BIOLOGICALLY-ACTIVE HETEROAROTINOIDS EXHIBITING ANTICANCER ACTIVITY AND DECREASED TOXICITY

A series of retinoids, containing heteroatoms in a cyclic ring and cal led heteroarotinoids, were synthesized, and their biological activity was evaluated using tissue culture lines that have measurable response s to trans-retinoic acid (t-RA). Transglutaminase (TGase) was assessed in the human erythroleukemia cell line (GM06141A) as an indicator of differentiation and apoptosis. Proliferation was evaluated in a human cervical cell line, CC-1, which exhibits dose-dependent alterations in growth rate in response to treatment with trans-retinoic acid. Activa tion of nuclear retinoic acid receptors was determined in a reporter c ell line established from CC-1. The reporter line, called CC-B, contai ns a reporter gene controlled by a retinoic acid responsive element (R ARE) and a thymidine kinase (tk) promoter. Treatment of the CC-B line with the heteroarotinoids resulted in a dose-responsive and retinoid-d ependent regulation of reporter gene expression. The heteroarotinoids exhibited activity in all assays and correlated in a statistically sig nificant manner between assays. RARE transactivation activity in CC-B cells correlated with induction of TGase in GM06141A (R = 0.96) and wi th a decrease in the growth rate of CC-1 cells (R = -0.90). The abilit y of the selected heteroarotinoids to induce differentation, inhibit p roliferation, and activate nuclear receptors demonstrates the chemothe rapeutic potential of these agents. In view of the biological activity cited, an in vivo toxicity study was conducted on male B6D2F1 mice wi th three heteroarotinoids, namely 8 7-dimethyl-7-(1,2,3,4-tetrahydro-4 ,4-dimethylthio- chroman-6-yl)-2,4,6-heptatrienoic acid], 10 ydro-4,4- dimethylchroman-6-yl)-2,4,6-heptatrienoic acid], and 13 E)-p-[2-(4,4-d imethylchroman-6-yl)propenyl]benzoic acid]. The mice were used with ga vage of heteroarotinoids in corn oil [0.1, 0.2, 0.4, or 0.8 mg/kg] and with 0.01 or 0.05 mg/kg of TTNPB (5) 8,8-tetramethyl-2-naphthalenyl)- 1-propenyl]benzoic acid] as reference controls. The target organs affe cted in the mice by the three heteroarotinoids were those typically as sociated with t-RA (1) toxicity. The maximum tolerated dose (MTD) of 1 3 was 9.4 mg/kg/day, which was equal in toxicity to that of t-RA (1) a nd 1000-fold less toxic than TTNPB (5). The MTDs of 8 and 10 were 34 a nd 32 mg/kg/day, respectively, which is 3-fold less toxic than t-RA (1 ) and 3000-fold less toxic than TTNPB (5). The 3000-fold reduced toxic ity, compared with only a 27% reduction biological activity of 8 and 1 0 with respect to that of TTNPB, observed in our assays indicates a go od therapeutic ratio of these heteroarotinoids over the parent compoun d. The biological activity and reduced toxicity of these heteroarotino ids demonstrate the potential efficacy as anticancer agents.