BACKGROUND: Most pancreatic carcinomas are clinically insensitive to chemotherapeutics. The exact mechanisms of their apoptosis and multiple drug resistance are obscure at present. This study was undertaken to explore the influence of chemotherapy on anti-proliferation, apoptosis and the cell cycle, and lay a fundamental basis for further research into the apoptotic mechanisms and prevention of multiple drug resistance in pancreatic carcinoma.
METHODS: The human pancreatic carcinoma cell line BxPC-3 was cultured in vitro. The growth inhibition rate, cell cycle and apoptotic rate of cells treated with 5-fluorouracil (5-FU), sulfasalazine alone or a combination at different concentrations were evaluated with the MTT method and flow cytometry. Phase-contrast microscopy was used to observe morphological changes in the cells treated with 5-FU, sulfasalazine or both for 24 hours.
RESULTS: The growth inhibition rate of the BxPC-3 cells treated with 5-FU and sulfasalazine significantly increased in a time- and dose-dependent manner. The growth inhibition rate of the cells treated with 5-FU gradually increased, but decreased at different concentrations of sulfasalazine for a prolonged period. The apoptotic rate of the BxPC-3 cells induced by sulfasalazine (200 mg/L), 5-FU (100 mg/L) or both for 12 hours were (2.68±0.36)%, (6.59±0.90)%, and (10.52±0.55)%, respectively, compared with the corresponding control values were (3.17±0.08)%, (1.50±0.06)%, and (4.08±0.31)% [(t=2.33 (P>0.05), 9.78 and 17.56 (P<0.01)]. It increased to (7.63±0.68)%, (40.43±1.79)%, and (64.69±0.82)% for 48 hours, in comparison with the control that was (29.20±2.18)%, (5.61±0.13)%, and (12.02±0.52)% [t=17.06, 33.66 and 94.51 (P<0.01)]. The apoptotic rate, proportion of cells in S-phase and proliferative index rose after use of 5-FU (12.5, 25, 50, 75, and 100 mg/L) alone for 24 hours. However, the apoptotic rate at augmented concentrations of sulfasalazine for 24 hours slowly increased from (1.47±0.08)% to (3.45±0.28)%, the proportion of cells in G0/G1-phase increased from (35.13±0.32)% to (54.32±1.45)%, the proportion of cells in S-phase decreased from (45.37±1.48)% to (16.67±2.73)%, and the proliferative index gradually lowered. The proportion of G0/G1-phase cells treated by 5-FU (100 mg/L) and sulfasalazine (200 mg/L) increased from (43.31±1.52)% (12 hours) to (85.05±0.24)% (48 hours) compared with the corresponding controls [t=7.93 (12 hours), 21.30 (48 hours), P<0.01], and the proportion of cells in S-phase decreased from (11.63±1.11)% (12 hours) to (4.47±0.68)% (48 hours) in contrast to the controls [t=37.68 (12 hours), 8.60 (48 hours), P<0.01]. Most cells after the combined use of the two agents for 24 hours displayed pyknosis and oval shape by phase-contrast microscopy. The cells treated with 5-FU (100 mg/L) for 24 hours were pyknotic and oval shaped. A few of cells in the group treated with sulfasalazine (200 mg/L) were pyknotic at 24 hours.
CONCLUSIONS: Sulfasalazine may enhance the inhibitory proliferation and apoptosis effect on BxPC-3 cells induced by 5-FU, which is closely related to synergistically the cell cycle arrested in G0/G1-phase.