Recent advances in cancer research: mouse models of tumorigenesis

Negative terpinen-4-ol modulate potentially malignant and malignant lingual lesions induced by 4-nitroquinoline-1-oxide in rat model

Our aim was to verify the modulative TP-4-ol capacity in 4-nitroquinoline-1-oxide induced oral rat cancer. The stereoisomers of TP-4-ol were used against the human tongue squamous cell line and the negative stereoisomer showed lower IC50. Thirty-one Holtzman rats (120-130 g) were cancer-induced by 4-nitroquinoline-1-oxide (4-NQO/8 weeks/25 ppm) and 32 Holtzman rats (120-130 g) were used to healthy and TP-4-ol toxicity experiments. Six groups were used, healthy, 0.1nL/g of TP-4-ol, 8nL/g of TP-4-ol, 4-NQO, 4-NQO + 0.1nL/g of TP-4-ol, and 4-NQO + 8nL/g of TP-4-ol. We performed the toxicity analysis by biochemical and histopathological analysis. The biochemistry analysis includes alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate transaminase (AST), urea, and creatinine and the histopathology analysis includes the liver, kidney, lung, and spleen. Specifically, for malign modulation, we performed a macroscopic and microscopic analysis. The group exposed to 0.1nL/g of TP-4-ol demonstrated a reduced risk of malignancy in dysplasia considering the criteria of architecture and cytology. Similarly, a drop of percentual rats with SCC diagnosis was observed in 4-NQO + 0.1nL/g (41.6%) when compared to 4-NQO (87.5%). Moreover, the 4-NQO group presented a median of 2.62 SCC/rat and the 4-NQO + 0.1nL/g demonstrated a median of 0.75 SCC/rat. For toxicity analysis, 4-NQO + 0.1nL/g showed focal necrosis in the kidney and 4-NQO showed lung hemorrhagic areas. The concentration of 0.1nL/g was more effective in reducing the tongue induction of potentially malignant and malignant lesions by 4-NQO. A kidney toxicity was observed in healthy animals exposed to 0.1nL/g of TP-4-ol. The negative isoform of terpinen-4-ol negatively modulates the development of potentially malignant and malignant lesions in rats (Rattus nonverdicts albinos, Holtzman) exposed to 4-NQO. (-)-Terpinen-4-ol reduced the mice percentual with squamous cell carcinoma, 87.5 to 41.6%, and decreased the cancer/rat ratio of 2.62 in 4-NQO to 0.75 in 4-NQO + 0.1nL/g. This represents 52.4% by group and 71.3% in the cancer/rat ratio.

Genetically engineered mouse models of esophageal cancer

BACKGROUND

Esophageal cancer is the most common cause of cancer-related death worldwide with a diverse geographical distribution, poor prognosis, and diagnosis in advanced stages of the disease. Identification of the mechanisms involved in esophageal cancer development is evaluative to improve outcomes for patients. Genetically engineered mouse models (GEMMs) of cancer provide the physiologic, molecular, and histologic features of the human tumors to determine the pathogenesis and treatments for cancer, hence exhibiting a source of tremendous potential for oncology research. The advancement of cancer modeling in mice has improved to the extent that researchers can observe and manipulate the disease process in a specific manner. Despite the significant differences between mice and humans, mice can be great models for human oncology researches due to similarities between them at the molecular and physiological levels. Due to most of the existing esophageal cancer GEMMs do not propose an ideal system for pathogenesis of the disease, genetic risks, and microenvironment exposure, so identification of challenges in GEM modeling and well-developed technologies are required to obtain the most value for patients. In this review, we describe the biology of human and mouse, followed by the exciting esophageal cancer mouse models with a discussion of applicability and challenges of these models for generating new GEMMs in future studies.

