The expression level of luciferase within tumour cells can alter tumour growth upon in vivo bioluminescence imaging

Overcoming Xenoantigen Immunity to Enable Cellular Tracking and Gene Regulation with Immune-competent "NoGlow" Mice

The ability to temporally regulate gene expression and track labeled cells makes animal models powerful biomedical tools. However, sudden expression of xenobiotic genes [e.g., GFP, luciferase (Luc), or rtTA3] can trigger inadvertent immunity that suppresses foreign protein expression or results in complete rejection of transplanted cells. Germline exposure to foreign antigens somewhat addresses these challenges; however, native fluorescence and bioluminescence abrogates the utility of reporter proteins and highly spatiotemporally restricted expression can lead to suboptimal xenoantigen tolerance. To overcome these unwanted immune responses and enable reliable cell tracking/gene regulation, we developed a novel mouse model that selectively expresses antigen-intact but nonfunctional forms of GFP and Luc, as well as rtTA3, after CRE-mediated recombination. Using tissue-specific CREs, we observed model and sex-based differences in immune tolerance to the encoded xenoantigens, illustrating the obstacles of tolerizing animals to foreign genes and validating the utility of these "NoGlow" mice to dissect mechanisms of central and peripheral tolerance. Critically, tissue unrestricted NoGlow mice possess no detectable background fluorescence or luminescence and exhibit limited adaptive immunity against encoded transgenic xenoantigens after vaccination. Moreover, we demonstrate that NoGlow mice allow tracking and tetracycline-inducible gene regulation of triple-transgenic cells expressing GFP/Luc/rtTA3, in contrast to transgene-negative immune-competent mice that eliminate these cells or prohibit metastatic seeding. Notably, this model enables de novo metastasis from orthotopically implanted, triple-transgenic tumor cells, despite high xenoantigen expression. Altogether, the NoGlow model provides a critical resource for in vivo studies across disciplines, including oncology, developmental biology, infectious disease, autoimmunity, and transplantation.

SIGNIFICANCE

Multitolerant NoGlow mice enable tracking and gene manipulation of transplanted tumor cells without immune-mediated rejection, thus providing a platform to investigate novel mechanisms of adaptive immunity related to metastasis, immunotherapy, and tolerance.

Development of an immunosuppressed orthotopic hepatocellular carcinoma rat model for the evaluation of chemo- and radioembolization therapies

Hepatocellular carcinoma (HCC) is widely known to be chemo-resistant and presents with significant liver disease resulting in low tolerability to systemic chemotherapy. As a counter measure, more targeted therapies such as trans-arterial chemoembolization (TACE) and trans-arterial radioembolization (TARE) have been developed. To further optimize these therapies, animal models are critical in elucidating the molecular events in disease progression and test new treatment options. The present study focuses on the development of a hepatoma bearing rat model. N1S1 rat hepatoma cells were transfected by a lentiviral method and injected into the liver of Sprague Dawley (SD) and Rowett Nude (RNU) rats. Longitudinal tumor growth was observed by bioluminescence imaging (BLI) and liver/tumor histology. In both models, tumors were visible within 4 days post cell inoculation. Tumor take rates were 52 % and 73 % for male and female SD rats, respectively, and 100 % for male RNU rats. By day 12 and 15 post inoculation, we recorded complete tumor regression in male and female SD rats. Liver histology showed advanced fibrosis in the tumor regressed SD rats, whilst RNU rats exhibited the characteristic sheet pattern of Novikoff tumor with mild liver fibrosis. Increased CD3 and TUNEL staining observed in SD rat livers may be key factors for tumor regression. Our data reveal that the immunocompetent SD rats are not recommended as a model for therapeutic investigations. The immunosuppressed RNU rats, however, are characterized by consistent and reliable tumor growth and thus a desirable model for future therapeutic investigations.

A sensitive and specific LC-MS/MS method for determination of a novel antihypertensive peptide FR-6 in rat plasma and pharmacokinetic study

