Clinical applications of mouse models for breast cancer engaging HER2/neu

Mammary Cancer Models: An Overview from the Past to the Future

Breast cancer research heavily relies on diverse model systems to comprehend disease progression, develop novel diagnostics, and evaluate new therapeutic strategies. This review offers a comprehensive overview of mammary cancer models, covering both ex vivo and in vivo approaches. We delve into established techniques, such as cell culture and explore cutting-edge advancements, like tumor-on-a-chip and bioprinting. The in vivo section encompasses spontaneous, induced, and transplanted models, genetically engineered models, chick chorioallantoic membrane assays, and the burgeoning field of in silico models. Additionally, this article briefly highlights the key discoveries made using these models, significantly enhancing our understanding of breast cancer. In essence, this article serves as a comprehensive compass, charting the trajectory of mammary cancer modeling from its early beginnings to the promising vistas of tomorrow.

The rexinoid V-125 reduces tumor growth in preclinical models of breast and lung cancer

Rexinoids are ligands which activate retinoid X receptors (RXRs), regulating transcription of genes involved in cancer-relevant processes. Rexinoids have anti-neoplastic activity in multiple preclinical studies. Bexarotene, used to treat cutaneous T cell lymphoma, is the only FDA-approved rexinoid. Bexarotene has also been evaluated in clinical trials for lung and metastatic breast cancer, wherein subsets of patients responded despite advanced disease. By modifying structures of known rexinoids, we can improve potency and toxicity. We previously screened a series of novel rexinoids and selected V-125 as the lead based on performance in optimized in vitro assays. To validate our screening paradigm, we tested V-125 in clinically relevant mouse models of breast and lung cancer. V-125 significantly (p < 0.001) increased time to tumor development in the MMTV-Neu breast cancer model. Treatment of established mammary tumors with V-125 significantly (p < 0.05) increased overall survival. In the A/J lung cancer model, V-125 significantly (p < 0.01) decreased number, size, and burden of lung tumors. Although bexarotene elevated triglycerides and cholesterol in these models, V-125 demonstrated an improved safety profile. These studies provide evidence that our screening paradigm predicts novel rexinoid efficacy and suggest that V-125 could be developed into a new cancer therapeutic.

The PTEN and ATM axis controls the G1/S cell cycle checkpoint and tumorigenesis in HER2-positive breast cancer

The tumor suppressor PTEN is disrupted in a large proportion of cancers, including in HER2-positive breast cancer, where its loss is associated with resistance to therapy. Upon genotoxic stress, ataxia telangiectasia mutated (ATM) is activated and phosphorylates PTEN on residue 398. To elucidate the physiological role of this molecular event, we generated and analyzed knock-in mice expressing a mutant form of PTEN that cannot be phosphorylated by ATM (PTEN-398A). This mutation accelerated tumorigenesis in a model of HER2-positive breast cancer. Mammary tumors in bi-transgenic mice carrying MMTV-neu and Pten^398A were characterized by DNA damage accumulation but reduced apoptosis. Mechanistically, phosphorylation of PTEN at position 398 is essential for the proper activation of the S phase checkpoint controlled by the PI3K-p27^Kip1-CDK2 axis. Moreover, we linked these defects to the impaired ability of the PTEN-398A protein to relocalize to the plasma membrane in response to genotoxic stress. Altogether, our results uncover a novel role for ATM-dependent PTEN phosphorylation in the control of genomic stability, cell cycle progression, and tumorigenesis.

The RXR Agonist MSU42011 Is Effective for the Treatment of Preclinical HER2+ Breast Cancer and Kras-Driven Lung Cancer

(1) Background: Notwithstanding numerous therapeutic advances, 176,000 deaths from breast and lung cancers will occur in the United States in 2021 alone. The tumor microenvironment and its modulation by drugs have gained increasing attention and relevance, especially with the introduction of immunotherapy as a standard of care in clinical practice. Retinoid X receptors (RXRs) are members of the nuclear receptor superfamily and upon ligand binding, function as transcription factors to modulate multiple cell functions. Bexarotene, the only FDA-approved RXR agonist, is still used to treat cutaneous T-cell lymphoma. (2) Methods: To test the immunomodulatory and anti-tumor effects of MSU42011, a new RXR agonist, we used two different immunocompetent murine models (MMTV-Neu mice, a HER2 positive model of breast cancer and the A/J mouse model, in which vinyl carbamate is used to initiate lung tumorigenesis) and an immunodeficient xenograft lung cancer model. (3) Results: Treatment of established tumors in immunocompetent models of HER2-positive breast cancer and Kras-driven lung cancer with MSU42011 significantly decreased the tumor burden and increased the ratio of CD8/CD4, CD25 T cells, which correlates with enhanced anti-tumor efficacy. Moreover, the combination of MSU42011 and immunotherapy (anti-PDL1 and anti-PD1 antibodies) significantly (p < 0.05) reduced tumor size vs. individual treatments. However, MSU42011 was ineffective in an athymic human A549 lung cancer xenograft model, supporting an immunomodulatory mechanism of action. (4) Conclusions: Collectively, these data suggest that the RXR agonist MSU42011 can be used to modulate the tumor microenvironment in breast and lung cancer.

