Transgenic Model Of Mammary Cancer Research Articles

Deletion of the murine ortholog of the 8q24 gene desert has anti-cancer effects in transgenic mammary cancer models

BackgroundThe gene desert on human chromosomal band 8q24 harbors multiple genetic variants associated with common cancers, including breast cancer. The locus, including the gene desert and its flanking genes, MYC, PVT1 and FAM84B, is also frequently amplified in human breast cancer. We generated a megadeletion (MD) mouse model lacking 430-Kb of sequence orthologous to the breast cancer-associated region in the gene desert. The goals were to examine the effect of the deletion on mammary cancer development and on transcript level regulation of the candidate genes within the locus.MethodsThe MD allele was engineered using the MICER system in embryonic stem cells and bred onto 3 well-characterized transgenic models for breast cancer, namely MMTV-PyVT, MMTV-neu and C3(1)-TAg. Mammary tumor growth, latency, multiplicity and metastasis were compared between homozygous MD and wild type mice carrying the transgenes. A reciprocal mammary gland transplantation assay was conducted to distinguish mammary cell-autonomous from non-mammary cell-autonomous anti-cancer effects. Gene expression analysis was done using quantitative real-time PCR. Chromatin interactions were evaluated by 3C. Gene-specific patient outcome data were analysed using the METABRIC and TCGA data sets through the cBioPortal website.ResultsMice homozygous for the MD allele are viable, fertile, lactate sufficiently to nourish their pups, but maintain a 10% lower body weight mainly due to decreased adiposity. The deletion interferes with mammary tumorigenesis in mouse models for luminal and basal breast cancer. In the MMTV-PyVT model the mammary cancer-reducing effects of the allele are mammary cell-autonomous. We found organ-specific effects on transcript level regulation, with Myc and Fam84b being downregulated in mammary gland, prostate and mammary tumor samples. Through analysis using the METABRIC and TCGA datasets, we provide evidence that MYC and FAM84B are frequently co-amplified in breast cancer, but in contrast with MYC, FAM84B is frequently overexpressed in the luminal subtype, whereas MYC activity affect basal breast cancer outcomes.ConclusionDeletion of a breast cancer-associated non-protein coding region affects mammary cancer development in 3 transgenic mouse models. We propose Myc as a candidate susceptibility gene, regulated by the gene desert locus, and a potential role for Fam84b in modifying breast cancer development.

Reversal by RARα agonist Am580 of c-Myc-induced imbalance in RARα/RARγ expression during MMTV-Myc tumorigenesis

IntroductionRetinoic acid signaling plays key roles in embryonic development and in maintaining the differentiated status of adult tissues. Recently, the nuclear retinoic acid receptor (RAR) isotypes α, β and γ were found to play specific functions in the expansion and differentiation of the stem compartments of various tissues. For instance, RARγ appears to be involved in stem cell compartment expansion, while RARα and RARβ are implicated in the subsequent cell differentiation. We found that over-expressing c-Myc in normal mouse mammary epithelium and in a c-Myc-driven transgenic model of mammary cancer, disrupts the balance between RARγ and RARα/β in favor of RARγ.MethodsThe effects of c-Myc on RAR isotype expression were evaluated in normal mouse mammary epithelium, mammary tumor cells obtained from the MMTV-Myc transgenic mouse model as well as human normal immortalized breast epithelial and breast cancer cell lines. The in vivo effect of the RARα-selective agonist 4-[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)carboxamido]benzoic acid (Am580) was examined in the MMTV-Myc mouse model of mammary tumorigenesis.ResultsModulation of the RARα/β to RARγ expression in mammary glands of normal mice, oncomice, and human mammary cell lines through the alteration of RAR-target gene expression affected cell proliferation, survival and tumor growth. Treatment of MMTV-Myc mice with the RARα-selective agonist Am580 led to significant inhibition of mammary tumor growth (~90%, P<0.001), lung metastasis (P<0.01) and extended tumor latency in 63% of mice. Immunocytochemical analysis showed that in these mice, RARα responsive genes such as Cyp26A1, E-cadherin, cellular retinol-binding protein 1 (CRBP1) and p27, were up-regulated. In contrast, the mammary gland tumors of mice that responded poorly to Am580 treatment (37%) expressed significantly higher levels of RARγ. In vitro experiments indicated that the rise in RARγ was functionally linked to promotion of tumor growth and inhibition of differentiation. Thus, activation of the RARα pathway is linked to tumor growth inhibition, differentiation and cell death.ConclusionsThe functional consequence of the interplay between c-Myc oncogene expression and the RARγ to RARα/β balance suggests that prevalence of RARγ over-RARα/β expression levels in breast cancer accompanied by c-Myc amplification or over-expression in breast cancer should be predictive of response to treatment with RARα-isotype-specific agonists and warrant monitoring during clinical trials.See related editorial by Garattini et al http://breast-cancer-research.com/content/14/5/111

