Comparison of the therapeutic effects of a new arotinoid, Ro 40-8757, and all-trans- and 13-cis-retinoic acids on rat breast cancer.

A novel arotinoid, 4-((2-(p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl- 2-naphthyl)propenyl]phenoxy))ethyl))-morpholine, was tested in rats bearing established chemically induced mammary tumors. At a dose of 0.35 mmol/kg/day of 4-((2-(p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthyl)propenyl]phenoxy)ethyl))-morpholine, decreased tumor growth was seen after 2 weeks. By weeks 4 and 5, tumor burdens were decreased to 10-30% of initial values and 50-70% of the animals became free of palpable tumors. Stabilization of tumor size through 15 weeks of treatment was seen in rats given 0.23 mmol/kg/day of the arotinoid. The predominate adverse effects of this compound were dose-dependent weight loss during the first 1-3 weeks, attributed to poor palatability of the food admix as well as flaking of the skin and alopecia at later times. Bone toxicity, a characteristic side effect of retinoids in rodents, was rare with this arotinoid, mainly confined to young rats treated for more than 12 weeks with high doses. In a comparative study, neither all-trans-retinoic acid nor 13-cis-retinoic acid had significant antitumor effects at doses that were tolerated by the animals. When all-trans-retinoic acid was administered at 0.08 mmol/kg/day, tumor reduction was seen during weeks 4-6, but treatment was terminated after week 6 due to severe skeletal toxicity and general deterioration in all the animals. Such marked toxicity was not evident with the arotinoid at doses having high antitumor activity. The high efficacy and relatively low toxicity of 4-((2-(p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2- naphthyl)propenyl]phenoxy)ethyl))-morpholine suggest that it may be a promising new anticancer agent.

Reversible, retinoid-induced secretion of canine ceruminous glands.

The long-term (12 months) oral administration of the aromatic retinoid Ro 10-1670 (etretin) to dogs in relatively high doses of 5.0, 15.0 and 50.0/30.0 mg/kg/day was followed by acanthotic hyperplasia of the epidermis in the external auditory meatus and dose-dependent hypertrophy and/or hyperplasia of the canine ceruminous glands. These morphological changes were accompanied by a secretory stimulation on the ceruminous glands which was slight in the low-dose dogs but in the majority of the high-dose dogs reached a degree that was followed by secondary acute infectious inflammation. The alterations in the external auditory canal ceased almost immediately when treatment of dogs with the aromatic retinoid was stopped but recommenced when it was restarted.

Therapeutic effect of the arotinoid Ro 15-0778 on chemically induced rat mammary carcinoma.

The arotinoid Ro 15-0778 (temarotene) is a third generation retinoid without a polar end-group. Established, palpable and measurable rat mammary tumours, chemically induced by oral administration of 12 mg/animal 7,12-dimethylbenz[a]anthracene, were treated with Ro 15-0778 as a feed-admix in daily doses of 100 mg/kg for 6 weeks and 200 and 400 mg/kg for 9 weeks. For comparison, tamoxifen (anti-oestrogen) was administered as a feed-admix in doses of 10 and 30 mg/kg/day for 9 weeks. Treatment with Ro 15-0778 resulted in a marked retardation of tumour growth in the groups treated with 100 and 200 mg/kg/day and in partial or even complete tumour regression in the group receiving 400 mg/kg/day. Tamoxifen treatment caused a transient tumour growth inhibition during weeks 1-5 with subsequent re-growth of mammary tumours. Both compounds were generally well tolerated. No signs or symptoms of hypervitaminosis A were noted with Ro 15-0778. One single convulsive attack occurred with 200 mg/kg/day of Ro 15-0778 and 400 mg/kg/day caused occasional convulsions in five out of 11 rats. The present investigation underlines the fact that the arotinoid Ro 15-0778 is not only a chemopreventive agent but also exerts a chemotherapeutic effect on established, chemically induced, mammary carcinomas of the rat.

The short term fate of dischargeable glass beads implanted surgically in the mouse urinary bladder.

Although both male and female mice of different ages expelled surgically implanted glass beads with diameters of 1 mm and 0.5 mm within 5 weeks in comparable numbers, urinary stones formed in relation to these implanted beads more frequently in male mice than in females. This stone formation in male mice may be a consequence of the relatively high mucoprotein content in the urine of the male mouse.

The relevance of the mouse papilloma test as a predictor of retinoid activity in human psoriasis.

The combination of the results of mouse antipapilloma tests with those from hypervitaminosis A tests in mice as the basis for calculating a therapeutic index has been used for more than 20 years in the search for retinoids as useful drugs in human dermatology. A number of retinoids identified as active or inactive when administered systemically in these mouse systems have gone into clinical trials; clinical results on 11 retinoids were available for a retrospective analysis on the predictive relevance of the mouse models for retinoid activity in human psoriasis. This analysis revealed that the therapeutic index in mice correctly identified eleven compounds and differentiated them into markedly active, moderately active or inactive retinoids when subsequently used clinically in the treatment of various forms of psoriasis. Acidic retinoids were more difficult to assess than nonacidic ones and the therapeutic index appeared to underestimate their potency in humans. One retinoid, motretinide, showed a favorable therapeutic index but failed to demonstrate antipsoriatic activity in the clinic. The reason for this discrepancy is that humans and mice metabolize this compound differently. Thus, although chemically induced skin papillomas in mice reflect only certain analogies to human psoriasis and other keratinizing dermatoses, they may be considered a useful tool in the search for retinoids for the treatment of keratinization disorders.