The investigation of peptide drugs has become essential in the development of innovative medications for hypertension. In this study, a sensitive high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method was developed to determine the plasma concentration and stability of the antihypertensive peptide FR-6 in rats. An isotopically labeled peptide (with an unchanged sequence) was utilized as an internal standard (IS) for validation purposes. Subsequently, this assay was employed to examine the pharmacokinetics of different administration methods (tail vein and gavage) in Sprague Dawley (SD) rats. Extracted plasma samples underwent sample preparation through methanol protein precipitation, followed by elution of FR-6 on Wondasil C18 Superb column (4.6 × 150 mm, 5 μm), using a mobile phase consisting of formic acid (0.1%) in water (A) and formic acid (0.125%)-ammonium formate (2 mM) in methanol (B). Ion pairs corresponding to FR-6 and IS were monitored via multiple reaction monitoring (MRM) under positive ion mode: m/z 400.7 → 285.1 for FR-6 and m/z 406.1 → 295.1 for IS detection respectively. The method exhibited excellent linearity with respect to FR-6 concentrations. In addition, the inter-day and intra-day precision were 0.61-6.85% and 1.76-11.75%; the inter-day and intra-day accuracy were -7.28-0.13% and -7.20-2.28%, respectively. In conclusion, the matrix effect, extraction recovery, and stability data were validated according to FDA recommended acceptance criteria for bioanalytical methods. This validated method serves as a reliable tool for determining the concentration of antihypertensive peptide FR-6, and has been successfully applied in pharmacokinetic studies involving rats.

TAMpepK Suppresses Metastasis through the Elimination of M2-Like Tumor-Associated Macrophages in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) accounts for approximately 10–15% of all breast cancer cases and is characterized by high invasiveness, high metastatic potential, relapse proneness, and poor prognosis. M2-like tumor-associated macrophages (TAMs) contribute to tumorigenesis and are promising targets for inhibiting breast cancer metastasis. Therefore, we investigated whether melittin-conjugated pro-apoptotic peptide (TAMpepK) exerts therapeutic effects on breast cancer metastasis by targeting M2-like TAMs. TAMpepK is composed of M2-like TAM binding peptide (TAMpep) and pro-apoptotic peptide d(KLAKLAK)₂ (dKLA). A metastatic mouse model was constructed by injecting 4T1-luc2 cells either orthotopically or via tail vein injection, and tumor burden was quantified using a bioluminescence in vivo imaging system. We found that TAMpepK suppressed lung and lymph node metastases of breast cancer by eliminating M2-like TAMs without affecting the viability of M1-like macrophages and resident macrophages in the orthotopic model. Furthermore, TAMpepK reduced pulmonary seeding and the colonization of tumor cells in the tail vein injection model. The number of CD8⁺ T cells in contact with TAMs was significantly decreased in tumor nodules treated with TAMpepK, resulting in the functional activation of cytotoxic CD8⁺ T cells. Taken together, our findings suggest that TAMpepK could be a novel therapeutic agent for the inhibition of breast cancer metastasis by targeting M2-like TAMs.

Expression of tdTomato and luciferase in a murine lung cancer alters the growth and immune microenvironment of the tumor

Imaging techniques based on fluorescence and bioluminescence have been important tools in visualizing tumor progression and studying the effect of drugs and immunotherapies on tumor immune microenvironment in animal models of cancer. However, transgenic expression of foreign proteins may induce immune responses in immunocompetent syngeneic tumor transplant models and augment the efficacy of experimental drugs. In this study, we show that the growth rate of Lewis lung carcinoma (LL/2) tumors was reduced after transduction of tdTomato and luciferase (tdTomato/Luc) compared to the parental cell line. tdTomato/Luc expression by LL/2 cells altered the tumor microenvironment by increasing tumor-infiltrating lymphocytes (TILs) while inhibiting tumor-induced myeloid-derived suppressor cells (MDSCs). Interestingly, tdTomato/Luc expression did not alter the response of LL/2 tumors to anti-PD-1 and anti-CTLA-4 antibodies. These results suggest that the use of tdTomato/Luc-transduced cancer cells to conduct studies in immune competent mice may lead to cell-extrinsic tdTomato/Luc-induced alterations in tumor growth and tumor immune microenvironment that need to be taken into consideration when evaluating the efficacy of anti-cancer drugs and vaccines in immunocompetent animal models.

Cellular MRI Reveals Altered Brain Arrest of Genetically Engineered Metastatic Breast Cancer Cells

Purpose

The combined use of anatomical magnetic resonance imaging (MRI), cellular MRI, and bioluminescence imaging (BLI) allows for sensitive and improved monitoring of brain metastasis in preclinical cancer models. By using these complementary technologies, we can acquire measurements of viable single cell arrest in the brain after systemic administration, the clearance and/or retention of these cells thereafter, the growth into overt tumours, and quantification of tumour volume and relative cancer cell viability over time. While BLI is very useful in measuring cell viability, some considerations have been reported using cells engineered with luciferase such as increased tumour volume variation, changes in pattern of metastatic disease, and inhibition of in vivo tumour growth.

Procedures

Here, we apply cellular and anatomical MRI to evaluate in vivo growth differences between iron oxide labeled naïve (4T1BR5) and luciferase-expressing (4T1BR5-FLuc-GFP) murine brain-seeking breast cancer cells. Balb/C mice received an intracardiac injection of 20,000 cells and were imaged with MRI on days 0 and 14. Mice that received 4T1BR5-FLuc-GFP cells were also imaged with BLI on days 0 and 14.

