Experimental mammary carcinogenesis - Rat models

Current views on in vivo models for breast cancer research and related drug development

INTRODUCTION

Animal models play a crucial role in breast cancer research, in particular mice and rats, who develop mammary tumors that closely resemble their human counterparts. These models allow the study of mechanisms behind breast carcinogenesis, as well as the efficacy and safety of new, and potentially more effective and advantageous therapeutic approaches. Understanding the advantages and disadvantages of each model is crucial to select the most appropriate one for the research purpose.

AREA COVERED

This review provides a concise overview of the animal models available for breast cancer research, discussing the advantages and disadvantages of each one for searching new and more effective approaches to treatments for this type of cancer.

EXPERT OPINION

Rodent models provide valuable information on the genetic alterations of the disease, the tumor microenvironment, and allow the evaluation of the efficacy of chemotherapeutic agents. However, in vivo models have limitations, and one of them is the fact that they do not fully mimic human diseases. Choosing the most suitable model for the study purpose is crucial for the development of new therapeutic agents that provide better care for breast cancer patients.

Advances in Antitumor Effects Using Liposomal Citrinin in Induced Breast Cancer Model

The study aimed to evaluate the antitumor and toxicogenetic effects of liposomal nanoformulations containing citrinin in animal breast carcinoma induced by 7,12-dimethylbenzanthracene (DMBA). Mus musculus virgin females were divided into six groups treated with (1) olive oil (10 mL/kg); (2) 7,12-DMBA (6 mg/kg); (3) citrinin, CIT (2 mg/kg), (4) cyclophosphamide, CPA (25 mg/kg), (5) liposomal citrinin, LP-CIT (2 μg/kg), and (6) LP-CIT (6 µg/kg). Metabolic, behavioral, hematological, biochemical, histopathological, and toxicogenetic tests were performed. DMBA and cyclophosphamide induced behavioral changes, not observed for free and liposomal citrinin. No hematological or biochemical changes were observed for LP-CIT. However, free citrinin reduced monocytes and caused hepatotoxicity. During treatment, significant differences were observed regarding the weight of the right and left breasts treated with DMBA compared to negative controls. Treatment with CPA, CIT, and LP-CIT reduced the weight of both breasts, with better results for liposomal citrinin. Furthermore, CPA, CIT, and LP-CIT presented genotoxic effects for tumor, blood, bone marrow, and liver cells, although less DNA damage was observed for LP-CIT compared to CIT and CPA. Healthy cell damage induced by LP-CIT was repaired during treatment, unlike CPA, which caused clastogenic effects. Thus, LP-CIT showed advantages for its use as a model of nanosystems for antitumor studies.

Current landscape of treating different cancers using nanomedicines: Trends and perspectives

The efforts to use novel nanotechnologies in medicine and cancer have been widespread. In order to understand better the focus areas of cancer nanomedicine research to date, we conducted a survey of nanomedicine developmental and clinical research in conjunction with treatment of various cancers. The survey has been performed based on number of publications, rate of citations, entry into clinical trials, and funding rates by the National Cancer Institute. Our survey indicates that breast and brain cancers are the most and one of the least studied by nanotechnology researchers, respectively. Breast cancer nano-therapies seem to also be most likely to achieve clinical translation as the number of publications produced, amount of funding, total citations, and clinical trials (active and completed) are the highest when compared with research in other cancers. Brain cancer, despite its low survival, has capture much less attention of nanomedicine research community as survey indicated, although nanotechnology can offer novel approaches which can address brain cancer challenges. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Realistic aspects behind the application of the rat model of chemically-induced mammary cancer: Practical guidelines to obtain the best results

Cancer is one of the most important public health problems worldwide. Despite the great contribution of in-vitro studies for biomedical research, animals are essential to study diseases' biopathology and diagnosis, and searching for new preventive and therapeutic strategies. Breast cancer is currently the most common cancer globally, accounting for 12.5% of all new annual cancer cases worldwide. Although the rat model of mammary cancer chemically-induced is widely used to study this disease, there is a lack of standardization in procedures for cancer induction, sample collection, and analysis. Therefore, it is important to provide a practical guide for researchers aiming to work with this model to make the analysis of results more uniform. Thus, in this review, we provide the researchers with a detailed step-by-step guide to implement a rat model of mammary cancer, based on our wide experience in this field, to obtain the best results, maximum throughput of each experiment, and easy comparison among researches.

