The therapeutic efficacy of S-1 against orthotopically implanted human pleural mesothelioma cells in severe combined immunodeficient mice

Abstract

Purpose: Malignant pleural mesothelioma (MPM) is a highly lethal neoplasm. S-1 has been developed as a novel oral antineoplastic agent based on the modulation of 5-fluorouracil (5-FU) bioactivity. This study was conducted to investigate the preclinical therapeutic effect of S-1 on MPM.

Methods: We used three human MPM cell lines, Y-MESO-14, NCI-H290 and MSTO-211H. In vitro proliferation of human MPM cells was determined by MTT assay. Human MPM cells were orthotopically implanted into thoracic cavity of SCID mice. Tumor-bearing mice were treated with S-1 or vehicle.

Results: The combination of 5-FU and 5-chloro-2,4-dihydroxypyridine (CDHP) was more effective than 5-FU alone in inhibiting MPM cell proliferation in vitro. This combination was most effective in Y-MESO-14 cells, which co-expressed high protein level of dihydropyrimidine dehydrogenase (DPD) and thymidine phosphorylase (TP). In vivo data showed that treatment with S-1 significantly reduced thoracic tumors and pleural effusion produced by Y-MESO-14 cells. Moreover, treatment with S-1 prolonged the survival of Y-MESO-14 cell-bearing SCID mice.

Conclusions: We demonstrated that S-1 was effective for inhibiting the proliferation of MPM cells, particularly with both DPD and TP expressions, suggesting that S-1 might be therapeutically effective for control of MPM.

Fig. 1

Expression of DPD and TP protein in human MPM cells. Cell lysates were harvested and subjected in duplicate to Western blotting analysis for DPD and TP. Images are representatives of three independent experiments with similar results (a). Thoracic tumors produced by human MPM cells in mice were harvested and subjected to immunohistochemical staining for DPD and TP protein. Images are representatives of two separate experiments with similar results (×200) (b)

Fig. 2

Therapeutic effect of S-1 on thoracic tumor and pleural effusion produced by MPM cells in SCID mice. Y-MESO-14, NCI-H290, and MSTO-211H cells were inoculated into thoracic cavity of SCID mice on day 0. The mice were daily treated with vehicle or S-1 (10 mg/kg) for 14 days from day 7 to 20, and sacrificed on day 21. Treatment with S-1 significantly reduced tumor and pleural effusion produced by Y-MESO-14 cells (a, b), but not by NCI-H290 cells (c, d), and MSTO-211H cells (e, f) in mice. Figure 2c and d showed the representative data of three separate experiments with similar results. Figure 2e and f showed the representative data of two separate experiments with similar results. The P values were obtained from Wilcoxon test

Fig. 3

Therapeutic effect of S-1 on the progression of Y-MESO-14 tumor in SCID mice. Y-MESO-14 cells developed thoracic tumors (upper left, black arrows) and pleural effusion (lower left, white arrows) in mice treated with vehicle. Treatment with S-1 significantly decreased the mass of tumors (upper right) and bloody pleural effusion (lower right)

Fig. 4

The dose–response study of S-1 given for treatment of Y-MESO-14 cells implanted in SCID mice. Y-MESO-14 cells were inoculated into thoracic cavity of SCID mice on day 0. The Y-MESO-14 cell-inoculated mice were daily treated with vehicle or with various doses of S-1 from day 7 to 20 and sacrificed on day 21. Treatment with S-1 was significantly effective to reduce tumor (a), and pleural effusion (b), in a dose dependent manner. The P values were obtained from Holm’s procedure (non-parametric Tukey test)

Fig. 5

Effect of various schedules of S-1 treatment on thoracic tumor and pleural effusion produced by Y-MESO-14 cells in SCID mice. Y-MESO-14 cells were inoculated into thoracic cavity of SCID mice on day 0. The mice were treated with vehicle or S-1 (10 mg/kg) for 10 days under two schedules from day 7–16 and from day 11–20. Both these two treatment schedules resulted in significant reduction of tumor (a), and pleural effusion (b). The schedule from day 11–20 appeared to be more effective than the schedule from day 7–16 in reducing pleural effusion. The P values were obtained from Holm’s procedure (non-parametric Tukey test)

Fig. 6

The effect of S-1 administration on the survival of MPM cell-bearing SCID mice. Y-MESO-14 cell-bearing mice were treated with vehicle or with S-1 (10 mg/kg, daily) for 10 days (day 11–20) or 14 days (day 7–20). There were significant differences between 10-day treatment and vehicle groups (P = 0.02) and between 14-day treatment and vehicle groups (P = 0.02). The median survival times were 31, 42 and 42 days in vehicle, 10-day and 14-day treatment groups, respectively. The probability of survival was calculated with the Kaplan–Meier method, and differences between curves were evaluated with the log-rank test