Mesenchymal stem cells as carriers and amplifiers in CRAd delivery to tumors

Enhancing oncolytic virus efficiency with methionine and N-(3-aminoprolil)methacrylamide modified acrylamide cationic block polymer

Oncolytic virus ablation of tumor cells has the advantages of high tumor selectivity, strong immunogenicity, and low side effects. However, the recognition and clearance of oncolytic viruses by the immune system are the main factors limiting their anti-tumor efficiency. As a highly biosafe and highly modifiable oncolytic virus vector, acrylamide can improve the long-term circulation of oncolytic viruses. Still, it is limited in its uptake efficiency by tumor cells. Herein, we constructed an N-hydroxymethyl acrylamide-b-(N-3-aminopropyl methacrylamide)-b-DMC block copolymer (NMA-b-APMA-b-DMA, NAD) as an oncolytic virus carrier, which not only improves the long-term circulation of oncolytic viruses in the body but also shows excellent stability for loading an oncolytic virus. The data shows that there was no obvious difference in the transfection effect of the NAD/Ad complex with or without neutralizing antibodies in the medium, which meant that the cationic carrier mediated by NAD/Ad had good serum stability. Only 10 micrograms of NAD carrier are needed to load the oncolytic virus, which can increase the transfection efficiency by 50 times. Cell experiments and mouse animal experiments show that NAD vectors can significantly enhance the anti-tumor effect of oncolytic viruses. We hope that this work will promote the application of acrylamide as an oncolytic virus vector and provide new ideas for methods to modify acrylamide for biomedical applications.

Oncolytic virotherapy: basic principles, recent advances and future directions

Oncolytic viruses (OVs) have attracted growing awareness in the twenty-first century, as they are generally considered to have direct oncolysis and cancer immune effects. With the progress in genetic engineering technology, OVs have been adopted as versatile platforms for developing novel antitumor strategies, used alone or in combination with other therapies. Recent studies have yielded eye-catching results that delineate the promising clinical outcomes that OVs would bring about in the future. In this review, we summarized the basic principles of OVs in terms of their classifications, as well as the recent advances in OV-modification strategies based on their characteristics, biofunctions, and cancer hallmarks. Candidate OVs are expected to be designed as "qualified soldiers" first by improving target fidelity and safety, and then equipped with "cold weapons" for a proper cytocidal effect, "hot weapons" capable of activating cancer immunotherapy, or "auxiliary weapons" by harnessing tactics such as anti-angiogenesis, reversed metabolic reprogramming and decomposing extracellular matrix around tumors. Combinations with other cancer therapeutic agents have also been elaborated to show encouraging antitumor effects. Robust results from clinical trials using OV as a treatment congruously suggested its significance in future application directions and challenges in developing OVs as novel weapons for tactical decisions in cancer treatment.

Mesenchymal stem cell-released oncolytic virus: an innovative strategy for cancer treatment

Oncolytic viruses (OVs) infect, multiply, and finally remove tumor cells selectively, causing no damage to normal cells in the process. Because of their specific features, such as, the ability to induce immunogenic cell death and to contain curative transgenes in their genomes, OVs have attracted attention as candidates to be utilized in cooperation with immunotherapies for cancer treatment. This treatment takes advantage of most tumor cells' inherent tendency to be infected by certain OVs and both innate and adaptive immune responses are elicited by OV infection and oncolysis. OVs can also modulate tumor microenvironment and boost anti-tumor immune responses. Mesenchymal stem cells (MSC) are gathering interest as promising anti-cancer treatments with the ability to address a wide range of cancers. MSCs exhibit tumor-trophic migration characteristics, allowing them to be used as delivery vehicles for successful, targeted treatment of isolated tumors and metastatic malignancies. Preclinical and clinical research were reviewed in this study to discuss using MSC-released OVs as a novel method for the treatment of cancer. Video Abstract.

Evaluation of Human Mesenchymal Stromal Cells as Carriers for the Delivery of Oncolytic HAdV-5 to Head and Neck Squamous Cell Carcinomas

Human multipotent mesenchymal stromal cells (hMSCs) are of significant therapeutic interest due to their ability to deliver oncolytic adenoviruses to tumors. This approach is also investigated for targeting head and neck squamous cell carcinomas (HNSCCs). HAdV-5-HexPos3, a recently reported capsid-modified vector based on human adenovirus type 5 (HAdV-5), showed strongly improved infection of both hMSCs and the HNSCC cell line UM-SCC-11B. Given that, we generated life cycle-unmodified and -modified replication-competent HAdV-5-HexPos3 vector variants and analyzed their replication within bone marrow- and adipose tissue-derived hMSCs. Efficient replication was detected for both life cycle-unmodified and -modified vectors. Moreover, we analyzed the migration of vector-carrying hMSCs toward different HNSCCs. Although migration of hMSCs to HNSCC cell lines was confirmed in vitro, no homing of hMSCs to HNSCC xenografts was observed in vivo in mice and in ovo in a chorioallantoic membrane model. Taken together, our data suggest that HAdV-5-HexPos3 is a potent candidate for hMSC-based oncolytic therapy of HNSCCs. However, it also emphasizes the importance of generating optimized in vivo models for the evaluation of hMSC as carrier cells.

