Modulation of matrix elasticity with PEG hydrogels to study melanoma drug responsiveness

Metastatic melanoma is highly resistant to drug treatment, and the underlying mechanisms of this resistance remain unclear. Increased tissue stiffness is correlated with tumor progression, but whether increased tissue stiffness contributes to treatment resistance in melanoma is not known. To investigate the effect of substrate stiffness on melanoma cell treatment responsiveness, PEG hydrogels were utilized as a cell culture system to precisely vary matrix elasticity and investigate melanoma cell responses to a commercially available pharmacological inhibitor (PLX4032). The tensile moduli were varied between 0.6 and 13.1 kPa (E) and the effects of PLX4032 on metabolic activity, apoptosis, and proliferation were evaluated on human cell lines derived from radial growth phase (WM35) and metastatic melanoma (A375). The A375 cells were found to be stiffness-independent; matrix elasticity did not alter cell morphology or apoptosis with PLX4032 treatment. The WM35 cells, however, were more dependent on substrate modulus, displaying increased apoptosis and smaller focal adhesions on compliant substrates. Culturing melanoma cells on PEG hydrogels revealed stage-dependent responses to PLX4032 that would have otherwise been masked if cultured strictly on TCPS. These findings demonstrate the utility of PEG hydrogels as a versatile in vitro culture platform with which to investigate the molecular mechanisms of melanoma biology and treatment responsiveness.