Jennifer Dembinski

Human Bone Marrow–Derived Mesenchymal Stem Cells in the Treatment of Gliomas

The poor survival of patients with human malignant gliomas relates partly to the inability to deliver therapeutic agents to the tumor. Because it has been suggested that circulating bone marrow-derived stem cells can be recruited into solid organs in response to tissue stresses, we hypothesized that human bone marrow-derived mesenchymal stem cells (hMSC) may have a tropism for brain tumors and thus could be used as delivery vehicles for glioma therapy. To test this, we isolated hMSCs from bone marrow of normal volunteers, fluorescently labeled the cells, and injected them into the carotid artery of mice bearing human glioma intracranial xenografts (U87, U251, and LN229). hMSCs were seen exclusively within the brain tumors regardless of whether the cells were injected into the ipsilateral or contralateral carotid artery. In contrast, intracarotid injections of fibroblasts or U87 glioma cells resulted in widespread distribution of delivered cells without tumor specificity. To assess the potential of hMSCs to track human gliomas, we injected hMSCs directly into the cerebral hemisphere opposite an established human glioma and showed that the hMSCs were capable of migrating into the xenograft in vivo. Likewise, in vitro Matrigel invasion assays showed that conditioned medium from gliomas, but not from fibroblasts or astrocytes, supported the migration of hMSCs and that platelet-derived growth factor, epidermal growth factor, or stromal cell-derived factor-1alpha, but not basic fibroblast growth factor or vascular endothelial growth factor, enhanced hMSC migration. To test the potential of hMSCs to deliver a therapeutic agent, hMSCs were engineered to release IFN-beta (hMSC-IFN-beta). In vitro coculture and Transwell experiments showed the efficacy of hMSC-IFN-beta against human gliomas. In vivo experiments showed that treatment of human U87 intracranial glioma xenografts with hMSC-IFN-beta significantly increase animal survival compared with controls (P < 0.05). We conclude that hMSCs can integrate into human gliomas after intravascular or local delivery, that this engraftment may be mediated by growth factors, and that this tropism of hMSCs for human gliomas can be exploited to therapeutic advantage.

Mesenchymal Stem Cell Transition to Tumor-Associated Fibroblasts Contributes to Fibrovascular Network Expansion and Tumor Progression

Background Tumor associated fibroblasts (TAF), are essential for tumor progression providing both a functional and structural supportive environment. TAF, known as activated fibroblasts, have an established biological impact on tumorigenesis as matrix synthesizing or matrix degrading cells, contractile cells, and even blood vessel associated cells. The production of growth factors, cytokines, chemokines, matrix-degrading enzymes, and immunomodulatory mechanisms by these cells augment tumor progression by providing a suitable environment. There are several suggested origins of the TAF including tissue-resident, circulating, and epithelial-to-mesenchymal-transitioned cells. Methodology/Principal Findings We provide evidence that TAF are derived from mesenchymal stem cells (MSC) that acquire a TAF phenotype following exposure to or systemic recruitment into adenocarcinoma xenograft models including breast, pancreatic, and ovarian. We define the MSC derived TAF in a xenograft ovarian carcinoma model by the immunohistochemical presence of 1) fibroblast specific protein and fibroblast activated protein; 2) markers phenotypically associated with aggressiveness, including tenascin-c, thrombospondin-1, and stromelysin-1; 3) production of pro-tumorigenic growth factors including hepatocyte growth factor, epidermal growth factor, and interleukin-6; and 4) factors indicative of vascularization, including alpha-smooth muscle actin, desmin, and vascular endothelial growth factor. We demonstrate that under long-term tumor conditioning in vitro, MSC express TAF–like proteins. Additionally, human MSC but not murine MSC stimulated tumor growth primarily through the paracrine production of secreted IL6. Conclusions/Significance Our results suggest the dependence of in vitro Skov-3 tumor cell proliferation is due to the presence of tumor-stimulated MSC secreted IL6. The subsequent TAF phenotype arises from the MSC which ultimately promotes tumor growth through the contribution of microvascularization, stromal networks, and the production of tumor-stimulating paracrine factors.