Mesenchymal stem/stromal cells in breast cancer development and management

Mesenchymal stem/stromal cells (MSCs) encompass a heterogeneous population of fibroblastic progenitor cells that reside in multiple tissues around the body. They are endowed with capacities to differentiate into multiple connective tissue lineages, including chondrocytes, adipocytes, and osteoblasts, and are thought to function as trophic cells recruited to sites of injury and inflammation where they contribute to tissue regeneration. In keeping with these roles, MSCs also to home to sites of breast tumorigenesis, akin to their migration to wounds, and participate in tumor stroma formation. Mounting evidence over the past two decades has described the critical regulatory roles for tumor-associated MSCs in various aspects of breast tumor pathogenesis, be it tumor initiation, growth, angiogenesis, tumor microenvironment formation, immune evasion, cancer cell migration, invasion, survival, therapeutic resistance, dissemination, and metastatic colonization. In this review, we present a brief summary of the role of MSCs in breast tumor development and progression, highlight some of the molecular frameworks underlying their pro-malignant contributions, and present evidence of their promising utility in breast cancer therapy.

Mesenchymal stem cells: A living carrier for active tumor-targeted delivery

The strategy of using mesenchymal stem cells (MSCs) as a living carrier for active delivery of therapeutic agents targeting tumor sites has been attempted in a wide range of studies to validate the feasibility and efficacy for tumor treatment. This approach reveals powerful tumor targeting and tumor penetration. In addition, MSCs have been confirmed to actively participate in immunomodulation of the tumor microenvironment. Thus, MSCs are not inert delivery vehicles but have a strong impact on the fate of tumor cells. In this review, these active properties of MSCs are addressed to highlight the advantages and challenges of using MSCs for tumor-targeted delivery. In addition, some of the latest examples of using MSCs to carry a variety of anti-tumor agents for tumor-targeted therapy are summarized. Recent technologies to improve the performance and safety of this delivery strategy will be introduced. The advances, applications, and challenges summarized in this review will provide a general understanding of this promising strategy for actively delivering drugs to tumor tissues.

Systemic administration of mesenchymal stem cells loaded with a novel oncolytic adenovirus carrying IL-24/endostatin enhances glioma therapy

Oncolytic adenovirus-mediated gene therapy shows promise for cancer treatment; however, the systemic delivery of oncolytic adenovirus to tumors remains challenging. Recently, mesenchymal stem cells (MSCs) have emerged as potential vehicles for improving delivery. Yet, because the oncolytic adenovirus replicates in MSCs, balancing MSC viability with viral load is key to achieving optimal therapeutic effect. We thus developed an all-in-one Tet-on system that can regulate replication of oncolytic adenovirus. Then, we loaded the novel oncolytic adenovirus carrying interleukin (IL)-24 and/or Endostatin in human umbilical cord blood-mesenchymal stem cells (hUCB-MSCs) for glioma therapy. In vitro assays demonstrated that this novel oncolytic adenovirus could efficiently replicate and kill glioma cells while sparing normal cells. Moreover, doxycycline effectively regulated oncolytic adenovirus replication in the hUCB-MSCs. The doxycycline induction group with dual expression of IL-24 and Endostatin exhibited significantly greater antitumor effects than other groups in a xenograft model of glioma. Thus, this strategy for systemic delivery of oncolytic adenovirus with its oncolytic activity controlled by a Tet-on system is a promising method for achieving antitumor efficacy in glioma, especially for metastatic tumors.

Arming Mesenchymal Stromal/Stem Cells Against Cancer: Has the Time Come?

Since mesenchymal stromal/stem cells (MSCs) were discovered, researchers have been drawn to study their peculiar biological features, including their immune privileged status and their capacity to selectively migrate into inflammatory areas, including tumors. These properties make MSCs promising cellular vehicles for the delivery of therapeutic molecules in the clinical setting. In recent decades, the engineering of MSCs into biological vehicles carrying anticancer compounds has been achieved in different ways, including the loading of MSCs with chemotherapeutics or drug functionalized nanoparticles (NPs), genetic modifications to force the production of anticancer proteins, and the use of oncolytic viruses. Recently, it has been demonstrated that wild-type and engineered MSCs can release extracellular vesicles (EVs) that contain therapeutic agents. Despite the enthusiasm for MSCs as cyto-pharmaceutical agents, many challenges, including controlling the fate of MSCs after administration, must still be considered. Preclinical results demonstrated that MSCs accumulate in lung, liver, and spleen, which could prevent their engraftment into tumor sites. For this reason, physical, physiological, and biological methods have been implemented to increase MSC concentration in the target tumors. Currently, there are more than 900 registered clinical trials using MSCs. Only a small fraction of these are investigating MSC-based therapies for cancer, but the number of these clinical trials is expected to increase as technology and our understanding of MSCs improve. This review will summarize MSC-based antitumor therapies to generate an increasing awareness of their potential and limits to accelerate their clinical translation.

