PURPOSE: To investigate the effect and mechanism of action of alkylphosphocholines (APCs) on proliferation of human retinal pigment epithelium (RPE) cells and RPE-mediated collagen matrix contraction in vitro. METHODS: Cultured RPE cells of five human donors were treated with four APCs in the presence of fetal calf serum. Proliferation was assessed by the tetrazolium dye-reduction (MTT) assay and by counting the number of cells dividing in culture. The effect of APCs on RPE-mediated matrix contraction was determined in three-dimensional collagen gels. Cell viability was tested by the trypan blue exclusion assay. As a possible mechanism of APC action, protein kinase C (PKC) activity was quantified by scintillation counting of (32)P-labeled phosphate transferred to a PKC-specific substrate. RESULTS: All APCs inhibited RPE proliferation and RPE-mediated collagen matrix contraction in a dose-dependent manner in vitro. The antiproliferative and anticontractile effect of APCs increased with elongation of the fatty acid chain beyond C20. IC(50)s of all APCs varied between 8.5 micro M (erucyl-phosphocholine, C22:1-PC), 9.0 micro M (Z)-12-heneicosenyl-phosphocholine, C21:1-PC), 11.0 micro M (Z)-10-eicosenyl-phosphocholine, C20:1-PC), and 26.5 micro M (oleyl-phosphocholine, C18:1-PC). Trypan blue staining revealed a toxicity below 5% for all APCs within the concentration interval tested. PKC activity was significantly reduced by all four APCs, with C22:1-PC being the most effective. CONCLUSIONS: APCs inhibit proliferation of RPE cells and RPE-mediated matrix contraction in vitro at nontoxic concentrations. This effect seems to be exerted through inhibition of PKC activity. Therefore, APCs are promising candidates for treatment of RPE-mediated proliferative processes such as proliferative vitreoretinopathy.