Role of Electron Microscopy in Early Detection of Altered Epithelium During Experimental Oral Carcinogenesis

Early detection of altered epithelium can help in controlling the further progression by timely intervention. Alterations in cellular adhesion are one of the hallmarks of cancer progression, which can be detected at the intracellular level using high-resolution electron microscopy. This study aimed to evaluate the role of electron microscopy in the establishment of ultrastructural markers for early detection of altered epithelium using tissues from 4-Nitroquinoline-1-Oxide (4NQO) induced rat tongue carcinogenesis. Our previous study using light microscopy displayed no histopathological alterations in 4NQO treated tissues until 40 days of treatment, while dysplasia, papilloma and carcinoma were detected at 80/120, 160 and 200 days, respectively. However, electron microscopy detected alterations such as detachment of desmosomes from cell membranes and their clustering in the cytoplasm, increased tonofilaments, keratohyaline granules and thickened corneum in 40 days treated corresponding tissues. These alterations are apparent with hyperkeratosis/hyperplasia but remained undetected using light microscopy. Further, in dysplasia, papilloma and carcinoma, gradual and significant loss of desmosomes, leading to the significant widening of intercellular spaces, was observed using iTEM software. These parameters may serve as indicators for progression of oral cancer. Our results highlight the importance of electron microscopy in the early detection of subcellular changes in the altered epithelium.

Interaction of kindlin-2 with integrin β3 promotes outside-in signaling responses by the αVβ3 vitronectin receptor

The bidirectional signaling and hemostatic functions of platelet αIIbβ3 are regulated by kindlin-3 through interactions with the β3 cytoplasmic tail. Little is known about kindlin regulation of the related "vitronectin receptor," αVβ3. These relationships were investigated in endothelial cells, which express αVβ3 and kindlin-2 endogenously. "β3ΔRGT" knock-in mice lack the 3 C-terminal β3 tail residues, whereas in "β3/β1(EGK)" mice, RGT is replaced by the corresponding residues of β1. The wild-type β3 tail pulled down kindlin-2 and c-Src in vitro, whereas β3ΔRGT bound neither protein and β3/β1(EGK) bound kindlin-2, but not c-Src. β3ΔRGT endothelial cells, but not β3/β1(EGK) endothelial cells, exhibited migration and spreading defects on vitronectin and reduced sprouting in 3-dimensional fibrin. Short hairpin RNA silencing of kindlin-2, but not c-Src, blocked sprouting by β3 wild-type endothelial cells. Moreover, defective sprouting by β3ΔRGT endothelial cells could be rescued by conditional, forced interaction of αVβ3ΔRGT with kindlin-2. Stimulation of β3ΔRGT endothelial cells led to normal extracellular ligand binding to αVβ3, pin-pointing their defect to one of outside-in αVβ3 signaling. β3ΔRGT mice, but not β3/β1(EGK) mice, exhibited defects in both developmental and tumor angiogenesis, responses that require endothelial cell function. Thus, the β3/kindlin-2 interaction promotes outside-in αVβ3 signaling selectively, with biological consequences in vivo.

Robust activation of the human but not mouse telomerase gene during the induction of pluripotency

Pluripotent stem cells (PSCs) express telomerase and have unlimited proliferative potential. To study telomerase activation during reprogramming, 3 classes of embryonic stem cell (ESC)-like clones were isolated from mouse fibroblasts containing a transgenic hTERT reporter. Class I expressed few pluripotency markers, whereas class II contained many, but not Oct4, Nanog, and Sox2. Neither class of cells differentiated efficiently. Class III cells, the fully reprogrammed induced PSCs (iPSCs), expressed all pluripotency markers, formed teratomas indistinguishable from those of mESCs, and underwent efficient osteogenic differentiation in vitro. Interestingly, whereas the endogenous mTERT gene expression was only moderately increased during reprogramming, the hTERT promoter was strongly activated in class II cells and was further elevated in class III cells. Treatment of class II cells with chemical inhibitors of MEKs and glycogen synthase kinase 3 resulted in their further reprogramming into class III cells, accompanied by a strong activation of hTERT promoter. In reprogrammed human cells, the endogenous telomerase level, although variable among different clones, was dramatically elevated. Only in cells with the highest telomerase were telomeres restored to the lengths in hESCs. Our data, for the first time, demonstrated that the hTERT promoter was strongly activated in discrete steps, revealing a critical difference in human and mouse cell reprogramming. Because telomere elongation is crucial for self-renewal of hPSCs and replicative aging of their differentiated progeny, these findings have important implications in the generation and applications of iPSCs.