Systemic administration of human mesenchymal stromal cells infected with polymer-coated oncolytic adenovirus induces efficient pancreatic tumor homing and infiltration

Oncolytic adenovirus (oAd)-mediated gene therapy is a promising approach for cancer treatment because of its cancer cell-restricted replication and therapeutic gene expression. However, systemic administration of oAd is severely restricted by their immunogenic nature and poor tumor homing ability, thus oAd cannot be utilized to treat disseminated metastases. In this study, human bone marrow-derived mesenchymal stromal cell (hMSCs) was used as a viral replication-permissive carrier for oAd with an aim to improve the systemic delivery of the virus to tumor tissues. To overcome the poor delivery of oAd into hMSCs, a relaxin (RLX)-expressing oncolytic Ad (oAd/RLX), which degrades dense tumor extracellular matrix of highly desmoplastic pancreatic cancer, was complexed with biodegradable polymer (poly (ethyleneimine)-conjugated poly(CBA-DAH); PCDP), generating oAd/RLX-PCDP complex. oAd/RLX-PCDP complex enhanced the internalization of oAd into hMSC, leading to superior viral production and release from hMSCs, along with high RLX expression. Furthermore, systemic administration of oAd/RLX-PCDP-treated hMSCs elicited more potent antitumor effect compared to naked oAd/RLX or oAd/RLX-treated hMSC in pancreatic tumor model. This potent antitumor effect of systemically administered oAd/RLX-PCDP-treated hMSCs was achieved by superior viral replication in tumor tissues than any other treatment group. In conclusion, these results demonstrate that hMSCs are effective carriers for the systemic delivery of oAd to tumor sites and treatment of pancreatic cancer.

Mesenchymal Stem Cell Expressing TRAIL as Targeted Therapy against Sensitised Tumour

Tapping into the ability of engineered mesenchymal stem cells (MSCs) to mobilise into the tumour has expanded the scope of cancer treatment. Engineered MSCs expressing tumour necrosis factor (TNF)-related apoptosis inducing ligand (MSC-TRAIL) could serve as a platform for an efficient and targeted form of therapy. However, the presence of cancer stem cells (CSCs) that are resistant to TRAIL and apoptosis may represent a challenge for effective treatment. Nonetheless, with the discovery of small molecular inhibitors that could target CSCs and tumour signalling pathways, a higher efficacy of MSC-TRAIL mediated tumour inhibition can be achieved. This might pave the way for a more effective form of combined therapy, which leads to a better treatment outcome. In this review, we first discuss the tumour-homing capacity of MSCs, its effect in tumour tropism, the different approach behind genetically-engineered MSCs, and the efficacy and safety of each agent delivered by these MSCs. Then, we focus on how sensitisation of CSCs and tumours using small molecular inhibitors can increase the effect of these cells to either TRAIL or MSC-TRAIL mediated inhibition. In the conclusion, we address a few questions and safety concerns regarding the utilization of engineered MSCs for future treatment in patients.

E1A-engineered human umbilical cord mesenchymal stem cells as carriers and amplifiers for adenovirus suppress hepatocarcinoma in mice

Gene therapy is an attractive approach for hepatocellular carcinoma (HCC) patients. Nevertheless, efficient transgene delivery remains a challenge. In this study, we explored a new targeted system based on human umbilical cord-derived mesenchymal stem cells (HUMSCs), which were engineered to deliver adenovirus to tumor sites, and to replicate and assemble into new adenovirus against HCC. Our results showed that HUMSCs infected by Ad-hTERTp-IL24 followed by LentiR.E1A infection could specifically migrate to HepG2 tumor cells and support adenoviral replication in vitro and in vivo 36 h after LentiR.E1A infection. Ad-hTERTp-IL24 specifically inhibited HepG2 cells growth, and this inhibitory effect was enhanced by low doses of 5-fluorouracil (5-Fu), because the expression levels of coxsackie adenovirus receptor (CAR) and integrin ανβ3 on tumor cells were significantly increased, causing higher viral uptake. Compared with the no treatment groups, Ad-hTERTp-IL24 and LentiR.E1A co-loaded HUMSCs exhibited significant anti-tumor activity in vivo, particularly in combination with low doses of 5-Fu. In summary, this study provides a promising targeted gene therapeutic strategy dependent on the tumor tropism of HUMSCs, to improve the outcome of virotherapy for tumor patients especially those with metastatic diseases.

