THE ANTIPROLIFERATIVE EFFECT OF A TRANSFERRIN-TOXIN ON HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS AND RABBIT FIBROBLASTS

Purpose. To determine the effect of a rabbit transferrin conjugated to recombinant ricin A chain (Tfr-rRA) and the carboxylic ionophore mone nsin on proliferating and density-arrested human retinal pigment epith elial cells and rabbit dermal fibroblasts. Methods. Cells were seeded on 24-well plates at 20,000 cells/cm2 and exposed to Tfr-rRA (0.1-10,0 00 ng/ml) with or without monensin (0.01 muM), and with or without hum an transferrin (65.7 mg/l) for 5 minutes to 7 days. Cells were studied morphologically and counted at 1, 2, 4, and 7 days. Results. Tfr-rRA (10-10,000 ng/ml) killed proliferating human retinal pigment epithelia l ells and rabbit dermal fibroblasts in a dose-dependent manner (p les s-than-or-equal-to 0.01) up to a maximum of 86% and 93%, respectively. In contrast, Tfr-rRA had minimal effect on density-arrested human ret inal pigment epithelial cells and rabbit dermal fibroblasts. The cytot oxicity of Tfr-rRA was inhibited by the addition of human transferrin (65.7 mg/1), an effect that was partially overcome by longer treatment with Tfr-rRA. Monensin (0.01 muM) increased the cytotoxicity of Tfr-r RA by 4.8-fold over Tfr-rRA alone, shortened the onset of cell kill wi th Tfr-rRA from 48 to 24 hours (P = 0.04), and partially reversed the neutralizing effect of human transferrin. Conclusions. The results ind icate that Tfr-rRA effectively inhibited the proliferation of human re tinal pigment epithelial cells and rabbit dermal fibroblasts in vitro. The inhibitory effect could be modified by the addition of human tran sferrin or monensin. Thus, this ricin A chain conjugate may interrupt the proliferation of cells necessary in the pathogenesis of proliferat ive vitreoretinopathy.