Cancer Chemopreventive Retinoids: Validation and Analysis of <i>in Vivo</i> and <i>in Vitro</i> Bioassay Results

Abstract

Several natural and synthetic retinoids (vitamin-A derived analogies) were examined for their potential anti-cancer activity in both in vivo animal models and a novel in vitro human keratinocyte clonal growth bioassay system. The natural retinoids included all-trans-retinoic (RA), 13-cis-retinoic acid, 4-oxoretinoic acid, and retinol. Among the synthetic retinoids tested were all trans N-(4-hydroxy(phenyl)retinamide, 3-substituted oxoretinoic acids, and 13 cis-N-ethylretinamide. The animal models employed were: 1) vitamin A-deficient hamster tracheal organ assay (HTOC); 2) the benzo(α)pyrene-induced squamous metaplasia in a hamster tracheal organ system (BP-HTOC); 3) the mouse skin tumor promoter (TPA)-induced ornithine decarboxylase enzyme assay(ODC); 4) the mouse skin papilloma (MPA) assay; and 5) a novel retinoid bioassay in which retinoids display IC 50 values to inhibit clonal growth of NHK. All-trans-RA, 4-oxoretinoic acid and retinol were consistently more active than any of the synthetic derivatives in all bioassays tested. A statistical model was developed and significant positive correlations were found between: 1) ED 50 values in the HTOC system and reduction in TPA-induced ODC enzyme activity; 2) tumors per animal in the MPA bioassay and suppression of TPA-induced ODC activity; and 3) a positive correlation between suppression of tumors per animal in the MPA assay, and retinoid inhibition of keratinocyte clonal growth. Test retinoids, were tested for their capacity to inhibit the clonal growth of a squamous carcinoma cell line (SCC-25), which were found to be 2-3 logs less sensitive for each tested retinoid than the corresponding activity against NHK cells. Antineoplastic retinoid drugs were reviewed.

Retinyl acetate mediates autocrine proliferation and wound healing of keratinocytes through a c-neu (erbB-2)-like receptor

“…Clonal growth assay studies also examined the effect of RetAc. Unlike t-RA, 7 we report that RetAc stimulates HaCaT clonal growth at physiological levels. We further explored the underlying biochemical events that reveal an autocrine signaling pathway and possible involvement of the c-neu (erbB-2) cytoplasmic receptor and a treatment-induced translocation to focal membrane areas.…”

“…6 By contrast, a panel of retinoids including t-RA, ROL, 13-cis RA, all inhibited the clonal growth of NHK in SFM supplemented with EGF and insulin in rapidly proliferating NHK. 7 The strength of inhibition was linearly correlated with their ability to suppress both ornithine decarboxylase enzyme induction by tumor promoter and papilloma formation in the mouse skin model of tumorigenesis. 7 By contrast, t-RA stimulates growth-arrested adult keratinocytes in protein growth factor-deficient SFM.…”

“…7 The strength of inhibition was linearly correlated with their ability to suppress both ornithine decarboxylase enzyme induction by tumor promoter and papilloma formation in the mouse skin model of tumorigenesis. 7 By contrast, t-RA stimulates growth-arrested adult keratinocytes in protein growth factor-deficient SFM. 8 These conflicting effects appear to involve differing growth media conditions.…”