Surface expression of anti-CD3scfv stimulates locoregional immunotherapy against hepatocellular carcinoma depending on the E1A-engineered human umbilical cord mesenchymal stem cells

Tumor antigens is at the core of cancer immunotherapy, however, the ideal antigen selection is difficult especially in poorly immunogenic tumors. In this study, we designed a strategy to modify hepatocellular carcinoma (HCC) cells by surface expressing anti-CD3scfv within the tumor site strictly, which depended on the E1A-engineered human umbilical cord mesenchymal stem cells (HUMSC.E1A) delivery system. Subsequently, membrane-bound anti-CD3scfv actived the lymphocytes which lysed HCC cells bypassing the expression of antigens or MHC restriction. First, we constructed the anti-CD3scfv gene driven by human α-fetoprotein (AFP) promoter into an adenoviral vector and the E1A gene into the lentiviral vector. Our results showed that anti-CD3scfv could specifically express on the surface of HCC cells and activate the lymphocytes to kill target cells effectively in vitro. HUMSC infected by AdCD3scfv followed by LentiR.E1A could support the adenoviral replication and packaging in vitro 36 h after LentiR.E1A infection. Using a subcutaneous HepG2 xenograft model, we confirmed that AdCD3scfv and LentiR.E1A co-transfected HUMSC could migrate selectively to the tumor site and produce considerable adenoviruses. The new generated AdCD3scfv infected and modified tumor cells successfully. Mice injected with the MSC.E1A.AdCD3scfv and lymphocytes significantly inhibited the tumor growth compared with control groups. Furthermore, 5-fluorouracil (5-FU) could sensitize adenovirus infection at low MOI resulting in improved lymphocytes cytotoxicity in vitro and in vivo. In summary, this study provides a promising strategy for solid tumor immunotherapy.

Mesenchymal stromal cells for the delivery of oncolytic viruses in gliomas

Mesenchymal stromal cells (MSCs) are a type of adult stem cell that has been exploited for the treatment of a variety of diseases, including cancer. In particular, MSCs have been studied extensively for their ability to treat glioblastoma (GBM), the most common and deadly form of brain cancer in adults. MSCs are attractive therapeutics because they can be obtained relatively easily from patients, are capable of being expanded numerically in vitro, can be easily engineered and are inherently capable of homing to tumors, making them ideal vehicles for delivering biological antitumoral agents. Oncolytic viruses are promising biological therapeutic agents that have been used in the treatment of GBMs, and MSCs are currently being explored as a means of delivering these viruses. Here we review the role of MSCs in the treatment of GBMs, focusing on the intersection of MSCs and oncolytic viruses.

Delivery of improved oncolytic adenoviruses by mesenchymal stromal cells for elimination of tumorigenic pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDA) is one of the most aggressive malignancies and has poor therapeutic options. We evaluated improved oncolytic adenoviruses (OAds), in which the adenoviral gene E1B19K was deleted or a TRAIL transgene was inserted. Bone marrow mesenchymal stromal cells (MSCs) served as carriers for protected and tumor-specific virus transfers. The infection competence, tumor migration, and oncolysis were measured in cancer stem cell (CSC) models of primary and established tumor cells and in tumor xenografts. All OAds infected and lysed CSCs and prevented colony formation. MSCs migrated into PDA spheroids without impaired homing capacity. Xenotransplantation of non-infected PDA cells mixed with infected tumor cells strongly reduced the tumor volume and the expression of the proliferation marker Ki67 along with a necrotic morphology. Adenoviral capsid protein was detected in tumor xenograft tissue after intravenous injection of infected MSCs, but not in normal tissue, implying tumor-specific migration. Likewise, direct in vivo treatment correlated with a strongly reduced tumor volume, lower expression of Ki67 and CD24, and enhanced activity of caspase 3. These data demonstrate that the improved OAds induced efficient oncolysis with the OAd-TRAIL as most promising candidate for future clinical application.

Mesenchymal stem cells deliver and release conditionally replicative adenovirus depending on hepatic differentiation to eliminate hepatocellular carcinoma cells specifically