Abstract 2795: Safety profile and therapeutic potential in breast cancer of STX140, an original tubulin binding agent

Abstract STX-140 is an anti-tubulin binding agent which has demonstrated a good anti-tumor efficacy profile. Although the binding site on tubulin differs from other classical tubulin binders, one could anticipate the same type of safety issues with such an agent, namely neurotoxicity. In order to differentiate this compound, we evaluated its efficacy in a transgenic model of mammary cancer, its neurotoxicity potential, and its therapeutic index in a breast cancer model. STX140 efficacy was evaluated in C3(1) Tag transgenic mice which develop mammary carcinomas. In those transgenic animals, the disease progresses in a similar fashion to human breast cancer, with the development of tumors which show the same histological characteristics as the human pathology. In these mice, STX140 was able to significantly increase the survival of the animals and to suppress the emergence of metastases, whereas paclitaxel was completely inactive on both parameters. Neurotoxicity potential was assessed in a thermal hyperalgesia model in comparison with paclitaxel. Continuous oral treatment of mice with STX-140 did not induce an increase sensibility to heat as measured by the latency of paw withdrawal after a heat stimulus. However, paclitaxel increased this heat sensitivity starting after the second i.v. administration, underlying the neurotoxicity of this compound, which is observed in the clinic. Finally, in MDA-MB-231 breast cancer xenografts, two different schedules of oral administration were evaluated in order to determine the therapeutic index and PK parameters were measured in parallel to the anti-tumor efficacy. Continuous (QD) and intermittent (Monday, Wednesday, Friday; MWF) treatments were evaluated and a large panel of doses were tested. The therapeutic index was determined as the ratio of the exposure observed between the first toxic dose and first active dose. The TI for the QD schedule was 2.1 and was 1.7 for the MWF schedule, showing the potential good safety index of this compound. Taking into account the previous data reported elsewhere and new data presented here, which underline the great efficacy and safety profile of STX140, this compound is considered for further preclinical and clinical development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2795. doi:1538-7445.AM2012-2795

T cell- but not tumor cell-produced TGF-β1 promotes the development of spontaneous mammary cancer

During their development, tumors acquire multiple capabilities that enable them to proliferate, disseminate and evade immunosurveillance. A putative mechanism is through the production of the cytokine TGF-β1. We showed in our recent studies that T cell-produced TGF-β1 inhibits antitumor T cell responses to foster tumor growth raising the question of the precise function of TGF-β1 produced by tumor cells in tumor development. Here, using a transgenic model of mammary cancer, we report that deletion of TGF-β1 from tumor cells did not protect mice from tumor development. However, ablation of TGF-β1 from T cells significantly inhibited mammary tumor growth. Additionally, absence of TGF-β1 in T cells prevented tumors from advancing to higher pathological grades and further suppressed secondary tumor development in the lungs. These findings reveal T cells but not tumor cells as a critical source of TGF-β1 that promotes tumor development.

Abstract B49: Use of MMTV-Neu/P53 KO transgenic mice to screen for potential chemopreventive agents

Abstract The MMTV-Neu transgenic model of mammary cancer was developed almost 20 years ago in which mice develop Neu over-expressing ER- mammary cancers. Since human ER- Neu over-expressing mammary cancers often also have mutations in P53, a heterozygous KO of P53 was incorporated into the model. We used this model to examine a wide variety of potential chemopreventive agents. The agents were routinely administered to virgin female MMTV-Neu/P53 KO mice beginning when they were 60 days of age. Initiation at this time is somewhat later than is often employed in other laboratories (i.e., agents are typically started when mice are roughly 5-6 weeks of age). Mice were routinely monitored until 360 days of age. In agreement with Brown and colleagues (e.g., Cancer Res. 62: 6376-6380, 2002), it was found both RXR agonists (Targretin, UAB-30) and EGFR 1 and/or 2 inhibitors (Tarceva, Lapatinib) were highly effective in preventing the development of these cancers. More surprisingly, tamoxifen which is ineffective as a therapeutic agent against ER- breast cancer in women was effective in this model. It was also observed that a wide variety of agents were ineffective; including Atorvastatin, rosiglitazone (a PPAR gamma agonist), SAHA (an HDAC inhibitor), metformin, and a soy isoflavones mixture. In separate studies, mice bearing small palpable mammary tumors were treated for five days with these various agents, and examined for alterations in potential biomarkers; including proliferation. Effective agents (e.g., Iressa, Tarceva, and Targretin) strongly inhibited cancer cell proliferation, whereas ineffective agents failed to significantly inhibit proliferation. Thus, such a short-term assay might be employed to determine potential chemopreventive compounds. Short-term treatment with the EGFR inhibitors also decreased levels of expression of phosphorylated EGFR and downstream proteins; e.g., AKT/ERK. Supported by NCI contract number HHSN26120043301C. Citation Information: Cancer Prev Res 2010;3(12 Suppl):B49.

