Advances in optical imaging and novel model systems for cancer metastasis research

Bone Metastasis in Bladder Cancer

Bladder cancer (BCa) is the 10th most common and 13th most deadly malignancy worldwide. About 5% of BCa patients present initially with metastatic disease, with bone being the most diagnosed site for distant metastasis. The overall one-year survival of patients with BCa is 84%, whereas it is only 21% in patients with bone metastasis (BM). Metastasis of BCa cells to bone occurs by epithelial-to-mesenchymal transition, angiogenesis, intravasation, extravasation, and interactions with the bone microenvironment. However, the mechanism of BCa metastasis to the bone is not completely understood; it needs a further preclinical model to completely explain the process. As different imaging mechanisms, PET-CT cannot replace a radionuclide bone scan or an MRI for diagnosing BM. The management of BCa patients with BM includes chemotherapy, immunotherapy, targeted therapy, antibody-drug conjugates, bisphosphonates, denosumab, radioisotopes, and surgery. The objective of these treatments is to inhibit disease progression, improve overall survival, reduce skeletal-related events, relieve pain, and improve the quality of life of patients.

Three-Dimensional Deep-Tissue Functional and Molecular Imaging by Integrated Photoacoustic, Ultrasound, and Angiographic Tomography (PAUSAT)

Non-invasive small-animal imaging technologies, such as optical imaging, magnetic resonance imaging and x -ray computed tomography, have enabled researchers to study normal biological phenomena or disease progression in their native conditions. However, existing small-animal imaging technologies often lack either the penetration capability for interrogating deep tissues (e.g., optical microscopy), or the functional and molecular sensitivity for tracking specific activities (e.g., magnetic resonance imaging). To achieve functional and molecular imaging in deep tissues, we have developed an integrated photoacoustic, ultrasound and acoustic angiographic tomography (PAUSAT) system by seamlessly combining light and ultrasound. PAUSAT can perform three imaging modes simultaneously with complementary contrast: high-frequency B-mode ultrasound imaging of tissue morphology, microbubble-enabled acoustic angiography of tissue vasculature, and multi-spectral photoacoustic imaging of molecular probes. PAUSAT can provide three-dimensional (3D) multi-contrast images that are co-registered, with high spatial resolutions at large depths. Using PAUSAT, we performed proof-of-concept in vivo experiments on various small animal models: monitoring longitudinal development of placenta and embryo during mouse pregnancy, tracking biodistribution and metabolism of near-infrared organic dye on the whole-body scale, and detecting breast tumor expressing genetically-encoded photoswitchable phytochromes. These results have collectively demonstrated that PAUSAT has broad applicability in biomedical research, providing comprehensive structural, functional, and molecular imaging of small animal models.

Chick Embryo Experimental Platform for Micrometastases Research in a 3D Tissue Engineering Model: Cancer Biology, Drug Development, and Nanotechnology Applications

Colonization of distant organs by tumor cells is a critical step of cancer progression. The initial avascular stage of this process (micrometastasis) remains almost inaccessible to study due to the lack of relevant experimental approaches. Herein, we introduce an in vitro/in vivo model of organ-specific micrometastases of triple-negative breast cancer (TNBC) that is fully implemented in a cost-efficient chick embryo (CE) experimental platform. The model was built as three-dimensional (3D) tissue engineering constructs (TECs) combining human MDA-MB-231 cells and decellularized CE organ-specific scaffolds. TNBC cells colonized CE organ-specific scaffolds in 2–3 weeks, forming tissue-like structures. The feasibility of this methodology for basic cancer research, drug development, and nanomedicine was demonstrated on a model of hepatic micrometastasis of TNBC. We revealed that MDA-MB-231 differentially colonize parenchymal and stromal compartments of the liver-specific extracellular matrix (LS-ECM) and become more resistant to the treatment with molecular doxorubicin (Dox) and Dox-loaded mesoporous silica nanoparticles than in monolayer cultures. When grafted on CE chorioallantoic membrane, LS-ECM-based TECs induced angiogenic switch. These findings may have important implications for the diagnosis and treatment of TNBC. The methodology established here is scalable and adaptable for pharmacological testing and cancer biology research of various metastatic and primary tumors.

Radionuclide-based molecular imaging allows CAR-T cellular visualization and therapeutic monitoring

Chimeric antigen receptor T cell (CAR-T) therapy is a new and effective form of adoptive cell therapy that is rapidly entering the mainstream for the treatment of CD19-positive hematological cancers because of its impressive effect and durable responses. Huge challenges remain in achieving similar success in patients with solid tumors. The current methods of monitoring CAR-T, including morphological imaging (CT and MRI), blood tests, and biopsy, have limitations to assess whether CAR-T cells are homing to tumor sites and infiltrating into tumor bed, or to assess the survival, proliferation, and persistence of CAR-T cells in solid tumors associated with an immunosuppressive microenvironment. Radionuclide-based molecular imaging affords improved CAR-T cellular visualization and therapeutic monitoring through either a direct cellular radiolabeling approach or a reporter gene imaging strategy, and endogenous cell imaging is beneficial to reflect functional information and immune status of T cells. Focusing on the dynamic monitoring and precise assessment of CAR-T therapy, this review summarizes the current applications of radionuclide-based noninvasive imaging in CAR-T cells visualization and monitoring and presents current challenges and strategic choices.