Currently, it is a key challenge to remove the postsurgical residuals and metastasis of hepatocellular carcinoma (HCC). Oncolytic adenoviral virotherapy is an attractive treatment modality for cancer; however, the difficulty remains regarding its intravenous administration. The aim of this study was to develop a targeted therapeutic system which has great potential to overcome the postsurgical residuals and metastasis of HCC. In this system, we developed a conditionally replicative adenovirus (CRAd) loaded on human umbilical cord-derived mesenchymal stem cells (HUMSCs), in which the CRAd contained an adenovirus E1A gene dual regulated by α-fetoprotein promoter and microRNA-122 target sequence. When HUMSCs homed to the tumor sites and differentiated into hepatocyte-like cells within tumor microenvironment, the CRAds were packaged and released strictly to the local tumor. Subsequently, the CRAd lysed tumor cells selectively with the post-infection regulation. The study showed the specific oncolytic effect of the CRAd to HCC cells and the production of the CRAd by differentiated HUMSCs in vitro. Furthermore, we proved the hepatocyte-like transformation of HUMSC in the microenvironment of orthotopic or heterotopic hepatoma. Finally, this therapeutic system exhibited dramatic tumor inhibition on both orthotopic and subcutaneous hepatic xenograft tumor model mice with less toxicity on normal organs. The study results have demonstrated that this targeted therapeutic strategy is a promising method to resolve the problem of postsurgical residuals and metastasis of HCC.

Practical Issues with the Use of Stem Cells for Cancer Gene Therapy

Stem cell-based drug delivery for cancer therapy has steadily gained momentum in the past decade as several studies have reported stem cells' inherent tropism towards tumors. Since this science is still in its early stages and there are many factors that could significantly impact tumor tropism of stem cells, some contradictory results have been observed. This review starts by examining a number of proof-of-concept studies that demonstrate the potential application of stem cells in cancer therapy. Studies that illustrate stem cells' tumor tropism and discuss the technical difficulties that could impact the therapeutic outcome are also highlighted. The discussion also emphasizes stem cell imaging/tracking, as it plays a crucial role in performing reliable dose-response studies and evaluating the therapeutic outcome of treatment protocols. In each section, the pros and cons associated with each method are highlighted, limitations are underlined, and potential solutions are discussed. The overall intention is to familiarize the reader with important practical issues related to stem cell cancer tropism and in vivo tracking, underline the shortcomings, and emphasize critical factors that need to be considered for effective translation of this science into the clinic.

Reprogramming of blood cells into induced pluripotent stem cells as a new cell source for cartilage repair

Background

An attempt was made to reprogram peripheral blood cells into human induced pluripotent stem cell (hiPSCs) as a new cell source for cartilage repair.

Methods

We generated chondrogenic lineage from human peripheral blood via hiPSCs using an integration-free method. Peripheral blood cells were either obtained from a human blood bank or freshly collected from volunteers. After transforming peripheral blood cells into iPSCs, the newly derived iPSCs were further characterized through karyotype analysis, pluripotency gene expression and cell differentiation ability. iPSCs were differentiated through multiple steps, including embryoid body formation, hiPSC-mesenchymal stem cell (MSC)-like cell expansion, and chondrogenic induction for 21 days. Chondrocyte phenotype was then assessed by morphological, histological and biochemical analysis, as well as the chondrogenic expression.

Results

hiPSCs derived from peripheral blood cells were successfully generated, and were characterized by fluorescent immunostaining of pluripotent markers and teratoma formation in vivo. Flow cytometric analysis showed that MSC markers CD73 and CD105 were present in monolayer cultured hiPSC–MSC-like cells. Both alcian blue and toluidine blue staining of hiPSC–MSC-chondrogenic pellets showed as positive. Immunohistochemistry of collagen II and X staining of the pellets were also positive. The sulfated glycosaminoglycan content was significantly increased, and the expression levels of the chondrogenic markers COL2, COL10, COL9 and AGGRECAN were significantly higher in chondrogenic pellets than in undifferentiated cells. These results indicated that peripheral blood cells could be a potential source for differentiation into chondrogenic lineage in vitro via generation of mesenchymal progenitor cells.

Conclusions

This study supports the potential applications of utilizing peripheral blood cells in generating seed cells for cartilage regenerative medicine in a patient-specific and cost-effective approach.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0290-7) contains supplementary material, which is available to authorized users.

Stem Cell-Based Cell Carrier for Targeted Oncolytic Virotherapy: Translational Opportunity and Open Questions

Oncolytic virotherapy for cancer is an innovative therapeutic option where the ability of a virus to promote cell lysis is harnessed and reprogrammed to selectively destroy cancer cells. Such treatment modalities exhibited antitumor activity in preclinical and clinical settings and appear to be well tolerated when tested in clinical trials. However, the clinical success of oncolytic virotherapy has been significantly hampered due to the inability to target systematic metastasis. This is partly due to the inability of the therapeutic virus to survive in the patient circulation, in order to target tumors at distant sites. An early study from various laboratories demonstrated that cells infected with oncolytic virus can protect the therapeutic payload form the host immune system as well as function as factories for virus production and enhance the therapeutic efficacy of oncolytic virus. While a variety of cell lineages possessed potential as cell carriers, copious investigation has established stem cells as a very attractive cell carrier system in oncolytic virotherapy. The ideal cell carrier desire to be susceptible to viral infection as well as support viral infection, maintain immunosuppressive properties to shield the loaded viruses from the host immune system, and most importantly possess an intrinsic tumor homing ability to deliver loaded viruses directly to the site of the metastasis—all qualities stem cells exhibit. In this review, we summarize the recent work in the development of stem cell-based carrier for oncolytic virotherapy, discuss the advantages and disadvantages of a variety of cell carriers, especially focusing on why stem cells have emerged as the leading candidate, and finally propose a future direction for stem cell-based targeted oncolytic virotherapy that involves its establishment as a viable treatment option for cancer patients in the clinical setting.

