Targeting tumor stroma using engineered mesenchymal stem cells reduces the growth of pancreatic carcinoma. Ann Surg. 2009;250:747-753. [PMID: 19826249 DOI: 10.1097/sla.0b013e3181bd62d0]

Multipotent mesenchymal stromal cells: clinical applications and cancer modeling

The recognition of the therapeutic potential of Multipotent Mesenchymal Stromal Cells (MSCs) is one of the most exciting recent advances in cell therapy. In just ten years, since the description of the multilineage potential of MSCs by Pittenger et al in 1999 until now, MSCs are being used in more than 150 clinical trials as therapeutic agents. The potential of these cells for cell-based therapies relies on several key properties: (1) their capacity to differentiate into several cell lineages; (2) their lack of immunogenicity and their immunomodulatory properties; (3) their ex vivo expansion potential; (4) their ability to secrete soluble factors which regulate crucial biological functions such as proliferation and differentiation over a broad spectrum of target cells; and (5) their ability to home to damaged tissues and tumor sites. Based on these properties MSCs are being exploited worldwide for a wide range of potential clinical applications including cell replacement strategies, treatment of graft-versus-host disease, autoimmune diseases and rejection after solid organ transplantation as well as their use as vehicles to deliver anti-cancer therapies. Importantly, the low inherent immunogenicity of MSCs means that they could be used not only for autologous but also for allogeneic cell therapies. In addition, increasing evidence has revealed a complex relationship between MSCs and cancer. Thus, solid evidence has placed MSCs transformed with specific mutations as the most likely cell of origin for certain sarcomas, and MSCs have been reported to both, inhibit or promote tumor growth depending on yet undefined conditions. Here we will thoroughly discuss the different potential clinical applications of MSC as well as the role of MSCs on sarcomagenesis and the control of tumor growth.

Great promise of tissue-resident adult stem/progenitor cells in transplantation and cancer therapies

Recent progress in tissue-resident adult stem/progenitor cell research has inspired great interest because these immature cells from your own body can act as potential, easily accessible cell sources for cell transplantation in regenerative medicine and cancer therapies. The use of adult stem/progenitor cells endowed with a high self-renewal ability and multilineage differentiation potential, which are able to regenerate all the mature cells in the tissues from their origin, offers great promise in replacing non-functioning or lost cells and regenerating diseased and damaged tissues. The presence of a small subpopulation of adult stem/progenitor cells in most tissues and organs provides the possibility of stimulating their in vivo differentiation, or of using their ex vivo expanded progenies for cell-replacement and gene therapies with multiple applications in humans without a high-risk of graft rejection and major side effects. Among the diseases that could be treated by adult stem cell-based therapies are hematopoietic and immune disorders, multiple degenerative disorders such as Parkinson's and Alzheimer's diseases, Types 1 and 2 diabetes mellitus as well as skin, eye, liver, lung, tooth and cardiovascular disorders. In addition, a combination of the current cancer treatments with an adjuvant treatment consisting of an autologous or allogeneic adult stem/progenitor cell transplantation also represents a promising strategy for treating and even curing diverse aggressive, metastatic, recurrent and lethal cancers. In this chapter, we reviewed the most recent advancements on the characterization of phenotypic and functional properties of adult stem/progenitor cell types found in bone marrow, heart, brain and other tissues and discussed their therapeutic implications in the stem cell-based transplantation therapy.

Mesenchymal stem cell-mediated cancer therapy: A dual-targeted strategy of personalized medicine

Cancer remains one of the leading causes of mortality and morbidity throughout the world. To a significant extent, current conventional cancer therapies are symptomatic and passive in nature. The major obstacle to the development of effective cancer therapy is believed to be the absence of sufficient specificity. Since the discovery of the tumor-oriented homing capacity of mesenchymal stem cells (MSCs), the application of specific anticancer gene-engineered MSCs has held great potential for cancer therapies. The dual-targeted strategy is based on MSCs' capacity of tumor-directed migration and incorporation and in situ expression of tumor-specific anticancer genes. With the aim of translating bench work into meaningful clinical applications, we describe the tumor tropism of MSCs and their use as therapeutic vehicles, the dual-targeted anticancer potential of engineered MSCs and a putative personalized strategy with anticancer gene-engineered MSCs.

