Polyprenoic acid, E-5166, is effective in inhibiting the proliferation of keratinocytes in vitro

E-5166 is a newly synthesized polyprenoic acid that has been reported to control epithelial differentiation and to have antiproliferative effects on various tumor cells in vitro. This study examined the effects of E-5166 on the proliferation of keratinocytes. Three kinds of keratinocytes were used: normal human keratinocytes, a human trichilemmoma-derived K-TL-1 cell line, and a Pam 212 cell line. Cell proliferation was measured by 3H-thymidine incorporation and also by determining cell numbers. E-5166 was found to have significant antiproliferative effects on each of the cell lines studied. When Pam 212 cells were cultured in the presence of E-5166, cell proliferation was inhibited in a dose-dependent fashion. The inhibitory effect appeared to be reversible, since removal of E-5166 from the culture medium resulted in a subsequent return of cell proliferation. For normal human keratinocytes and K-TL-1 cells, E-5166 inhibited 3H-thymidine incorporation in a dose-dependent fashion. Furthermore, E-5166 showed significantly stronger antiproliferative capacity than Ro 10-9359, one of the aromatic retinoids, on Pam 212 cells and normal human keratinocytes.