Establishment and characterization of a new murine cell line (SR-4987) derived from marrow stromal cells

Mesenchymal stromal cells loaded with paclitaxel induce cytotoxic damage in glioblastoma brain xenografts

INTRODUCTION

The goal of cancer chemotherapy is targeting tumor cells and/or tumor-associated microvessels with the lowest systemic toxicity. Mesenchymal stromal cells (MSCs) are promising vehicles for selective drug delivery due to their peculiar ability to home to pathological tissues. We previously showed that MSCs are able to uptake and subsequently to release the chemotherapeutic compound Paclitaxel (PTX) and to impair the growth of subcutaneous glioblastoma multiforme (GBM) xenografts. Here we used an orthotopic GBM model 1) to assess whether PTX-loaded MSCs (PTX-MSCs) retain a tropism towards the tumor cells in the brain context, and 2) to characterize the cytotoxic damage induced by MSCs-driven PTX release in the tumor microenvironment.

METHODS

U87MG GBM cells were fluorescently labeled with the mCherry protein and grafted onto the brain of immunosuppressed rats. In adjacent brain regions, we injected green fluorescent protein-expressing murine MSCs, either loaded with PTX or unloaded. After 1 week survival, the xenografted brain was assessed by confocal microscopy for PTX-induced cell damage.

RESULTS

Overall, MSCs showed remarkable tropism towards the tumor. In rats grafted with PTX-MSCs, the nuclei of U87MG cells showed changes that are typically induced by PTX, including multi-spindle mitoses, centrosome number alterations, and nuclear fragmentation. Multi-spindle mitoses resulted in multinucleated cells that were significantly higher in tumors co-grafted with PTX-MSCs than in controls. Nuclear changes did not occur in astrocytes and neurons surrounding the tumor.

CONCLUSIONS

MSCs appear particularly suited for anti-neoplastic drug delivery in the brain since PTX-specific damage of GBM cells can be achieved avoiding side effects to the normal tissue.

Paclitaxel is incorporated by mesenchymal stromal cells and released in exosomes that inhibit in vitro tumor growth: a new approach for drug delivery

Mesenchymal stromal cells (MSCs) have been proposed for delivering anticancer agents because of their ability to home in on tumor microenvironment. We found that MSCs can acquire strong anti-tumor activity after priming with Paclitaxel (PTX) through their capacity to uptake and then release the drug. Because MSCs secrete a high amount of membrane microvesicles (MVs), we here investigated the role of MVs in the releasing mechanism of PTX. The murine SR4987 line was used as MSC model. The release of PTX from SR4987 in the conditioned medium (CM) was checked by HPLC and the anti-tumor activity of both CM and MVs was tested on the human pancreatic cell line CFPAC-1. MVs were isolated by ultracentrifugation, analyzed by transmission (TEM) and scanning electron microscopy (SEM), and the presence of PTX by the Fourier transformed infrared (FTIR) microspectroscopy. SR4987 loaded with PTX (SR4987PTX) secreted a significant amount of PTX and their CM possessed strong anti-proliferative activity on CFPAC-1. At TEM and SEM, SR4987PTX showed an increased number of "vacuole-like" structures and shed a relevant number of MVs, but did not differ from untreated SR4987. However, SR4987PTX-derived-MVs (SR4987PTX-MVs) demonstrated a strong anti proliferative activity on CFPAC-1. FTIR analysis of SR4987PTX-MVs showed the presence of an absorption spectrum in the corresponding regions of the PTX marker, absent in MVs from SR4987. Our work is the first demonstration that MSCs are able to package and deliver active drugs through their MVs, suggesting the possibility of using MSCs as a factory to develop drugs with a higher cell-target specificity.

Large-scale in-vitro expansion of RBCs from hematopoietic stem cells

The quest for RBCs in transfusion medicine has prompted scientists to explore the large-scale expansion of human RBCs from various sources. The successful production of RBCs in the laboratory depends on the selection of potential cell source, optimized culture, bio-physiological parameters, clinically applicable culture media that yields a scalable, contamination-free, non-reactive, non-tumorogenic, stable and functional end product. The expansion protocol considering the in vivo factors involved in homeostasis can generate a cost-effective and readily available cell source for transfusion. This review paper discusses several approaches used to expand RBCs from various sources of stem cells.

Mesenchymal stromal cells primed with paclitaxel provide a new approach for cancer therapy

BACKGROUND

Mesenchymal stromal cells may represent an ideal candidate to deliver anti-cancer drugs. In a previous study, we demonstrated that exposure of mouse bone marrow derived stromal cells to Doxorubicin led them to acquire anti-proliferative potential towards co-cultured haematopoietic stem cells (HSCs). We thus hypothesized whether freshly isolated human bone marrow Mesenchymal stem cells (hMSCs) and mature murine stromal cells (SR4987 line) primed in vitro with anti-cancer drugs and then localized near cancer cells, could inhibit proliferation.