Multimodality reporter gene imaging: Construction strategies and application

Molecular imaging has played an important role in the noninvasive exploration of multiple biological processes. Reporter gene imaging is a key part of molecular imaging. By combining with a reporter probe, a reporter protein can induce the accumulation of specific signals that are detectable by an imaging device to provide indirect information of reporter gene expression in living subjects. There are many types of reporter genes and each corresponding imaging technique has its own advantages and drawbacks. Fused reporter genes or single reporter genes with products detectable by multiple imaging modalities can compensate for the disadvantages and potentiate the advantages of each modality. Reporter gene multimodality imaging could be applied to trace implanted cells, monitor gene therapy, assess endogenous molecular events, screen drugs, etc. Although several types of multimodality imaging apparatus and multimodality reporter genes are available, more sophisticated detectors and multimodality reporter gene systems are needed.

Automated quantitative image analysis for ex vivo metastasis assays reveals differing lung composition requirements for metastasis suppression by KISS1

Imaging is broadly used in biomedical research, but signal variation complicates automated analysis. Using the Pulmonary Metastasis Assay (PuMA) to study metastatic colonization by the metastasis suppressor KISS1, we cultured GFP-expressing melanoma cells in living mouse lung ex vivo for 3 weeks. Epifluorescence images of cells were used to measure growth, creating large datasets which were time consuming and challenging to quantify manually due to scattering of light from outside the focal plane. To address these challenges, we developed an automated workflow to standardize the measurement of disseminated cancer cell growth by applying statistical quality control to remove unanalyzable images followed and a filtering algorithm to quantify only in-focus cells. Using this tool, we demonstrate that expression of the metastasis suppressor KISS1 does not suppress growth of melanoma cells in the PuMA, in contrast to the robust suppression of lung metastasis observed in vivo. This result may suggest that a factor required for metastasis suppression is present in vivo but absent in the PuMA, or that KISS1 suppresses lung metastasis at a step in the metastatic cascade not tested by the PuMA. Together, these data provide a new tool for quantification of metastasis assays and further insight into the mechanism of KISS1 mediated metastasis suppression in the lung.

In vivo models in breast cancer research: progress, challenges and future directions

Research using animal model systems has been instrumental in delivering improved therapies for breast cancer, as well as in generating new insights into the mechanisms that underpin development of the disease. A large number of different models are now available, reflecting different types and stages of the disease; choosing which one to use depends on the specific research question(s) to be investigated. Based on presentations and discussions from leading experts who attended a recent workshop focused on in vivo models of breast cancer, this article provides a perspective on the many varied uses of these models in breast cancer research, their strengths, associated challenges and future directions. Among the questions discussed were: how well do models represent the different stages of human disease; how can we model the involvement of the human immune system and microenvironment in breast cancer; what are the appropriate models of metastatic disease; can we use models to carry out preclinical drug trials and identify pathways responsible for drug resistance; and what are the limitations of patient-derived xenograft models? We briefly outline the areas where the existing breast cancer models require improvement in light of the increased understanding of the disease process, reflecting the drive towards more personalised therapies and identification of mechanisms of drug resistance.

Bone metastasis imaging with SPECT/CT/MRI: a preclinical toolbox for therapy studies

Bone is one of the most common metastatic target sites in breast cancer, with more than 200 thousand new cases of invasive cancer diagnosed in the US alone in 2011. We set out to establish a multimodality imaging platform for bone metastases in small animals as a tool to non-invasively quantify metastasis growth, imaging the ensuing bone lesions and possibly the response to treatment. To this end, a mouse model of osteolytic metastatic bone tumors was characterized with SPECT/CT and MRI over time. A cell line capable of forming bone metastases, MDA-MB-231, was genetically modified to stably express the reporter gene herpes simplex virus-1 thymidine kinase (hsv-1 tk). The intracellular accumulation of the radiolabeled tracer [(123)I]FIAU promoted by HSV-1 TK specifically pinpoints the location of tumor cells which can be imaged in vivo by SPECT. First, a study using tumors implanted subcutaneously was performed. The SPECT/MRI overlays and the ex vivo γ-counting showed a linear correlation in terms of %ID/cm(3) (R(2)=0.93) and %ID/g (R(2)=0.77), respectively. Then, bone metastasis growth was imaged weekly by SPECT/CT and T2-weighted MRI over a maximum of 40 days post-intracardiac injection of tumor cells. The first activity spots detectable with SPECT, around day 20 post-cell injection, were smaller than 2mm(3) and not yet visible by MRI and increased in volume and in %ID over the weeks. Osteolytic bone lesions were visible by CT (in vivo) and μCT (ex vivo). The SPECT/MRI overlays also showed a linear correlation in terms of %ID/cm(3) (R(2)=0.86). In conclusion, a new multimodality imaging platform has been established that non-invasively combines images of active tumor areas (SPECT), tumor volume (MRI) and the corresponding bone lesions (CT and μCT). To our knowledge this is the first report where the combination of soft tissue information from MRI, bone lesions by CT, and reporter gene imaging by SPECT is used to non-invasively follow metastatic bone lesions.

