A chlorodiazirine analog of pentamidine with anti-trypanosomal activity.

A chlorodiazirine derivative of pentamidine was synthesized and tested for anti-trypanosomal activity using EATRO stock 164 trypanosomes in cell culture. Anti-trypanosomal activity was measured as a decrease in [3H]hypoxanthine incorporation by the organisms. The derivative, 3,3'-[1,5-pentanediylbis(oxy-4,1-phenylene)]bis(3-chloro-3H-diazir ine), at a treatment level of 0.1 microM inhibited isotope incorporation by 40-50% compared to nontreated controls. At this concentration, pentamidine inhibited incorporation only 10-15%. The derivative is a nonionic molecule with much different solubility properties than the parent compound and should readily cross the blood-brain barrier.

Anticonvulsant activity of 4-urea-5,7-dichlorokynurenic acid derivatives that are antagonists at the NMDA-associated glycine binding site.

Twelve 4-urea-5,7-dichlorokynurenic acid derivatives were synthesized by reacting the 4-tosylimino derivative of 5,7-dichlorokynurenate methyl ester first with triphosgene and then with a secondary amine. Compounds were screened in mice for anticonvulsant activity using maximal electroshock (MES), subcutaneous pentylenetetrazole (Met), and threshold tonic extension (TTE) tests. A rotorod test was used to determine neurotoxicity. Seven of the derivatives had anticonvulsant activity in TTE testing at 100 mg/kg. One compound, 2-methyl carboxylate-5,7-dichloro-4-([¿diphenylamino¿-carbonyl]amino)-quino line, had an ED50 value of 134 mg/kg (95% conf. int.: low-78.5, high-205.7; slope 1.9, SE = 0.44) in TTE testing. Two derivatives had MES activity. Only one compound, an N,N-diethylamino derivative, was neurotoxic in the rotorod test. Compounds were screened at a 10-microM concentration for activity in displacing 5,7-dichlorokynurenic acid from synaptosomal membrane fragments. Since 9 of the 12 compounds synthesized and tested have demonstrated anticonvulsant activity, this class of chemicals offers promise for the production of useful therapeutic agents.

Kinetoplasts play an important role in the drug responses of Trypanosoma brucei.

Trypanosoma brucei E164 and a dyskinetoplastic derivative, Dysk164, were injected into mice that were treated subsequently with methylglyoxal-bis-guanylhydrazone, berenil, ethidium bromide, and acriflavine. Additionally, parasites were photoaffinity labeled with ethidium monoazide to effect covalent drug attachment prior to injection into animals. In all cases, killing of animals with E164 was blocked by the drug treatment, whereas killing due to Dysk164 was not. These findings are consistent with the view that the intact kinetoplast plays an essential role in the action of these drugs.

Use of drug-specific antibodies to identify ethidium adducts produced in Trypanosoma brucei by photoaffinity labeling.

A photoreactive azido analog of the trypanocide ethidium bromide, 3-amino-8-azido-5-ethyl-6-phenylphenanthridinium chloride, attached covalently to calf thymus DNA (CT DNA) by photoaffinity labeling, was used to generate antibodies for the drug analog. The specificity of the antiserum was tested using enzyme-linked immunoadsorbant assays (ELISA) against immobilized antigen (photoaffinity labeled DNA) and by both the avidin-biotin peroxidase reaction and indirect immunofluorescence performed on smears of drug treated trypanosomes. The reaction of the antiserum with the covalently bound drug adduct was diminished effectively by prior incubation with an excess of ethidium monoazide, ethidium diazide, and ethidium bromide, and to a lesser extent by the DNA-ethidium complex, the diazide-DNA or RNA adduct, and the monoazide-RNA adduct. DNA which had been photoaffinity labeled with either the propidium or the acridine moiety did not react. The antiserum recognition of DNA photoaffinity labeled with ethidium monoazide was based on the substituted phenanthridinium ring system of the parent ethidium, as evidenced by competition binding studies involving the free monoazido analog (EA1), the diazido analog (EA2), and the parent compound, ethidium bromide (EB). This approach and the sensitivity it provides should prove useful for identifying the distribution and fate of covalently bound drugs resulting from antiparasitic drug treatment, and for studying their roles in antiparasitic action.

Primary and secondary risk factors for birth defects.

