PGP and glioma: The combination group wasn't effective in the inhibition of P-gp levels, however Spiegl-Kreinecker et al. found that a considerable expression of P-gp was relatively rare in glioma cells, in contrast to MRP-1 which was constitutively overexpressed in cells derived from astrocytomas as well as GBMs as T98G and SW1088 cells [29].