fig6

Figure 6. PTTP-DC6 enhances DOX efficacy in drug-resistant cells and spheroids. (A) Cytotoxicity of DOX to MCF-7/ADR cells after PTTP-DC6 (1 μM, 24 h) treatment under dark or light irradiation (525 nm, 0.2 mW·cm^-2, 30 min) (one-way ANOVA with Tukey’s test, ^***P < 0.001); (B) Relative viability rates of PTTP-D6-treated group under dark or light irradiation referring to viabilities of control group treated with DOX only. V: The cell viability of combinations, V_DOX: the cell viability of DOX only, V₀, V_DOX,0: the cell viability in the 0 μM DOX group; (C) In vitro cytotoxicity of DOX (100 μg·mL^-1) to MCF-7/ADR cell spheroids for 48 h with or without the pretreatment of PTTP-DC6 (5 μM, 24 h) and the followed irradiation of a 525 nm LED light (1 mW·cm^-2, 30 min) (one-way ANOVA with Tukey’s test, ^***P < 0.001); (D) Representative bright-field images of MCF-7/ADR cell spheroids with different treatments on day 0 and day 3. Scale bar: 200 µm; (E) Corresponding SEM images of MCF-7/ADR cell spheroids of various treatment conditions on day 3. Scale bar: 10 µm. Data presented as mean ± SD. PTTP-DC6: Benzene-pyridothiadiazole-thienothiophene-pyridothiadiazole-benzene conjugated framework with quaternary ammonium-terminated C6 alkyl chains at both ends; DOX: doxorubicin; MCF-7/ADR: Michigan Cancer Foundation-7/adriamycin-resistant; ANOVA: analysis of variance; LED: light emitting diode; SEM: scanning electron microscope; SD: standard deviation.