Using optical spectroscopy to longitudinally monitor physiological changes within solid tumors

The feasibility of using quantitative diffuse reflectance spectroscopy to longitudinally monitor physiological response to cancer therapy was evaluated in a preclinical model. This study included two groups of nude mice bearing 4T1 flank tumors (N = 50), half of which were treated with a maximum tolerated dose of doxorubicin (DOX). Diffuse reflectance spectra were collected from tumors during a period of 2 weeks using a fiber-optic probe coupled to a spectrometer. These spectra were quantified using an inverse scalable Monte Carlo model of light transport in tissue to extract the concentrations of oxygenated, deoxygenated hemoglobin (dHb), and a wavelength mean reduced scattering coefficient (<micro(s)'>). The tumor growth rates of the treated and control groups were nearly identical, as were changes in the scattering parameter <micro(s)'> during this time frame. However, tumors treated with DOX showed a transient but significant increase in blood oxygen saturation. A comparison between the optically derived and immunohistochemical end points in a subset of the 50 animals showed that the temporal kinetics of dHb concentration and <micro(s)'> were highly concordant with those of hypoxic and necrotic fractions, respectively. In conclusion, optical methods could function as a "screening" technology in longitudinal studies of small animal tumor models to accelerate development and testing of new anticancer drugs. This technique could isolate specific landmark time points at which more expensive and sophisticated imaging methods or immunohistochemistry could be performed.

Intestinal adenomagenesis involves core molecular signatures of the epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) occurs commonly during carcinoma invasion and metastasis, but not during early tumorigenesis. Microarray data demonstrated elevation of vimentin, a mesenchymal marker, in intestinal adenomas from Apc Min/+ (Min) mice. We have tested the involvement of EMT in early tumorigenesis in mammalian intestines by following EMT-associated markers. Elevated vimentin RNA expression and protein production were detected within neoplastic cells in murine intestinal adenomas. Similarly, vimentin protein was detected in both adenomas and invasive adenocarcinomas of the human colon, but not in the normal colonic epithelium or in hyperplastic polyps. Expression of E-cadherin varied inversely with vimentin. In addition, the expression of fibronectin was elevated while that of E-cadherin decreased. Canonical E-cadherin suppressors, such as Snail, were not elevated in the same tumor. Elevated vimentin expression in the adenoma was not correlated with persistent Ras signaling, but was strongly correlated with reduced proliferation indices, active Wnt signaling, and TGF-beta signaling, as demonstrated by its dependence on Smad3. We designate our observations of expression of only some of the canonical features of EMT as "truncated EMT". These unexpected observations are interpreted as reflecting the involvement of a core of the EMT system during the tissue remodeling of early tumorigenesis.

Mouse models in oncogenesis and cancer therapy

Animal models have been critical in the study of the molecular mechanisms of cancer and in the development of new antitumor agents; nevertheless, there is still much room for improvement. The relevance of each particular model depends on how close it replicates the histology, physiological effects, biochemical pathways and metastatic pattern observed in the same human tumor type. Metastases are especially important because they are the main determinants of the clinical course of the disease and patient survival, and are the target of systemic therapy. The generation of clinically relevant models using the mouse requires their humanization, since differences exist in transformation and oncogenesis between human and mouse. Although genetically modified (GM) mice have been instrumental in understanding the molecular mechanisms involved in tumor initiation, they have been less successful in replicating advanced cancer. Moreover, a particular genetic alteration frequently leads to different tumor types in human and mouse and to lower metastastatic rates in GM mice than in humans. These findings question the capacity of current GM mouse carcinoma models to predict clinical response to therapy. On the other hand, orthotopic (ORT) xenografts of human tumors, or tumor cell lines, in nude mice reproduce the histology and metastatic pattern of most human tumors at advanced stage. Using ex vivo genetic manipulation of human tumor cells, ORT models can be used to molecularly dissect the metastatic process and to evaluate in vivo tumor response to therapy, using non-invasive procedures. Nevertheless, this approach is not useful in the study of the initial stages of tumorigenesis or the contribution of the immune system in this process. Despite ORT models are more promising than the most commonly used subcutaneous xenografts in preclinical drug development, their capacity to predict clinical response to antitumor agents remains to be studied. Humanizing mouse models of cancer will most likely require the combined use of currently available methodologies.