Fibroblastic reticular cells from lymph nodes attenuate T cell expansion by producing nitric oxide

Adaptive immune responses are initiated when T cells encounter antigen on dendritic cells (DC) in T zones of secondary lymphoid organs. T zones contain a 3-dimensional scaffold of fibroblastic reticular cells (FRC) but currently it is unclear how FRC influence T cell activation. Here we report that FRC lines and ex vivo FRC inhibit T cell proliferation but not differentiation. FRC share this feature with fibroblasts from non-lymphoid tissues as well as mesenchymal stromal cells. We identified FRC as strong source of nitric oxide (NO) thereby directly dampening T cell expansion as well as reducing the T cell priming capacity of DC. The expression of inducible nitric oxide synthase (iNOS) was up-regulated in a subset of FRC by both DC-signals as well as interferon-γ produced by primed CD8+ T cells. Importantly, iNOS expression was induced during viral infection in vivo in both LN FRC and DC. As a consequence, the primary T cell response was found to be exaggerated in Inos(-/-) mice. Our findings highlight that in addition to their established positive roles in T cell responses FRC and DC cooperate in a negative feedback loop to attenuate T cell expansion during acute inflammation.

Cancer suicide gene therapy with TK.007: superior killing efficiency and bystander effect

Suicide gene therapy is a promising concept in oncology. We have recently introduced a novel suicide gene, TK.007, which was shown to excel established herpes simplex virus thymidine kinase (HSVtk) variants when used for donor-lymphocyte modification in adoptive immunotherapy models. Here, the potential of TK.007 in killing cancer cells was studied. Initially, we transduced tumour cell lines derived from different neoplasias (glioblastoma, melanoma, lung cancer, colon cancer) with lentiviral LeGO vectors encoding TK.007 or the splice-corrected (sc)HSVtk together with an eGFP/Neo-marker. Based on direct in vitro comparison, we found that TK.007 facilitates more efficient tumour cell killing at significantly lower ganciclovir doses in all tumour cell lines tested. Also, using different readout systems, we found a significantly stronger bystander effect of TK.007 as compared to scHSVtk. Importantly, in vitro data were confirmed in vivo using a subcutaneous G62 glioblastoma model in NOD/SCID mice. In mice transplanted with scHSVtk-positive tumours, treatment with low (10 mg/kg) or standard (50 mg/kg) ganciclovir doses resulted only in short-term growth inhibition or transient tumour remission, respectively. In striking contrast, in the TK.007 group, all animals achieved continuous complete remission after both standard and low-dose ganciclovir. Finally, a substantial bystander effect for TK.007 was also confirmed with the G62 model in vivo, where significantly prolonged survival for mice bearing tumours containing only 10% or 50% TK.007-expressing cells was observed. In summary, our data indicate strongly improved anti-tumour activity of TK.007 as compared to conventional HSVtk. We therefore suppose that TK.007 is an excellent candidate for cancer suicide gene therapy.

Potential implications of mesenchymal stem cells in cancer therapy

Mesenchymal stem cells (MSCs) are the first type of stem cells to be utilized in clinical regenerative medicine, mainly owing to their capacity for multipotent differentiation and the feasibility of autologous transplantation. More recently, the specific tumor-oriented migration and incorporation of MSCs have been demonstrated in various pre-clinical models, highlighting the potential for MSCs to be used as an ideal carrier for anticancer gene delivery. Engineered with specific anticancer genes, MSCs possess the ability of dual-targeting tumor cells. This contrasts with non-engineered native MSCs which have intrinsic pro- and anti-tumorigenic properties. Engineered MSCs are capable of producing specific anticancer agents locally and constantly. Astute investigation on engineered MSCs may lead to a new avenue toward an efficient therapy for patients with cancer.