Results

The number of signal voids in the brain (representing iron-labeled cancer cells) on day 0 was significantly higher in mice receiving 4T1BR5 cells compared to mice receiving 4T1BR5-FLuc-GFP cells (p < 0.0001). Mice that received 4T1BR5 cells also had significantly higher total brain tumour burden and number of brain metastases than mice that received 4T1BR5-FLuc-GFP cells (p < 0.0001).

Conclusions

By employing highly sensitive cellular MRI tools, we demonstrate that engineered cells did not form tumours as well as their naïve counterparts, which appear to primarily be due to a reduction in cell arrest. These results indicate that engineering cancer cells with reporter genes may alter their tropism towards particular organs and highlight another important consideration for research groups that use reporter gene imaging to track metastatic cancer cell fate in vivo.

Targeting Cancer with Peptide RNAi Nanoplexes

With the recent explosion of genomic information on the root causes of disease, there is an increased interest in nucleic acid therapeutics, including siRNA and gene therapy, all of which require delivery of highly charged nucleic acids from siRNA with a molecular weight of about 1.4 × 10⁴ to plasmids with an approximate molecular weight of 2.0-3.0 × 10⁶. This chapter describes the delivery of shRNA via plasmid or siRNA with a peptide-based carrier. We focus on the histidine-lysine peptide which serves as an example for other peptides and polymeric carrier systems. When the HK peptide and nucleic acids are mixed together and interact with one another through ionic and nonionic interactions, nanoplexes are formed. These nanoplexes, carrying either shRNA or siRNA that target oncogenes, provide promising options for the treatment of cancer. We describe methods of preparation and characterization of these nanoplexes using dynamic light scattering, zeta potential, and gel retardation assays. We also provide protocols for transfection in vitro and in vivo for these nanoplexes.

Hepa1-6-FLuc cell line with the stable expression of firefly luciferase retains its primary properties with promising bioluminescence imaging ability

Reliable animal models are required for the in vivo study of the molecular mechanisms and effects of chemotherapeutic drugs in hepatocarcinoma. In vivo tracing techniques based on firefly luciferase (FLuc) may optimize the non-invasive monitoring of experimental animals. The present study established a murine Hepa1-6-FLuc cell line that stably expressed a retrovirus-delivered FLuc protein gene. The cell morphology, proliferation, migration and invasion ability of Hepa1-6-FLuc cells were the same as that of the Hepa1-6 cells, and thus is suitable to replace Hepa1-6 cells in the construction of hepatocarcinoma animal models. No differences in subcutaneous tumor mass and its pathomorphology from implanted Hepa1-6-FLuc cells were observed compared with Hepa1-6 control tumors. Bioluminescence imaging indicated that the Luc signal of the Hepa1-6-FLuc cells was consistently strengthened with increases in tumor mass; however, the Luc signal of Hepa1-6-AdFLuc became weaker and eventually disappeared during tumor development. Therefore, compared with the transient expression by adenovirus, stable expression of the FLuc gene in Hepa1-6 cells may better reflect cell proliferation and survival in vivo, and provide a reliable source for the establishment of hepatocarcinoma models.

Luciferase Expression Allows Bioluminescence Imaging But Imposes Limitations on the Orthotopic Mouse (4T1) Model of Breast Cancer

Implantation of reporter-labeled tumor cells in an immunocompetent host involves a risk of their immune elimination. We have studied this effect in a mouse model of breast cancer after the orthotopic implantation of mammary gland adenocarcinoma 4T1 cells genetically labelled with luciferase (Luc). Mice were implanted with 4T1 cells and two derivative Luc-expressing clones 4T1luc2 and 4T1luc2D6 exhibiting equal in vitro growth rates. In vivo, the daughter 4T1luc2 clone exhibited nearly the same, and 4T1luc2D6, a lower growth rate than the parental cells. The metastatic potential of 4T1 variants was assessed by magnetic resonance, bioluminescent imaging, micro-computed tomography, and densitometry which detected 100-μm metastases in multiple organs and bones at the early stage of their development. After 3-4 weeks, 4T1 generated 11.4 ± 2.1, 4T1luc2D6, 4.5 ± 0.6; and 4T1luc2, <1 metastases per mouse, locations restricted to lungs and regional lymph nodes. Mice bearing Luc-expressing tumors developed IFN-γ response to the dominant CTL epitope of Luc. Induced by intradermal DNA-immunization, such response protected mice from the establishment of 4T1luc2-tumors. Our data show that natural or induced cellular response against the reporter restricts growth and metastatic activity of the reporter-labelled tumor cells. Such cells represent a powerful instrument for improving immunization technique for cancer vaccine applications.