Mammary Glands of Women, Female Dogs and Female Rats: Similarities and Differences to Be Considered in Breast Cancer Research

Breast cancer is one of the most common and well-known types of cancer among women worldwide and is the most frequent neoplasm in intact female dogs. Female dogs are considered attractive models or studying spontaneous breast cancer, whereas female rats are currently the most widely used animal models for breast cancer research in the laboratory context. Both female dogs and female rats have contributed to the advancement of scientific knowledge in this field, and, in a "One Health" approach, they have allowed broad understanding of specific biopathological pathways, influence of environmental factors and screening/discovery of candidate therapies. This review aims to clearly showcase the similarities and differences among woman, female dog and female rat concerning to anatomical, physiological and histological features of the mammary gland and breast/mammary cancer epidemiology, in order to better portray breast tumorigenesis, and to ensure appropriate conclusions and extrapolation of results among species. We also discuss the major aspects that stand out in these species. The mammary glands of female dogs and women share structural similarities, especially with respect to the lactiferous ducts and lymphatic drainage. In contrast, female rats have only one lactiferous duct per nipple. A comprehensive comparison between humans and dogs is given a special focus, as these species share several aspects in terms of breast/mammary cancer epidemiology, such as age of onset, hormonal etiology, risk factors, and the clinical course of the disease. Holistically, it is clear that each species has advantages and limitations that researchers must consider during the development of experimental designs and data analysis.

Editorial: Special Issue "Addressing New Therapeutic Strategies Using Models"

A disease model displays pathological processes observed in human or animal diseases [...].

Induced mammary cancer in rat models: pathogenesis, genetics, and relevance to female breast cancer

Mammary cancer, or breast cancer in women, is a polygenic disease with a complex etiopathogenesis. While much remains elusive regarding its origin, it is well established that chemical carcinogens and endogenous estrogens contribute significantly to the initiation and progression of this disease. Rats have been useful models to study induced mammary cancer. They develop mammary tumors with comparable histopathology to humans and exhibit differences in resistance or susceptibility to mammary cancer depending on strain. While some rat strains (e.g., Sprague-Dawley) readily form mammary tumors following treatment with the chemical carcinogen, 7,12-dimethylbenz[a]-anthracene (DMBA), other strains (e.g., Copenhagen) are resistant to DMBA-induced mammary carcinogenesis. Genetic linkage in inbred strains has identified strain-specific quantitative trait loci (QTLs) affecting mammary tumors, via mechanisms that act together to promote or attenuate, and include 24 QTLs controlling the outcome of chemical induction, 10 QTLs controlling the outcome of estrogen induction, and 4 QTLs controlling the outcome of irradiation induction. Moreover, and based on shared factors affecting mammary cancer etiopathogenesis between rats and humans, including orthologous risk regions between both species, rats have served as useful models for identifying methods for breast cancer prediction and treatment. These studies in rats, combined with alternative animal models that more closely mimic advanced stages of breast cancer and/or human lifestyles, will further improve our understanding of this complex disease.

The antimammary tumor effects of ethanolic extract of propolis from Adamawa region (Cameroon) are by apoptosis via reactive oxygen species-mediated mitochondrial pathway

Identification of novel natural treatment to combat cancer is a current need. This study was aimed at assessing the anticancer effects of ethanol-extracted Cameroonian propolis (EEP). The antitumor effect of EPP was evaluated in vitro by measuring; cell viability, cell cycle, cell death mechanism, cell migration/invasion, reactive oxygen species (ROS), mitochondrial potential (ΔΨm), caspase activity, and apoptosis-regulating proteins (Bcl-2 and Bcl-XL) in cell lines. In vivo, the effect of EEP against 7,12 dimethylbenz(a)anthracene (DMBA)-induced breast tumorigenesis in rats was assessed. EEP was found to induce cytotoxicity against ER negative MDA-MB-231 breast cancer cells by activating apoptosis through ROS-mediated mitochondrial pathway. The extract equally triggered caspase-3 and caspase-9, increment of ROS level, disruption of ΔΨm and down-regulation of Bcl-XL and Bcl-2 proteins. Besides, EPP prevented migration and invasion activities by inhibiting MMP-2 activity. At all doses it prevented breast tumor incidence (20% in EEP 150 mg/kg vs 70% in DMBA) as well as tumor burden. Tumor sections from EEP-treated rats showed middle proliferation of mammary ducts with weak inflammatory responses. In summary, Cameroonian propolis exhibited antimammary tumor effects via the intrinsic pathway of apoptosis.