In vivo fluorescence imaging and urinary monoamines as surrogate biomarkers of disease progression in a mouse model of pheochromocytoma

Pheochromocytoma (PHEO) is a rare but potentially lethal neuroendocrine tumor arising from catecholamine-producing chromaffin cells. Especially for metastatic PHEO, the availability of animal models is essential for developing novel therapies. For evaluating therapeutic outcome in rodent PHEO models, reliable quantification of multiple organ lesions depends on dedicated small-animal in vivo imaging, which is still challenging and only available at specialized research facilities. Here, we investigated whether whole-body fluorescence imaging and monitoring of urinary free monoamines provide suitable parameters for measuring tumor progression in a murine allograft model of PHEO. We generated an mCherry-expressing mouse PHEO cell line by lentiviral gene transfer. These cells were injected subcutaneously into nude mice to perform whole-body fluorescence imaging of tumor development. Urinary free monoamines were measured by liquid chromatography with tandem mass spectrometry. Tumor fluorescence intensity and urinary outputs of monoamines showed tumor growth-dependent increases (P < .001) over the 30 days of monitoring post-tumor engraftment. Concomitantly, systolic blood pressure was increased significantly during tumor growth. Tumor volume correlated significantly (P < .001) and strongly with tumor fluorescence intensity (rs = 0.946), and urinary outputs of dopamine (rs = 0.952), methoxytyramine (rs = 0.947), norepinephrine (rs = 0.756), and normetanephrine (rs = 0.949). Dopamine and methoxytyramine outputs allowed for detection of lesions at diameters below 2.3 mm. Our results demonstrate that mouse pheochromocytoma (MPC)-mCherry cell tumors are functionally similar to human PHEO. Both tumor fluorescence intensity and urinary outputs of free monoamines provide precise parameters of tumor progression in this sc mouse model of PHEO. This animal model will allow for testing new treatment strategies for chromaffin cell tumors.

Reporter gene approaches for mapping cell fate decisions by MRI: promises and pitfalls

The central dogma of molecular biology, namely the process by which information encoded in the DNA serves as the template for transcriptional activation of specific mRNA resulting in temporal and spatial control of the translation of specific proteins, stands at the basis of normal and pathological cellular processes. Serving as the primary mechanism linking genotype to phenotype, it is clearly of significant interest for in vivo imaging. While classically, imaging revolutionized the ability to phenotype the anatomical and physiological impact of induction of changes in gene expression, the preceding molecular events remained invisible. Reporter gene-based imaging techniques provide a window for in vivo visualization of such transcriptional activation events. In addition to the widespread use of fluorescent and bioluminescent reporter genes and development of a number of reporter genes for positron emission tomography (PET) imaging, there has been significant progress in the development of reporter genes for MRI. With the development of strategies for cellular based therapies, such imaging tools could become central components for personalized patient monitoring.

Different molecular profiles are associated with breast cancer cell homing compared with colonisation of bone: evidence using a novel bone-seeking cell line

Advanced breast cancer is associated with the development of incurable bone metastasis. The two key processes involved, tumour cell homing to and subsequent colonisation of bone, remain to be clearly defined. Genetic studies have indicated that different genes facilitate homing and colonisation of secondary sites. To identify specific changes in gene and protein expression associated with bone-homing or colonisation, we have developed a novel bone-seeking clone of MDA-MB-231 breast cancer cells that exclusively forms tumours in long bones following i.v. injection in nude mice. Bone-homing cells were indistinguishable from parental cells in terms of growth rate in vitro and when grown subcutaneously in vivo. Only bone-homing ability differed between the lines; once established in bone, tumours from both lines displayed similar rates of progression and caused the same extent of lytic bone disease. By comparing the molecular profile of a panel of metastasis-associated genes, we have identified differential expression profiles associated with bone-homing or colonisation. Bone-homing cells had decreased expression of the cell adhesion molecule fibronectin and the migration and calcium signal binding protein S100A4, in addition to increased expression of interleukin 1B. Bone colonisation was associated with increased fibronectin and upregulation of molecules influencing signal transduction pathways and breakdown of extracellular matrix, including hRAS and matrix metalloproteinase 9. Our data support the hypothesis that during early stages of breast cancer bone metastasis, a specific set of genes are altered to facilitate bone-homing, and that disruption of these may be required for effective therapeutic targeting of this process.