Image-guided, tumor stroma-targeted 131I therapy of hepatocellular cancer after systemic mesenchymal stem cell-mediated NIS gene delivery

Due to its dual role as reporter and therapy gene, the sodium iodide symporter (NIS) allows noninvasive imaging of functional NIS expression by (123)I-scintigraphy or (124)I-PET imaging before the application of a therapeutic dose of (131)I. NIS expression provides a novel mechanism for the evaluation of mesenchymal stem cells (MSCs) as gene delivery vehicles for tumor therapy. In the current study, we stably transfected bone marrow-derived CD34(-) MSCs with NIS cDNA (NIS-MSC), which revealed high levels of functional NIS protein expression. In mixed populations of NIS-MSCs and hepatocellular cancer (HCC) cells, clonogenic assays showed a 55% reduction of HCC cell survival after (131)I application. We then investigated body distribution of NIS-MSCs by (123)I-scintigraphy and (124)I-PET imaging following intravenous (i.v.) injection of NIS-MSCs in a HCC xenograft mouse model demonstrating active MSC recruitment into the tumor stroma which was confirmed by immunohistochemistry and ex vivo γ-counter analysis. Three cycles of systemic MSC-mediated NIS gene delivery followed by (131)I application resulted in a significant delay in tumor growth. Our results demonstrate tumor-specific accumulation and therapeutic efficacy of radioiodine after MSC-mediated NIS gene delivery in HCC tumors, opening the prospect of NIS-mediated radionuclide therapy of metastatic cancer using MSCs as gene delivery vehicles.

Linking transgene expression of engineered mesenchymal stem cells and angiopoietin-1-induced differentiation to target cancer angiogenesis

OBJECTIVE

To specifically target tumor angiogenesis by linking transgene expression of engineered mesenchymal stem cells to angiopoietin-1-induced differentiation.

BACKGROUND

Mesenchymal stem cells (MSCs) have been used to deliver therapeutic genes into solid tumors. These strategies rely on their homing mechanisms only to deliver the therapeutic agent.

METHODS

We engineered murine MSC to express reporter genes or therapeutic genes under the selective control of the Tie2 promoter/enhancer. This approach uses the differentiative potential of MSCs induced by the tumor microenvironment to drive therapeutic gene expression only in the context of angiogenesis.

RESULTS

When injected into the peripheral circulation of mice with either, orthotopic pancreatic or spontaneous breast cancer, the engineered MSCs were actively recruited to growing tumor vasculature and induced the selective expression of either reporter red florescent protein or suicide genes [herpes simplex virus-thymidine kinase (TK) gene] when the adoptively transferred MSC developed endothelial-like characteristics. The TK gene product in combination with the prodrug ganciclovir (GCV) produces a potent toxin, which affects replicative cells. The homing of engineered MSC with selective induction of TK in concert with GCV resulted in a toxic tumor-specific environment. The efficacy of this approach was demonstrated by significant reduction in primary tumor growth and prolongation of life in both tumor models.

CONCLUSION

This "Trojan Horse" combined stem cell/gene therapy represents a novel treatment strategy for tailored therapy of solid tumors.

Concise review: stem cells as an emerging platform for antibody therapy of cancer

Monoclonal antibodies are important tools for cancer therapy, however, three factors limit their effectiveness: toxicity, poor tumor penetration, and inability to cross the blood-brain barrier. This review discusses the emerging field of stem cell-mediated antibody delivery and how this approach may improve antibody therapy of cancer by overcoming these obstacles. STEM CELLS 2010;28:2084–2087

Mesenchymal stem cells at the intersection of cell and gene therapy

IMPORTANCE OF THE FIELD

Mesenchymal stem cells have the ability to differentiate into osteoblasts, chondrocytes and adipocytes. Along with differentiation, MSCs can modulate inflammation, home to damaged tissues and secrete bioactive molecules. These properties can be enhanced through genetic-modification that would combine the best of both cell and gene therapy fields to treat monogenic and multigenic diseases.

