Purpose: The effect of antiproliferative agents with high voltage electric pulses (EP) on the proliferation of retinal pigment epithelial (RPE) cells was investigated.
Methods: Bovine RPE cells were cultured and exposed briefly to an antiproliferative agent: 0.005 to 500 microM of bleomycin (BLM), 0.005 to 500 microM of mitomycin C (MMC) or 0.05 to 5000 microM of 5-fluorouracil (5-FU) with or without high voltage electric pulses (EP: 2,000V/cm, 98 microseconds, 8 pulses). Streptomycin (SM) was used as a negative control. Cell proliferation with or without antiproliferative agents was assessed on day 3. DNA fragmentation was assessed by flow cytometric analysis.
Results: Treatment with BLM, MMC or 5-FU inhibited cell proliferation in a dose-dependent manner, with and without EP (p < 0.05). EP enhanced the inhibitory effect of BLM as much as 3,000 times (ID50: BLM without EP; 163.7 microM, BLM with EP; 0.0574 microM, MMC without EP; 132.4 microM, MMC with EP; 26.2 microM, 5-FU without EP; 616.4 microM, 5-FU with EP; 873.8 microM). EP treatment showed an inhibitory effect of BLM on cell proliferation more prominently than BLM alone. The cell numbers of 0.5 microM BLM treatment without EP were 87.4 +/- 11.7% (mean +/- SD), whereas the cell numbers of 0.5 microM BLM with EP were 21.1 +/- 2.16% (p < 0.005). BLM treatment with EP increased the apoptosis like DNA fragmentation in the flow cytometric DNA histogram, showing dominant accumulation in the A0 region, which is the population of DNA fragmentation. (The cell population of the A0 region: control, 3.4%; EP alone, 18.9%; BLM treatment without EP, 32.0%; with EP, 93.8%.)
Conclusions: EP treatment enhances the inhibitory effect of BLM on RPE cell proliferation. The combination of electric pulse and BLM treatment can localize the drug effect and reduce the necessary dose of the antiproliferative agent in comparison to BLM treatment alone.