Refinement of Animal Model of Colorectal Carcinogenesis through the Definition of Novel Humane Endpoints

Simple Summary

Ensuring animal welfare is essential in protocols using laboratory animals. Applying a score sheet with 14 biological parameters, we assessed the welfare of 29 male Wistar rats used as models of colorectal carcinogenesis (CRC). We found a uniformity of characteristics preceding the premature animals’ death, including an increase of 10% in body weight, swollen abdomen, diarrhea, and priapism. In addition, we observed that surface abdominal temperature was higher in animals with CRC. We considered that the parameters already described in other cancer models are insufficient and considered assessing the abdominal temperature, priapism, and sudden increase in the body weight in the model of CRC.

Abstract

This study aimed to define appropriate humane endpoints (HEs) for an animal model of colorectal carcinogenesis (CRC). Twenty-nine male Wistar rats were divided into two control groups (CTRL1 and CTRL2) injected with ethylenediamine tetraacetic acid (EDTA)–saline solutions and two induced groups (CRC1 and CRC2) injected with 1,2-dimethylhydrazine (DMH) for seven weeks. A score sheet with 14 biological parameters was used to assess animal welfare. Groups CRC1 and CTRL1 and groups CRC2 and CTRL2 were euthanized 11 and 17 weeks after the first DMH administration, respectively. Five animals from the induced groups died unexpectedly during the protocol (survival rates of 75.0% and 66.7% for groups CRC1 and CRC2, respectively). The final mean body weight (BW) was smaller in the CRC groups when compared with that in the CTRL groups. A uniformity of characteristics preceding the premature animals’ death was observed, namely an increase of 10% in mean BW, swollen abdomen, diarrhea, and priapism. The surface abdominal temperature of group CRC2 was significantly higher, when compared with that of group CTRL2. The parameters already described in other cancer models proved to be insufficient. For the CRC model, we considered assessing the abdominal temperature, priapism, and sudden increase in the BW.

Intraductal administration of N-methyl-N-nitrosourea as a novel rodent mammary tumor model

Background

Chemically induced animal models of breast cancer (BC) using N-methyl-N-nitrosourea (MNU) have been widely used in preclinical research. The conventional approach entails intraperitoneal (i.p) or intravenous injection of a carcinogen, leading to tumor induction at unpredictable locations. This study aimed to establish a modified MNU-induced rat mammary tumor model using intraductal (i.duc) administration and to evaluate its biological behavior, morphology, and response to chemotherapy drugs.

Methods

In a pilot experiment, female Sprague-Dawley (SD) rats were injected with either i.duc MNU or vehicle to test the feasibility of this approach. We explored the appropriate dosage for stable tumor formation in pubescent female SD rats by testing a single i.duc dose of MNU (0.5, 1.0 and 2.0 mg) or vehicle.

Results

An i.duc injection of 20 µL (1 mg/per duct) MNU in the fourth rat mammary gland induced stable carcinomas in situ. Immunohistochemical (IHC) analysis showed positive expression of estrogen receptor (ER), negative expression of human epidermal growth factor receptor 2 (Her-2), and low expression of Ki-67. Histopathology revealed atypical hyperplasia in the mammary gland 4 weeks after carcinogen injection, developing into carcinoma in situ 5-6 weeks after treatment, with loss of α-SMA and calponin expressions during tumor progression. Albumin-bound paclitaxel (nab-PTX) was injected i.duc and intravenously (i.v) 5 weeks after administration of MNU. The tumor growth rate of the nab-PTX i.duc-treated group was lower than in the i.v and control groups. The number of TUNEL-positive apoptotic cells was significantly higher in the nab-PTX i.duc-treated group.

Conclusions

Using i.duc MNU (20 µL, 1 mg) to establish a rat mammary tumor model resulted in a predictable location in the rat mammary gland and exhibited better consistency; i.duc administration of nab-PTX permitted a smaller drug dose, but produced a better drug response, than i.v injection.

Nicotinamide riboside relieves paclitaxel-induced peripheral neuropathy and enhances suppression of tumor growth in tumor-bearing rats

Nicotinamide riboside (NR) is a vitamin B3 precursor of NAD that blunts diabetic and chemotherapy-induced peripheral neuropathy in preclinical models. This study examined whether NR also blunts the loss of intraepidermal nerve fibers induced by paclitaxel, which is associated with peripheral neuropathy. The work was conducted in female rats with N-methyl-nitrosourea (MNU)-induced tumors of the mammary gland to increase its translational relevance, and to assess the interaction of NR with paclitaxel and NR's effect on tumor growth. Once daily oral administration of 200 mg/kg NR p.o. beginning with the first of 3 i.v. injections of 6.6 mg/kg paclitaxel to tumor-bearing rats significantly decreased paclitaxel-induced hypersensitivity to tactile and cool stimuli, as well as place-escape avoidance behaviors. It also blunted the loss of intraepidermal nerve fibers in tumor-bearing rats, as well as a separate cohort of tumor-naive rats. Unexpectedly, concomitant administration of NR during paclitaxel treatment further decreased tumor growth; thereafter, tumor growth resumed at the same rate as vehicle-treated controls. Administration of NR also decreased the percentage of Ki67-positive tumor cells in these rats. Once daily administration of NR did not seem to alter tumor growth or the percentage of Ki67-positive tumor cells in rats that were not treated with paclitaxel and followed for 3 months. These results further support the ability of NR to play a protective role after nerve injury. They also suggest that NR may not only alleviate peripheral neuropathy in patients receiving taxane chemotherapy, but also offer an added benefit by possibly enhancing its tumor-suppressing effects.

