Monitoring of xenograft tumor growth and response to chemotherapy by non-invasive in vivo multispectral fluorescence imaging

Rapid directed molecular evolution of fluorescent proteins in mammalian cells

In vivo imaging of model organisms is heavily reliant on fluorescent proteins with high intracellular brightness. Here we describe a practical method for rapid optimization of fluorescent proteins via directed molecular evolution in cultured mammalian cells. Using this method, we were able to perform screening of large gene libraries containing up to 2 × 107 independent random genes of fluorescent proteins expressed in HEK cells, completing one iteration of directed evolution in a course of 8 days. We employed this approach to develop a set of green and near-infrared fluorescent proteins with enhanced intracellular brightness. The developed near-infrared fluorescent proteins demonstrated high performance for fluorescent labeling of neurons in culture and in vivo in model organisms such as Caenorhabditis elegans, Drosophila, zebrafish, and mice. Spectral properties of the optimized near-infrared fluorescent proteins enabled crosstalk-free multicolor imaging in combination with common green and red fluorescent proteins, as well as dual-color near-infrared fluorescence imaging. The described method has a great potential to be adopted by protein engineers due to its simplicity and practicality. We also believe that the new enhanced fluorescent proteins will find wide application for in vivo multicolor imaging of small model organisms.

Imidazole Analogs of Vascular-Disrupting Combretastatin A-4 with Pleiotropic Efficacy against Resistant Colorectal Cancer Models

Specific targeting of the tumoral vasculature by vascular-disrupting agents (VDA), of which combretastatin A-4 (CA-4) is a main representative, has been considered a new therapeutic strategy against multidrug-resistant tumors. In addition, CA-4 and analogs are tubulin-targeting agents and can exert direct antitumor effects by different mechanisms. Herein, we analyzed a series of synthetic CA-4 analogs featuring N-methylimidazole-bridged Z-alkenes with different halo- or amino-substituted aryl rings in vitro and in vivo, focusing on models of colorectal cancer. Combined in vitro/in vivo structure-activity relationship studies using cell lines and xenograft tumors susceptible to VDA-induced vascular damage demonstrated a clear association of cytotoxic and vascular-disrupting activity with the ability to inhibit tubulin polymerization, which was determined by specific substitution constellations. The most active compounds were tested in an extended panel of colorectal cancer (CRC) cell lines and showed activity in CA-4-resistant and chemotherapy-resistant cell lines. The bromo derivative brimamin was then compared with the known fosbretabulin (CA-4P) by activity tests on DLD-1- (multidrug-resistant) and HT29- (CA-4-resistant) derived xenograft tumors. Treatment did not induce pronounced vascular-disrupting effects in these tumors. Histological analyses revealed distinct tumor substructures and vessel compositions of DLD-1/HT29 tumors, which clearly differed from the tumor models susceptible to VDA treatment. Even so, brimamin effectively retarded the growth of DLD-1 tumors, overcoming their resistance to standard treatment, and it inhibited the outgrowth of disseminated HT29 tumor cells in an experimental metastasis model. In conclusion, combretastatin analogous N-methylimidazoles proved capable of inducing vascular-disrupting effects, comparable to those of CA-4P. In addition, they showed antitumor activities in models of drug-resistant colorectal cancer, independent of vascular-disrupting effects.

Role of hydrogen sulfide donors in cancer development and progression

In recent years, a vast number of potential cancer therapeutic targets have emerged. However, developing efficient and effective drugs for the targets is of major concern. Hydrogen sulfide (H2S), one of the three known gasotransmitters, is involved in the regulation of various cellular activities such as autophagy, apoptosis, migration, and proliferation. Low production of H2S has been identified in numerous cancer types. Treating cancer cells with H2S donors is the common experimental technique used to improve H2S levels; however, the outcome depends on the concentration/dose, time, cell type, and sometimes the drug used. Both natural and synthesized donors are available for this purpose, although their effects vary independently ranging from strong cancer suppressors to promoters. Nonetheless, numerous signaling pathways have been reported to be altered following the treatments with H2S donors which suggest their potential in cancer treatment. This review will analyze the potential of H2S donors in cancer therapy by summarizing key cellular processes and mechanisms involved.

