Fig. 4: The combination of MEKi/PARPi enhances the apoptotic death of MPM cells.

A Dose-response curves of MPM cells treated for 72 h with trametinib (MEKi) and olaparib (PARPi), alone or in combination. Data are shown as mean ± s.d. (n = 3). B Dose-response curves of the indicated MPM cells treated with trametinib and talazoparib (PARPi). Data are shown as mean ± s.d. (n = 3). C Clonogenic assay of MPM cells (BE261T, MSTO-211H, H2052) treated with trametinib and olaparib, alone or in combination (1–2 weeks). D Apoptotic assay of BE261T and MSTO-211H cells treated with MEKi (trametinib; 0.5 μM) and PARPi (olaparib; 5 μM), alone and in combination for 72 h. The percentage of early and late apoptotic cells, defined by Annexin V⁺/PI^- and Annexin V⁺/PI⁺ populations, respectively, were highlighted in red. E MEK1 knockdown (si-MAP2K1) sensitizes MPM cells to PARPi (olaparib). MPM cells transfected with si-scrambled or si-MAP2K1 (48 h post-transfection) were treated with MEKi/PARPi (trametinib, 0.1 μM; olaparib, 5 μM) for additional 72 h and subjected to viability assay. Scrambled siRNAs were used as control. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 by Welch’s t-test (compared with si-MAP2K1 + PARPi). F MEK1 overexpression compromises MEKi/PARPi efficacy. MPM cells transfected with control (GFP) or MEK1-GFP vectors were subjected to immunoblot analysis 48 h post-transfection or viability assay after being treated for 72 h with the MEKi/PARPi combination (trametinib, 0.1 μM; olaparib, 5 μM). ****p < 0.0001 by Welch’s t-test. G Viability assay of MPM cells treated with trametinib (0.1 µM) and olaparib (5 µM) (combination), in the absence or presence of the indicated inhibitors for 96 h. Q-VD-Oph (20 μM), pan-caspase inhibitor; necrostatin-1 (10 μM), necroptosis inhibitor; Fer-1 (2 μM), ferroptosis inhibitor; HCQ (5 μM), autophagy inhibitor. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 by one-way ANOVA.