A Step Forward in Breast Cancer Research: From a Natural-Like Experimental Model to a Preliminary Photothermal Approach

Breast cancer is one of the most frequently diagnosed malignancies and common causes of cancer death in women. Recent studies suggest that environmental exposures to certain chemicals, such as 7,12-Dimethylbenzanthracene (DMBA), a chemical present in tobacco, may increase the risk of developing breast cancer later in life. The first-line treatments for breast cancer (surgery, chemotherapy or a combination of both) are generally invasive and frequently associated with severe side effects and high comorbidity. Consequently, novel approaches are strongly required to find more natural-like experimental models that better reflect the tumors' etiology, physiopathology and response to treatments, as well as to find more targeted, efficient and minimally invasive treatments. This study proposes the development and an in deep biological characterization of an experimental model using DMBA-tumor-induction in Sprague-Dawley female rats. Moreover, a photothermal therapy approach using a near-infrared laser coupled with gold nanoparticles was preliminarily assessed. The gold nanoparticles were functionalized with Epidermal Growth Factor, and their physicochemical properties and in vitro effects were characterized. DMBA proved to be a very good and selective inductor of breast cancer, with 100% incidence and inducing an average of 4.7 tumors per animal. Epigenetic analysis showed that tumors classified with worst prognosis were hypomethylated. The tumor-induced rats were then subjected to a preliminary treatment using functionalized gold nanoparticles and its activation by laser (650-900 nm). The treatment outcomes presented very promising alterations in terms of tumor histology, confirming the presence of necrosis in most of the cases. Although this study revealed encouraging results as a breast cancer therapy, it is important to define tumor eligibility and specific efficiency criteria to further assess its application in breast cancer treatment on other species.

Altered prolactin and androgen receptors expression in companion rat benign mammary tumours

Benign mammary tumours are among the most common tumours of companion rats (Rattus norvegicus domestica), as well as a major animal welfare concern and euthanasia. The first objective of this study was to evaluate the expression of oestrogen, progesterone, androgen, and prolactin receptors in neoplastic and normal mammary gland tissues and compare the expression of these receptors between groups. The second objective was to determine if the expression of these receptors in neoplastic mammary gland tissue correlates with overall survival and occurrence of an additional mass after initial mammary mass excision. The third objective was to determine if the expression of oestrogen, progesterone, androgen and prolactin receptors was associated with mammary tumor clinical parameters or with the age of the animals. Thirty-two benign mammary tumours were collected from companion rats and submitted for immunohistochemistry staining of prolactin receptor, oestrogen receptor alpha (ERa), progesterone and androgen receptors (AR). Allred score were obtained for mammary tumours (n = 32) and surrounding normal mammary tissue (n = 20) when present. Prolactin receptor expression increased significantly with mammary gland tumorigenesis (P < .0001), while AR expression decreased with tumorigenesis (P < .0001). Lower expression of ERa in tumor stroma was associated with shorter survival (P = .02). Hormonal receptor expression was not significantly associated with age, mass diameter, location nor likelihood of additional mass development. Further studies should investigate the effects of prolactin antagonists in a prospective study involving companion rats with benign mammary tumours.

Marine-Derived Penicillium purpurogenum Reduces Tumor Size and Ameliorates Inflammation in an Erlich Mice Model