An enhanced chimeric firefly luciferase-inspired enzyme for ATP detection and bioluminescence reporter and imaging applications

Firefly luciferases, which emit visible light in a highly specific ATP-dependent process, have been adapted for a variety of applications, including gene reporter assays, whole-cell biosensor measurements, and in vivo imaging. We previously reported the approximately 2-fold enhanced activity and 1.4-fold greater bioluminescence quantum yield properties of a chimeric enzyme that contains the N-domain of Photinus pyralis luciferase joined to the C-domain of Luciola italica luciferase. Subsequently, we identified 5 amino acid changes based on L. italica that are the main determinants of the improved bioluminescence properties. Further engineering to enhance thermal and pH stability produced a novel luciferase called PLG2. We present here a systematic comparison of the spectral and physical properties of the new protein with P. pyralis luciferase and demonstrate the potential of PLG2 for use in assays based on the detection of femtomole levels of ATP. In addition, we compared the performance of a mammalian codon-optimized version of the cDNA for PLG2 with the luc2 gene in HEK293T cells. Using an optimized low-cost assay system, PLG2 activity can be monitored in mammalian cell lysates and living cells with 4.4-fold and approximately 3.0-fold greater sensitivity, respectively. PLG2 could be an improved alternative to Promega's luc2 for reporter and imaging applications.

Luciferase does not Alter Metabolism in Cancer Cells

Luciferase transfected cell lines are used extensively for cancer models, revealing valuable biological information about disease mechanisms. However, these genetically encoded reporters, while useful for monitoring tumor response in cancer models, can impact cell metabolism. Indeed firefly luciferase and fatty acyl-CoA synthetases differ by a single amino acid, raising the possibility that luciferase activity might alter metabolism and introduce experimental artifacts. Therefore knowledge of the metabolic response to luciferase transfection is of significant importance, especially given the thousands of research studies using luciferase as an in vivo bioluminescence imaging (BLI) reporter. Untargeted metabolomics experiments were performed to examine three different types of lymphoblastic leukemia cell lines (Ramos, Raji and SUP T1) commonly used in cancer research, each were analyzed with and without vector transduction. The Raji model was also tested under perturbed starvation conditions to examine potential luciferase-mediated stress responses. The results showed that no significant metabolic differences were observed between parental and luciferase transduced cells for each cell line, and that luciferase overexpression does not alter cell metabolism under basal or perturbed conditions.

Bioluminescence imaging correlates with tumor serum marker, organ weights, histology, and human DNA levels during treatment of orthotopic tumor xenografts with antibodies

PURPOSE

In this study, we correlate results of bioluminescence measurements with established readouts for assessing therapeutic efficacy of antibodies in orthotopic cancer xenografts.

PROCEDURES

An orthotopic tumor model of pancreatic cancer (AsPC-1-luc) and experimental lung metastasis (A549-luc) were established. Whole-body bioluminescence imaging (BLI) was performed to observe tumor progression under therapy with antibodies targeting different receptor kinases (primary readout). For purpose of verification, anti-tumoral efficacy was cross-validated with results obtained by measurement of organ weights, histology, tumor serum marker analysis (CYFRA 21-1), and quantification of human DNA concentration in the organ of interest (secondary readouts).

RESULTS

Anti-tumoral efficacy is demonstrated for the antibodies tested. In the pancreas xenograft, a tumor growth inhibition of 95% (p < 0.01) was achieved as compared to control. Therapeutic efficacy could be identified as soon as 1 week after initiation of treatment. In the model of experimental lung metastasis, antibody treatment significantly suppressed tumor growth up to 75% (p < 0.05). All imaging results were confirmed by correlation analysis showing excellent agreement with the secondary readouts.

CONCLUSIONS

BLI was demonstrated to be a reliable tool for monitoring early drug responses in orthotopic small animal cancer models. BLI allows rapid and non-invasive assessment of tumor load in the animal over time and, thus, provides a suitable method for routine use in preclinical cancer research.