Birth defects may be inherited in the germ line or may result primarily from a wide spectrum of predictable physical, chemical, and infectious processes that can operate in the mother, the father, or in the zygote. The systematic consideration of these mechanisms can lead to a fresh awareness of risk and possible strategies toward recognizing and avoiding such risks. Birth defects also depend heavily on secondary factors that may even be of greater concern than any single primary insult because they may simultaneously affect the consequences of more than one primary exposure. Under the influence of secondary factors, the frequency, timing, and intensity of developmental deficiencies can be quite varied. It is particularly interesting that expression can be delayed until quite late in life, and deficiencies may occur or be expressed only in response to the appropriate environmental stress or functional demand. Any discussion of teratogenic mechanisms, therefore, is not complete without taking into account the important concept of co-teratogenesis, or the operation of secondary risk mechanisms. The principle of secondary risk or co-teratogenesis has been demonstrated by means of enhancement of radiation-induced terata by the administration of drugs that inhibit DNA repair. An example of late-onset expression of prenatal damage was illustrated with postnatal retinal degeneration occurring after prenatal damage to the developing retina. It is suggested that a systematic consideration of primary and secondary risk mechanisms can lead to a better understanding of the problem of birth defects.

Effect of verapamil on antitrypanosomal activity of drugs in mice.

The effects of verapamil on drug responses of Trypanosoma brucei brucei were studied to determine whether drug resistance of this organism could be related to expression of a drug resistance gene as has been described for drug-resistant cancer cells and malaria. Concomitant administration of verapamil during treatment of two different strains of the parasite with ethidium or berenil resulted in enhancement of the drug effect as shown by increased formation of dyskinetoplastic organisms, increased rates of clearing of the parasites from the blood, and by enhanced survival of infected mice. Verapamil treatment was associated with increased intracellular accumulation of drug, as shown by fluorescence of cells exposed to ethidium or DAPI, a fluorescent surrogate for berenil. These results suggest the importance of exploring the expression of the multiple drug-resistance gene in this series of parasites.

Anticonvulsant activity of antagonists for the NMDA-associated glycine binding site.

Coupled to the N-methyl-D-aspartate (NMDA) receptor-channel complex is a strychnine-insensitive binding site for glycine. Pharmacological antagonism of glycine binding at this site can produce anticonvulsant activity. Derivatives of the glycine antagonists kynurenic acid and 2-carboxy-indole were synthesized and evaluated for anticonvulsant effects. Compounds were tested in mice against seizures induced by electroshock and pentylenetetrazole, and in the rotorod assay for neurological deficit. The derivatives were also assayed for binding at the NMDA-associated glycine site. The most potent anticonvulsant was ethyl 4-methylamino-5,7-dichloro-2-quinoline carboxylate. This compound provided protection against maximal electroshock (MES) induced seizures at a dose level including 5-fluoro-2-indole carboxylic acid and the diethyl ester of 2,6-pyridine dicarboxylic acid.

The antioxidant butylated hydroxytoluene can retard cerebellar degeneration induced transplacentally by a single low dosage of N-methyl-N-nitrosourea.

Late-onset cerebellar degeneration can be induced transplacentally in mice by a single low-dose (1 mg/kg) injection of the direct-acting DNA alkylating agent N-methyl-N-nitrosourea (MNU) on day 16 of pregnancy. The offspring develop a mild ataxia that manifests by 12-16 weeks of age postnatally when the animals are challenged with a motor coordination task. Morphological evidence of degeneration includes pyknosis of Purkinje cells and abnormal foliation patterns. Additionally, these animals demonstrate a progressive retinopathy characterized by thinning of the nuclear and plexiform layers of the retina. Efforts to retard the cerebellar degeneration were undertaken in the present study. MNU-exposed and control animals were fed a standard mouse chow diet supplemented with 0.75% butylated hydroxytoluene (BHT), an antioxidant. This supplementation commenced 24 h following exposure to the teratogen and continued throughout the life of the offspring. A second group of MNU-exposed and control mice were fed a non-BHT-supplemented, standard Purina mouse chow diet. Quantitative histological evaluation of cerebellar coronal sections indicated that by 4 weeks of age BHT-fed, MNU-exposed mice had significantly fewer pyknotic Purkinje cells than non-BHT-fed, MNU-exposed animals. This was true for the vermal, paravermal, and lateral areas of the cerebellum. The findings suggest the usefulness of teratogenic models of degenerative diseases for the testing of potential intervention strategies.

Retinal degeneration in the mouse induced transplacentally by N-methyl-N-nitrosourea: effects of constant illumination or total darkness.

The DNA alkylating agent, N-methyl-N-nitrosourea (MNU), when administered prenatally (on day 16 of gestation) provokes a progressive retinal degeneration in CD-1 albino mice reared in standard fluorescent lighting conditions (12 L: 12 D). This degeneration begins at about 4 weeks postnatally and worsens with age. To determine whether light was essential to the development of this lesion, animals in the present study were maintained in either constant light or constant darkness. Systematic measurement of the inner and outer segment lengths, the number of rows of photoreceptor cells and the thicknesses of the outer nuclear layer and whole retina were made to quantify degenerative changes in animals at 2-, 4-, 6-, 8-, 12-, and 16 weeks of age. The constant light caused a drastic reduction in thickness of the retinas of MNU-treated and control mice. The MNU-exposed animals reared in the dark did not demonstrate this reduction in retinal thickness, at least up to 16 weeks of age. Rather, measurements from this group were much like those for dark-reared control mice. The results of the present study suggest that the retinopathy induced by this dose of MNU may require secondary insults such as light, to amplify the lesions induced in utero by the drug.