METHODS AND PRINCIPAL FINDINGS

Paclitaxel (PTX) was used to prime culture of hMSCs and SR4987. Incorporation of PTX into hMSCs was studied by using FICT-labelled-PTX and analyzed by FACS and confocal microscopy. Release of PTX in culture medium by PTX primed hMSCs (hMSCsPTX) was investigated by HPLC. Culture of Endothelial cells (ECs) and aorta ring assay were used to test the anti-angiogenic activity of hMSCsPTX and PTX primed SR4987(SR4987PTX), while anti-tumor activity was tested in vitro on the proliferation of different tumor cell lines and in vivo by co-transplanting hMSCsPTX and SR4987PTX with cancer cells in mice. Nevertheless, despite a loss of cells due to chemo-induced apoptosis, both hMSCs and SR4987 were able to rapidly incorporate PTX and could slowly release PTX in the culture medium in a time dependent manner. PTX primed cells acquired a potent anti-tumor and anti-angiogenic activity in vitro that was dose dependent, and demonstrable by using their conditioned medium or by co-culture assay. Finally, hMSCsPTX and SR4987PTX co-injected with human cancer cells (DU145 and U87MG) and mouse melanoma cells (B16) in immunodeficient and in syngenic mice significantly delayed tumor takes and reduced tumor growth.

CONCLUSIONS

These data demonstrate, for the first time, that without any genetic manipulation, mesenchymal stromal cells can uptake and subsequently slowly release PTX. This may lead to potential new tools to increase efficacy of cancer therapy.

Cell processing engineering for ex-vivo expansion of hematopoietic cells

The cell processing engineering for ex vivo expansion of hematopoietic cells is reviewed. All hematopoietic cells of different lineages and/or at various stages of differentiation are derived from the same precursor, pluripotent hematopoietic stem cells. Bone marrow stromal cells promote and regulate the self-renewal, commitment, differentiation, and proliferation of stem cells and progenitors through their secreted extracellular matrices and cytokine environment in the hematopoietic microenvironment. Although stroma-mediated hematopoiesis has been studied in vitro using the Dexter culture system in tissue culture flasks, hematopoiesis in the Dexter culture system is almost limited to a granulocyte lineage and the system could not expand primitive cells. The addition of large amounts of cytokines to the culture of hematopoietic cells enabled their expansion, but is too expensive. Some clonal stromal cell lines have been established from the Dexter culture of murine bone marrow cells in order to simplify and stimulate the ex vivo expansion of hematopoietic cells. In order to solve the problem regarding the usage of exogeneic stromal cell lines, a novel membrane-separated coculture system, in which stromal cells adhere onto the lower surface of a porous membrane and hematopoietic cells are incubated on the upper surface of the membrane, was proposed. In order to mimic the contact between stromal and hematopoietic cells in vivo in the bone marrow, several types of three-dimensional (3-D) culture of hematopoietic cells were developed. The 3-D coculture of hematopoietic cells with spatial development of stromal cells in nonwoven fabrics enabled the expansion of progenitors without cytokine addition. Progenitors in cord blood mononucleated cells were also successfully expanded without the addition in the 3-D coculture with primary human bone marrow stromal cells in 3-D. Heparin addition to the 3-D coculture and coating the nonwoven fabrics with N-(O-beta-(6-O-sulfogalactopyranosyl)-6-oxyhexyl)-3,5-bis(dodecyloxy)-benzamide further increased the number of progenitors.

Metabolism of doxorubicin in long-term bone marrow cultures and SR-4987 stromal established cell line

The metabolism of doxorubicin was studied in murine long-term bone marrow cultures (LTBMC) and in SR-4987 established stromal cells in comparison with primary cultures of murine and rat hepatocytes. The toxicity of metabolites was verified by testing their effects on the clonogenicity of granulo-macrophage progenitors. Metabolic activity was compared in subcellular fractions of SR-4987 cells and murine hepatocytes. Doxorubicin was transformed in long-term bone marrow cultures, SR-4987 cells and murine/rat hepatocytes to less toxic metabolites: 13-OH doxorubicin and a less polar metabolite which were non-toxic on granulo-macrophage progenitors. Among the hemopoietic compartments, stromal cells were responsible for the biotransformation of doxorubicin. The capability of the SR-4987 established stromal cell line to metabolize doxorubicin was higher than that of primary cultures of hepatocytes and bone marrow, and the highest activity was concentrated in the microsomes. These results suggest that in vitro models using primary cell cultures and established cell lines could be a useful tool for investigating the mechanisms underlying detoxification in the bone marrow stromal population.