Mesenchymal Stem Cells Facilitate In Vitro Development of Human Preantral Follicle

Biological folliculogenesis is a lengthy and complicated process, and follicle growth microenvironment is poorly understood. Mesenchymal stem cells (MSCs) have been shown to establish a supportive microenvironment for wound repair, autoimmune diseases amelioration, and tumor development. Therefore, this study is aimed to investigate whether MSCs could help to reconstruct a microenvironment to facilitate the in vitro follicle development. Here we show human MSCs significantly promote the survival rates, increase the growth velocity, and improve the viability of preantral follicles in a dose-dependent manner. Further analyses reveal that growth differentiation factor 9 and bone morphogenetic protein 15 in oocytes and inhibin βA and transforming growth factor β1 in granulose cells within the follicles cocultured with MSCs express notably higher than those in the follicles cultured without MSCs. In summary, our findings demonstrate a previously unrecognized function of MSCs in promoting preantral follicle development and provide a useful strategy to optimize fertility preservation and restoration by facilitating in vitro follicle growth.

Mesenchymal stem cells as delivery vectors for anti-tumor therapy

Recent studies have demonstrated mesenchymal stem cells (MSCs) are able to migrate specifically to tumors and their metastatic sites when administered intravenously. This characteristic tumor tropism has opened up an emerging field to utilize MSCs as vectors to deliver anti-cancer agents for targeted therapies. Genetically engineered MSCs can specifically migrate to various tumors and locally secrete therapeutic proteins, such as interferon β (IFN-β) and IFN-γ, interleukin 12 and 24, tumor necrosis factor-related apoptosis inducing ligand (TRAIL) or suicide gene/enzyme prodrug. In addition, MSCs have also been engineered to deliver oncolytic viruses and drug-loaded nanoparticles. Here, we present the characteristics of MSCs, the current progress on MSC mediated anti-cancer agents delivery systems and the interaction between MSCs and tumors.

Bone marrow mesenchymal stem cells suppress metastatic tumor development in mouse by modulating immune system

Introduction

Bone marrow mesenchymal stem cells (BMSCs) have been studied extensively because of their potential use in clinical therapy, regenerative medicine, and tissue engineering. However, their application in tumor therapy remains yet in preclinical stage because of the distinct results from different researches and vagueness of their functional mechanism. In this study, the influence of BMSCs on tumor growth was observed and the potential mechanism was investigated.

Method

Two animal models, H22 ascitogenous hepatoma in BALb/c mouse and B16-F10 pulmonary metastatic melanoma in C57 mouse, were adopted in experience in vivo and treated with BMSCs by intravenous injection. The percentage of Gr-1⁺CD11b⁺ myeloid-derived suppressor cells (MDSCs) and IFN-γ⁺ T cells were observed in peripheral blood (PB) and bone marrow (BM) by Flow Cytometry. BMSCs were co-cultured in vitro with tumor cells and MDSCs in a tumor conditioned medium separately in order to illustrate the mechanism.

Results

Our results demonstrated that BMSCs treatment caused a delayed tumor growth and a prolonged survival in both tumor models, the homing fraction of BMSCs in BM was 2% - 5% in 24–72 hours after transfusion and the percentage of Gr-1⁺CD11b⁺ MDSCs was downregulated in peripheral blood and BM. Meanwhile, IFN-γ⁺ T lymphocytes in PB increased. In vitro co-culture showed that BMSCs inhibited the induction and proliferation of MDSCs in tumor conditioned medium, whereas they didn’t affect the proliferation of B16-F10 and H22 cells by in vitro co-culture. Both in vivo and in vitro results showed that BMSCs have a systemic suppressive effect on MDSCs.

Conclusion

Our data suggest that BMSCs has suppressive effect on tumor and is feasible to be applied in cancer treatment. BMSCs inhibiting MDSCs induction and proliferation is likely one of the mechanism.