Use of MMTV-Neu/P53 KO Transgenic Mice To Screen for Potential Chemopreventive Agents.

Abstract The MMTV-Neu transgenic model of mammary cancer was developed almost 20 years ago in which the mice develop Neu over-expressing ER- mammary cancers. Since human ER- Neu over-expressing mammary cancers often also have mutations in P53, a heterozygous KO of P53 was incorporated into the model. We used this model to examine a wide variety of potential chemopreventive agents. The agents were administered to virgin female MMTV-Neu/P53 KO mice beginning when they were 60 days of age. Initiation of treatment with the agents was later than that typically employed by other investigators (e.g., 35 days of age). Mice were monitored until 360 days of age. In agreement with Brown and colleagues (e.g., Cancer Research 62, 6376-6380, 2002), it was found that both RXR agonists (Targretin, UAB-30) and EGFR 1 and/or 2 inhibitors (Tarceva, Lapatinib) were highly effective in preventing the development of these cancers. We also observed that a wide variety of agents were ineffective; including Atorvastatin, rosiglitazone (a PPAR gamma agonist), SAHA (an HDAC inhibitor), and a soy isoflavones mixture. In separate studies, mice bearing small palpable mammary tumors were treated for five days with these various agents, and examined for alterations in potential biomarkers; including proliferation. As previously shown by our lab in an ER+ rat model of mammary cancer, effective agents (e.g., Iressa and Targretin) strongly inhibited cancer cell proliferation, whereas ineffective agents failed to significantly inhibit proliferation. Thus, such a short-term assay might be employed to predict potential chemopreventive compounds. Short-term treatment with the EGFR inhibitors also decreased levels of expression of phosphorylated EGFR and downstream proteins; e.g., AKT/ERK. Thus, this model is useful in identifying agents that will prevent the development of human breast cancers that over-express Neu. This is important since Neu over-expressing ER- cancers have a relatively poor prognosis, and Neu over-expressing ER+ tumors are relatively unresponsive to standard hormonal therapies (e.g., tamoxifen and aromatase inhibitors). Supported by NCI contract HHSN261200433001C. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1042.

Inhibition of VEGF receptors significantly impairs mammary cancer growth in C3(1)/Tag transgenic mice through antiangiogenic and non-antiangiogenic mechanisms

Cancer growth and progression is often critically influenced by the production of vascular endothelial growth factor (VEGF), a key mediator of angiogenesis. VEGF produced by tumor cells stimulates endothelial cell growth through the binding and activation of the KDR/Flk-1 receptor (VEGFR-2) on endothelial cells. Recently, some human breast cancer epithelial cells have been shown to express VEGF receptors, suggesting a potential autocrine-mediated growth stimulation of a subset of cancers by VEGF. We demonstrate that mammary tumors in the C3(1)/Tag transgenic model express VEGF and VEGF receptors and tumor growth is stimulated by this autocrine mechanism. GW654652, an indazolylpyrimidine, is a VEGFRs tyrosine kinase inhibitor that dramatically reduces both angiogenesis and tumor cell growth in this model, as demonstrated using both in vitro and in vivo assays. GW654652 significantly decreased cell proliferation and induced apoptosis in human umbilical vein endothelial cells and M6 mammary tumor cells derived from C3(1)/Tag (Tag: simian virus 40 T-antigen) transgenic mice. A 75% reduction in VEGF-induced angiogenesis was observed with GW654652 using the chick chorioallantoic membrane assay, whereas GW654652 produced an approximately 85% reduction in angiogenesis as assessed by the Matrigel plug assay. A profound inhibitory effect on tumor growth in the C3(1)/Tag transgenic model of human breast cancer was observed with oral administration of GW654652 as measured by delayed tumor onset, decreased multiplicity, reduced tumor volume, and extended animal survival. The antitumor effects of GW654652 were associated with reduced tumor vascularization and no apparent toxicity. Tumor growth, however, rapidly advanced following cessation of treatment. This is the first demonstration that a VEGF receptor inhibitor, GW654652, has a strong inhibitory effect on angiogenesis and tumor progression in a transgenic model of mammary cancer, suggesting that this is a useful approach for preclinical testing of such agents.

Validation of transgenic mammary cancer models: goals of the NCI Mouse Models of Human Cancer Consortium and the mammary cancer CD-ROM.

Validation of transgenic mammary cancer models: goals of the NCI Mouse Models of Human Cancer Consortium and the mammary cancer CD-ROM.