NONINVASIVE OPTICAL IMAGING FOR TRACKING GENE DELIVERY AND RECOMBINATION IN TUMOR

Here, we report the generation of optical imaging reporter breast tumor cells that allow the longitudinal, in vivo, noninvasive imaging of gene recombination in tumor. Tumor-gene targeting is a promising approach of treating cancers, and a suitable gene delivery method is the criteria for success. By using the cre lox genetic engineering tool, we targeted stable green fluorescent protein expression in metastatic-prone human breast cancer MDA-MB231 cells that switch to express firefly luciferase upon the exogenous delivery and expression of cre DNA recombinase. We tested this model in vivo by intratumor injection of cre adenovirus and demonstrated the usefulness of this model to achieve longitudinal bioluminescence imaging of DNA recombination in tumor. This optical imaging vector and tumor model will facilitate the research for biomaterial solutions for carriers in gene therapy, and in studies on tumor targeting, tracking for tumor metastasis and migration of tumor stem cells, and for determining the anticancer drug efficacy.

Preclinical imaging of the cellular and molecular events in the multistep process of bone metastasis

Bone metastasis is a complex process that ultimately leads to devastating metastatic bone disease. It is therefore of key interest to unravel the mechanisms underlying the multistep process of skeletal metastasis and cancer-induced bone disease, and to develop better treatment and management of patients with this devastating disease. Fortunately, novel technologies are rapidly emerging that allow real-time imaging of molecules, pathogenic processes, drug delivery and drug response in preclinical in vivo models. The outcome of these experimental studies will facilitate clinical cancer research by improving the detection of cancer cell invasion, metastasis and therapy response.

Xenograft models for preclinical drug testing: implications for adrenocortical cancer

Adrenocortical carcinoma (ACC) is a very rare but aggressive tumor, whose biological and cellular features and processes underlying the development, progression and metastatic evolution are still obscure. Despite many attempts to use general cytostatic and cytotoxic drugs, the only available drug therapy for advanced ACC is still represented by mitotane (MTT). However, the mechanism of action of this adrenolytic derivative of the pesticide DDT has still been poorly characterized. In this context, the development of more specific drugs for ACC treatment is based on the knowledge of the molecular pathways involved in the tumor growth. Xenograft models for the screening of such drugs at preclinical levels is mandatory. In the first part of this review, we will summarize the "pro" and "con" of the different xenograft models available for anticancer drug testing in different types of tumors in general and in the last part, we will focus on the preclinical evidence obtained so far with the use of such models applied to drug screening for anticancer effects in ACC.

Preclinical models that illuminate the bone metastasis cascade

In this chapter currently available preclinical models of tumor progression and bone metastasis, including genetically engineered mice that develop primary and metastatic carcinomas and transplantable animal models, will be described. Understanding the multistep process of incurable bone metastasis is pivotal to the development of new therapeutic strategies. Novel technologies for imaging molecules or pathologic processes in cancers and their surrounding stroma have emerged rapidly and have greatly facilitated cancer research, in particular the cellular behavior of osteotropic tumors and their response to new and existing therapeutic agents. Optical imaging, in particular, has become an important tool in preclinical bone metastasis models, clinical trials and medical practice. Advances in experimental and clinical imaging will-in the long run-result in significant improvements in diagnosis, tumor localization, enhanced drug delivery and treatment.

Zebrafish embryos and larvae: a new generation of disease models and drug screens

Technological innovation has helped the zebrafish embryo gain ground as a disease model and an assay system for drug screening. Here, we review the use of zebrafish embryos and early larvae in applied biomedical research, using selected cases. We look at the use of zebrafish embryos as disease models, taking fetal alcohol syndrome and tuberculosis as examples. We discuss advances in imaging, in culture techniques (including microfluidics), and in drug delivery (including new techniques for the robotic injection of compounds into the egg). The use of zebrafish embryos in early stages of drug safety-screening is discussed. So too are the new behavioral assays that are being adapted from rodent research for use in zebrafish embryos, and which may become relevant in validating the effects of neuroactive compounds such as anxiolytics and antidepressants. Readouts, such as morphological screening and cardiac function, are examined. There are several drawbacks in the zebrafish model. One is its very rapid development, which means that screening with zebrafish is analogous to "screening on a run-away train." Therefore, we argue that zebrafish embryos need to be precisely staged when used in acute assays, so as to ensure a consistent window of developmental exposure. We believe that zebrafish embryo screens can be used in the pre-regulatory phases of drug development, although more validation studies are needed to overcome industry scepticism. Finally, the zebrafish poses no challenge to the position of rodent models: it is complementary to them, especially in early stages of drug research.

Iterative reconstruction of projection images from a microlens-based optical detector

A microlens-based optical detector was developed to perform small animal optical imaging. In this paper we present an iterative reconstruction algorithm yielding improved image quality and spatial resolution as compared to conventional inverse mapping. The reconstruction method utilizes the compressive sensing concept to cope with the undersampling nature of the problem. Each iteration in the algorithm contains two separate steps to ensure both the convergence of the least-square solution and the minimization of the l(1)-norm of the sparsifying transform. The results estimated from measurements, employing a Derenzo-like pattern and a Siemens star phantom, illustrate significant improvements in contrast and spatial resolution in comparison to results calculated by inverse mapping.

