Effects of blank PLLA particles, free ATRA, and ATRA-PLLA microparticles on viability of HuH7, PLC and L-02 cells after treating for the indicated times were assayed by MTT method, (a) Viability of HuH7 cells after treating with blank PLLA particles (0–0.5 mg/mL) for 72 h. Viability of HuH7 cells after treating with free ATRA or ATRA-PLLA particles (ATRA concentration ranging from 0 to 40 μM) for (b) 24 h, (c) 48 h, and (d) 72 h. (e) Viability of PLC cells after treating with blank PLLA particles (0–0.5 mg/mL) for 72 h. Viability of PLC cells after treating with free ATRA or ATRA-PLLA particles (ATRA concentration ranging from 0 to 40 μM) for (f) 24 h, (g) 48 h, and (h) 72 h. (I) Corresponding IC50 values of free ATRA and ATRA-PLLA particles for treating HuH7 or PLC cells for 72 h. Viability of L-02 cells after treating with free ATRA or ATRA-PLLA particles at a dose of (j) 10 μM and (k) 20 μM for the indicated times. (1) Expression of PIN1 in normal cultured HuH7, PLC and L-02 cells were determined by western blot analysis. β-Actin was used as an internal control. Each value is the mean ± standard deviation of triplicate determinations; *p < 0.05, **p < 0.01.