Onset of abnormal blood and lymphatic vessel function and interstitial hypertension in early stages of carcinogenesis

Recent improvements in diagnostic methods have opened avenues for detection and treatment of (pre)malignant lesions at early stages. However, due to the lack of spontaneous tumor models that both mimic human carcinogenesis and allow direct optical imaging of the vasculature, little is known about the function of blood and lymphatic vessels during the early stages of cancer development. Here, we used a spontaneous carcinogenesis model in the skin of DNA polymerase eta-deficient mice and found that interstitial fluid pressure was already elevated in the hyperplastic/dysplastic stage. This was accompanied by angiogenic blood vasculature that exhibited altered permeability, vessel compression, and decreased alpha-smooth muscle actin-positive perivascular cell coverage. In addition, the lymphatic vessels in hyperplastic/dysplastic lesions were partly compressed and nonfunctional. These novel insights may aid early detection and treatment strategies for cancer.

An animal model for the rapid induction of tongue neoplasms in human c-Ha-ras proto-oncogene transgenic rats by 4-nitroquinoline 1-oxide: its potential use for preclinical chemoprevention studies

Oral squamous cell carcinoma is one of the most common human neoplasms, and prevention of this malignancy requires a better understanding of its carcinogenesis process. To this end, we tried to establish an animal model using the human c-Ha-ras proto-oncogene-carrying transgenic (Tg) rats and the carcinogen 4-nitroquinoline 1-oxide (4-NQO). 4-NQO (20 p.p.m.) was administered to Tg and non-Tg rats for 8 weeks in their drinking water, and then the occurrence of tongue carcinogenesis was compared during the experimental period of 22 weeks. In addition, we determined the DNA ploidy in tongue lesions and examined the immunohistochemical expression of five biomarkers such as cyclin D1, glutathione S-transferase placental form, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS) and beta-catenin. Next, the cancer chemopreventive effects of nimesulide, pioglitazone and a synthetic geranylated derivative, which have been reported to be inhibitors of tongue carcinogenesis, were examined in Tg rats treated with 4-NQO. Either during or after treatment with 4-NQO in the drinking water, tongue dysplasia and tumors were observed on the tongues of both Tg and non-Tg rats, with a greater incidence and multiplicity in Tg rats. Histopathologically, squamous cell dysplasia, papilloma and carcinoma with or without invasion were present in the tongue. Immunohistochemistry revealed that expression levels against five biomarkers increase with disease progression, and the changes correlated with those of the DNA ploidy pattern. Interestingly, a strong expression of COX-2, iNOS and beta-catenin was observed on the invasive front of squamous cell carcinomas. A subsequent chemoprevention study using Tg rats showed that the chemicals tested suppressed the occurrence of tongue carcinomas when they were administered after 4-NQO-exposure. These results may thus indicate that our 4-NQO-induced Tg rat tongue carcinogenesis model simulates many aspects of human oral carcinogenesis and it can be applied for an analysis of oral cancer development while also helping to identify potentially effective cancer chemopreventive agents against oral cancer.