Engineered adenoviruses combine enhanced oncolysis with improved virus production by mesenchymal stromal carrier cells

Oncolytic viruses have demonstrated in pre-clinical and clinical studies safety and a unique pleiotropic activity profile of tumor destruction. Yet, their delivery suffers from virus inactivation by blood components and sequestration to healthy tissues. Therefore, mesenchymal stromal cells (MSCs) have been applied as carrier cells for shielded virus delivery to tumors after ex vivo infection with oncolytic viruses. However, infection and particle production by MSCs have remained unsatisfying. Here, we report engineered oncolytic adenoviruses (OAds) for improved virus production and delivery by MSCs. OAds are uniquely amenable to molecular engineering, which has facilitated improved tumor cell destruction. But for MSC-mediated regimens, OAd engineering needs to achieve efficient infection and replication in both MSCs and tumor cells. We show that an Ad5/3 chimeric OAd capsid, containing the adenovirus serotype 3 cell-binding domain, strongly increases the entry into human bone marrow-derived MSCs and into established and primary pancreatic cancer cells. Further, we reveal that OAd with engineered post-entry functions-by deletion of the anti-apoptotic viral gene E1B19K or expression of the death ligand TRAIL--markedly increased virus titers released from MSCs, while MSC migration was not hampered. Finally, these virus modifications, or viral expression of FCU1 for local 5-FC prodrug activation, improved tumor cell killing implementing complementary cytotoxicity profiles in a panel of pancreatic cancer cell cultures. Together, our study establishes post-entry modification of OAd replication for improving virus delivery by carrier cells and suggests a panel of optimized OAds for future clinical development in personalized treatment of pancreatic cancer.

Mesenchymal Stem Cells Enhance Angiogenesis and Follicle Survival in Human Cryopreserved Ovarian Cortex Transplantation

Transplantation of cryopreserved ovarian tissue is a novel technique to restore endocrine function and fertility especially for cancer patients. However, the main obstacle of the technique is massive follicle loss as a result of ischemia in the process of transplantation. Mesenchymal stem cells (MSCs) have been acknowledged to play an important role in supporting angiogenesis and stabilizing long-lasting blood vessel networks through release of angiogenic factors and differentiation into pericytes and endothelial cells. This study is aimed to investigate whether MSCs could be applied to overcome the above obstacle to support the ovarian tissue survival in the transplantation. Here we show that human MSCs could enhance the expression level of VEGF, FGF2, and especially the level of angiogenin, significantly stimulate neovascularization, and increase blood perfusion of the grafts in the cryopreserved ovarian tissue transplantation. Further studies reveal that MSCs could notably reduce the apoptotic rates of primordial follicles and decrease follicle loss in the grafted ovarian tissues. In summary, our findings demonstrate a previously unrecognized function of MSCs in improving human ovarian tissue transplantation and provide a useful strategy to optimize fertility preservation and restoration.

Locally-delivered T-cell-derived cellular vehicles efficiently track and deliver adenovirus delta24-RGD to infiltrating glioma

Oncolytic adenoviral vectors are a promising alternative for the treatment of glioblastoma. Recent publications have demonstrated the advantages of shielding viral particles within cellular vehicles (CVs), which can be targeted towards the tumor microenvironment. Here, we studied T-cells, often having a natural capacity to target tumors, for their feasibility as a CV to deliver the oncolytic adenovirus, Delta24-RGD, to glioblastoma. The Jurkat T-cell line was assessed in co-culture with the glioblastoma stem cell (GSC) line, MGG8, for the optimal transfer conditions of Delta24-RGD in vitro. The effect of intraparenchymal and tail vein injections on intratumoral virus distribution and overall survival was addressed in an orthotopic glioma stem cell (GSC)-based xenograft model. Jurkat T-cells were demonstrated to facilitate the amplification and transfer of Delta24-RGD onto GSCs. Delta24-RGD dosing and incubation time were found to influence the migratory ability of T-cells towards GSCs. Injection of Delta24-RGD-loaded T-cells into the brains of GSC-bearing mice led to migration towards the tumor and dispersion of the virus within the tumor core and infiltrative zones. This occurred after injection into the ipsilateral hemisphere, as well as into the non-tumor-bearing hemisphere. We found that T-cell-mediated delivery of Delta24-RGD led to the inhibition of tumor growth compared to non-treated controls, resulting in prolonged survival (p = 0.007). Systemic administration of virus-loaded T-cells resulted in intratumoral viral delivery, albeit at low levels. Based on these findings, we conclude that T-cell-based CVs are a feasible approach to local Delta24-RGD delivery in glioblastoma, although efficient systemic targeting requires further improvement.

Advances in stem cells, induced pluripotent stem cells, and engineered cells: delivery vehicles for anti-glioma therapy

INTRODUCTION

A limitation of small molecule inhibitors, nanoparticles (NPs) and therapeutic adenoviruses is their incomplete distribution within the entirety of solid tumors such as malignant gliomas. Currently, cell-based carriers are making their way into the clinical setting as they offer the potential to selectively deliver many types of therapies to cancer cells.

