Evaluation of 9-cis retinoic acid for a new remedy of human retinoblastoma

We investigated the effect of two isomers of retinoic acid (RA), all-trans RA and g-cis RA, on the proliferation of Y79 human retinoblastoma cells. Th e two isomers inhibited the cell proliferation in a concentration-dependent manner. The IC50 for this inhibition by all-trans RA and g-cis RA was 1.50 and 0.15 mu M, respectively. The inhibitory effect of g-cis RA on Y79 cell growth was observed within 24 hr, thereafter the cell number was gradually decreased. In contrast, no inhibition by all-trans RA of Y79 cell growth w as observed within 24 hr, thereafter the cell number was slightly increased . In these cases, the cell viability at 4 days after the addition of 9-cis RA and all-trans RA was more than 90 % and 95 %, respectively. These result s indicate that the two RA inhibit the proliferation of Y79 human retinobla stoma cells without inducing the cell death and that the effect of 9-cis RA on the inhibition of Y79 cell growth is much greater than that of all-tran s RA.