Real-time cancer cell tracking by bioluminescence in a preclinical model of human bladder cancer growth and metastasis

BACKGROUND

Bladder cancer is the fifth most common malignancy in the Western world and the second most frequently diagnosed genitourinary tumor. In the majority of cases, death from bladder cancer results from metastatic disease. Understanding the multistep process of carcinogenesis and metastasis in urothelial cancers is pivotal to the development of new therapeutic strategies. Molecular imaging of cancer growth and metastasis in preclinical models provides the essential link between cell-based experiments and clinical translation.

OBJECTIVE

Develop preclinical models for sensitive bladder cancer cell tracking during tumor progression and metastasis.

DESIGN, SETTING, AND PARTICIPANTS

A human transitional cell carcinoma UM-UC-3 cell line was generated that stably expresses luciferase 2 (UM-UC-3luc2), a mammalian codon-optimized firefly luciferase with superior expression. Preclinical models were developed with human UM-UC-3luc2 cells xenografted into the bladder (orthotopic model with metastases) or inoculated into the left cardiac ventricle (bone metastasis model) of immunocompromised mice.

MEASUREMENTS

Noninvasive, sensitive bioluminescent imaging of human firefly luciferase 2-positive bladder cancer in mice using the IVIS100 imaging system.

RESULTS AND LIMITATIONS

In the orthotopic model (intravesical inoculation), tumor growth could be followed directly after inoculation of UM-UC-3luc2 cells. Importantly, micrometastatic lesions originating from orthotopically implanted cancer cells could be detected in the locoregional lymph nodes and in distant organs. In addition, the superior bioluminescent indicator firefly luciferase 2 allows the detection and monitoring of micrometastatic lesions in real time after intracardiac inoculation of human bladder cancer cells in mice. The main disadvantage is the lack of T-cell immunity in the preclinical models.

CONCLUSIONS

The new bioluminescence-based preclinical bladder cancer models enable superior, noninvasive, and real-time tracking of cancer cells, tumor progression, and micrometastasis. Because of the significant improvement in detection of small cell numbers, the presented models are ideally suited for functional studies dealing with minimal residual disease as well as real-time imaging of drug response.

In vivo targeted contrast enhanced micro-ultrasound to measure intratumor perfusion and vascular endothelial growth factor receptor 2 expression in a mouse orthotopic bladder cancer model

PURPOSE

We evaluated the feasibility of using targeted contrast enhanced micro-ultrasound imaging to assess intratumor perfusion and vascular endothelial growth factor receptor 2 expressions in a mouse orthotopic bladder cancer model.

MATERIALS AND METHODS

We created an orthotopic mouse model by implanting MBT-2 murine bladder cancer cell lines in the bladder of syngeneic C3H/He mice (Jackson Laboratory, Bar Harbor, Maine). Successful tumor implantation was confirmed by transabdominal micro-ultrasound imaging on post-implantation day 11. Contrast enhanced micro-ultrasound imaging was done on days 14 and 21. Vascular endothelial growth factor receptor 2 targeted contrast agent was prepared by adding biotinylated anti-vascular endothelial growth factor receptor 2 monoclonal antibodies to streptavidin coated microbubbles. The targeted contrast agents were injected via the retro-orbital route. We quantified intratumor perfusion, vascular endothelial growth factor receptor 2 endothelial expression and blood volume in real time.

RESULTS

In the initial study intratumor perfusion data and vascular endothelial growth factor receptor 2 expression could only be measured in 10 of 14 mice (71%) due to motion artifact. We modified our technique by applying an elastic band over the lower abdomen to minimize body wall movement. After the modification complete images were acquired in all mice at 2 consecutive imaging sessions. Measurements were made of intratumor perfusion and in vivo vascular endothelial growth factor receptor 2 expression. No adverse effects occurred due to anesthesia or the ultrasound contrast agent.

CONCLUSIONS

Targeted contrast enhanced micro-ultrasound imaging enables investigators to detect and monitor vascular changes in orthotopic bladder tumors. It may be useful for direct, noninvasive, in vivo evaluation of novel anti-angiogenesis therapeutic agents. With the modified technique target enhanced contrast ultrasound can be applied in an orthotopic bladder cancer model.

A phage-targeting strategy for the design of spatiotemporal drug delivery from grafted matrices

Background

The natural response to injury is dynamic and normally consists of complex temporal and spatial cellular changes in gene expression, which, when acting in synchrony, result in patent tissue repair and, in some instances, regeneration. However, current therapeutic regiments are static and most rely on matrices, gels and engineered skin tissue. Accordingly, there is a need to design next-generation grafting materials to enable biotherapeutic spatiotemporal targeting from clinically approved matrices. To this end, rather then focus on developing completely new grafting materials, we investigated whether phage display could be deployed onto clinically approved synthetic grafts to identify peptide motifs capable of linking pharmaceutical drugs with differential affinities and eventually, control drug delivery from matrices over both space and time.