Differential post-surgical metastasis and survival in SCID, NOD-SCID and NOD-SCID-IL-2Rγ(null) mice with parental and subline variants of human breast cancer: implications for host defense mechanisms regulating metastasis

We compare for the first time, the metastatic aggressiveness of the parental MDA-MB-231 breast cancer cell line and two luciferase-tagged in vivo-derived and selected pro-metastatic variants (LM2-4/luc⁺ and 164/8-1B/luc⁺) in SCID, NOD-SCID and NOD-SCID-IL-2Rγ^null (NSG) mice following orthotopic implantation and primary tumour resection. The variants are known to be more aggressively metastatic in SCID mice, compared to the parental line which has limited spontaneous metastatic competence in these mice. When 2×10⁶ cells were injected into the mammary fat pad, the growth of the resultant primary tumours was identical for the various cell lines in the three strains of mice. However, metastatic spread of all three cell lines, including the MDA-MB-231 parental cell line, was strikingly more aggressive in the highly immunocompromised NSG mice compared to both NOD-SCID and SCID mice, resulting in extensive multi-organ metastases and a significant reduction in overall survival. While these studies were facilitated by monitoring post-surgical spontaneous metastases using whole body bioluminescence imaging, we observed that the luciferase-tagged parental line showed altered growth and diminished metastatic properties compared to its untagged counterpart. Our results are the first to show that host immunity can have a profound impact on the spread of spontaneous visceral metastases and survival following resection of a primary tumour in circumstances where the growth of primary tumours is not similarly affected; as such they highlight the importance of immunity in the metastatic process, and by extension, suggest certain therapeutic strategies that may have a significant impact on reducing metastasis.

Noninvasive visualization of tumor growth in a human colorectal liver metastases xenograft model using bioluminescence in vivo imaging

BACKGROUND

Bioluminescence imaging (BLI) is an ideal tool for noninvasive, quantitative monitoring of tumor progression/regression in animal models. The effectiveness of different treatment strategies is displayed by an altered intensity of bioluminescence, demonstrating a change of the tumor burden. The aim of this study was to establish a reliable, reproducible colorectal hepatic metastases cancer animal model.

METHODS

Cells of the human colon carcinoma cell line HCT-116 Luc(pos) expressing the firefly luciferase enzyme gene were used. HCT-116 Luc(pos) cells (2.5 × 10(6)) were injected through the portal vein into the liver of immunoincompetent nude mice. BLI was used to analyze intrahepatic tumor burden and growth kinetic.

RESULTS

HCT-116 Luc(pos) cells demonstrated a progressive and reproducible growth in the liver after intraportal injection. Four days after injection, the animals were analyzed for tumor growth by BLI, and mice without or too low bioluminescence signals were excluded (between 10% and 20% animals). HCT-116 Luc(pos) intrahepatic tumors responded successfully to different dosages (5 and 10 mg/kg) of 5-fluorouracil.

CONCLUSIONS

BLI is an important tool with many potential advantages for investigators. The measurement of intrahepatic tumor growth by imaging luciferase activity noninvasively provides valuable information on tumor burden and effectiveness of therapy. Thus, the presented intrahepatic metastases model based on the growth of HCT-116 Luc(pos) cells is suitable for in vivo testing of different cancer therapy strategies.

Intraosseous inoculation of tumor cells into bone marrow promotes distant metastatic tumor development: A novel tool for mechanistic and therapeutic studies

Bone marrow-derived cells have a potent impact on the formation and progression of tumor metastasis. This study demonstrates that bone marrow directly promotes metastasis to distant sites from tumor cells residing in the bone marrow in multiple types of tumors and multiple mouse strains. The bone marrow environment requires less tumor cells for inducing distant metastasis and overcomes the inhibition of metastasis resulting from engineering the tumor cells with reporter genes. This discovery provides an effective approach to generate spontaneous-like metastatic tumor models which will satisfy the urgent need for studying metastasis biology and discovering novel therapeutics.

Extracellular protease imaging for cell mass tracking of xenografted human malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is locally aggressive and challenging to quantitate non-invasively in vivo, particularly in orthotopic models of disease. We describe imaging of extracellular protease activity, typically elevated in locally aggressive tumors, as a novel method for tracking MPM in vivo. Mice bearing human MPM subcutaneous flank xenografted tumors were imaged with ProSense 680, an optical imaging agent of extracellular cysteine protease activity. The relative contribution of extracellular cysteine proteases to the ProSense tumor signal was estimated using RT-PCR quantitation of cysteine protease RNA expression of the MPM cell lines and compared to ArrayExpress microarray RNA expression data from human MPM tumors. Feasibility of orthotopic intraperitoneal MPM cell mass tracking with fluorescence signal was evaluated using CellVue Maroon-coated MSTO-211H and compared to bioluminescent signal using luciferase-transfected MSTO-211H cells. ProSense 680 yielded a robust tumor signal in MPM subcutaneous grafts, primarily resulting from MPM secretion of cathepsin L demonstrated not only by RT-PCR data on MPM cell lines but also by microarray expression data from resected human patient tumors. CellVue Maroon intraperitoneal tumor signal was robust and durable indicating feasibility of intraperitoneal cell mass tracking of orthotopically-xenografted MPM. Optical imaging of extracellular cysteine protease activity is useful for tracking MPM tumor cell mass in vivo. Intraperitoneal MPM cell mass tracking of fluorescently labeled tumor is feasible.

