was shown to be capable of mediating transcriptional trans-activation in HER2/neu-overexpressing MDA-MB453 cells while having little effect in a control cell line that expresses basal levels of HER2/neu. Knowledge on interactions between this DNA element and nuclear protein factors may help us better understand the molecular mechanisms regulating HER2/neu overexpression in breast cancer cells.

Activated neu induces rapid tumor progression

Expression of the activated neu oncogene in transgenic mice has been associated with both the synchronous (single-step) and the stochastic (multistep) transformation of the mammary epithelium. To determine the basis for these conflicting observations, additional strains of transgenic mice carrying the activated neu oncogene under the transcriptional control of the mouse mammary tumor virus promoter/enhancer were produced. Activated neu transgene expression, as measured by in situ hybridization and ribonuclease protection assays, resulted in rapid conversion of the normal mammary epithelium to malignant phenotype in three independent strains of mice. Expression of the transgene in male mice led to epithelial hyperplasia of the epididymis and male infertility but not malignancy. These results indicate that tissue context is an important parameter in malignant progression and that expression of appropriate levels of activated neu is sufficient for rapid production of mammary tumors in transgenic mice.

Transgenic mouse models of breast cancer

Although valuable initial information can be gathered about transformation from in vitro studies, human cancer occurs in the context of a complex interaction with its environment and must ultimately be studied in living animals. Transgenic animal models have been used to study breast transformation for a number of years and have yielded valuable information on the subject. In this paper, we will summarize results from our laboratories, and others, regarding the use of transgenic mice to study breast tumorigenesis. We will also suggest future directions for the use of transgenic models to understand, and hopefully, one day to cure the disease.

Current status of histogenetic and morphogenetic concepts of salivary gland tumorigenesis

Because of their complexity and relative infrequency, salivary gland tumors commonly result in diagnostic problems. Histogenetic and morphogenetic concepts of tumorigenesis in these glands are reviewed and their relevance to routine diagnosis and classification of salivary gland tumors evaluated. Evidence is presented from animal and human studies that under steady-state and pathophysiological conditions, all cell types present in the normal gland, including acinar cells, are capable of rapidly entering the cell cycle and are, therefore, possible targets for neoplastic transformation.