Haploinsufficiency Interactions between RALBP1 and p53 in ERBB2 and PyVT Models of Mouse Mammary Carcinogenesis

Simple Summary

Rlip knockout has been reported to prevent cancer in highly cancer-susceptible mice lacking p53, and Rlip knockdown kills many types of cancer cells. In humans, breast cancer shows diverse characteristics, including HER2-driven subtypes and viral-driven subtypes. HER2 can be targeted; however, escape of the cancer from targeted therapies remains a problem. In this work we evaluated the capacity of Rlip knockout to prevent breast cancer in genetically engineered mouse models of HER2-driven breast cancer (Erbb2 model) and polyomavirus-driven breast cancer (PyVT model). We found that in Erbb2 mice, Rlip knockout significantly delayed oncogenesis and reduced the expression of genes associated with poor prognosis in patients. In PyVT mice, Rlip knockout did not delay oncogenesis or tumor growth, but Rlip knockdown reduced tumor metastasis to the lung. We conclude that Rlip inhibitors may significantly improve survival in HER2-positive patients, but are unlikely to offer benefits to patients with polyomavirus-associated tumors.

Abstract

We recently reported that loss of one or both alleles of Ralbp1, which encodes the stress-protective protein RLIP76 (Rlip), exerts a strong dominant negative effect on both the inherent cancer susceptibility and the chemically inducible cancer susceptibility of mice lacking one or both alleles of the tumor suppressor p53. In this paper, we examined whether congenital Rlip deficiency could prevent genetically-driven breast cancer in two transgenic mouse models: the MMTV-PyVT model, which expresses the polyomavirus middle T antigen (PyVT) under control of the mouse mammary tumor virus promoter (MMTV) and the MMTV-Erbb2 model which expresses MMTV-driven erythroblastic leukemia viral oncogene homolog 2 (Erbb2, HER2/Neu) and frequently acquires p53 mutations. We found that loss of either one or two Rlip alleles had a suppressive effect on carcinogenesis in Erbb2 over-expressing mice. Interestingly, Rlip deficiency did not affect tumor growth but significantly reduced the lung metastatic burden of breast cancer in the viral PyVT model, which does not depend on either Ras or loss of p53. Furthermore, spontaneous tumors of MMTV-PyVT/Rlip+/+ mice showed no regression following Rlip knockdown. Finally, mice lacking one or both Rlip alleles differentially expressed markers for apoptotic signaling, proliferation, angiogenesis, and cell cycling in PyVT and Erbb2 breast tumors. Our results support the efficacy of Rlip depletion in suppressing p53 inactivated cancers, and our findings may yield novel methods for prevention or treatment of cancer in patients with HER2 mutations or tumor HER2 expression.

Melatonin Administered before or after a Cytotoxic Drug Increases Mammary Cancer Stabilization Rates in HER2/Neu Mice

INTRODUCTION

The effects of chemotherapy are known to depend on the time of administration. Circadian rhythms are disturbed in tumors and in tumor bearers. Agents involved in controlling the circadian rhythms (chronobiotics) potentially can modify the outcomes of chemotherapeutics administered at different times of the day. Pineal hormone melatonin (MT) is a prototypic chronobiotic.

OBJECTIVE

The aim of the study was to investigate if MT can affect efficacy or toxicity of chemotherapy drugs administered at the extreme time points of the working day of hospital personnel.

METHODS

Cyclophosphamide, adriamycin, and 5-fluorouracil (CAF) and adriamycin and docetaxel (AT) cytotoxic drug combinations were administered on day 0 at 11:00 a.m. or at 5:00 p.m. (UTC+03:00) to 6-month-old female HER2/neu transgenic FVB/N mice bearing mammary adenocarcinomas. Some mice were additionally provided with MT in drinking water (20 mg/L) at night 1 week before or 3 weeks after treatment or during both periods. Tumor node sizes, body weight, and blood cell counts were determined right before treatment and on days 2, 7, 14, and 21.

