A 3-Dimensional Co-Culture Model to Investigate Adhesion-Mediated Drug Resistance in Multiple Myeloma

In multiple myeloma (MM), evidence suggests that the adhesion of malignant plasma cells to bone marrow microenvironment elements is central to MM growth and drug resistance, otherwise referred to as adhesion–mediated drug resistance. As other investigators have shown, the MM-stroma interaction is in part mediated by adhesion molecules like N-cadherin.

To develop a 3-dimensional MM in vitro co-culture model where MM cells interact with stromal elements mimicking the bone marrow microenvironment and use the model to investigate N-cadherin mediated drug resistance.

We co-cultured U266 cells, a MM cell line, with mesenchymal stromal cells (MSCs) isolated from Wharton's jelly (WJ) in a synthetic copolymer (polyglycolic acid/ poly L-lactic acid 90/10 copolymer) (3-dimensional culture conditions). For controls, we cultured U266 cells over a monolayer of WJMCS (2-dimensional conditions) or U266 cells in suspension. Cell proliferation was measured by Ki-67 immunohistochemistry (IHC) stain and lambda light chain expression was measure by enzyme-linked immunosorbent assay (ELISA) and IHC stains. Bortezomib in 1, 5, and 10 nM concentrations was used to treat U266 cells for 24 hours under the three culture conditions. Cytotoxicity was measured by modified Alamar Blue assay.

U266 cells in our 3-D model adhered to stromal cells and formed clusters close to matrix material. U266 cells proliferated as evidenced by positive Ki-67 stain, and expressed lambda light chain by IHC and ELISA. Lambda light expression measured by ELISA peaked at 1 week of co-culture in the 3-D model. Though N-cadherin was expressed in both stromal cells and U266 MM cells in 3-D, it was expressed only in stromal cells in 2-D culture conditions. Finally, pre-incubating U266 cells with N-cadherin blocking antibody resulted in less population of the 3-D model by U266 MM cells. Treatment of U266 with bortezomib resulted in less cell cytotoxicity in 3-D and 2-D co-culture conditions compared to U266 cells treated in suspension.

Using a 3-D in vitro co-culture model, we demonstrated that only 3-D co-culture conditions resulted in N-cadherin expression in U266 MM cell line. We also demonstrated that U266 population of the 3-D model was successfully blocked using an N-cadherin blocking antibody. We propose N-cadherin mediated adhesion as a mechanism to explain reduced cytotoxicity to bortezomib in 3-D. We propose this model to be used to investigate adhesion-mediated drug resistance.

No relevant conflicts of interest to declare.