Biologically Active Heteroarotinoids Exhibiting Anticancer Activity and Decreased Toxicity

Abstract

A series of retinoids, containing heteroatoms in a cyclic ring and called heteroarotinoids, were synthesized, and their biological activity was evaluated using tissue culture lines that have measurable responses to trans-retinoic acid (t-RA). Transglutaminase (TGase) was assessed in the human erythroleukemia cell line (GMO6141A) 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. Activation of nuclear retinoic acid receptors was determined in a reporter cell line established from CC-1. The reporter line, called CC-B, contains a reporter gene controlled by a retinoic acid responsive element (RARE) and a thymidine kinase (tk) promoter. Treatment of the CC-B line with the heteroarotinoids resulted in a dose-responsive and retinoid-dependent regulation of reporter gene expression. The heteroarotinoids exhibited activity in all assays and correlated in a statistically significant manner between assays. RARE transactivation activity in CC-B cells correlated with induction of TGase in GMO6141A (R = 0.96) and with a decrease in the growth rate of CC-1 cells (R = -0.90). The ability of the selected heteroarotinoids to induce differentiation, inhibit proliferation, and activate nuclear receptors demonstrates the chemotherapeutic potential of these agents. In view of the biological activity cited, an in vivo toxicity study was conducted on male B6D2F1 mice with three heteroarotinoids, namely 8 [(2E,4E,6E)-3,7-dimethyl-7-(1,2,3,4-tetrahydro-4,4-dimeth ylthiochroman-6-yl)-2,4,6-heptatrienoic acid], 10 [(2E,4E,6E)-3,7-dimethyl-7-(1,2,3,4-tetrahydro-4,4-dimeth ylchroman-6-yl)-2, 4,6-heptatrienoic acid], and 13 [(E)-p-[2-(4,4-dimethylchroman-6-yl)propenyl]benzoic acid]. The mice were used with gavage 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) [(E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1- propenyl]benzoic acid] as reference controls. The target organs affected in the mice by the three heteroarotinoids were those typically associated with t-RA (1) toxicity. The maximum tolerated dose (MTD) of 13 was 9.4 mg/kg/day, which was equal in toxicity to that of t-RA (1) and 1000-fold less toxic than TTNPB (5). The MTDs of 8 and 10 were 34 and 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 toxicity, compared with only a 27% reduction biological activity of 8 and 10 with respect to that of TTNPB, observed in our assays indicates a good therapeutic ratio of these heteroarotinoids over the parent compound. The biological activity and reduced toxicity of these heteroartinoids demonstrate the potential efficacy as anticancer agents.

Role of AP-1 Antagonism in Growth Inhibition of Cervical Cancer Cell Lines by Retinoids

“…Therefore, it is likely that other retinoid activities contribute to the mechanism of growth inhibition. In support of this, our previous studies demonstrated that retinoid RARE transactivation significantly correlated with growth inhibition in the CC-1 cervical cancer cell line [11,20] . AP-1 repression therefore, may not be the only mechanism of retinoid growth inhibition and designing retinoids specifically targeted at AP-1 repression may be less efficient than designing retinoids targeted to a larger subset of activities involved in the mechanism of retinoid growth inhibition.…”

“…Media were replenished every 2 days. The synthetic retinoids (heteroarotinoids -gifts of K. Darrell Berlin, Oklahoma State University) were synthesized as previously described [11,21,22] . The 9-cis-RA (BIOMOL, Plymouth Meeting, PA), heteroarotinoids and TPA (Sigma, St. Louis, MO) were dissolved in dimethyl sulfoxide (DMSO) as 1000× stock solutions, so that the final concentration of DMSO in all cultures was less than 0.1%, which is not cytotoxic and does not induce differentiation.…”

“…Thousands of different aromatic retinoids, called arotinoids, have been synthesized and many were found to be selective for retinoid receptors and retinoid activities [7,8] . The first arotinoid thoroughly evaluated, TTNPB, was found to be 1000-fold more toxic than trans-RA [9][10][11] . Incorporation of a heteroatom into the cyclic ring of arotinoids resulting in compounds called heteroarotinoids reduced the toxicity 1000-fold in the diaryl TTNPB structure and 3000 fold in the monoaryl heteroarotinoid structure [11] .…”

“…The first arotinoid thoroughly evaluated, TTNPB, was found to be 1000-fold more toxic than trans-RA [9][10][11] . Incorporation of a heteroatom into the cyclic ring of arotinoids resulting in compounds called heteroarotinoids reduced the toxicity 1000-fold in the diaryl TTNPB structure and 3000 fold in the monoaryl heteroarotinoid structure [11] . Therefore, this class of compounds has the potential for clinical application as anticancer drugs.…”

Cell Surface Receptor Theory of Disease Infectivity; Body's Defence and Normal Body Functioning in Living Things

“…IT follows from the findings of this study that drugs like plant extracts [like Carica papaya extract which contains retinoids] are themselves the endogenous defence substances of their own organism and they defend the human or other organism's body from disease infection and disorder just as they protect their own organism (Guruswamy and Benbrook, 2006;Holmes et al, 2004;Benbrook et al, 1997;Chiu et al, 2006). The structure of such benevolent substances would therefore resemble those of a host organism's defence mediator.…”