RESULTS

Significant decrease in the mean tumor node volume was found by days 14 and 21 upon all CAF and AT treatment schedules, except in animals treated with AT at 5:00 p.m. without supplementation with MT. In the latter case, mean tumor node volume on day 21 was the same as in the control. Supplementation of AT administered at 5:00 p.m. with MT improved the tumor response. CAF and AT regimens supplemented with MT also augmented the number of tumor nodes that did not increase by more than 20% by day 21 as compared to CAF or AT alone, respectively. This effect was significant in groups treated with AT at 5:00 p.m. and consistent upon other schedules. On day 7, leukopenia and anemia were registered in groups treated with CAF regimen; however, blood cell counts normalized by day 14. Both CAF and AT were associated with drop in the body weight registered on day 7. Supplementation with MT did not affect changes of the body weight and blood counts.

CONCLUSIONS

MT supplementation to cytotoxic drugs can improve antitumor response, especially if it is blunted because of an inappropriate time of administration.

Tracking cells in epithelial acini by light sheet microscopy reveals proximity effects in breast cancer initiation

Cancer clone evolution takes place within tissue ecosystem habitats. But, how exactly tumors arise from a few malignant cells within an intact epithelium is a central, yet unanswered question. This is mainly due to the inaccessibility of this process to longitudinal imaging together with a lack of systems that model the progression of a fraction of transformed cells within a tissue. Here, we developed a new methodology based on primary mouse mammary epithelial acini, where oncogenes can be switched on in single cells within an otherwise normal epithelial cell layer. We combine this stochastic breast tumor induction model with inverted light-sheet imaging to study single-cell behavior for up to four days and analyze cell fates utilizing a newly developed image-data analysis workflow. The power of this integrated approach is illustrated by us finding that small local clusters of transformed cells form tumors while isolated transformed cells do not.

Retinoid X receptor agonist LG100268 modulates the immune microenvironment in preclinical breast cancer models

Despite numerous therapeutic advances in the past decade, breast cancer is expected to cause over 42,000 deaths in the United States in 2019. Breast cancer had been considered an immunologically silent tumor; however recent findings suggest that immune cells play important roles in tumor growth even in the breast. Retinoid X receptors (RXRs) are a subclass of nuclear receptors that act as ligand-dependent transcription factors that regulate a variety of cellular processes including proliferation and differentiation; in addition, they are essential for macrophage biology. Rexinoids are synthetic molecules that bind and activate RXRs. Bexarotene is the only rexinoid approved by the FDA for the treatment of refractory cutaneous T-cell lymphoma. Other more-potent rexinoids have been synthesized, such as LG100268 (LG268). Here, we report that treatment with LG 268, but not bexarotene, decreased infiltration of myeloid-derived suppressor cells and CD206-expressing macrophages, increased the expression of PD-L1 by 50%, and increased the ratio of CD8/CD4, CD25 T cells, which correlates with increased cytotoxic activity of CD8 T cells in tumors of MMTV-Neu mice (a model of HER2-positive breast cancer). In the MMTV-PyMT murine model of triple negative breast cancer, LG268 treatment of established tumors prolonged survival, and in combination with anti-PD-L1 antibodies, significantly (p = 0.05) increased the infiltration of cytotoxic CD8 T cells and apoptosis. Collectively, these data suggest that the use of LG268, a RXR agonist, can improve response to immune checkpoint blockade in HER2+ or triple-negative breast cancer.

c-MYB and DMTF1 in Cancer

The c-Myb gene encodes a transcription factor that regulates cell proliferation, differentiation, and apoptosis through protein-protein interaction and transcriptional regulation of signaling pathways. The protein is frequently overexpressed in human leukemias, breast cancers, and other solid tumors suggesting that it is a bona fide oncogene. c-MYB is often overexpressed by translocation in human tumors with t(6;7)(q23;q34) resulting in c-MYB-TCRβ in T cell ALL, t(X;6)(p11;q23) with c-MYB-GATA1 in acute basophilic leukemia, and t(6;9)(q22-23;p23-24) with c-MYB-NF1B in adenoid cystic carcinoma. Antisense oligonucleotides to c-MYB were developed to purge bone marrow cells to eliminate tumor cells in leukemias. Recently, small molecules that inhibit c-MYB activity have been developed to disrupt its interaction with p300. The Dmp1 (cyclin D binding myb-like protein 1; Dmtf1) gene was isolated through its virtue for binding to cyclin D2. It is a transcription factor that has a Myb-like repeat for DNA binding. The Dmtf1 protein directly binds to the Arf promoter for transactivation and physically interacts with p53 to activate the p53 pathway. The gene is hemizygously deleted in 35-42% of human cancers and is associated with longer survival. The significances of aberrant expression of c-MYB and DMTF1 proteins in human cancers and their clinical significances are discussed.

