Priming of bone marrow stromal cells with the epigenetic modifier decitabine overcomes stroma-mediated resistance to bortezomib in multiple myeloma cells.

Abstract Title of the project Priming of bone marrow stromal cells with the epigenetic modifier decitabine overcomes stroma-mediated resistance to bortezomib in multiple myeloma cells. Introduction. In multiple myeloma (MM), the malignant plasma cells reside in the bone marrow microenvironment. Within this environment, MM cells are protected against anti-myeloma drugs through interaction with bone marrow mesenchymal stromal cells (MSCs). This form of stroma-mediated protection may partly explain poor treatment response in some MM patients. One approach to overcome this resistance is using a combination of drugs which target both the cancer cells and disrupt the above interaction at the same time. In this project we investigated whether pre-treatment (priming) of MSCs with an epigenetic modifier decitabine could overcome the above resistance when MM cells are exposed to the anti-myeloma drug bortezomib (BTZ). Methods. The luciferase-tagged MM cell line (U266) and the bone marrow MSC line (HS.5) were cultivated and maintained in their specific culture media. First, HS.5 cells were seeded on 96-well plates and treated with different doses of decitabine for 24h. Then, the decitabine was removed and wells washed, U266 cells were added on top of the HS.5 cells (co-culture), BTZ was added to the wells and plate incubation continued for another 24h. Finally, luminescence of the 96-well plate was measured using a luminescence plate reader to calculate % cytotoxicity. Results. MM cells' death by BTZ was the highest in the absence of HS.5 cells (n=3, mean=67%), however, it was significantly reduced when MM cells were co-cultured with HS.5 cells (n=3, mean=44.5%, p<0.001) implying stroma-induced drug resistance. On the other hand, when HS.5 cells were primed with decitabine, cell death in MM cells was increased to the level close to MM cells' death in monoculture (n=3, mean= 63.5%, p=0.171) indicating rescue effect of decitabine treatment of HS.5 cells.Conclusions. Our findings indicate that MSCs may at least partly employ an epigenetic mechanism to induce resistance to drugs in MM cells via direct interaction with latter cells. However, further investigation is ongoing to establish whether this could be a potential underlying mechanism.