Since, on the one hand, MRPs affect the intracellular concentrations of cAMP and cGMP [16] and, on the other hand, MRP inhibitors were shown to sensitise glioblastoma cells to the cytotoxic action of other drugs [19,20], we investigated the effect of treatments with PF-2545920 and/or MY-5445 in combination with MRP1 inhibitors MK-571 and reversan on glioblastoma cells (Figure 6). The gene discussed is ABCC1; the disease is glioblastoma.