Antiproliferative Effect of 4-Thiouridylate on OCM-1 Uveal Melanoma Cells

Abstract

Purpose

Brachytherapy is a well-established, effective treatment for uveal melanoma with a failure rate of 15%. The fatal consequence of unsuccessful treatments offers reason for improvement of the method. The authors propose using an apoptosis inducing agent locally, concomitantly with the well-established therapy, to sensitize the tumor cells. The authors propose a new nontoxic moderately active apoptosis inducing agent, 4-thio-uridylate (s4UMP), for this purpose.

Methods

OCM-1 uveal melanoma cells were treated with various concentrations of s4UMP and its effect was monitored by measuring the cell viability (MTT assay). The following apoptosis detecting methods were performed to reveal the mechanism of decreased cell viability: light microscopy, DNA fragmentation assay, determination of caspase 9 activity, and FACS analysis.

Results

The viability of uveal melanoma cells was decreased by 32%, 40%, and 9% after 24, 48, and 72 hours of treatment with 10 μg/mL (30 μM) S⁴UMP. The effect was not dose dependent; it rather followed a saturation-type inhibition and the cells at lower drug concentration recovered after 72 hours. Characteristic apoptotic cell morphology and DNA fragmentation was detected in treated cells. The caspase-9 was activated upon treatment showing maximal activity at 48 hours suggesting the induction of apoptosis. The annexin binding activity further verified the apoptogenic activity of s⁴UMP.

Conclusions

Uveal melanoma, more than other solid tumors, is resistant to most of the chemotherapeutic protocols as indicated by the high mortality rate of metastatic disease. The authors showed that s⁴UMP, a naturally occurring nucleotide, could induce apoptosis in uveal melanoma cells, suggesting a potential supplementary therapeutic application of the compound.