In vivo longitudinal and multimodal imaging of hypoxia-inducible factor 1α and angiogenesis in breast cancer

Background

Angiogenesis and hypoxia-inducible factor 1α (HIF-1α) play major roles in solid tumors. This study aimed to establish a longitudinal and multimodal imaging model for in vivo evaluation of HIF1α and angiogenesis in breast cancer.

Methods

By transfection of a 5 hypoxia-responsive element (HRE)/green fluorescent protein (GFP) plasmid, the cell line Ca761-hre-gfp was established, which emitted green fluorescence triggered by HIF-1α under hypoxia. The cells were subjected to CoCl₂-simulated hypoxia to confirm the imaging strategy. We grew Ca761-hre-gfp cells in the left rear flanks of twelve 615 mice. Experiments were conducted on days 4, 9, 15, and 19. For in vivo analysis, Ca761-hre-gfp subcutaneous allografted tumors were imaged in vivo using contrast-enhanced ultrasound (CEUS) and fluorescence imaging (FLI) during tumor development. The tumor size, CEUS peak intensity, and FLI photons were measured to evaluate tumor growth, angiogenesis, and HIF-1α activity, respectively. After each experiment, three mice were randomly sacrificed and tumor specimens were collected to examine HIF-1α activity and the microvessel density (MVD).

Results

In vitro, both green fluorescence and HIF-1α expression were detected in Ca761-hre-gfp cells treated with CoCl₂, indicating the suitability of the cells to detect HIF-1α activity. In vivo, HIF-1α activity first increased and then decreased, which was significantly correlated with angiogenic changes (r = 0.803, P = 0.005). These changes were confirmed by immunohistochemical staining of HIF-1α and MVD.

Conclusions

The findings validated the Ca761-hre-gfp murine allograft model for reliable evaluation of HIF-1α activity and angiogenesis longitudinally using both molecular and pre-clinical non-invasive imaging modalities. The cell line may be useful for studies of anti-HIF pathway therapies.

Strategy to enhance transgene expression in proximity of amyloid plaques in a mouse model of Alzheimer's disease

Gene therapy can be designed to efficiently counter pathological features characteristic of neurodegenerative disorders. Here, we took advantage of the glial fibrillary acidic protein (GFAP) promoter to preferentially enhance transgene expression near plaques composed of amyloid-beta peptides (Aβ), a hallmark of Alzheimer's disease (AD), in the TgCRND8 mouse model of amyloidosis. Methods: The delivery of intravenously injected recombinant adeno-associated virus mosaic serotype 1/2 (rAAV1/2) to the cortex and hippocampus of TgCRND8 mice was facilitated using transcranial MRI-guided focused ultrasound in combination with microbubbles (MRIgFUS), which transiently and locally increases the permeability of the blood-brain barrier (BBB). rAAV1/2 expression of the reporter green fluorescent protein (GFP) under a GFAP promoter was compared to GFP expression driven by the constitutive human beta actin (HBA) promoter. Results: MRIgFUS targeting the cortex and hippocampus facilitated the entry of rAAV1/2 and GFP expression under the GFAP promoter was localized to GFAP-positive astrocytes. Adjacent to Aβ plaques where GFAP is upregulated, the volume, surface area, and fluorescence intensity of the transgene GFP were greater in rAAV1/2-GFAP-GFP compared to rAAV1/2-HBA-GFP treated animals. In peripheral organs, GFP expression was particularly strong in the liver, irrespective of the promoter. Conclusion: The GFAP promoter enhanced transgene expression in proximity of Aβ plaques in the brain of TgCRND8 mice, and it also resulted in significant expression in the liver. Future gene therapies for neurological disorders could benefit from using a GFAP promoter to regulate transgene expression in response to disease-induced astrocytic reactivity.

