HSV-tk expressing mesenchymal stem cells exert bystander effect on human glioblastoma cells

Selective targeting of genetically engineered mesenchymal stem cells to tumor stroma microenvironments using tissue-specific suicide gene expression suppresses growth of hepatocellular carcinoma

BACKGROUND

The use of engineered mesenchymal stem cells (MSCs) as therapeutic vehicles for the treatment of experimental pancreatic and breast cancer has been previously demonstrated. The potential application of MSCs for the treatment of hepatocellular carcinoma (HCC) has been controversial. The general approach uses engineered MSCs to target different aspects of tumor biology, including angiogenesis or the fibroblast-like stromal compartment, through the use of tissue-specific expression of therapeutic transgenes. The aim of the present study was (1) to evaluate the effect of exogenously added MSCs on the growth of HCC and (2) the establishment of an MSC-based suicide gene therapy for experimental HCC.

METHODS

Mesenchymal stem cells were isolated from bone marrow of C57/Bl6 p53(-/-) mice. The cells were injected into mice with HCC xenografts and the effect on tumor proliferation and angiogenesis was evaluated. The cells were then stably transfected with red fluorescent protein (RFP) or Herpes simplex virus thymidine kinase (HSV-Tk) gene under control of the Tie2 promoter/enhancer or the CCL5 promoter. Mesenchymal stem cells were injected intravenously into mice with orthotopically growing xenografts of HCC and treated with ganciclovir (GCV).

RESULTS

Ex vivo examination of hepatic tumors revealed tumor-specific recruitment, enhanced tumor growth, and increased microvessel density after nontherapeutic MSC injections. After their homing to the hepatic xenografts, engineered MSCs demonstrated activation of the Tie2 or CCL5 promoter as shown by RFP expression. Application of CCL5/HSV-TK transfected MSCs in combination with GCV significantly reduced tumor growth by 56.4% as compared with the control group and by 71.6% as compared with nontherapeutic MSC injections. CCL5/HSV-TK(+) transfected MSCs proved more potent in tumor inhibition as compared with Tie2/HSV-TK(+) MSCs.

CONCLUSION

Exogenously added MSCs are recruited to growing HCC xenografts with concomitant activation of the CCL5 or Tie2 promoters within the MSCs. Stem cell-mediated introduction of suicide genes into the tumor followed by prodrug administration was effective for treatment of experimental HCC and thus may help fill the existing gap in bridging therapies for patients suffering from advanced HCCs.

Examination of mesenchymal stem cell-mediated RNAi transfer to Huntington's disease affected neuronal cells for reduction of huntingtin

Huntington's disease (HD) is a fatal, autosomal dominant neurodegenerative disorder caused by an expanded trinucleotide (CAG) repeat in exon 1 of the huntingtin gene (Htt). This expansion creates a toxic polyglutamine tract in the huntingtin protein (HTT). Currently, there is no treatment for either the progression or prevention of the disease. RNA interference (RNAi) technology has shown promise in transgenic mouse models of HD by reducing expression of mutant HTT and slowing disease progression. The advancement of RNAi therapies to human clinical trials is hampered by problems delivering RNAi to affected neurons in a robust and sustainable manner. Mesenchymal stem cells (MSC) have demonstrated a strong safety profile in both completed and numerous ongoing clinical trials. MSC exhibit a number of innate therapeutic effects, such as immune system modulation, homing to injury, and cytokine release into damaged microenvironments. The ability of MSC to transfer larger molecules and even organelles suggested their potential usefulness as delivery vehicles for therapeutic RNA inhibition. In a series of model systems we have found evidence that MSC can transfer RNAi targeting both reporter genes and mutant huntingtin in neural cell lines. MSC expressing shRNA antisense to GFP were found to decrease expression of GFP in SH-SY5Y cells after co-culture when assayed by flow cytometry. Additionally MSC expressing shRNA antisense to HTT were able to decrease levels of mutant HTT expressed in both U87 and SH-SY5Y target cells when assayed by Western blot and densitometry. These results are encouraging for expanding the therapeutic abilities of both RNAi and MSC for future treatments of Huntington's disease.

