Effect of PDT on the viability and proliferation of HU-231 cells. (A) Effects of various photosensitizer (MPPa) concentrations (5, 10, 15 and 20 µmol/l) on the viability of HU-231 cells. (B) Effects of different activin receptor-like kinase-1 inhibitor (K02288) concentrations (2.5, 5, 10, 20 and 40 µmol/l) on HU-231 cell viability. (C) Cell viability under different light intensities (1.6, 3.2, 4, 8, 16 and 24 ×10−2 J/cm2). (D) Cell viability of the control group, PDT group, K02288 group and PDT + K02288 group. (E and F) Cell proliferation of the control, PDT, K02288 and PDT + K02288 groups (scale bars, 200 µm). (G and H): Proliferative ability of the cells in the four groups. The red colour represents the proliferating cells stained with EdU, and the blue colour represents all cells stained with Hoechst 33342 (scale bars, 20 µm). *P<0.05, **P<0.01, ***P<0.001 and ****P<0.0001. PDT, photodynamic therapy; MPPa, pyropheophorbide-a methyl ester.