Increased proliferation and chemosensitivity of human mesenchymal stromal cells expressing fusion yeast cytosine deaminase

Mesenchymal stromal cells (MSCs) are considered to be suitable vehicles for cellular therapy in various conditions. The expression of reporter and/or effector protein(s) enabled both the identification of MSCs within the organism and the exploitation in targeted tumor therapies. The aim of this study was to evaluate cellular changes induced by retrovirus-mediated transgene expression in MSCs in vitro. Human Adipose Tissue-derived MSCs (AT-MSCs) were transduced to express (i) the enhanced green fluorescent protein (EGFP) reporter transgene, (ii) the fusion yeast cytosine deaminase::uracil phosphoribosyltransferase (CDy::UPRT) enzyme along with the expression of dominant positive selection gene NeoR or (iii) the selection marker NeoR alone (MOCK). CDy::UPRT expression resulted in increased proliferation of CDy::UPRT-MSCs versus naïve AT-MSCs, MOCK-MSCs or EGFP-MSCs. Furthermore, CDy::UPRT-MSCs were significantly more sensitive to 5-fluorouracil (5FU), cisplatin, cyclophosphamide and cytosine arabinoside as determined by increased Caspase 3/7 activation and/or decreased relative proliferation. CDy::UPRT-MSCs in direct cocultures with breast cancer cells MDA-MB-231 increased tumor cell killing induced by low concentrations of 5FU. Our data demonstrated the changes in proliferation and chemoresistance in engineered MSCs expressing transgene with enzymatic function and suggested the possibilities for further augmentation of targeted MSC-mediated antitumor therapy.