Time-dependent inhibition of growth of human keratinocytes and fibroblasts by cyclosporin A: effect on keratinocytes at therapeutic blood levels.

The effect of cyclosporin A (CyA) on the growth of cultured normal human keratinocytes and fibroblasts was studied. Tritiated thymidine incorporation per DNA content was used for short-term studies (1-2 days) and cell counting for longer term studies (up to 14 days). CyA caused a dose- and time-dependent inhibition of growth of both cell types. Keratinocytes (serum free, 70 microM Ca2+) were more sensitive to CyA than fibroblasts (10% serum). For keratinocytes, at 2 days growth was 61% and 6% of controls with 3 and 10 micrograms/ml CyA, respectively, at 4 days growth was 51% with 1 microgram/ml with complete inhibition at 10 micrograms/ml, and at 11 days growth was 58 and 39% with 0.1 and 1 micrograms/ml. For fibroblasts, at 4 days growth was 72 and 58% of controls with 10 and 30 micrograms/ml CyA, respectively, at 10 days growth was 76, 43 and 10% with 3, 10 and 30 micrograms/ml, and at 14 days growth was 41 and 11% with 3 and 10 micrograms/ml with complete inhibition with 30 micrograms/ml. For keratinocytes the effect of 24 h of CyA on growth was reversible. Growth of keratinocytes was inhibited by 10% delipidized serum, and 1% serum had a small stimulatory effect, but the action of CyA was unaltered. We conclude that increasing the duration of exposure to CyA increases the concentration-dependent growth inhibition. At therapeutic blood levels of CyA the growth of cultured keratinocytes but not fibroblasts is inhibited. The benefit of CyA in reducing the hyperproliferation of psoriasis may include a direct effect on keratinocytes.