AREAS COVERED IN THIS REVIEW

Findings demonstrating the immunomodulation, homing and paracrine activities of MSCs followed by a summary of the current research utilizing MSCs as a vector for gene therapy, focusing on skeletal disorders, but also cardiovascular disease, ischemic damage and cancer.

WHAT THE READER WILL GAIN

MSCs are a possible therapy for many diseases, especially those related to the musculoskeletal system, as a standalone treatment, or in combination with factors that enhance the abilities of these cells to migrate, survive or promote healing through anti-inflammatory and immunomodulatory effects, differentiation, angiogenesis or delivery of cytolytic or anabolic agents.

TAKE HOME MESSAGE

Genetically-modified MSCs are a promising area of research that would be improved by focusing on the biology of MSCs that could lead to identification of the natural and engrafting MSC-niche and a consensus on how to isolate and expand MSCs for therapeutic purposes.

Pancreatic cancer gene therapy: from molecular targets to delivery systems

The continuous identification of molecular changes deregulating critical pathways in pancreatic tumor cells provides us with a large number of novel candidates to engineer gene-targeted approaches for pancreatic cancer treatment. Targets—both protein coding and non-coding—are being exploited in gene therapy to influence the deregulated pathways to facilitate cytotoxicity, enhance the immune response or sensitize to current treatments. Delivery vehicles based on viral or non-viral systems as well as cellular vectors with tumor homing characteristics are a critical part of the design of gene therapy strategies. The different behavior of tumoral versus non-tumoral cells inspires vector engineering with the generation of tumor selective products that can prevent potential toxic-associated effects. In the current review, a detailed analysis of the different targets, the delivery vectors, the preclinical approaches and a descriptive update on the conducted clinical trials are presented. Moreover, future possibilities in pancreatic cancer treatment by gene therapy strategies are discussed.

Mesenchymal stem cells and cancer: tumor-specific delivery vehicles or therapeutic targets?

Mesenchymal stem cells (MSCs) are a subset of nonhematopoietic multipotent cells found primarily within the bone marrow stroma. The ability of MSCs to specifically home to sites of tumors and their metastases, while escaping host immune surveillance, holds tremendous promise for tumor-targeted delivery of therapeutic agents. Concerns that MSCs may have an inherent capacity for transformation have led to a number of studies investigating their stability in vitro, as significant ex vivo expansion will be necessary to yield the number of cells required for therapeutic applications. MSCs have also been seen to influence the morphology and proliferation of cells within their vicinity through a combination of cell-to-cell interactions and the secretion of chemoattractant cytokines. Understanding interactions between MSCs and tumor cells is required to support realization of their clinical potential. This review discusses MSCs and cancer in terms of (1) potential for transformation and de novo tumor formation, (2) interactions with epithelial cancer cells in tumor establishment, and (3) potential role after engraftment at the site of an established tumor. Elucidation of any potential negative effect of MSCs in the tumor setting will support development of protocols to minimize these effects while taking full advantage of the remarkable tumor-homing capacity of these cells.

Advances in mesenchymal stem cell-mediated gene therapy for cancer

Mesenchymal stem cells have a natural tropism for tumours and their metastases, and are also considered immunoprivileged. This remarkable combination of properties has formed the basis for many studies investigating their potential as tumour-specific delivery vehicles for suicide genes, oncolytic viruses and secreted therapeutic proteins. The aim of the present review is to discuss the range of approaches that have been used to exploit the tumour-homing capacity of mesenchymal stem cells for gene delivery, and to highlight advances required to realize the full potential of this promising approach.