AREAS COVERED

Here, we review the properties of stem cells, induced pluripotent stem cells and engineered cells that possess the tumor-tropic behavior necessary to serve as cell carriers. We also report on the different types of therapeutic agents that have been delivered to tumors by these cell carriers, including: i) therapeutic genes; ii) oncolytic viruses; iii) NPs; and iv) antibodies. The current challenges and future promises of cell-based drug delivery are also discussed.

EXPERT OPINION

While the emergence of stem cell-mediated therapy has resulted in promising preclinical results and a human clinical trial utilizing this approach is currently underway, there is still a need to optimize these delivery platforms. By improving the loading of therapeutic agents into stem cells and enhancing their migratory ability and persistence, significant improvements in targeted cancer therapy may be achieved.

The therapeutic potential of bone marrow-derived mesenchymal stromal cells on hepatocellular carcinoma

Mesenchymal stromal cells (MSCs) are more often obtained from adult and extraembryonic tissues, with the latter sources being likely better from a therapeutic perspective. MSCs show tropism towards inflamed or tumourigenic sites. Mechanisms involved in MSC recruitment into tumours are comprehensively analysed, including chemoattractant signalling axes, endothelial adhesion and transmigration. In addition, signals derived from hepatocellular carcinoma (HCC) tumour microenvironment and their influence in MSC tropism and tumour recruitment are dissected, as well as the present controversy regarding their influence on tumour growth and/or metastasis. Finally, evidences available on the use of MSCs and other selected progenitor/stem cells as vehicles of antitumourigenic genes are discussed. A better knowledge of the mechanisms involved in progenitor/stem cell recruitment to HCC tumours is proposed in order to enhance their tumour targeting which may result in improvements in cell-based gene therapy strategies.

Appraising iniparib, the PARP inhibitor that never was--what must we learn?

Several drugs targeting poly(ADP-ribose) polymerase (PARP) enzymes are under development. Responses have been observed in patients with germline mutations in BRCA1 and BRCA2, with further data supporting antitumour activity of PARP inhibitors in sporadic ovarian cancer. Strategies to identify other predictive biomarkers remain under investigation. Iniparib was purported to be a PARP inhibitor that showed promising results in randomized phase II trials in patients with triple-negative breast cancer. Negative results from a phase III study in this disease setting, however, tempered enthusiasm for this agent. Recently, data from in vitro experiments suggest that iniparib is not only structurally distinct from other described PARP inhibitors, but is also a poor inhibitor of PARP activity. In this context, the negative iniparib phase III data might have erroneously promulgated the notion that PARP inhibition is not an effective therapeutic strategy. Here, we scrutinize the development of iniparib from preclinical studies to registration trials, and identify and discuss the pitfalls in the development of anticancer drugs to prevent future late-stage trial failures.

Mesenchymal stem cells as delivery vehicle of porphyrin loaded nanoparticles: effective photoinduced in vitro killing of osteosarcoma

Mesenchymal stem cells (MSC) have the unique ability to home and engraft in tumor stroma. These features render them potentially a very useful tool as targeted delivery vehicles which can deliver therapeutic drugs to the tumor stroma. In the present study, we investigate whether fluorescent core-shell PMMA nanoparticles (FNPs) post-loaded with a photosensitizer, namely meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) and uploaded by MSC could trigger osteosarcoma (OS) cell death in vitro upon specific photoactivation. In co-culture studies we demonstrate using laser confocal microscopy and time lapse imaging, that only after laser irradiation MSC loaded with photosensitizer-coated fluorescent NPs (TPPS@FNPs) undergo cell death and release reactive oxygen species (ROS) which are sufficient to trigger cell death of all OS cells in the culture. These results encourage further studies aimed at proving the efficacy of this novel tri-component system for PDT applications.

Migratory properties of mesenchymal stem cells

Mesenchymal stem cells raise great expectations in regenerative medicine due to their capacity to regenerate damaged tissues, thereby restoring organ tissue integrity and functionality. Even though it is not yet clear how mesenchymal stem cells are guided to injured tissue it is generally assumed that the directed migration of these cells is facilitated by the same soluble factors that also recruit immune competent cells to inflamed tissue areas. Tumor tissue represents another type of (chronically) inflamed tissue and because of that mesenchymal stem cells are highly attracted. Although some data indicate that esenchymal stem cells might have a beneficial effect on tumor growth due to anti-tumor effects the plethora of data suggest that tumor tissue recruited mesenchymal stem cells rather promote tumor growth and metastasis formation. Nonetheless, the enhanced tumor tropism of mesenchymal stem cells makes them ideal candidates for novel anti-cancer strategies. Like Trojan Horses genetically modified mesenchymal stem cells will deliver their deadly cargo, such as anti-tumor cytokines or oncolytic viruses, into cancerous tissues, thereby destroying the tumor form within. In this chapter we will summarize the current concepts of genetic modification of mesenchymal stem cells for future anti-cancer therapies.