Differential effects of MAPK pathway inhibitors on migration and invasiveness of BRAFV600E mutant thyroid cancer cells in 2D and 3D culture

• Compartmentalized invasion model of BRAFV600E mutant thyroid cancer cells.
• Differential response to MAPK inhibitors of 2D/3D cultured tumor cells.
• Rebound MEK/ERK activation does not abrogate growth inhibition by PLX4720.
• Dual treatment with RAF and MEK inhibitors does not prevent tumor cell invasion.

Tumor microenvironment influences targeted drug therapy. In this study we compared drug responses to RAF and MEK inhibitors on tumor cell migration in 2D and 3D culture of BRAFV600E mutant cell lines derived from human papillary (BCPAP) and anaplastic (SW1736) thyroid carcinomas. Scratch wounding was compared to a double-layered collagen gel model developed for analysis of directed tumor cell invasion during prolonged culture. In BCPAP both PLX4720 and U0126 inhibited growth and migration in 2D and decreased tumor cell survival in 3D. In SW1736 drugs had no effect on migration in 2D but decreased invasion in 3D, however this related to reduced growth. Dual inhibition of BRAFV600E and MEK reduced but did not prevent SW1736 invasion although rebound phosphorylation of ERK in response to PLX4720 was blocked by U0126. These findings indicate that anti-tumor drug effects in vitro differ depending on culture conditions (2D vs. 3D) and that the invasive features of anaplastic thyroid cancer depend on non-MEK mechanism(s).