Bone Marrow Stroma-Derived Mesenchymal Cell Cultures from Nude/Nude Rat Showing Both Ex Vivo Differentiation Properties and High Metastatic Potential in Nude Mice.

Recent studies have revealed that stem cell like cancer cells can be isolated from different types of primary tumor tissue from brain, breast and skin. Such cells have high capability to form tumors when transplanted into experimental animals. Here we describe a newly developed nude rat mesenchymal stem cellS (rMSCs), which spontaneously changed in vivo properties during culturing. Rat bone marrow cells were isolated from the femur and tibia of a male nude/nude rat and cultured in DMEM medium supplemented with 20% bovine fetal serum (FCS). Non- adherent cells were removed after 72 hours of incubation and the adherent bone marrow cells were cultured until a confluent layer appeared. Adherent cells were detached by trypsin, washed and continued to be cultured. After 23 passages by high-density culture the rMSCs spontaneously became more homogenous and formed spheroids in three-dimensional culture. Following ex vivo culturing under different growth conditions these cells were still able to differentiate into fat and neural like cells. The rMSCs also contain high numbers of colony-forming-unit-fibroblasts(cfu-f). The “tumourigenic” growth pattern observed ex vivo prompted us to examine the rMSCs in vivo. Following subcutaneous injection of 1 x10⁶ cells into nude/nude mice a solid tumor appeared under the skin after 12 days. Moreover, intravenous injections and direct injections into left heart ventricle of rMSCs created solid tumors both in the lung, abdominal cavity, bone and skin. Both phenotypic and genetic characterization of early and late passages of the rMSCs and the tumors formed in the mice are being investigated and more details will be presented at the meeting.