Inflammation and tumor microenvironments: defining the migratory itinerary of mesenchymal stem cells.

Mesenchymal stem cells (MSC) exhibit tropism for sites of tissue damage as well as the tumor microenvironment. Many of the same inflammatory mediators that are secreted by wounds are found in the tumor microenvironment and are thought to be involved in attracting MSC to these sites. Cell migration is dependent on a multitude of signals ranging from growth factors to chemokines secreted by injured cells and/or respondent immune cells. MSC are likely to have chemotactic properties similar to other immune cells that respond to injury and sites of inflammation. Thus, the well-described model of leukocyte migration can serve as a reasonable example to facilitate the identification of factors involved in MSC migration.Understanding the factors involved in regulating MSC migration to tumors is essential to ultimately develop novel clinical strategies aimed at using MSC as vehicles to deliver antitumor proteins or suppress MSC migration to reduce tumor growth. For example, radiation enhances inflammatory signaling in the tumor microenvironment and may be used to potentiate site-specific MSC migration. Alternatively, restricting the migration of the MSC to the tumor microenvironment may prevent competent tumor-stroma formation, thereby hindering the growth of the tumor. In this review, we will discuss the role of inflammatory signaling in attracting MSC to tumors.

Direct Evidence of Mesenchymal Stem Cell Tropism for Tumor and Wounding Microenvironments Using In Vivo Bioluminescent Imaging

Multipotent mesenchymal stromal/stem cells (MSC) have shown potential clinical utility. However, previous assessments of MSC behavior in recipients have relied on visual detection in host tissue following sacrifice, failing to monitor in vivo MSC dispersion in a single animal and limiting the number of variables that can be observed concurrently. In this study, we used noninvasive, in vivo bioluminescent imaging to determine conditions under which MSC selectively engraft in sites of inflammation. MSC modified to express firefly luciferase (ffLuc‐MSC) were injected into healthy mice or mice bearing inflammatory insults, and MSC localization was followed with bioluminescent imaging. The inflammatory insults investigated included cutaneous needle‐stick and surgical incision wounds, as well as xenogeneic and syngeneic tumors. We also compared tumor models in which MSC were i.v. or i.p. delivered. Our results demonstrate that ffLuc‐expressing human MSC (hMSC) systemically delivered to nontumor‐bearing animals initially reside in the lungs, then egress to the liver and spleen, and decrease in signal over time. However, hMSC in wounded mice engraft and remain detectable only at injured sites. Similarly, in syngeneic and xenogeneic breast carcinoma‐bearing mice, bioluminescent detection of systemically delivered MSC revealed persistent, specific colocalization with sites of tumor development. This pattern of tropism was also observed in an ovarian tumor model in which MSC were i.p. injected. In this study, we identified conditions under which MSC tropism and selective engraftment in sites of inflammation can be monitored by bioluminescent imaging over time. Importantly, these consistent findings were independent of tumor type, immunocompetence, and route of MSC delivery. STEM CELLS 2009;27:2614–2623

The pro-inflammatory peptide LL-37 promotes ovarian tumor progression through recruitment of multipotent mesenchymal stromal cells