MRTF-A controls myofibroblastic differentiation of human multipotent stromal cells and their tumour-supporting function in xenograft models

Tumour growth and metastatic colonization is strongly influenced by the tumour stroma, including cancer-associated fibroblasts (CAF). Multipotent mesenchymal stromal cells (MSC) are a possible source of CAF following myofibroblastic differentiation, and we have previously shown that MSC support tumour growth. Triggered by tumour cell-derived factors like transforming growth factor β1 (TGF-β1), myofibroblastic MSC differentiation is associated with the increased expression of markers including alpha smooth muscle actin (α-SMA). Here we show that myocardin-related transcription factor A (MRTF-A) plays an important role in myofibroblastic differentiation of primary human MSC in vitro and their tumour-supporting function in vivo. Recombinant TGF-β1 or tumour cell conditioned medium (TCM) elevated α-SMA, calponin 1 and collagen 1 A1 (COL1A1) amount on mRNA and protein level in MSC. This correlated with increased MRTF-A activity during MSC differentiation. MRTF-A knockdown by siRNA or shRNA impaired TGF-β1 and TCM induction of α-SMA and calponin 1, but not of COL1A1. Mixed xenograft experiments using HCT8 colorectal carcinoma cells and primary MSC of different donors revealed a significant reduction in tumour weight and volume upon MRTF-A knockdown in MSC. Our study suggests that MRTF-A is involved in the functional differentiation of MSC towards a tumour-promoting CAF phenotype in vivo.

Preparation and Testing of Cells Expressing Fluorescent Proteins for Intravital Imaging of Tumor Microenvironment

Intravital microscopy is widely used for in vivo studies of the mechanisms of carcinogenesis and response to antitumor therapy. For visualization of tumor cells in vivo, cell lines expressing fluorescent proteins are needed. Expression of exogenous proteins can affect cell growth rate and their tumorigenic potential. Therefore, comprehensive analysis of the morphofunctional properties of transduced cells is required for creating appropriate models of tumor microenvironment. In the present study, six lines of mouse tumor cells expressing green and red fluorescent proteins were derived. Analysis of cells morphology, growth kinetics, and response to chemotherapy in vitro revealed no significant differences between wild-type and transduced cell lines. Introduction of fluorescent proteins into the genome of 4T1 (murine breast cancer) and B16-F10 (murine melanoma) cells did not affect tumor growth rate after subcutaneous implantation to mice, while both CT26-GFP and CT26-RFP cells (murine colon cancer) were rejected starting from day 8 after implantation. Elucidation of the mechanisms underlying CT26-GFP/RFP rejection is required to modify transduction technique for creating the models of tumor microenvironment accessible for in vivo visualization. Transduced 4T1 and B16-F10 cell lines can be used for intravital microscopic imaging of tumor cells, neoplastic vasculature, and leukocyte subpopulations.

A step towards valid detection and quantification of lung cancer volume in experimental mice with contrast agent-based X-ray microtomography

Tumor volume is a parameter used to evaluate the performance of new therapies in lung cancer research. Conventional methods that are used to estimate tumor size in mouse models fail to provide fast and reliable volumetric data for tumors grown non-subcutaneously. Here, we evaluated the use of iodine-staining combined with micro-computed tomography (micro-CT) to estimate the tumor volume of ex vivo tumor-burdened lungs. We obtained fast high spatial resolution three-dimensional information of the lungs, and we demonstrated that iodine-staining highlights tumors and unhealthy tissue. We processed iodine-stained lungs for histopathological analysis with routine hematoxylin and eosin (H&E) staining. We compared the traditional tumor burden estimation performed manually with H&E histological slices with a semi-automated method using micro-CT datasets. In mouse models that develop lung tumors with well precise boundaries, the method that we describe here enables to perform a quick estimation of tumorous tissue volume in micro-CT images. Our method overestimates the tumor burden in tumors surrounded by abnormal tissue, while traditional histopathological analysis underestimates tumor volume. We propose to embed micro-CT imaging to the traditional workflow of tumorous lung analyses in preclinical cancer research as a strategy to obtain a more accurate estimation of the total lung tumor burden.

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.

