In previous studies, we have demonstrated that replicating murine leukemia virus (RMLV)-based vectors can achieve highly efficient in vivo delivery of prodrug activating genes in glioblastoma models, with infection restricted to actively dividing tumor cells without spread to extratumoral sites, resulting in significantly prolonged survival upon prodrug administration; this approach is now being tested in a multi-center clinical trial.

RMLV vectors can eventually spread to almost all actively dividing GBM cells over time. We are seeking to further improve the efficiency of this novel therapeutic strategy by engineering human mesenchymal stem cells (MSC) to function as RMLV vector producer cells (MSC-VPC). Primary MSC have been shown to actively migrate through tumor masses beyond the immediate injection site and track to diffusely infiltrating tumor foci. In the present study, we developed optimized methods for engineering MSC-VPC, and we then further examined tumor transduction efficiency of MSC-mediated RMLV delivery, and how this delivery method might affect vector replication kinetics in vivo.

First, we evaluated the vector productivity of MSC-VPC in U87 human glioblastoma cells in vitro. Primary human MSCs were infected with RMLV vector AC3-GFP, expressing the GFP marker gene. These MSC were then re-plated at very low density onto a monolayer of naïve U87 glioma cells, and fluorescence was monitored over time. Under the fluorescent microscope, progressive spread of the RMLV vector released from the MSCs could be confirmed, as indicated by increasing GFP(+) U87 cells over time. Next, we tested MSC-VPC in intracranial U87 tumor models in vivo. Five days after intracranial tumor cell implantation, 1E3 transduction units (TU) of AC3-GFP vector or 5E3 MSC-VPC (∼20% pretransduced with AC3-GFP) were stereotactically injected at the tumor site. Tumors were harvested and digested on day 9 for FACS analysis to detect GFP expression. While the highest percentage of GFP(+) cells was 28.6% in the vector supernatant-treated group, up to 45% transduction efficiency was achieved in the MSC-VPC group. These results suggest the use of MSCs as tumor-homing carriers may be provide more efficient delivery of RMLV vectors in human glioma models.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5397. doi:10.1158/1538-7445.AM2011-5397