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Inhibitory Effects of Acyclic Retinoid (Polyprenoic Acid) and Its Hydroxy Derivative on Cell Growth and on Secretion of α‐Fetoprotein in Human Hepatoma‐derived Cell Line (PLC/PRF/5)

Acyclic retinoid (polyprenoic acid) has a slightly different structure from retinoic acid. However, acyclic retinoid acts similarly to retinoic acid, because both bind to cellular retinoic acid‐binding protein and cellular retinoid‐binding protein, F‐type, with the same strong binding affinity. We studied the effects of acyclic retinoid, the 7‐hydroxy derivative of acyclic retinoid (7OH‐acyclic retinoid) and retinoic acid on a human hepatoma‐derived cell line PLC/PRF/5 (Alexander cells). Acyclic retinoid inhibited cell growth with an ID50 value of 14 μM, and reduced cell viability with an LD50 value of 86 μM. The ratios of LD50 value to ID50 value were 6.1 for acyclic retinoid, 2.4 for 7OH‐acyclic retinoid and 1.4 for all‐trans‐retinoic acid. Taking this ratio as a parameter of relative cytotoxicity, we concluded that acyclic retinoid is the least toxic compound. Growth inhibition of cells by acyclic retinoid was associated with the incorporation of 3H‐thymidine in the logarithmic phase. Acyclic retinoid reduced secretion of α‐fetoprotein (AFP) and reciprocally increased secretion of albumin in the culture media, suggesting that acyclic retinoid influences gene expression of these proteins. Thus, acyclic retinoid, one of the less toxic retinoids, inhibits cell growth of human cancer cell line PLC/PRF/5 and appears to alter gene expression of AFP and albumin toward a “normal’direction.