Methods

To test this hypothesis, we biopanned combinatorial peptide libraries onto different formulations of a wound-healing matrix (Integra^®) and eluted the bound peptides with 1) high salt, 2) collagen and glycosaminoglycan or 3) low pH. After three to six rounds of biopanning, phage recovery and phage amplification of the bound particles, any phage that had acquired a capacity to bind the matrix was sequenced.

Results

In this first report, we identify distinct classes of matrix-binding peptides which elute differently from the screened matrix and demonstrate that they can be applied in a spatially relevant manner.

Conclusions

We suggest that further applications of these combinatorial techniques to wound-healing matrices may offer a new way to improve the performance of clinically approved matrices so as to introduce temporal and spatial control over drug delivery.

Modeling metastasis biology and therapy in real time in the mouse lung

Pulmonary metastasis remains the leading ca use of death for cancer patients. Opportunities to improve treatment outcomes for patients require new methods to study and view the biology of metastatic progression. Here, we describe an ex vivo pulmonary metastasis assay (PuMA) in which the metastatic progression of GFP-expressing cancer cells, from a single cell to the formation of multicellular colonies, in the mouse lung microenvironment was assessed in real time for up to 21 days. The biological validity of this assay was confirmed by its prediction of the in vivo behavior of a variety of high- and low-metastatic human and mouse cancer cell lines and the discrimination of tumor microenvironments in the lung that were most permissive to metastasis. Using this approach, we provide what we believe to be new insights into the importance of tumor cell interactions with the stromal components of the lung microenvironment. Finally, the translational utility of this assay was demonstrated through its use in the evaluation of therapeutics at discrete time points during metastatic progression. We believe that this assay system is uniquely capable of advancing our understanding of both metastasis biology and therapeutic strategies.

Bioluminescent imaging: a critical tool in pre-clinical oncology research

Bioluminescent imaging (BLI) is a non-invasive imaging modality widely used in the field of pre-clinical oncology research. Imaging of small animal tumour models using BLI involves the generation of light by luciferase-expressing cells in the animal following administration of substrate. This light may be imaged using an external detector. The technique allows a variety of tumour-associated properties to be visualized dynamically in living models. The increasing use of BLI as a small-animal imaging modality has led to advances in the development of xenogeneic, orthotopic, and genetically engineered animal models expressing luciferase genes. This review aims to provide insight into the principles of BLI and its applications in cancer research. Many studies to assess tumour growth and development, as well as efficacy of candidate therapeutics, have been performed using BLI. More recently, advances have also been made using bioluminescent imaging in studies of protein-protein interactions, genetic screening, cell-cycle regulators, and spontaneous cancer development. Such novel studies highlight the versatility and potential of bioluminescent imaging in future oncological research.

PD 0332991, a selective cyclin D kinase 4/6 inhibitor, preferentially inhibits proliferation of luminal estrogen receptor-positive human breast cancer cell lines in vitro

INTRODUCTION

Alterations in cell cycle regulators have been implicated in human malignancies including breast cancer. PD 0332991 is an orally active, highly selective inhibitor of the cyclin D kinases (CDK)4 and CDK6 with ability to block retinoblastoma (Rb) phosphorylation in the low nanomolar range. To identify predictors of response, we determined the in vitro sensitivity to PD 0332991 across a panel of molecularly characterized human breast cancer cell lines.

METHODS

Forty-seven human breast cancer and immortalized cell lines representing the known molecular subgroups of breast cancer were treated with PD 0332991 to determine IC50 values. These data were analyzed against baseline gene expression data to identify genes associated with PD 0332991 response.

RESULTS

Cell lines representing luminal estrogen receptor-positive (ER+) subtype (including those that are HER2 amplified) were most sensitive to growth inhibition by PD 0332991 while nonluminal/basal subtypes were most resistant. Analysis of variance identified 450 differentially expressed genes between sensitive and resistant cells. pRb and cyclin D1 were elevated and CDKN2A (p16) was decreased in the most sensitive lines. Cell cycle analysis showed G0/G1 arrest in sensitive cell lines and Western blot analysis demonstrated that Rb phosphorylation is blocked in sensitive lines but not resistant lines. PD 0332991 was synergistic with tamoxifen and trastuzumab in ER+ and HER2-amplified cell lines, respectively. PD 0332991 enhanced sensitivity to tamoxifen in cell lines with conditioned resistance to ER blockade.

CONCLUSIONS

These studies suggest a role for CDK4/6 inhibition in some breast cancers and identify criteria for patient selection in clinical studies of PD 0332991

Animal models of breast cancer for the study of pathogenesis and therapeutic insights

Activation of oncogenes and inactivation of tumour suppressor genes are common events during breast cancer initiation and progression and often determine treatment responsiveness. Indeed, these events need to be recreated in in vitro systems and in mouse cancer models in order to unravel the molecular mechanisms involved in breast cancer initiation and metastasis and assess their possible impact on responses to anticancer drugs. Optical-based imaging models are used to investigate and to follow important tumour progression processes. Moreover, the development of novel anticancer strategies requires more sensitive and less invasive methods to detect and monitor in vivo drug responses in breast cancer models. This review highlights some of the current strategies for modelling breast cancer in vitro and in the mouse, in order to answer biological or translational questions about human breast malignancies.