Bone marrow-derived mesenchymal stem cells or multipotent mesenchymal stromal cells (MSCs) have been shown to engraft into the stroma of several tumor types, where they contribute to tumor progression and metastasis. However, the chemotactic signals mediating MSC migration to tumors remain poorly understood. Previous studies have shown that LL-37 (leucine, leucine-37), the C-terminal peptide of human cationic antimicrobial protein 18, stimulates the migration of various cell types and is overexpressed in ovarian, breast, and lung cancers. Although there is evidence to support a pro-tumorigenic role for LL-37, the function of the peptide in tumors remains unclear. Here, we demonstrate that neutralization of LL-37 in vivo significantly reduces the engraftment of MSCs into ovarian tumor xenografts, resulting in inhibition of tumor growth as well as disruption of the fibrovascular network. Migration and invasion experiments conducted in vitro indicated that the LL-37-mediated migration of MSCs to tumors likely occurs through formyl peptide receptor like-1. To assess the response of MSCs to the LL-37-rich tumor microenvironment, conditioned medium from LL-37-treated MSCs was assessed and found to contain increased levels of several cytokines and pro-angiogenic factors compared with controls, including IL-1 receptor antagonist, IL-6, IL-10, CCL5, VEGF, and matrix metalloproteinase-2. Similarly, Matrigel mixed with LL-37, MSCs, or the combination of the two resulted in a significant number of vascular channels in nude mice. These data indicate that LL-37 facilitates ovarian tumor progression through recruitment of progenitor cell populations to serve as pro-angiogenic factor-expressing tumor stromal cells.

Tumor Irradiation Increases the Recruitment of Circulating Mesenchymal Stem Cells into the Tumor Microenvironment

Mesenchymal stem cells (MSC) migrate to and proliferate within sites of inflammation and tumors as part of the tissue remodeling process. Radiation increases the expression of inflammatory mediators that could enhance the recruitment of MSC into the tumor microenvironment. To investigate this, bilateral murine 4T1 breast carcinomas (expressing renilla luciferase) were irradiated unilaterally (1 or 2 Gy). Twenty-four hours later, 2 x 10(5) MSC-expressing firefly luciferase were injected i.v. Mice were then monitored with bioluminescent imaging for expression of both renilla (tumor) and firefly (MSC) luciferase. Forty-eight hours postirradiation, levels of MSC engraftment were 34% higher in tumors receiving 2 Gy (P = 0.004) than in the contralateral unirradiated limb. Immunohistochemical staining of tumor sections from mice treated unilaterally with 2 Gy revealed higher levels of MSC in the parenchyma of radiated tumors, whereas a higher proportion of MSC remained vasculature-associated in unirradiated tumors. To discern the potential mediators involved in MSC attraction, in vitro migration assays showed a 50% to 80% increase in MSC migration towards conditioned media from 1 to 5 Gy-irradiated 4T1 cells compared with unirradiated 4T1 cells. Irradiated 4T1 cells had increased expression of the cytokines, transforming growth factor-beta1, vascular endothelial growth factor, and platelet-derived growth factor-BB, and this up-regulation was confirmed by immunohistochemistry in tumors irradiated in vivo. Interestingly, the chemokine receptor CCR2 was found to be up-regulated in MSC exposed to irradiated tumor cells and inhibition of CCR2 led to a marked decrease of MSC migration in vitro. In conclusion, clinically relevant low doses of irradiation increase the tropism for and engraftment of MSC in the tumor microenvironment.

Mesenchymal Stem Cells in Cancer: Tumor-Associated Fibroblasts and Cell-Based Delivery Vehicles

Recent evidence suggests that mesenchymal stem cells (MSC) selectively home to tumors, where they contribute to the formation of tumor-associated stroma. This effect can be opposed by genetically modifying MSC to produce high levels of anti-cancer agents that blunt tumor growth kinetics and inhibit the growth of tumors in situ. In this review article, we describe the biological properties of MSC within the tumor microenvironment and discuss the potential use of MSC and other bone marrow-derived cell populations as delivery vehicles for antitumor proteins.

Reduction of nontarget infection and systemic toxicity by targeted delivery of conditionally replicating viruses transported in mesenchymal stem cells

The fiber-modified adenoviral vector Δ-24-RGD (D24RGD) offers vast therapeutic potential. Direct injection of D24RGD has been used to successfully target ovarian tumors in mice. However, systemic toxicity, especially in the liver, profoundly limits the efficacy of direct viral vector delivery. Mesenchymal stem cells (MSC) have the ability to function as a vector for targeted gene therapy because of their preferential engraftment into solid tumors and participation in tumor stroma formation. We show that MSC-guided delivery of D24RGD is specific and efficient and reduces the overall systemic toxicity in mice to negligible levels compared with D24RGD alone. In our model, we found efficient targeted delivery of MSC-D24RGD to both breast and ovarian cell lines. Furthermore, immunohistochemical staining for adenoviral hexon protein confirmed negligible levels of systemic toxicity in mice that were administered MSC-D24RGD compared with those that were administered D24RGD. These data suggest that delivery of D24RGD through MSC not only increases the targeted delivery efficiency, but also reduces the systemic exposure of the virus, thereby reducing overall systemic toxicity to the host and ultimately enhancing its value as an anti-tumor therapeutic candidate.