Tumor suppression by the EGR1, DMP1, ARF, p53, and PTEN Network

Recent studies have indicated that EGR1 is a direct regulator of tumor suppressors including TGFβ1, PTEN, and p53. The Myb-like transcription factor Dmp1 is a physiological regulator of the Arf-p53 pathway through transactivation of the Arf promoter and physical interaction of p53. The Dmp1 promoter has binding sites for Egr proteins, and Egr1 is a target for Dmp1. Crosstalks between p53 and PTEN have been reported. The Egr1-Dmp1-Arf-p53-Pten pathway displays multiple modes of interaction with each other, suggesting the existence of a functional network of tumor suppressors that maintain normal cell growth and prevent the emergence of incipient cancer cells.

Cancer immunoprevention: from mice to early clinical trials

Cancer immunoprevention is based on the fact that a functioning immune system controls tumor onset and development in humans and animals, thus leading to the idea that the enhancement of immune responses in healthy individuals could effectively reduce cancer risk later in life. Successful primary immunoprevention of tumors caused by hepatitis B and papilloma viruses is already implemented at the population level with specific vaccines. The immunoprevention of human tumors unrelated to infectious agents is an outstanding challenge. Proof-of-principle preclinical studies in genetically-modified or in carcinogen-exposed mice clearly demonstrated that vaccines and other immunological treatments induce host immune responses that effectively control tumor onset and progression, eventually resulting in cancer prevention. While a straightforward translation to healthy humans is currently unfeasible, a number of pioneering clinical trials showed that cancer immunoprevention can be effectively implemented in human cohorts affected by specific cancer risks, such as preneoplastic/early neoplastic lesions. Future developments will see the implementation of cancer immunoprevention in a wider range of conditions at risk of tumor development, such as the exposure to known carcinogens and genetic predispositions.

Aberrant expression of ETS1 and ETS2 proteins in cancer

The ETS transcription factors regulate expression of genes involved in normal cell development, proliferation, differentiation, angiogenesis, and apoptosis, consisting of 28 family members in humans. Dysregulation of these transcription factors facilitates cell proliferation in cancers, and several members participate in invasion and metastasis by activating gene transcription. ETS1 and ETS2 are the founding members of the ETS family and regulate transcription by binding to ETS sequences. They are both involved in oncogenesis and tumor suppression depending on the biological situations used. The essential roles of ETS proteins in human telomere maintenance have been suggested, which have been linked to creation of new Ets binding sites. Recently, preferential binding of ETS2 to gain-of-function mutant p53 and ETS1 to wild type p53 (WTp53) has been suggested, raising the tumor promoting role for the former and tumor suppressive role for the latter. The oncogenic and tumor suppressive functions of ETS1 and 2 proteins have been discussed.

Engineered exosomes emerging from muscle cells break immune tolerance to HER2 in transgenic mice and induce antigen-specific CTLs upon challenge by human dendritic cells

We recently described a novel biotechnological platform for the production of unrestricted cytotoxic T lymphocyte (CTL) vaccines. It relies on in vivo engineering of exosomes, i.e., nanovesicles constitutively released by all cells, with full-length antigens of choice upon fusion with an exosome-anchoring protein referred to as Nef^mut. They are produced upon intramuscular injection of a DNA vector and, when uploaded with a viral tumor antigen, were found to elicit an immune response inhibiting the tumor growth in a model of transplantable tumors. However, for a possible application in cancer immunotherapy, a number of key issues remained unmet. Among these, we investigated: (i) whether the immunogenic stimulus induced by the engineered exosomes can break immune tolerance, and (ii) their effectiveness when applied in human system. As a model of immune tolerance, we considered mice transgenic for the expression of activated rat HER2/neu which spontaneously develop adenocarcinomas in all mammary glands. When these mice were injected with a DNA vector expressing the product of fusion between Nef^mut and the extracellular domain of HER2/neu, antigen-specific CD8⁺ T lymphocytes became readily detectable. This immune response associated with a HER2-directed CTL activity and a significant delay in tumor development. On the other hand, through cross-priming experiments, we demonstrated the effectiveness of the engineered exosomes emerging from transfected human primary muscle cells in inducing antigen-specific CTLs. We propose our CTL vaccine platform as part of new immunotherapy strategies against tumors expressing self-antigens, i.e., products highly expressed in oncologic lesions but tolerated by the immune system.

KEY MESSAGES

We established a novel, exosome-based method to produce unrestricted CTL vaccines. This strategy is effective in breaking the tolerance towards tumor self-antigens. Our method is also useful to elicit antigen-specific CTL immunity in humans. These findings open the way towards the use of this antitumor strategy in clinic.