Preclinical safety testing of species-specific proteins produced with recombinant DNA-techniques. An attempt to transfer current experience into future testing strategies.

Preclinical toxicity studies in animals with species-specific recombinant DNA products have now been performed for several years. An interim statement on the significance of these animal tests and their ability to predict adverse effects in humans therefore appears indicated, with the aim of deducing future testing strategies. The experience accumulated so far shows that the animal models have failed to predict adverse effects subsequently observed in man. Immunogenicity of these proteins further restricted the usefulness of standard toxicity tests. There is also increasing evidence that animal tests on the toxic potential of impurities contained in the products are markedly inferior in sensitivity to analytical and quality control methods. Thus, modified testing programs are proposed to demonstrate safety rather than target organ toxicity using rodents and small non-rodent species and restricted dosing; furthermore the study duration should be limited by the detection of immunogenic responses.

Ro 15-1570, a new sulfur-containing retinoid devoid of bone toxicity in rats.

Repeated ingestion of high doses of retinoids cause the so-called hypervitaminosis A syndrome. In rats the main symptoms are weight loss, alopecia, erythema, desquamation of the skin, and alterations of the skeletal system, including bone fractures. In the present study, three retinoids (Ro 15-1570, arotinoid ethylsulfone, 6 mg/kg; retinoic acid, 100 mg/kg and etretinate, 50 mg/kg) were administered orally to rats for 1 and 2 weeks, respectively, to six male and six female rats/group. All the above changes were induced by all three retinoids, with the exception that the arotinoid ethylsulfone Ro 15-1570 did not cause bone alterations. The absence of toxic effects on the bones by Ro 15-1570 was confirmed by X-ray-film examinations, densitometry of the X-rayed femora and tibiae, examination of the thickness of the femoral and tibial compacta in histological slides plus the determination of the femoral ash weight and its main inorganic constituents (calcium, magnesium, sodium, and potassium). The present demonstration that the arotinoid ethylsulfone Ro 15-1570 was devoid of bone toxicity constitutes major progress in the pharmacologic development of retinoids with a better balance between therapeutic and adverse effects.

Preclinical safety evaluation of intravenously administered mixed micelles.

Mixed micelles, with their main constituents lecithin and glycocholic acid, form a new principle for the parenteral administration of compounds which are poorly water-soluble. Their composition of mainly physiological substances as well as their comparatively good stability substantiate their attractivity in comparison to existing solvents. A decomposition due to physical influences such as heat or storage for several years will almost exclusively affect the lecithin component in the form of hydrolysis into free fatty acids and lysolecithin. Their toxicity was examined experimentally in various studies using both undecomposed and artificially decomposed mixed micelles. In these studies the mixed micelles were locally and systemically well tolerated and proved to be neither embryotoxic, teratogenic nor mutagenic. Only when comparatively high doses of the undecomposed mixed micelles were administered, corresponding to approximately 30 to 50 times the anticipated clinical injection volume (of e.g. diazepam mixed micelles), did some vomitus (dogs), slight liver enzyme elevation (rats and dogs), and slightly increased liver weights (dogs) occur. After repeated injections of the artificially decomposed formulation (approximately 25% of lecithin hydrolyzed to free fatty acids and lysolecithin) effects such as intravascular haemolysis, liver enzyme elevations and intrahepatic cholestasis (dogs only) were observed but only when doses exceeding a threshold of approximately 40 to 60 mg lysolecithin/kg body weight were administered. All alterations were reversible after cessation of treatment.

The anti-tumor arotinoid Ro 40-8757 protects bone marrow from the toxic effects of cyclophosphamide.

The arotinoid Ro 40-8757 is a novel compound that has significant therapeutic activity against chemically induced breast tumors in rats. The results of combination therapy with cyclophosphamide, plus the arotinoid showed that the anti-tumor effects were additive. However, all of the rats given CPA alone died between week 6 and week 10 of treatment. None of the animals in the group treated with the combination died. Administration of a single dose of Ro 40-8757 to non-tumor bearing mice resulted in a transient increase in bone-marrow-progenitor cells after 2 days and a decrease in splenic progenitors at day 4. Treatment of mice with the combination demonstrated that the marrow progenitors were protected from the toxic effects of CPA by the arotinoid. Direct addition of Ro 40-8757 to mouse bone-marrow cells in clonogenic assay cultures containing WEHI-3-conditioned medium plus erythropoietin showed no significant enhancement by the arotinoid. The results suggest that this compound may exert its protective effect through the hemopoietic micro-environment.