Intended and Unintended Targeting of Polymeric Nanocarriers: The Case of Modified Poly(glycerol adipate) Nanoparticles

Biodegradable nanoparticles based on stearic acid-modified poly(glycerol adipate) (PGAS) are promising carriers for drug delivery. In order to investigate the impact of the particle interface characteristics on the biological fate, PGAS nanoparticles are covalently and noncovalently coated with N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers. HPMA copolymer-modified PGAS nanoparticles have similar particle sizes, but less negative zeta-potentials. Nanoparticles are double labeled with the fluorescent dyes DiR (noncovalently) and DYOMICS-676 (covalently bound to HPMA copolymer), and their biodistribution is investigated noninvasively by multispectral optical imaging. Both covalent and noncovalent coatings cause changes in the pharmacokinetics and biodistribution in healthy and tumor-bearing mice. In addition to the intended tumor accumulation, high signals of both fluorescent dyes are also observed in other organs, including liver, ovaries, adrenal glands, and bone. The unintended accumulation of nanocarriers needs further detailed and systematic investigations, especially with respect to the observed ovarian and adrenal gland accumulation.

Evaluation of Early Therapeutic Effects after Near-Infrared Photoimmunotherapy (NIR-PIT) Using Luciferase-Luciferin Photon-Counting and Fluorescence Imaging

Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed cancer treatment that induces highly selective immunogenic cell death. It is based on an antibody-photoabsorber conjugate (APC) that is activated by NIR light. The purpose of this study was to investigate the effects of NIR-PIT as measured by luciferase-luciferin photon-counting and fluorescence imaging. Six days after subcutaneous injection of A431-luc-GFP cells tumors formed in a xenograft mouse model. The EGFR-targeting antibody, panitumumab, was conjugated to the photoabsorber, IRDye-700DX (pan-IR700), and was intravenously administered to tumor-bearing mice. Serial luciferase-luciferin photon-counting images and both green fluorescent protein (GFP) and IR700 fluorescence images were obtained from the same mice before and after NIR-PIT treatment (0, 10, 20, 30 min (early phase), and 24, 48 h (late phase) after NIR light exposure). Optical signal intensities were compared for each modality. IR700 fluorescence and luciferase-luciferin photon-counting images showed decreased intensities in both the early and late phases after NIR-PIT (p < 0.01). On the other hand, GFP fluorescence images showed decreased intensities only in the late phase (p < 0.01). In the early phase, GFP fluorescence images showed smaller intensity reductions compared to IR700 fluorescence and luciferase-luciferin photon-counting (p < 0.01), while in the late phase, IR700 fluorescence showed smaller intensity reductions than luciferase-luciferin photon-counting and GFP fluorescence (p < 0.05), due to redistribution of pan-IR700 within the tumor bed. In conclusion, luciferase-luciferin photon-counting imaging is suitable to evaluate early phase NIR-PIT effects, while both luciferase-luciferin photon-counting and GFP reflected later phase effects.

Hydrophobically modified polyethylenimine-based ternary complexes for targeting brain tumor: stability, in vitro and in vivo studies

Hydrophobic modification of low molecular weight polyethylenimine (PEI 2 kDa) by cholic acid (ChA) was done to obtain PEI2-ChA. The nanoplexes of PEI2-ChA with gWIZ-GFP demonstrated increase transfection efficiency (∼27%) in NT8e cell lines. The cell-cycle analysis of NT8e cells (p53 mutant) treated with transferrin containing nanoplexes showed increased apoptosis of cells. In vitro protein expression revealed expression of exogenous p53 protein. In vivo imaging of mice showed localized signal for GFP protein in brain region. The tumors of mice treated with transferrin containing nanoplexes of PEI2-ChA were ∼5 times smaller in size than the tumor of untreated animals.

Deep Digging: Far Red Imaging for the Monitoring of Transplanted Hepatocytes in Rats

Technologies for in vivo imaging of the distribution and integration of cell transplants gain significance for the use of novel cell therapy approaches in regenerative medicine. Applied to adequate animal models, they provide information on the spatio-temporal engraftment and functional performance of the cells transplanted. This chapter includes a detailed description of the in vivo tracking of transplanted hepatocytes in rat liver including the conjugation of antibodies to fluorochromes for far red imaging using a multispectral optical imager.

