Figure 2. Polymeric particles conjugated to tumour cell surface amplify TRAIL-mediated apoptosis in the presence of fluid shear stress.

(a) Schematic of polymeric particles acting as mechanical amplifiers by increasing TRAIL-mediated tumour cell apoptosis in presence of a fluid shear force. (b) Brightfield micrographs of particle-functionalized COLO 205 tumour cells after 30 min of exposure to various treatment conditions. TRAIL-treated samples incubated with 0.1 μg ml⁻¹ TRAIL for 30 min. Sheared samples were exposed to a fluid shear stress of 4.0 dyn cm⁻². Tumour cells were treated with 240 PS (500 nm diameter) particles per tumour cell before exposure to TRAIL and fluid shear stress. Insets denote viable and apoptotic tumour cells after treatment conditions. Scale bar, 30 μm. (c,d) Viability of particle-functionalized COLO 205 (c) and PC-3 (d) tumour cells after treatment with TRAIL (0.1 μg ml⁻¹) in the presence of fluid shear stress. N=4 per treatment. (e) Viability of particle-functionalized, TRAIL-resistant HT29 tumour cells after treatment with TRAIL (0.1 μg ml⁻¹) in the presence of fluid shear stress for 6 h. For combination therapies, cells were treated with 15 μM piperlongumine (PL) in addition to TRAIL (0.1 μg ml⁻¹). N=4 per treatment. (f) Viability of particle-functionalized COLO 205 tumour cells after treatment with doxorubicin (DOX; concentration: 20 μM) in the presence of fluid shear stress. N=4 per treatment. Particle diameter: 500 nm. (g,h) Annexin-V/propidium iodide (PI) flow cytometry plots of nonfunctionalized (g) and particle (500 nm)-functionalized (h) PC-3 tumour cells after treatment with TRAIL (0.1 μg ml⁻¹) in the presence of static conditions and fluid shear stress, respectively. Particle diameter: 500 nm. N=5 per treatment. (i,j) Percentage of annexin-V+, particle-functionalized COLO 205 (i) and PC-3 (j) tumour cells after treatment with TRAIL (0.1 μg ml⁻¹) in the presence of fluid shear stress. N=5 per treatment. (k) Viability of biodegradable PLGA particle-functionalized COLO 205 tumour cells after treatment with TRAIL (0.1 μg ml⁻¹) in the presence of fluid shear stress. Data are reported as the mean±s.e. Different treatment groups were compared for statistical significance using Student's two-tailed t-test. Particle diameter: 500 nm. N=5 per treatment. *P<0.05, **P<0.01 and ***P<0.001. NS, not significant.