Novel therapies against aggressive and recurrent epithelial cancers by molecular targeting tumor- and metastasis-initiating cells and their progenies

A growing body of experimental evidence has revealed that the highly tumorigenic cancer stem/progenitor cells endowed with stem cell-like properties might be responsible for initiation and progression of numerous aggressive epithelial cancers into locally invasive, metastatic and incurable disease states. The malignant transformation of tissue-resident adult stem/progenitor cells or their progenies into tumorigenic and migrating cancer stem/progenitor cells and their resistance to current cancer therapies have been associated with their high expression levels of specific oncogenic products and drug resistance-associated molecules. In this regard, we describe the tumorigenic cascades that are frequently activated in cancer stem/progenitor cells versus their differentiated progenies during the early and late stages of the epithelial cancer progression. The emphasis is on the growth factor signaling pathways involved in the malignant behavior of prostate and pancreatic cancer stem/progenitor cells and their progenies. Of clinical interest, the potential molecular therapeutic targets to eradicate the tumor- and metastasis-initiating cells and their progenies and develop new effective combination therapies against locally advanced and metastatic epithelial cancers are also described.

Mesenchymal stem cells: a promising targeted-delivery vehicle in cancer gene therapy

The targeting drug delivery systems (TDDS) have attracted extensive attention of researchers in recent years. More and more drug/gene targeted delivery carriers, such as liposome, magnetic nanoparticles, ligand-conjugated nanoparticles, microbubbles, etc., have been developed and under investigation for their application. However, the currently investigated drug/gene carriers have several disadvantages, which limit their future use in clinical practice. Therefore, design and development of novel drug/gene delivery vehicles has been a hot area of research. Recent studies have shown the ability of mesenchymal stem cells (MSCs) to migrate towards and engraft into the tumor sites, which make them a great hope for efficient targeted-delivery vehicles in cancer gene therapy. In this review article, we examine the promising of using mesenchymal stem cells as a targeted-delivery vehicle for cancer gene therapy, and summarize various challenges and concerns regarding these therapies.

Molecular imaging and targeted therapies

Targeted therapeutic and imaging agents are becoming more prevalent, and are used to treat increasingly smaller segments of the patient population. This has lead to dramatic increases in the costs for clinical trials. Biomarkers have great potential to reduce the numbers of patients needed to test novel targeted agents by predicting or identifying non-response early-on and thus enriching the clinical trial population with patients more likely to respond. Biomarkers are characteristics that are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers can be used to predict response to specific therapies, predict response regardless of therapy, or to monitor response once a therapy has begun. In terms of drug development, predictive biomarkers have the greatest impact, as they can be used as inclusion criteria for patient segmentation. Prognostic markers are used routinely in clinical practice but do not provide direction for the use of targeted therapies. Imaging biomarkers have distinct advantages over those that require a biopsy sample in that they are "non-invasive" and can be monitored longitudinally at multiple time points in the same patient. This review will examine the role of functional and molecular imaging in predicting response to specific therapies; will explore the advantages and disadvantages of targeting intracellular or extracellular markers; and will discuss the attributes of useful targets and methods for target identification and validation.

Toward brain tumor gene therapy using multipotent mesenchymal stromal cell vectors

Gene therapy of solid cancers has been severely restricted by the limited distribution of vectors within tumors. However, cellular vectors have emerged as an effective migratory system for gene delivery to invasive cancers. Implanted and injected multipotent mesenchymal stromal cells (MSCs) have shown tropism for several types of primary tumors and metastases. This capacity of MSCs forms the basis for their use as a gene vector system in neoplasms. Here, we review the tumor-directed migratory potential of MSCs, mechanisms of the migration, and the choice of therapeutic transgenes, with a focus on malignant gliomas as a model system for invasive and highly vascularized tumors. We examine recent findings demonstrating that MSCs share many characteristics with pericytes and that implanted MSCs localize primarily to perivascular niches within tumors, which might have therapeutic implications. The use of MSC vectors in cancer gene therapy raises concerns, however, including a possible MSC contribution to tumor stroma and vasculature, MSC-mediated antitumor immune suppression, and the potential malignant transformation of cultured MSCs. Nonetheless, we highlight the novel prospects of MSC-based tumor therapy, which appears to be a promising approach.