74. Specific Delivery of hTRAIL and Inhibition of Ewing's Sarcoma Growth by Transplantation of Viral Vector-Transduced Bone Marrow-Derived Mesenchymal Stem Cells (MSC)

Abstract

Top of pageAbstract For the majority of pediatric patients with soft tissue tumors, some form of selective systemic therapy is required. Here we show that bone marrow-derived non-hematopoietic mesenchymal stem cells (MSCs) integrate into pediatrics soft tissue sarcoma xenografts as stromal fibroblasts. Importantly, exogenously administered MSC preferentially engraft at the sites of disseminated tumor nodules throughout the body. These findings suggest the development of novel anti-cancer therapies based on the local production of biological agents by gene manipulated MSC. We show that human MSC can be effectively transduced with adenovirus type 5-based vectors and with vectors based on adeno-associated virus (AAV). The majority of AAV serotypes tested (AAV1/6, 2, 3, 4, 5, and 8) are capable of transducing hMSC, albeit with relatively low efficiencies. Vector modifications to the AAV capsid, such as the inclusion of the RGD-tripeptide motif in capsids of either AAV1 or AAV2-based vectors, or modification of the vector genome to generate |[ldquo]|double-stranded|[rdquo]|, or |[ldquo]|self-complementary|[rdquo]| AAV vectors, both lead to significant increases in AAV-mediated hMSC gene transduction. Here, we examined whether hMSC producing human TNF-related apoptosis inducing ligand (hTRAIL) (hTRAIL-MSC) can inhibit the growth of subcutaneous human Ewing's Sarcoma xenografts in nude mice. MSC were transduced with an hTRAIL expressing adenovirus, or AAV vector. These hTRAIL-MSC produced hTRAIL and could directly induce apoptosis of A673 Ewing's sarcoma cells in co-culture experiments in vitro. When co-injected with A673 sarcoma cells into the flanks of nude mice (1:2 ratio of hMSC to A673 sarcoma cells), all treated animals failed to develop tumors (n=5). Control animals co-injected with eGFP-MSC (Ad-eGFP transduced hMSC) and A673 sarcoma cells (n=5), or A673 sarcoma cells alone (n=10) all developed tumors. We then injected hTRAIL-MSC intravenously (IV) (single dose of 5 |[times]| 105 MSC) into nude mice bearing established subcutaneous A673 tumors; tumor growth was inhibited approximately 30% as compared to untreated controls, and as compared to controls treated with eGFP-MSC (n=5) (p=0.01). Immunohistochemical analysis of hTRAIL-MSC treated animals showed engraftment and differentiation of hMSC into myofibroblast-like tumor-associated stroma cells. IV injected hTRAIL-MSC prolonged the survival of mice bearing A673 Ewing sarcoma grafts as compared to untreated animals, or control (eGFP-MSC) treated animals. These data suggest that IV administered gene-modified MSC can inhibit the growth of pediatric soft tissue sarcomas. Importantly, the antitumor effects were only achieved when MSC were integrated into the tumor microenvironment, but not when MSC were injected subcutaneously into the opposite flank. Therefore, tumor inhibition required spatial proximity of MSC to the malignant cells. These findings suggest that TRAIL can serve as a direct inhibitor of tumor proliferation and suggest the use of gene-manipulated MSC for pediatric cancer therapy.