Studies of Tumor and MSCs Interactions

Eradication of cancer, especially when it has metastasized is extremely difficult and conventional cancer therapies are simply unable to specifically target tumors/cancers, thus causing unwanted side effects and complications. Recently, it has been shown that bone marrow mesenchymal stem cells (MSCs) are able to migrate specifically to tumors and contribute to the formation of tumor-associated stroma. The aims of the current study are: (1) to study the role and fate of MSCs homed into the tumors; (2) to establish human bone marrow MSCs that stably express the TK genes; (3) to investigate the methods that enhance the anti-tumor efficiency of TKMSCs.;In this study, bone marrow-derived mesenchymal stem cells from mice or human fetus were isolated and characterized. Effects of BM-MSCs on tumor cell proliferation in vitro were analyzed in a co-culture system with mouse breast cancer cell 4T1 cells. Both co-culture with BM-MSCs and treatment with MSC-conditioned medium led to enhanced growth of 4T1 cells. Co-injection of 4T1 cells and MSCs into nude mice led to increased tumor size compared with injection of 4T1 cells alone. Identical experiments using human prostate cancer cell DU145 cells and hBM-MSCs instead of 4T1 cells and mBM-MSCs yielded similar results. These results indicate that MSCs promote tumor growth both in vitro and in vivo and suggest that tumor promotion in vivo may be attributable in part to enhanced angiogenesis.;Immortalized human fetal bone marrow-derived MSCs (hfBMSCs) expressing herpes simplex virus thymidie kinase was established by conventional lentiviral transduction method. Functional expression of TK was evaluated by cytotoxicity in the presence of its prodrug GCV. SV40-TK-hfBMSCs exhibited comparable proliferation, surface phenotype expression, multi-differentiation potential and tumor-tropic migration ability as hfBMSCs. By measurement of tumor volume, repeated injection of the SV40-TK-hfBMSCs and subsequent consecutive GCV administration could suppress tumor growth in DU145 or PC3 human prostate tumor xenograft nude mice model without causing weight loss. However, its clinical applications are still limited. Alternative strategies have been pursued in this study by the use of combination therapy with cytotoxic chemotherapy to improve the overall efficacy of the TKhfBMSCs/ GCV system.;TK-hfBMSCs/GCV was evaluated alone or combined with low-dose doxorubicin in human prostate carcinoma DU145 xenografts in nude mice, testing for effects on local growth and overall survival. Tissues were evaluated through immunofluorescence and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining (TUNEL) for treatment effects on tumor cell proliferation and apoptosis. Transwell migration assay was used to access the migration ability of TK-hfBMSCs to tumor cells upon doxorubicin treatment and caspase-3 activity was conducted for test the tumor cells apoptosis under TK-hfBMSCs/GCV, doxorubicine, or combination of the two compound treatments respectively. Only minimal growth inhibition was observed in DU145 after treatment with TK-hfBMSCs/GCV or doxorubicin alone at doses and time points as indicated. In contrast, the combination of both agents resulted in a significant growth inhibition. Caspase-3, plays a central role in the execution-phase of cell apoptosis, was increased by TK-hfBMSCs/GCV or doxorubicine and also to a much greater extent by the combination treatment. Treatment by TK-hfBMSCs/GCV resulted in only a slight decrease in tumor growth compared with controls. Treatment with low-dose doxorubicin alone resulted in a small, nonstatistically significant decrease in tumor growth; In contrast, combined low-dose doxorubicin and TKhfBMSCs/ GCV was markedly inhibitory compared with control, doxorubicin alone, or TK-hfBMSCs/GCV alone. During the whole treatment process, no significant weight loss was observed. Furthermore, combined therapy induced increased area of necrosis, significant apoptosis and decreased tumor cell proliferation in treated tumors. Taken together, low dosage of doxorubicin could be used in combination with TKhfBMSCs based suicide gene therapy. (Abstract shortened by UMI.).