Gap junctions propagate opposite effects in normal and tumor testicular cells in response to cisplatin

Gap junctions propagate toxic effects among tumor cells during chemotherapy, but could also enhance killing of normal cells by the same mechanism. We show that the effect of gap junctional intercellular communication (GJIC) on cisplatin toxicity differs between normal and tumor testicular cells. Downregulation of GJIC by each of several different manipulations (no cell contact, pharmacological inhibition, siRNA suppression) decreased cisplatin cytoxicity in tumor cells but enhanced it in normal cells. Enhanced toxicity due to GJIC downregulation in normal cells correlated with increased DNA interstrand crosslinks. Thus, GJIC protects normal cells from cisplatin toxicity while enhancing it in tumor cells, suggesting that enhancement/maintenance of GJIC increases therapeutic efficacy while decreasing off-target toxicity.

Cancer nanotheranostics: improving imaging and therapy by targeted delivery across biological barriers

Cancer nanotheranostics aims to combine imaging and therapy of cancer through use of nanotechnology. The ability to engineer nanomaterials to interact with cancer cells at the molecular level can significantly improve the effectiveness and specificity of therapy to cancers that are currently difficult to treat. In particular, metastatic cancers, drug-resistant cancers, and cancer stem cells impose the greatest therapeutic challenge for targeted therapy. Targeted therapy can be achieved with appropriately designed drug delivery vehicles such as nanoparticles, adult stem cells, or T cells in immunotherapy. In this article, we first review the different types of nanotheranostic particles and their use in imaging, followed by the biological barriers they must bypass to reach the target cancer cells, including the blood, liver, kidneys, spleen, and particularly the blood-brain barrier. We then review how nanotheranostics can be used to improve targeted delivery and treatment of cancer cells. Finally, we discuss development of nanoparticles to overcome current limitations in cancer therapy.

Human adipose tissue-derived mesenchymal stem cells expressing yeast cytosinedeaminase::uracil phosphoribosyltransferase inhibit intracerebral rat glioblastoma

Prodrug cancer gene therapy by mesenchymal stem cells (MSCs) targeted to tumors represents an attractive tool to activate prodrugs directly within the tumor mass, thus avoiding systemic toxicity. In this study, we tested the feasibility and efficacy of human adipose tissue-derived MSCs, engineered to express the suicide gene cytosine deaminase::uracil phosphoribosyltransferase to treat intracranial rat C6 glioblastoma. Experiments were designed to simulate conditions of future clinical application for high-grade glioblastoma therapy by direct injections of therapeutic stem cells into tumor. We demonstrated that genetically modified therapeutic stem cells still have the tumor tropism when injected to a distant intracranial site and effectively inhibited glioblastoma growth after 5-fluorocytosine (5-FC) therapy. Coadministration of C6 cells and therapeutic stem cells with delayed 5-FC therapy improved the survival in a therapeutic stem cell dose-dependent manner and induced complete tumor regression in a significant number of animals. Continuous intracerebroventricular delivery of 5-FC using osmotic pump reduced the dose of prodrug required for the same therapeutic effect, and along with repeated administration of therapeutic stem cells increased the survival time. Intracerebral injection of therapeutic stem cells and treatment with 5-FC did not show any detectable adverse effects. Results support the arguments to begin clinical studies for treatment of high-grade brain tumors.

Pigment epithelial-derived factor and melanoma differentiation associated gene-7 cytokine gene therapies delivered by adipose-derived stromal/mesenchymal stem cells are effective in reducing prostate cancer cell growth