Monitoring of tumour progression using bioluminescence imaging and computed tomography scanning in a nude mouse orthotopic model of human small cell lung cancer

Human small cell lung carcinoma (SCLC) is the most aggressive type of lung cancer but no clinically relevant animal model has been developed to date. Such a model would be valuable to study the molecular aspects of tumour progression and to test the effectiveness of new treatment agents. We generated a reproducible and reliable nude mouse orthotopic model of human SCLC with NCI-H209 tumour cells genetically modified to express firefly luciferase. Cells were analysed for long-term stability of bioluminescence and a clone was passaged twice subcutaneously to enhance tumorigenicity. Cells resuspended in Matrigel and/or EDTA RPMI medium containing a (99m)Tc-labelled tin colloid used as tracer were implanted intrabronchially with a catheter inserted into the trachea and positioned in the main bronchus using X-ray-guided imaging. Deposition of cells into the lung was then assessed by scintigraphy. The growth of the primary tumour was sensitively and non-invasively followed by bioluminescence imaging that allowed real-time monitoring of tumour progression in the same animals over a 2-12-week period. Additional 3D bioluminescence imaging and computed tomography scanning were used to document tumour location and measurements that were confirmed by histological analyses. In conclusion, this original nude mouse orthotopic model resembles various stages of human small cell lung cancer, and therefore could be used to evaluate new treatment strategies.

Cardiovascular magnetic resonance imaging in small animals

Noninvasive imaging studies involving small animals are becoming increasingly important in preclinical pharmacological, genetic, and biomedical cardiovascular research. Especially small animal magnetic resonance imaging (MRI) using high field and clinical MRI systems has gained significant importance in recent years. Compared to other imaging modalities, like computer tomography, MRI can provide an excellent soft tissue contrast, which enables the characterization of different kinds of tissues without the use of contrast agents. In addition, imaging can be performed with high spatial and temporal resolution. Small animal MRI cannot only provide anatomical information about the beating murine heart; it can also provide functional and molecular information, which makes it a unique imaging modality. Compared to clinical MRI examinations in humans, small animal MRI is associated with additional challenges. These included a smaller size of all cardiovascular structures and a up to ten times higher heart rate. Dedicated small animal monitoring devices make a reliable cardiac triggering and respiratory gating feasible. MRI in combination with molecular probes enables the noninvasive imaging of biological processes at a molecular level. Different kinds of iron oxide or gadolinium-based contrast agents can be used for this purpose. Compared to other molecular imaging modalities, like single photon emission computed tomography (SPECT) and positron emission tomography (PET), MRI can also provide imaging with high spatial resolution, which is of high importance for the assessment of the cardiovascular system. The sensitivity for detection of MRI contrast agents is however lower compared to sensitivity of radiation associated techniques like PET and SPECT. This chapter is divided into the following sections: (1) "Introduction," (2) "Principals of Magnetic Resonance Imaging," (3) "MRI Systems for Preclinical Imaging and Experimental Setup," and (4) "Cardiovascular Magnetic Resonance Imaging."

The intraportal injection model for liver metastasis: advantages of associated bioluminescence to assess tumor growth and influences on tumor uptake of radiolabeled anti-carcinoembryonic antigen antibody

BACKGROUND

Radioimmunotherapy is emerging as a new tool for adjuvant therapy of colorectal cancer. The liver remains the main site for metastases, carrying a high mortality rate. Many animal models are available but none associates easy, reliable implantation and in-vivo follow-up for experimental therapeutic studies. The aims of this study were to develop a reliable hepatic metastatic colonic cancer model in mice using the intraportal route for injection, with follow-up by bioluminescence (BLI) and to evaluate the impact of tumor location on tumor antigen direct targeting using radiolabeled anti-CEA (carcinoembryonic antigen) antibodies.

METHODS

Ls-174T Luc+ is a colon carcinoma cell line strongly expressing CEA, transfected with the luciferase gene for BLI. Isolated or aggregated cells (1×10(6)) were injected through the portal vein. The tumor burden was investigated using BLI to assess hepatic implantation and growth kinetics. The biodistribution of the 125I anti-CEA antibody fragment (F6) was studied in this model and was compared with subcutaneous implantation.

RESULTS

The tumor implantation rate was 100% using aggregated cells compared with 26.6% of isolated cells. Photons emitted by 1×10(6) cells were detected by BLI immediately after injection and allowed visual confirmation of hepatic distribution. The tumor growth was assessed over time to select homogeneous groups of animals. Radiolabeled anti-CEA antibody biodistributions showed a significantly higher uptake in hepatic than in subcutaneous tumors.