Upregulation of metastasis-associated gene 2 promotes cell proliferation and invasion in nasopharyngeal carcinoma

Aims

Metastasis-associated gene 2 (MTA2) is reported to play an important role in tumor progression, but little is known about the role of MTA2 in nasopharyngeal carcinoma (NPC). The aim of the study was to explore the expression and function of MTA2 in NPC.

Methods

Expression of MTA2 in NPC tissues and cell lines was detected by immunohistochemistry and Western blotting. Relationship between MTA2 expression and clinicopathological features was analyzed. Stable MTA2-overexpressing and MTA2-siliencing NPC cells were established by transfection with plasmids encoding MTA2 cDNA and lentivirus-mediated short hairpin RNA, respectively. Cell viability was determined by Cell Counting Kit-8 and colony formation assay. Cell migration ability was evaluated by wound healing and transwell invasion assay. The impact of MTA2 knockdown on growth and metastasis of CNE2 cells in vivo was determined by nude mouse xenograft models. Expression of several Akt pathway proteins was detected by Western blotting.

Results

MTA2 was upregulated in NPC tissues and three NPC cell lines detected (CNE1, CNE2, and HNE1). MTA2 expression was related to clinical stage and lymph node metastasis of patients with NPC. MTA2 upregulation promoted proliferation and invasion of CNE1 cells, while MTA2 depletion had opposite effects on CNE2 cells. Moreover, MTA2 depletion suppressed growth and metastasis of CNE2 cells in vivo. MTA2 overexpression activated Akt and upregulated the expression of matrix metalloproteinase 7 and cyclin D1.

Conclusion

We conclude that MTA2 acts as an oncogene in tumorigenesis of NPC. MTA2 may be a potential target for gene therapy in NPC.

Fluorescence optical imaging in anticancer drug delivery

In the past several decades, nanosized drug delivery systems with various targeting functions and controlled drug release capabilities inside targeted tissues or cells have been intensively studied. Understanding their pharmacokinetic properties is crucial for the successful transition of this research into clinical practice. Among others, fluorescence imaging has become one of the most commonly used imaging tools in pre-clinical research. The development of increasing numbers of suitable fluorescent dyes excitable in the visible to near-infrared wavelengths of the spectrum has significantly expanded the applicability of fluorescence imaging. This paper focuses on the potential applications and limitations of non-invasive imaging techniques in the field of drug delivery, especially in anticancer therapy. Fluorescent imaging at both the cellular and systemic levels is discussed in detail. Additionally, we explore the possibility for simultaneous treatment and imaging using theranostics and combinations of different imaging techniques, e.g., fluorescence imaging with computed tomography.

Multipotent mesenchymal stromal cells promote tumor growth in distinct colorectal cancer cells by a β1-integrin-dependent mechanism

Tumor-stroma interactions play an essential role in the biology of colorectal carcinoma (CRC). Multipotent mesenchymal stromal cells (MSC) may represent a pivotal part of the stroma in CRC, but little is known about the specific interaction of MSC with CRC cells derived from tumors with different mutational background. In previous studies we observed that MSC promote the xenograft growth of the CRC cell-line DLD1. In the present study, we aimed to analyze the mechanisms of MSC-promoted tumor growth using various in vitro and in vivo experimental models and CRC cells of different mutational status. MSC specifically interacted with distinct CRC cells and supported tumor seeding in xenografts. The MSC-CRC interaction facilitated three-dimensional spheroid formation in CRC cells with dysfunctional E-cadherin system. Stable knock-downs revealed that the MSC-facilitated spheroid formation depended on β1-integrin in CRC cells. Specifically in α-catenin-deficient CRC cells this β1-integrin-dependent interaction resulted in a MSC-mediated promotion of early tumor growth in vivo. Collagen I and other extracellular matrix compounds were pivotal for the functional MSC-CRC interaction. In conclusion, our data demonstrate a differential interaction of MSC with CRC cells of different mutational background. Our study is the first to show that MSC specifically compared to normal fibroblasts impact early xenograft growth of distinct α-catenin deficient CRC cells possibly through secretion of extracellular matrix. This mechanism could serve as a future target for therapy and metastasis prevention.

