PEG-peptide hydrogels reveal differential effects of matrix microenvironmental cues on melanoma drug sensitivity.

Metastatic melanoma is highly drug resistant, though the exact mechanisms of this resistance are not completely understood. One method to study melanoma drug responsiveness in vitro is through the use of multicellular spheroids, which have been found to exhibit decreased drug sensitivity compared to traditional 2D culture on various substrates. Because it is unclear whether dimensionality, cell-matrix interactions, and/or cell-cell contacts may influence melanoma drug responsiveness, we utilized a synthetic PEG-based hydrogel to compare the responses of cells cultured on top of or encapsulated within matrices with the same adhesive ligand density, polymer density, and material properties. We found that depending on the stage of progression at which the melanoma cells were derived, the cells responded differently to PLX4032 treatment, a commercially available melanoma drug. In particular, early stage WM35 cells were insensitive to dimensionality (i.e., 2D versus 3D culture), while metastatic A375 cells exhibited decreased responsiveness in 3D compared to 2D. To further understand the role of the microenvironment in early stage melanoma cells, we tested single WM35 cells and multicellular WM35 spheroids in 3D. The results revealed that the spheroids were similarly sensitive to PLX4032 treatment compared to single cell encapsulations. Collectively, this study implicates the role that 3D microenvironments (i.e., dimensionality) may play in observed melanoma drug responsiveness, and the potential lack of influence of cell-matrix interactions over cell-cell contacts in early stages of melanoma resistance to PLX4032-induced apoptosis.