CONCLUSION

The association of hepatic tumor graft through the portal route and BLI provides a reliable animal model and permits sensitive in-vivo detection and follow-up of hepatic metastases. The hepatic model seems to more closely reproduce colon cancer metastases compared with subcutaneous metastasis. The hepatic model is of particular interest for studying radioimmunotherapy.

In vivo imaging of immune cell trafficking in cancer

Tumour establishment, progression and regression can be studied in vivo using an array of imaging techniques ranging from MRI to nuclear-based and optical techniques that highlight the intrinsic behaviour of different cell populations in the physiological context. Clinical in vivo imaging techniques and preclinical specific approaches have been used to study, both at the macroscopic and microscopic level, tumour cells, their proliferation, metastasisation, death and interaction with the environment and with the immune system. Fluorescent, radioactive or paramagnetic markers were used in direct protocols to label the specific cell population and reporter genes were used for genetic, indirect labelling protocols to track the fate of a given cell subpopulation in vivo. Different protocols have been proposed to in vivo study the interaction between immune cells and tumours by different imaging techniques (intravital and whole-body imaging). In particular in this review we report several examples dealing with dendritic cells, T lymphocytes and macrophages specifically labelled for different imaging procedures both for the study of their physiological function and in the context of anti-neoplastic immunotherapies in the attempt to exploit imaging-derived information to improve and optimise anti-neoplastic immune-based treatments.

Pharmacokinetic modeling of tumor bioluminescence implicates efflux, and not influx, as the bigger hurdle in cancer drug therapy

In vivo bioluminescence imaging is a powerful tool for assessing tumor burden and quantifying therapeutic response in xenograft models. However, this technique exhibits significant variability as a consequence of differences in substrate administration, as well as the tumor size, type, and location. Here, we present a novel pharmacokinetic (PK) approach that utilizes bioluminescence image data. The sample data are taken from mice implanted with a melanoma tumor cell line that was transfected to express the firefly (Photinus pyralis) luciferase gene. At 5, 7, and 10 days postimplant, intraperitoneal injections of D-luciferin were given to monitor the uptake into the tumor, and the tumor volume was measured using ultrasound. A multicompartment PK model was used to simultaneously fit all experiments for each mouse. We observed that the rates of luciferin transport in and out of the tumor exhibited a clear dependence on the tumor volume. Also, the rate of tumor influx increased faster than did the efflux, resulting in a shortening of the time to peak-luciferin concentration as the tumor grows. The time of the peak concentration correlated poorly with the tumor volume, but the peak bioluminescence signal and the area under the curve both exhibited a dependence on the tumor surface area. These results agree with Starling's hypothesis relating the higher interstitial fluid pressure in the tumor with flux across the boundary, and suggest that drug transport may depend more strongly on the surface area of the tumor than its volume. These observations provide a quantitative physical rationale for molecular targeting of therapeutics that enhance trapping and overcome the accelerated efflux kinetics.

Luciferase expression and bioluminescence does not affect tumor cell growth in vitro or in vivo

Live animal imaging is becoming an increasingly common technique for accurate and quantitative assessment of tumor burden over time. Bioluminescence imaging systems rely on a bioluminescent signal from tumor cells, typically generated from expression of the firefly luciferase gene. However, previous reports have suggested that either a high level of luciferase or the resultant light reaction produced upon addition of D-luciferin substrate can have a negative influence on tumor cell growth. To address this issue, we designed an expression vector that allows simultaneous fluorescence and luminescence imaging. Using fluorescence activated cell sorting (FACS), we generated clonal cell populations from a human breast cancer (MCF-7) and a mouse melanoma (B16-F10) cell line that stably expressed different levels of luciferase. We then compared the growth capabilities of these clones in vitro by MTT proliferation assay and in vivo by bioluminescence imaging of tumor growth in live mice. Surprisingly, we found that neither the amount of luciferase nor biophotonic activity was sufficient to inhibit tumor cell growth, in vitro or in vivo. These results suggest that luciferase toxicity is not a necessary consideration when designing bioluminescence experiments, and therefore our approach can be used to rapidly generate high levels of luciferase expression for sensitive imaging experiments.

Bioluminescence assays: multicolor luciferase assay, secreted luciferase assay and imaging luciferase assay

IMPORTANCE OF THE FIELD

By selecting the most appropriate bioluminescence assay, the researcher can study the underlying molecular mechanisms of a physiological system and the effects of a drug throughout the body.

AREAS COVERED IN THIS REVIEW

This review covers three luciferase assay systems: the multicolor luciferase assay, secreted luciferase assay and imaging luciferase assay. These assays are applied to drug screening in vitro, in cellulo and in vivo.