Development of a three-dimensional in vitro model for longitudinal observation of cell behavior: monitoring by magnetic resonance imaging and optical imaging

Purpose

The aim of this study is the development of a three-dimensional multicellular spheroid cell culture model for the longitudinal comparative and large-scale screening of cancer cell proliferation with noninvasive molecular imaging techniques under controlled and quantifiable conditions.

Procedures

The human glioblastoma cell line Gli36ΔEGFR was genetically modified to constitutively express the fluorescence protein mCherry, and additionally labeled with iron oxide nanoparticles for high-field MRI detection. The proliferation of aggregates was longitudinally monitored with fluorescence imaging and correlated with aggregate size by light microscopy, while MRI measurements served localization in 3D space. Irradiation with γ-rays was used to detect proliferational response.

Results

Cell proliferation in the stationary three-dimensonal model can be observed over days with high accuracy. A linear relationship of fluorescence intensity with cell aggregate size was found, allowing absolute quantitation of cells in a wide range of cell amounts. Glioblastoma cells showed pronounced suppression of proliferation for several days following high-dose γ-irradiation.

Conclusions

Through the combination of two-dimensional optical imaging and 3D MRI, the position of individual cell aggregates and their corresponding light emission can be detected. This allows an exact quantification of cell proliferation, with a focus on very small cell amounts (below 100 cells) using high resolution noninvasive techniques as a well-controlled basis for further cell transplantation studies.

In vivo bioluminescence imaging of murine xenograft cancer models with a red-shifted thermostable luciferase

PURPOSE

Conventional in vivo bioluminescence imaging using wild-type green-emitting luciferase is limited by absorption and scattering of the bioluminescent signal through tissues. Imaging methods using a red-shifted thermostable luciferase from Photinus pyralis were optimized to improve the sensitivity and image resolution. In vivo bioluminescence imaging performance of red- and green-emitting luciferases were compared in two different xenograft mouse models for cancer.

METHODS

Human hepatoblastoma cell line (HepG2) and human acute monocytic leukemia cell line (Thp1) cells were genetically engineered using retroviral vector technology to stably express the red-shifted or the wild-type green luciferase. A xenograft model of liver cancer was established by subcutaneous injection of the HepG2-engineered cells in the flank regions of mice, and a leukemia model was generated by intravenous injection of the engineered Thp1 cells. The cancer progression was monitored with an ultrasensitive charge-coupled device camera. The relative intensities of the green- and red-emitting luciferases were measured, and the resulting spatial resolutions of the images were compared. Imaging was performed with both intact and scarified live animals to quantify the absorption effects of the skin and deep tissue.

RESULTS

The red-emitting luciferase was found to emit a bioluminescence signal with improved transmission properties compared to the green-emitting luciferase. By imaging the HepG2 models, which contained tumors just beneath the skin, before and after scarification, the percentage of light absorbed by the skin was calculated. The green bioluminescent signal was 75 +/- 8% absorbed by the skin, whereas the red signal was only 20 +/- 6% absorbed. The Thp1 model, which contains cancer cells within the bones, was likewise imaged before and after scarification to calculate the percentage of light absorbed by all tissue under the skin. This tissue was responsible for 90 +/- 5% absorption of the green signal, but only 65 +/- 6% absorption of the red signal.

CONCLUSION

Two different bioluminescent mouse cancer models demonstrate the utility of a new red-shifted thermostable luciferase, Ppy RE-TS, that improved the in vivo imaging performance when compared with wild-type P. Pyralis luciferase. While wild-type luciferase is currently a popular reporter for in vivo imaging methods, this study demonstrates the potential of red-emitting firefly luciferase mutants to enhance the performance of bioluminescence imaging experiments.

Visualisation and quantitative analysis of the rodent malaria liver stage by real time imaging

The quantitative analysis of Plasmodium development in the liver in laboratory animals in cultured cells is hampered by low parasite infection rates and the complicated methods required to monitor intracellular development. As a consequence, this important phase of the parasite's life cycle has been poorly studied compared to blood stages, for example in screening anti-malarial drugs. Here we report the use of a transgenic P. berghei parasite, PbGFP-Luc_con, expressing the bioluminescent reporter protein luciferase to visualize and quantify parasite development in liver cells both in culture and in live mice using real-time luminescence imaging. The reporter-parasite based quantification in cultured hepatocytes by real-time imaging or using a microplate reader correlates very well with established quantitative RT-PCR methods. For the first time the liver stage of Plasmodium is visualized in whole bodies of live mice and we were able to discriminate as few as 1–5 infected hepatocytes per liver in mice using 2D-imaging and to identify individual infected hepatocytes by 3D-imaging. The analysis of liver infections by whole body imaging shows a good correlation with quantitative RT-PCR analysis of extracted livers. The luminescence-based analysis of the effects of various drugs on in vitro hepatocyte infection shows that this method can effectively be used for in vitro screening of compounds targeting Plasmodium liver stages. Furthermore, by analysing the effect of primaquine and tafenoquine in vivo we demonstrate the applicability of real time imaging to assess parasite drug sensitivity in the liver. The simplicity and speed of quantitative analysis of liver-stage development by real-time imaging compared to the PCR methodologies, as well as the possibility to analyse liver development in live mice without surgery, opens up new possibilities for research on Plasmodium liver infections and for validating the effect of drugs and vaccines on the liver stage of Plasmodium.