Mesenchymal Stem/Stromal Cells as Cellular Vehicles for Tumor Targeting

Data published over the last 10 years suggest that mesenchymal stem/stromal cells (MSC) possess the innate capacity to home to sites of inflammation, including tumors and wounding microenvironments. Evidence suggests that the increased production of inflammatory mediators found at these sites is potential attractants for recruitment and engraftment. This innate homing response can be exploited by using MSC as a cellular delivery vehicle to deliver anticancer agents directly to tumors. The high-level intratumoral production of these agents controls tumor growth and prolongs survival in numerous animal models. In this review, we examine the ability of MSC to selectively home to and engraft within the tumor microenvironment and the multiple gene products delivered by MSC when used as delivery vehicles for anticancer therapies.

447. Mesenchymal Stem Cells as Delivery Systems for Cancer Therapy: Evaluation of Tropism and Efficacy

Top of pageAbstract We have previously demonstrated that bone marrow-derived mesenchymal stem cells (MSC) integrate into solid tumors as stromal elements following intravenous injection (JNCI 96(21):1593, 2004, Cancer Res 62:3603, 2002). These finding suggests the development of novel anti-cancer therapies based on the local production of biological agents by gene-manipulated MSC. However, no direct evidence has demonstrated this migration and incorporation into the tumor microenvironment. To this end, we utilized noninvasive imaging of migrating MSC in animal models. MSC were labeled by a fiber modified Ad vector expressing firefly luciferase (AdLux-F/RGD) and these MSC-Lux were injected into normal (healthy) SCID mice or mice bearing established metastatic breast or ovarian tumors. Biodistributed MSC-Lux were imaged utilizing the Xenogen IVIS detection system. In normal mice, human MSC (hMSC) migrated to the lungs where they remained resident for 7-10 days. In animals bearing established metastatic lung tumors, IV injected hMSC again migrated to the lungs. However, in contrast to control mice, the Lux signal remained strong over a 15 day period with only a slight decrease over the first 10 days. After IP injection, hMSC-LUX were detected in the peritoneum, and after 7 days, no hMSC-LUX was detected in normal animals, while strong punctate regions of LUX-activity were observed in ovarian tumors. In contrast to SCID mice injected with hMSC, healthy Balb/C mice injected with Balb/C derived MSC-LUX initially migrated to the lungs and within 2.5 hrs had exited the lungs to remain liver and spleen resident for 5-7 days. We then examined whether hMSC producing interferon-beta (MSC-IFNb) can inhibit the growth of metastatic tumors in the lungs of SCID mice. When injected IV (4 doses of 10E6 MSC/week) into SCID mice bearing pulmonary metastases of carcinomas or melanomas, tumor growth was significantly inhibited as compared to untreated or vector-control MSC controls (p= 0.007), while recombinant IFNb protein (50,000 IU qod) was ineffective (p=0.14). IV injected MSC-IFNb prolonged the survival of mice bearing metastatic breast carcinomas (p=0.001) Intraperitoneal (IP) injections of MSC-IFNb into mice carrying ovarian carcinomas resulted in doubling of survival in SKOV-3, and cures in 70% of mice carrying OVAR-3 tumors. These data suggest that systemically administered gene-modified MSC selectively engraft into the tumor microenvironment and remain resident as part of the tumor architecture. MSC-expressing IFN-b inhibit the growth of metastatic breast cancer, and ovarian cancers in vivo and prolong the survival of mice bearing established tumors. Clinical trials are in preparation.