Adipose-derived stromal/mesenchymal stem cells (ASC) have gained interest as promising tools for delivering cancer therapy. Adipose tissue can be obtained readily in amounts sufficient for ASC isolation, which can be expanded rapidly, allowing its use at low passage numbers, and can be transduced by viral and nonviral means. Our goal was to examine the potential of ASC to deliver cytokine gene therapies melanoma differentiation associated gene-7 (MDA-7) or pigment epithelial-derived factor (PEDF) to cancer cells. These novel cytokines are a potent proapoptotic and an antiangiogenesis mediator, respectively, with potential as antitumor agents. Expression of cytokine therapies did not adversely affect ASC biology, and these cells were still able to differentiate and retain normal viability. The ASC cytokine therapies were efficient in reducing tumor cell growth in coculture and also in suppressing in vitro angiogenesis phenotypes. We also observed that ASC retained their innate ability to migrate toward tumor cells in coculture, and this ability could be blocked by inhibition of CXCR4 signaling. The ASC were found to be nontumorigenic in vitro using a soft agar assay, as well as in vivo, utilizing 2 prostate cancer xenograft models. The ASC-MDA7 only reduced tumor growth in the TRAMP-C2-Ras (TC2Ras) prostate cancer model. The ASC-PEDF, however, reduced growth in both the TC2Ras and the PC3 highly aggressive prostate cancer models, and it was able to completely prevent prostate tumor establishment in vivo. In conclusion, ASC expressing PEDF and MDA7 could effectively reduce prostate tumor growth in vivo, suggesting ASC-cytokine therapies might have translational applications, especially the PEDF modality.

Stem cell based cancer gene therapy

The attractiveness of prodrug cancer gene therapy by stem cells targeted to tumors lies in activating the prodrug directly within the tumor mass, thus avoiding systemic toxicity. Suicide gene therapy using genetically engineered mesenchymal stem cells has the advantage of being safe, because prodrug administration not only eliminates tumor cells but consequently kills the more resistant therapeutic stem cells as well. This review provides an explanation of the stem cell-targeted prodrug cancer gene therapy principle, with focus on the choice of prodrug, properties of bone marrow and adipose tissue-derived mesenchymal stem and neural stem cells as well as the mechanisms of their tumor homing ability. Therapeutic achievements of the cytosine deaminase/5-fluorocytosine prodrug system and Herpes simplex virus thymidine kinase/ganciclovir are discussed. In addition, delivery of immunostimulatory cytokines, apoptosis inducing genes, nanoparticles and antiangiogenic proteins by stem cells to tumors and metastases is discussed as a promising approach for antitumor therapy. Combinations of traditional, targeted and stem cell-directed gene therapy could significantly advance the treatment of cancer.

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.

Mesenchymal stem cells in the pathogenesis and therapy of breast cancer

Mesenchymal stem cells (MSCs) are a heterogeneous mix of stromal stem cells that can give rise to cells of mesodermal lineages, namely adipocytes, osteocytes and chondrocytes. They can home to sites of injury where they promote the repair and regeneration of damaged tissues. MSCs also home to sites of tumorigenesis, and as such, are utilized as efficient cellular vehicles for the delivery of anti-neoplastic therapeutics. Recently, MSCs within the tumor microenvironment have been shown to contribute to the desmoplastic reaction and to facilitate tumor formation and progression, sparking renewed interest in their pro-tumorigenic attributes and their roles as tumor stromal cells. Here, we describe the evidence linking MSCs to inflammatory processes and breast cancer development, and discuss their newly discovered physiological roles in the context of the tumor microenvironment.

Gap junctions and connexins as therapeutic targets in cancer

IMPORTANCE OF THE FIELD

Connexins (Cxs) and gap junctional intercellular communications (GJICs) play roles in cancer development, growth and metastasis. Experimental studies suggest that targeting Cxs may be a novel technique, either to inhibit tumor cell growth directly or to sensitize to various therapies.

AREAS COVERED IN THIS REVIEW

A brief introduction to the role of Cxs in cancer. The focus is mainly on data available in the literature regarding therapeutic aspects.

WHAT THE READER WILL GAIN

This article reviews the various strategies that take advantage of gap junctions and connexins to eliminate cancer cells, including use of the bystander effect (BE) in gene therapy, the effect of connexins on chemosensitization, the role of apoptotic processes and interactions with the microenvironment. Attempts to restore connexin expression at the transcriptional and post-transcriptional levels are described, as well as promising strategies recently explored. The potential and limitations of the approaches are discussed.

