Teratogenicity of arotinoid ethyl ester (RO 13-6298) in mice

Attempts to Improve Lipophilic Drugs' Solubility and Bioavailability: A Focus on Fenretinide

The development of numerous drugs is often arrested at clinical testing stages, due to their unfavorable biopharmaceutical characteristics. It is the case of fenretinide (4-HPR), a second-generation retinoid, that demonstrated promising in vitro cytotoxic activity against several cancer cell lines. Unfortunately, response rates in early clinical trials with 4-HPR did not confirm the in vitro findings, mainly due to the low bioavailability of the oral capsular formulation that was initially developed. Capsular 4-HPR provided variable and insufficient drug plasma levels attributable to the high hepatic first-pass effect and poor drug water solubility. To improve 4-HPR bioavailability, several approaches have been put forward and tested in preclinical and early-phase clinical trials, demonstrating generally improved plasma levels and minimal systemic toxicities, but also modest antitumor efficacy. The challenge is thus currently still far from being met. To redirect the diminished interest of pharmaceutical companies toward 4-HPR and promote its further clinical development, this manuscript reviewed the attempts made so far by researchers to enhance 4-HPR bioavailability. A comparison of the available data was performed, and future directions were proposed.

Teratology of retinoids

Either an excess or a deficiency of vitamin A and related compounds (retinoids) causes abnormal morphological development (teratogenesis). Potential retinoid sources come from dietary intake, nutritional supplements, and some therapeutic drugs. Therefore, understanding the mechanisms of retinoid teratogenesis is important. This review first gives an overview of the principles of teratology as they apply to retinoid-induced malformations. It then describes relevant aspects of the biochemical pathway and signal transduction of retinoids. The teratogenic activity of various retinoid compounds, the role of the retinoid receptors, and important toxicokinetic parameters in teratogenesis are reviewed.

Analysis of high dysmorphogenic activity of Ro 13-6307, a tetramethylated tetralin analog of retinoic acid

Certain synthetic retinoids differ widely from retinoic acid (RA) in teratogenic potency, being much more or much less effective than RA. It is assumed that the potency of a retinoid may depend on the nature of its interaction with cellular binding components (nuclear retinoic acid receptors or cytoplasmic binding proteins) and, as in the case of retinoids that are mammalian teratogens, on factors that determine its accessibility to the embryo. To investigate some of the factors that contribute to potency, we used a new synthetic retinoid Ro 13-6307 that differs in structure from RA in having an aromatic ring inserted in its side chain along with gem dimethyl modification of the natural cyclohexenyl ring. Pregnant ICR mice were given a single oral dose (0, 1, or 10 mg/kg) on day 11 of gestation, and the resultant teratogenic outcome was monitored on day 17. Direct effects on cell differentiation were obtained by exposing high density cultures of limb bud mesenchymal cells to a range of concentrations (0.3 ng/ml-3 micrograms/ml) of Ro 13-6307 and scoring for chondrogenic suppression. Concentrations reaching the embryo after maternal administration of Ro 13-6307 were measured by HPLC to quantify the analog for a period of 4 h after administration of the oral dose. We found that this retinoid was 40-fold as active as RA in both inducing teratogenesis and suppressing chondrogenesis, yet its concentration in the affected embryo was only a fraction of that achieved after an equivalent dose of RA was employed in a similar protocol.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative teratogenicity of three retinoids: the arotinoids Ro 13-7410, Ro 13-6298 and Ro 15-1570

Three retinoids of the arotinoid series, namely the free carboxylic acid Ro 13-7410, its ethyl ester Ro 13-6298, and the new arotinoid ethyl sulfone Ro 15-1570, were tested for their embryotoxic and teratogenic activity in rats. The retinoids were administered orally on either day 9 or 13 of gestation. Treatment on day 9 of gestation resulted mainly in malformations of the head and the trunk; whereas, on day 13 limb malformations were prominent. Ro 13-7410 and Ro 13-6298 were about 1000 times more embryotoxic and teratogenic than retinoic acid but induced a similar malformation pattern to retinoic acid. In contrast, the sulfur-containing arotinoid Ro 15-1570 was active at similar dose levels to retinoic acid but caused a peculiar malformation pattern on day 13 of gestation. This finding supports the hypothesis that the arotinoid ethyl sulfone Ro 15-1570 has unique biological properties, inducing no bone toxicity in adult rats and distinctly affecting limb development.

Pharmacokinetics, tissue distribution and placental permeability of tetrahydro-tetramethyl-naphthalenyl-propenyl benzoic acid (a retinoidal benzoic acid derivative) in hamsters

Tritiated tetrahydro-tetramethyl-naphthalenyl-propenyl benzoic acid (TTNPB; Ro 13-7410) was administered as a single oral bolus to pregnant hamsters (day 8) to determine the maternal plasma pharmacokinetic profile and peripheral tissue distribution patterns. Blood and tissue, including embryo or fetus, were collected at specific time intervals to 96 h and assayed for total radioactive compounds and/or parent retinoid. No lag time was required to describe retinoid absorption (t 1/2 pi = 1.2 h) with peak plasma levels at 2.4 h; the concentrations then declined with exponential elimination from the central compartment (t 1/2 e = 3 h). The maximum concentrations of circulating radioactive compound or metabolites after 100 micrograms/kg [3H]2-TTNPB occurred in liver greater than fetus greater than adrenal greater than lung approximately equal to kidney greater than plasma; after 1000 micrograms/kg, maternal liver accumulated the highest concentration followed by plasma greater than fetus = placenta = uterus. An unidentified, polar metabolite was detected in plasma at 0.5 h and by 12 h constituted greater than 90% of the total circulating radioactivity. TTNPB was absorbed and cleared more slowly, concentrated in the conceptus to a higher degree and possessed greater intrinsic activity than the naturally-occurring tetraene retinoids. These properties contribute to the marked teratogenic activity of TTNPB as compared to the tetraene retinoids.