50 Years of Preclinical Anticancer Drug Screening: Empirical to Target-Driven Approaches

The number of anticancer agents that fail in the clinic far outweighs those considered effective, suggesting that the selection procedure for progression of molecules into the clinic requires improvement. The value of any preclinical model will ultimately depend on its ability to accurately predict clinical response. This review focuses on the major contributions of preclinical screening models to anticancer drug development over the past 50 years. Over time, a general transition has been observed from the empirical drug screening of cytotoxic agents against uncharacterized tumor models to the target-orientated drug screening of agents with defined mechanisms of action. New approaches to anticancer drug development involve the molecular characterization of models along with an appreciation of the pharmacodynamic and pharmacokinetic properties of compounds [e.g., the US National Cancer Institute (NCI) in vitro 60-cell line panel, hollow fiber assay, and s.c. xenograft]. Contributions of other potentially more clinically relevant in vivo tumor models including orthotopic, metastatic, and genetically engineered mouse models are also reviewed. Although this review concentrates on the preclinical screening efforts of the NCI, European efforts are not overlooked. Europe has played a key role in the development of new anticancer agents. The two largest academic drug development groups, the European Organisation for Research and Treatment of Cancer and Cancer Research UK, have been collaborating with the NCI in the acquisition and screening of compounds since the 1970s. As with the drug development process internationally, rational pharmacodynamic approaches have more recently been adopted by these two groups.

Genetically engineered mouse models for lung cancer

The lung is a complex organ consisting of numerous cell types that function to ensure sufficient gas exchange to oxygenate the blood. In order to accomplish this function, the lung must be exposed to the external environment and at the same time maintain a homeostatic balance between its function in gas exchange and the maintenance of inflammatory balance. During the past two decades, as molecular methodologies have evolved with the sequencing of entire genomes, the use of in vivo models to elucidate the molecular mechanisms involved in pulmonary physiology and disease have increased. The mouse has emerged as a potent model to investigate pulmonary physiology due to the explosion in molecular methods that now allow for the developmental and tissue-specific regulation of gene transcription. Initial efforts to manipulate gene expression in the mouse genome resulted in the generation of transgenic mice characterized by the constitutive expression of a specific gene and knockout mice characterized by the ablation of a specific gene. The utility of these original mouse models was limited, in many cases, by phenotypes resulting in embryonic or neonatal lethality that prevented analysis of the impact of the genetic manipulation on pulmonary biology. Second-generation transgenic mouse models employ multiple strategies that can either activate or silence gene expression thereby providing extensive temporal and spatial control of the experimental parameters of gene expression. These highly regulated mouse models are intended to serve as a foundation for further investigation of the molecular basis of human disease such as tumorigenesis. This review describes the principles, progress, and application of systems that are currently employed in the conditional regulation of gene expression in the investigation of lung cancer.

Selection of more aggressive variants of the gI101A human breast cancer cell line: a model for analyzing the metastatic phenotype of breast cancer

In vivo models utilizing orthotopic injection of tumor cells into nude mice have proven valuable for the study of metastasis. However, breast cancers are among the more difficult of human tumors to grow in immunodeficient mice, with a relatively low tumor take. Fewer still develop spontaneous metastases. The injection of GI101A breast cancer cells into the mammary fatpad (mfp) produced lung metastases in 25% of tumor-bearing mice. Selecting cells from the lung metastases and recycling in vivo resulted in the isolation of a series of variant cell lines. These cell lines were tested for tumorigenicity and metastasis in nude mice following mfp injection compared with the original cell line, and in vitro expression of factors associated with the metastatic phenotype measured. The in vivo selected cell lines were more aggressive, with higher tumor take, faster local growth rate and increased incidence (> or = 85%) and extent of lung metastasis. However, the metastasis-selected variants showed no increases in expression of the growth factor receptors EGFR or HER-2, and the pro-angiogenic factors VEGF-A and IL-8. Immunohistochemistry of mfp tumors revealed no differences in microvessel density (counting CD-31 positive structures) and cell proliferation (PCNA-positive cells) comparing the GI101A line with selected variants. No TUNEL-positive cells were detected in the tumors of the metastasis-derived variant, with a small number of cells undergoing apoptosis detected in sections of GI101A tumors. In vitro, the metastasis-derived variants were found to have a more robust expression of phosphorylated PKB/Akt, with or without EGF or serum stimulation, suggesting an association between Akt activation and metastatic ability. This new series of isogenic cell lines may be valuable for identifying molecular mechanisms involved in the metastatic progression of breast cancer.