TAKE HOME MESSAGE

Connexins have multiple facets, singly, in hemichannel complexes, in gap junctions or interacting with different proteins. The regulation of their expression is not fully resolved and selective manipulation of Cxs expression is therefore a challenge. Although the therapeutic potential of connexins is undeniable, more effort is needed to study the regulation and functions of these proteins.

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.

Tumor cell behaviour modulation by mesenchymal stromal cells

Background

Human mesenchymal stromal cells (MSC) hold a promise for future cell-based therapies due to their immunomodulatory properties and/or secretory activity. Nevertheless non-neoplastic tumor compartment could also originate from MSC. We aimed to show whether multipotent MSC derived from human adipose tissue (AT-MSC) could create tumor cell-protective milieu and affect tumor cell behaviour in vitro and in vivo.

Results

Here we have demonstrated tumor-promoting effect of AT-MSC on human melanoma A375 cells. AT-MSC coinjection mediated abrogation of tumor latency and supported subcutaneous xenotransplant growth from very low melanoma cell doses. Tumor incidence was also significantly increased by AT-MSC-derived soluble factors. AT-MSC supported proliferation, suppressed apoptosis and modulated melanoma cell responses to cytotoxic drugs in vitro. Expression and multiplex cytokine assays confirmed synergistic increase in VEGF that contributed to the AT-MSC-mediated support of A375 xenotransplant growth. Production of G-CSF and other factors implicated in formation of supportive proinflammatory tumor cell microenvironment was also confirmed. SDF-1α/CXCR4 signalling contributed to tumor-promoting effect of systemic AT-MSC administration on A375 xenotransplants. However, no support was observed for human glioblastoma cells 8MGBA co-injected along with AT-MSC that did not sustain tumor xenotransplant growth in vivo. Tumor-inhibiting response could be attributed to the synergistic action of multiple cytokines produced by AT-MSC on glioblastoma cells.

Conclusions

Herein we provide experimental evidence for MSC-mediated protective effect on melanoma A375 cells under nutrient-limiting and hostile environmental conditions resulting from mutual crosstalk between neoplastic and non-malignant cells. This tumor-favouring effect was not observed for the glioblastoma cells 8MGBA. Collectively, our data further strengthen the need for unravelling mechanisms underlying MSC-mediated modulation of tumor behaviour for possible future MSC clinical use in the context of malignant disease.

Activation of CD74 inhibits migration of human mesenchymal stem cells

Therapeutic administration of mesenchymal stem cells (MSCs) by systemic delivery utilizes the innate ability of the cells to home to damaged tissues, but it can be an inefficient process due to a limited knowledge of cellular cues that regulate migration and homing. Our lab recently discovered that a potent pro-inflammatory cytokine, macrophage migration inhibitory factor (MIF), inhibits MSC migration. Because MIF may act on multiple cellular targets, an activating antibody (CD74Ab) was employed in this study to examine the effect of one MIF receptor, CD74 (major histocompatibility complex class II-associated invariant chain), on MSC motility. CD74 activation inhibits in a dose-dependent manner up to 90% of in vitro migration of MSCs at 40 mug/ml CD74Ab (p < 0.001), with consistent effects observed among three MSC donor preparations. A blocking peptide from the C-terminus of CD74 eliminates the effect of CD74Ab on MSCs. This suggests that MIF may act on MSCs, at least in part, through CD74. Late-passage MSCs exhibit less chemokinesis than those at passage 2. However, MSCs remain responsive to CD74 activation during ex vivo expansion: MSC migration is inhibited approximately 2-fold in the presence of 5 microg/ml CD74Ab at passage 9 vs. approximately 3-fold at passage 2 (p < 0.001). Consistent with this result, there were no significant differences in CD74 expression at all tested passages or after CD74Ab exposure. Targeting CD74 to regulate migration and homing potentially may be a useful strategy to improve the efficacy of a variety of MSC therapies, including those that require ex vivo expansion.