A better experimental method to detect the sensitivity of cancer cells to anticancer drugs after adenovirus-mediated introduction of two kinds of p53 in vivo

p53 plays an important role in drug responses by regulating cell cycle progression and inducing programmed cell death. The C-terminal of p53 self-regulates the protein negatively; however, whether it affects the sensitivity of cancer cells to anticancer drugs is unclear. In this study, two experimental methods were used to compare the sensitivity to anticancer drugs of human lung 801D cancer cells transfected with adenovirus bearing either full-length p53 or the deleted-C-terminal p53 in vivo. Adenovirus-mediated deliveries of full-length or deleted-C-terminal p53 were performed after development of tumors (the first method) or by infection into cells before xenotransplantation (the second method). The results showed that infection with the deleted-C-terminal p53 increased 801D cell sensitivity to anticancer drugs in the second, but not in the first method, as indicated by greater tumor-inhibition rates. In addition, compared with the first method, the second method resulted in viruses with more uniformly infected cells and the infection rates between groups were similar. This yielded smaller within-group variations and greater uniformity among transplanted tumors. The second method could circumvent the difficulties associated with intratumoral injection.

Photoimmunotherapy of gastric cancer peritoneal carcinomatosis in a mouse model

Photoimmunotherapy (PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by photosensitizers after exposure to near infrared (NIR) light. We performed PIT in a model of disseminated gastric cancer peritoneal carcinomatosis and monitored efficacy with in vivo GFP fluorescence imaging. In vitro and in vivo experiments were conducted with a HER2-expressing, GFP-expressing, gastric cancer cell line (N87-GFP). A conjugate comprised of a photosensitizer, IR-700, conjugated to trastuzumab (tra-IR700), followed by NIR light was used for PIT. In vitro PIT was evaluated by measuring cytotoxicity with dead staining and a decrease in GFP fluorescence. In vivo PIT was evaluated in a disseminated peritoneal carcinomatosis model and a flank xenograft using tumor volume measurements and GFP fluorescence intensity. In vivo anti-tumor effects of PIT were confirmed by significant reductions in tumor volume (at day 15, p<0.0001 vs. control) and GFP fluorescence intensity (flank model: at day 3, PIT treated vs. control p<0.01 and peritoneal disseminated model: at day 3 PIT treated vs. control, p<0.05). Cytotoxic effects in vitro were shown to be dependent on the light dose and caused necrotic cell rupture leading to GFP release and a decrease in fluorescence intensity in vitro. Thus, loss of GFP fluorescence served as a useful biomarker of cell necrosis after PIT.

MTA1 promotes nasopharyngeal carcinoma growth in vitro and in vivo

BACKGROUND

The prognostic value of metastasis-associated gene 1 (MTA1) in nasopharyngeal carcinoma (NPC) has been suggested. However, there is still no direct evidence that MTA1 promotes NPC growth in vivo. In this study, we aimed to investigate the function of MTA1 in the regulation of NPC cell proliferation and tumorigenesis in vitro and in vivo.

METHODS

Stable MTA1 knockdown or overexpression NPC cell lines were employed. The effects of MTA1 depletion or overexpression on cell proliferation, colony formation, cell cycle progression were examined by MTT, colony formation and flow cytometry assay. The effects of MTA1 depletion on tumor growth in vivo were examined in mouse xenograft model.

RESULTS

MTA1 knockdown or overexpression drastically changed the proliferation, colony formation and cell cycle of NPC cells in vitro. MTA1 depletion significantly suppressed NPC tumorigenesis in vivo.

CONCLUSION

MTA1 promotes NPC cell proliferation via enhancing G1 to S phase transition, leading to increased tumor growth. Targeting MTA1 is a promising approach to reduce tumor burden of NPC.