WHAT THE READER WILL GAIN

Different solutions for reporter assay in vitro, in cellulo and in vivo are presented. A suitable bioluminescence system depending on the assay purpose is also discussed.

TAKE HOME MESSAGE

Bioluminescence is a manifold system based on the different types of luciferin and its luciferase. Namely, luciferin catalyzed by corresponding luciferases resulted in the production of different color lights. We must understand the manifold mechanisms of bioluminescence reaction.

Cardiovascular MRI in small animals

Imaging studies of cardiovascular disease in small rodents have become a prerequisite in preclinical cardiovascular research. Transgenic and gene-knockout models of cardiovascular diseases enables the investigation of the influence of single genes or groups of genes on disease pathogenesis. In addition, experimental and genetically altered models provide valuable in vivo platforms to investigate the efficacy of novel drugs and contrast agents. Owing to the excellent soft tissue contrast, high spatial and temporal resolution, as well as the tomographic nature of MRI, anatomy and function can be assessed with unique accuracy and reproducibility. Furthermore, using novel targeted MRI contrast agents, molecular changes associated with cardiovascular disease can be investigated in the same imaging session. This review focuses on recent advances in hardware, imaging sequences and probe design.

Generation of a syngeneic mouse model to study the intraperitoneal dissemination of ovarian cancer with in vivo luciferase imaging

In order to facilitate the discovery and investigation of anti-cancer therapeutics under physiological conditions, we have engineered the ovarian cancer cell line, HM-1/luc, in mice. This cell stably expresses firefly luciferase and produces light that can be detected using an in vivo imaging system (IVIS). Parental HM-1 cells cause severe carcinomatous peritonitis to B6C3F1 mice, but not to C57BL6 mice. Established HM-1/luc cells showed pathologically similar findings to HM-1 cells. HM-1/luc cells were injected into the peritoneal cavity of B6C3F1 mice and IVIS 2000 was conducted weekly after inoculation to monitor intra-peritoneal tumor growth. The mice were divided into three groups: non-CDDP-treated (control) and CDDP-treated (0.2 and 0.4 mg). A disease-suppressive effect of the CDDP was reflected by the significantly prolonged survival of the CDDP-treated mice (control 23 +/- 1.9 days, CDDP 0.2 mg 29.6 +/- 2.9 days; p < 0.05); the total photon and area of flux were decreased. The optical imaging of intraperitoneal tumors via in vivo bioluminescence is effective for noninvasive monitoring and semi-quantitative analysis. Our syngeneic mouse model has the relevant clinical features of ovarian cancer, which makes it a useful model for developing new ovarian cancer therapies.

Measuring Brain Tumor Growth: Combined Bioluminescence Imaging–Magnetic Resonance Imaging Strategy

Small-animal tumor models are essential for developing translational therapeutic strategies in oncology research, with imaging having an increasingly important role. Magnetic resonance imaging (MRI) offers tumor localization, volumetric measurement, and the potential for advanced physiologic imaging but is less well suited to high-throughput studies and has limited capacity to assess early tumor growth. Bioluminescence imaging (BLI) identifies tumors early, monitors tumor growth, and efficiently measures response to therapeutic intervention. Generally, BLI signals have been found to correlate well with magnetic resonance measurements of tumor volume. However, in our studies of small-animal models of malignant brain tumors, we have observed specific instances in which BLI data do not correlate with corresponding MRIs. These observations led us to hypothesize that use of BLI and MRI together, rather than in isolation, would allow more effective and efficient measures of tumor growth in preclinical studies. Herein we describe combining BLI and MRI studies to characterize tumor growth in a mouse model of glioblastoma. The results led us to suggest a cost-effective, multimodality strategy for selecting cohorts of animals with similar tumor growth patterns that improves the accuracy of longitudinal in vivo measurements of tumor growth and treatment response in preclinical therapeutic studies.

A quantitative study of factors affecting in vivo bioluminescence imaging

In vivo bioluminescence imaging (BLI) has the advantages of high sensitivity and low background. By counting the number of photons emitted from a specimen, BLI can quantify biological events such as tumour growth, gene expression and drug response. The intensities and kinetics of the BL signal are affected by many factors and may confound the quantitative results acquired from consecutive imaging sessions or different specimens. We used three different mouse models of tumours to examine whether anaesthetics, positioning and tumour growth may affect the consistency of the BL signal. The results showed that BLI signal could be affected by different anaesthetics and repetitive positioning. Using the same anaesthetics produced consistent peak times, while other factors were held constant. However, as the tumours grew the peak times shifted and the time course of BL signals had different shapes, depending on the positioning of the mice. The data indicate that a carefully designed BLI experiment is required to generate optimal and consistent results.