Background: This study addresses the antitumoral properties of Penicillium purpurogenum isolated from a polluted lagoon in Northeastern Brazil. Methods: Ethyl Acetate Extracellular Extract (EAE) was used. The metabolites were studied using direct infusion mass spectrometry. The solid Ehrlich tumor model was used for antitumor activity. Female Swiss mice were divided into groups (n = 10/group) as follows: The negative control (CTL−), treated with a phosphate buffered solution; the positive control (CTL+), treated with cyclophosphamide (25 mg/kg); extract treatments at doses of 4, 20, and 100 mg/kg; animals without tumors or treatments (Sham); and animals without tumors treated with an intermediate dose (EAE20). All treatments were performed intraperitoneally, daily, for 15 days. Subsequently, the animals were euthanized, and the tumor, lymphoid organs, and serum were used for immunological, histological, and biochemical parameter evaluations. Results: The extract was rich in meroterpenoids. All doses significantly reduced tumor size, and the 20 and 100 mg/kg doses reduced tumor-associated inflammation and tumor necrosis. The extract also reduced the cellular infiltration of lymphoid organs and circulating TNF-α levels. The extract did not induce weight loss or renal and hepatic toxic changes. Conclusions: These results indicate that P. purpurogenum exhibits immunomodulatory and antitumor properties in vivo. Thus, fungal fermentation is a valid biotechnological approach to the production of antitumor agents.

Daucosterol from Crateva adansonii DC (Capparaceae) reduces 7,12-dimethylbenz(a)anthracene-induced mammary tumors in Wistar rats

This study aimed to evaluate the in vivo anticancer effects of daucosterol which was earlier reported to possess in vitro anticancer effects. Breast tumor was induced in 30 rats using the environmental carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) while 6 control rats received olive oil (NOR). Animals with palpable tumors were randomized into five groups (n = 6) each as follows: negative control group treated with the vehicle (DMBA); positive control group treated with 5 mg/kg BW doxorubicin (DOXO + DMBA); three groups treated with daucosterol at doses of 2.5, 5, and 10 mg/kg BW (DAU + DMBA). Treatment lasted 28 days afterward, tumor (mass, volume, cancer antigen [CA] 15-3 level and histoarchitecture), hematological and toxicological parameters were examined. The tumor volume gradually increased in the DMBA group during the 28 days, with a tumor volume gain of ∼390 cm³ . Daucosterol at all doses reduced tumor volume (∼133.7 cm³ at 10 mg/kg) as well as protein, malondialdehyde (MDA), and CA 15-3 levels compared to DMBA rats. Tumor sections in daucosterol-treated rats showed a lower proliferation of mammary ducts with mild (5 and 10 mg/kg) to moderate (2.5 mg/kg) inflammatory responses. Moreover, it exhibited an antioxidant effect, evidenced by a significant and dose-dependent decreased in MDA levels, as well as an increase in catalase activity compared to the DMBA group. Daucosterol showed for the first time in vivo antitumor effects that corroborate its previous in vitro effects.

Experimental Models as Refined Translational Tools for Breast Cancer Research

Breast cancer is one of the most common cancers worldwide, which makes it a very impactful malignancy in the society. Breast cancers can be classified through different systems based on the main tumor features and gene, protein, and cell receptors expression, which will determine the most advisable therapeutic course and expected outcomes. Multiple therapeutic options have already been proposed and implemented for breast cancer treatment. Nonetheless, their use and efficacy still greatly depend on the tumor classification, and treatments are commonly associated with invasiveness, pain, discomfort, severe side effects, and poor specificity. This has demanded an investment in the research of the mechanisms behind the disease progression, evolution, and associated risk factors, and on novel diagnostic and therapeutic techniques. However, advances in the understanding and assessment of breast cancer are dependent on the ability to mimic the properties and microenvironment of tumors in vivo, which can be achieved through experimentation on animal models. This review covers an overview of the main animal models used in breast cancer research, namely in vitro models, in vivo models, in silico models, and other models. For each model, the main characteristics, advantages, and challenges associated to their use are highlighted.

Management and potentialities of primary cancer cultures in preclinical and translational studies

The use of patient-derived primary cell cultures in cancer preclinical assays has increased in recent years. The management of resected tumor tissue remains complex and a number of parameters must be respected to obtain complete sample digestion and optimal vitality yield. We provide an overview of the benefits of correct primary cell culture management using different preclinical methodologies, and describe the pros and cons of this model with respect to other kinds of samples. One important advantage is that the heterogeneity of the cell populations composing a primary culture partially reproduces the tumor microenvironment and crosstalk between malignant and healthy cells, neither of which is possible with cell lines. Moreover, the use of patient-derived specimens in innovative preclinical technologies, such as 3D systems or bioreactors, represents an important opportunity to improve the translational value of the results obtained. In vivo models could further our understanding of the crosstalk between tumor and other tissues as they enable us to observe the systemic and biological interactions of a complete organism. Although engineered mice are the most common model used in this setting, the zebrafish (Danio rerio) species has recently been recognized as an innovative experimental system. In fact, the transparent body and incomplete immune system of zebrafish embryos are especially useful for evaluating patient-derived tumor tissue interactions in healthy hosts. In conclusion, ex vivo systems represent an important tool for cancer research, but samples require correct manipulation to maximize their translational value.