Transabdominal micro-ultrasound imaging of bladder cancer in a mouse model: a validation study

OBJECTIVES

To validate the use of transabdominal micro-ultrasound imaging (MUI) in an orthotopic murine bladder cancer model. The current in vivo imaging systems for murine bladder cancer include magnetic resonance imaging, bioluminescent and fluorescent imaging, and intravesical ultrasound.

METHODS

We implanted murine bladder tumor-2 tumor cells into C3H/He female mice. Mice underwent MUI before, and every 3 days after instillation of tumor cells. Three mice were killed at every MUI session. Bladder tumors were measured and tumor volumes were calculated during MUI and gross stereomicroscopy. Bladders were harvested and examined under gross stereomicroscopy to confirm the presence, location, and size of bladder tumors, and were prepared for histology review.

RESULTS

Overall, 15 of 33 (45%) mice were confirmed to have tumors, using MUI, gross stereomicroscopy, and histology. Measurements of tumor size by MUI and gross microscopy had a high correlation coefficient (r = 0.97). MUI identified all tumors that were present on final histology. The smallest confirmed tumor on MUI was detected at 0.52 mm(3), and mean tumor volume was 0.95 mm(3). No tumors that were not detected first using MUI were found on final histology.

CONCLUSIONS

Transabdominal MUI is a valuable tool to use for translational studies involving orthotopic mouse bladder cancer models. MUI provides real-time, high resolution in vivo images of bladder tumors. Tumor presence can be confirmed with a high degree of accuracy pertaining to tumor volume before initiation of treatment. In addition, tumor growth or regression can be followed up in vivo longitudinally.

In vivo optical imaging: preclinical applications and considerations

There has recently been an explosion in the availability of new technologies to noninvasively detect biological processes in preclinical models. One such modality, optical imaging, comprises using bioluminescent and fluorescent reporters and probes to repetitively interrogate molecular events and monitor disease progression in animal models. This review includes an overview of optical imaging technologies (e.g., hardware, reporters, probes) available for small animal imaging and their application in monitoring disease progression, therapeutic efficacy, and molecular processes such as proliferation, apoptosis, and angiogenesis. Also discussed are some of the challenges associated with in vivo optical imaging and the necessary controls and biological correlates one must include in experimental design and interpretation for successful preclinical studies.

Molecular imaging as a tool for translating breast cancer science

The ability to measure biochemical and molecular processes underlies progress in breast cancer biology and treatment. These assays have traditionally been performed by analysis of cell culture or tissue samples. More recently, functional and molecular imaging has allowed the in vivo assay of biochemistry and molecular biology, which is highly complementary to tissue-based assays. This review briefly describes different imaging modalities used in molecular imaging and then reviews applications of molecular imaging to breast cancer, with a focus on translational work. It includes sections describing work in functional and physiological tumor imaging, imaging gene product expression, imaging the tumor microenvironment, reporter gene imaging, and cell labeling. Work in both animal models and human is discussed with an eye towards studies that have relevance to breast cancer treatment in patients.

Bevacizumab inhibits breast cancer-induced osteolysis, surrounding soft tissue metastasis, and angiogenesis in rats as visualized by VCT and MRI

The aim of this study was to evaluate the effect of an antiangiogenic treatment with the vascular endothelial growth factor antibody bevacizumab in an experimental model of breast cancer bone metastasis and to monitor osteolysis, soft tissue tumor, and angiogenesis in bone metastasis noninvasively by volumetric computed tomography (VCT) and magnetic resonance imaging (MRI). After inoculation of MDA-MB-231 human breast cancer cells into nude rats, bone metastasis was monitored with contrast-enhanced VCT and MRI from day 30 to day 70 after tumor cell inoculation, respectively. Thereby, animals of the treatment group (10 mg/kg bevacizumab IV weekly, n = 15) were compared with sham-treated animals (n = 17). Treatment with bevacizumab resulted in a significant difference versus control in osteolytic as well as soft tissue lesion sizes (days 50 to 70 and 40 to 70 after tumor cell inoculation, respectively; P < .05). This observation was paralleled with significantly reduced vascularization in the treatment group as shown by reduced increase in relative signal intensity in dynamic contrast-enhanced MRI from days 40 to 70 (P < .05). Contrast-enhanced VCT and histology confirmed decreased angiogenesis as well as new bone formation after application of bevacizumab. In conclusion, bevacizumab significantly inhibited osteolysis, surrounding soft tissue tumor growth, and angiogenesis in an experimental model of breast cancer bone metastasis as visualized by VCT and MRI.