Spatial development of the cultivation of a bone marrow stromal cell line in porous carriers

The spatial development of the cultivation of a bone marrow stromal cell line (SR-4987) in porous carriers was investigated in order to construct a three-dimensional hematopoietic culture system. Low-rate continuous agitation, 20 rpm, was an appropriate method to achieve initial adhesion of cells onto a cellulose porous beads (CPB, 100 mum pore diameter) in a spinner bottle, compared with other methods such as centrifugation and intermittent agitation. Cell growth with continuous agitation at 70 rpm after initial cell adhesion was not inferior to that at 20 rpm. A 2- and 10-fold increase in the inoculum cell concentration for CPB and another type of porous cellulose beads (Micro-cube (MC), 500 mum pore diameter) resulted in a 1.2- and 2-fold increase in final cell concentrationm, respectively. Cells attached to the MC beads and a polyester nonwoven dic (Fibra-cell (FC)) could grow and spread well on the carriers and a fibroblast-like shape was observed under scanning electron microscopy while the cells on CPB were globular. The flatness and inner surface area of these carriers may be the reason for the differences in cell morphology.

Role of SR-4987 stromal cells in the modulation of doxorubicin toxicity to in vitro granulocyte-macrophage progenitors (CFU-GM)

Bone marrow stromal microenvironment is essential for the maintenance of the hematopoietic stem cell renewal both by cell-cell interaction and cytokine production. However, stromal cells also exhibit drug metabolizing activities and they may accumulate the drug and successively affect hematopoietic progenitors by a retarded release. Our study investigated the role of both primary culture of murine bone marrow stroma and established stromal cells (SR-4987) in modulating the "in vitro" toxic activity of Doxorubicin (DXR) against murine granulocyte-macrophage progenitors (CFU-GM). The main part of the study has been performed by a "in vitro" agar bilayer technique based on the CFU-GM assay performed over a feederlayer of stromal cells. The results suggest that bone marrow stromal cells play also an important role in decreasing the toxicity of Doxorubicin. Further SR-4987 stromal cells produce a Doxorubicin metabolite (not belonging to the series of metabolites described in literature) which is completely ineffective in inhibiting the growth of CFU-GM and the activity of topoisomerase I. Our data suggest that bone marrow stromal cells must be considered as a cell population having opposite pharmacological roles in modulating the drug toxicity on hematopoietic progenitors. In our model a mechanism of detoxification concerns the capacity of SR-4987 stromal cells to inactivate the drug. For a better prediction of drug hematotoxicity, it is very important to develop "in vitro" cell models able to discriminate between positive and negative modulation of drug toxicity that stromal cells can exert in the bone marrow microenvironment.

Induction of murine macrophage growth by oxidized low density lipoprotein is mediated by granulocyte macrophage colony-stimulating factor

We have examined whether certain secreted factor(s) is involved in oxidized low density lipoprotein (Ox-LDL)-induced murine macrophage growth. An antibody against granulocyte-macrophage colony-stimulating factor (GM-CSF) effectively inhibited Ox-LDL-induced macrophage growth by >80%. Ox-LDL as well as phospholipase A2-treated acetylated LDL enhanced mRNA levels and protein release of GM-CSF from macrophages, while neither acetylated LDL nor lysophosphatidylcholine (lyso-PC) showed such effects. The maximal induction of GM-CSF by Ox-LDL was noted at 4 h, followed by a time-dependent decrease to a basal level within 24 h. Ox-LDL-induced macrophage growth was inhibited by 75% by replacement of the culture medium at 24 h by a fresh medium containing the same concentration of Ox-LDL, when GM-CSF had already returned to the basal level. Thus, a cytokine(s) other than GM-CSF is also expected to participate in Ox-LDL-induced macrophage growth in a later phase. The Ox-LDL-induced GM-CSF release was inhibited by calphostin C, a protein kinase C inhibitor, and was significantly reduced in macrophages from the knockout mice lacking class A, type I and type II macrophage scavenger receptors (MSR-AI/AII). These results taken together indicate that effective endocytosis of lyso-PC of Ox-LDL by macrophages through MSR-AI/AII and subsequent protein kinase C activation have led to GM-CSF release into the medium which may play a priming role in conjunction with other cytokines in Ox-LDL-induced macrophage growth.

In vitro myelotoxicity of environmental contaminants

Myelotoxicity of pesticides and algal toxins was detected in vitro by using the granulocyte-macrophage colony forming unit assay (CFU-GM), and the MTT test with SR-4987 cells, an established stromal cell line derived from a long term murine bone marrow culture, which may represent a suitable in vitro model for studying haematotoxicity. Comparison of the IC50s and NOELs obtained with the CFU-GM assay and those determined by testing the established stromal cells in the MTT cytotoxicity test indicate that inhibition of the proliferation of SR-4987 stromal cells is a sensitive in vitro endpoint for measuring myelotoxicity. It is suggested that this assay could be used as rapid and easy screening test for determining the haematotoxicity of environmental toxins. A comparison with results obtained with the MTT test on a non-differentiated cell line, 3T3-L1, was carried out to distinguish between non-specific interference with cell proliferation and specific toxicity on haemopoietic cells.