Effects of the antioxidant butylated hydroxytoluene (BHT) on retinal degeneration induced transplacentally by a single low dosage of N-methyl-N-nitrosourea (MNU).

A 1 mg/kg dose of the DNA alkylating agent, N-methyl-N-nitrosourea (MNU), when administered on day 16 of gestation provokes a progressive retinal degeneration in CD-1 albino mice reared under standard fluorescent lighting conditions (12 hr light: 12 hr dark); this degeneration begins at about 4 weeks post-natally and worsens with age. It is accelerated by constant fluorescent light exposure but is retarded greatly by constant darkness, suggesting the importance of secondary insults in the post-natal period for development of the degenerative disease. To determine whether the secondary photochemical damage might be specifically blocked, MNU-exposed and control animals in the present study were fed an antioxidant-enriched diet of Purina mouse chow supplemented with 0.75% butylated hydroxytoluene (BHT). A second group of MNU-exposed and control animals were fed a non-BHT supplemented standard Purina mouse chow diet. Systematic measurements of the number of rows of photoreceptor cell nuclei, the thickness of the inner/outer segment layer, and the thickness of the whole retina were made, to quantify and degenerative changes in animals 2, 4, 6, and 8 weeks of age. By 8 weeks, retinas of BHT-fed, MNU-exposed animals were significantly thicker and had more rows of photoreceptor cell nuclei than regular-diet, MNU-exposed animals. Moreover, the retinas of BHT-fed animals, both for MNU-exposed and controls, demonstrated sporadic morphologic changes in the form of circular configurations composed of ganglion cells, arcades of nuclear and plexiform layers, and, in one control animal, a hyperplastic nodule. These experiments suggested that MNU-induced retinal degeneration may be retarded by a BHT-enriched diet; however, continuous high doses of this compound pre- and postnatally may induce other retinal abnormalities.

Application of the fiber-optic perfusion fluorometer to absorption and exsorption studies in hairless mouse skin.

This study was undertaken to test the fiber-optic perfusion fluorometer as a direct means of evaluating skin absorption and exsorption in hairless mice. Skin-barrier compromise was accomplished in the absorption experiments by application of dimethyl sulfoxide to the skin surface or by partial removal of the stratum corneum with sticky tape. Absorbed fluorescein was measured easily in unanesthetized control (skin-barrier intact) and experimental mice. Unabsorbed chemical did not fluoresce 15 minutes after application, although it was present on the surface of the skin as a dry powder. The time course of fluorescein elimination from the skin was related to a rapid phase (vascular removal) and a slow phase (reservoir entrapment). In the exsorption experiments the fluorescein was injected intraperitoneally. Back skin on the right side was swabbed with either dimethyl sulfoxide or 1% capsaicin in alcohol prior to the injections, and differences in skin fluorescence on the left (control) and right sides were recorded. One application of dimethyl sulfoxide or capsaicin increased the level of skin exsorption. Three applications of dimethyl sulfoxide almost doubled the amount of exsorbed dye, whereas three applications of the capsaicin inhibited the exsorption process. It was concluded that the fiber-optic perfusion fluorometer provides an excellent technique in support of other methods of investigating the skin.

Late-onset cerebellar degeneration in mice induced transplacentally by methylnitrosourea.

A late-onset degenerative disease in the cerebellum was produced in the offspring of mice exposed to 1 mg/kg of the direct-acting DNA alkylating agent methylnitrosourea (MNU) on day 16 of gestation. This intrauterine exposure to MNU also provoked a progressive retinal degeneration that was described elsewhere. Mild ataxia in the MNU-exposed animals was expressed by 20 weeks of age. Although animals appeared normal in the immediate post-natal period, quantitative histological evaluation of cerebellar coronal sections indicated that MNU-exposed animals had a significantly greater number of pyknotic Purkinje cells than age-matched controls. The number of pyknotic Purkinje cells declined with age in the drug exposed animals; however, the percentage of pyknotic Purkinje cells to total number of Purkinje cells still was greater in MNU-induced animals at 36 weeks than in controls, suggesting that a slow degenerative process was ongoing in the MNU-exposed animals. Furthermore, the folia were grossly disrupted in 90% of the older MNU-exposed animals (ages greater than 12 weeks), suggesting permanent cerebellar disruption macroscopically. Such intrauterine exposure to low doses of alkylating agents may be potentially useful in modeling degenerative neuronal diseases.

Retinal degeneration in the mouse. A model induced transplacentally by methylnitrosourea.

A model of retinal degeneration has been developed in mice which is induced by the DNA alkylating agent methylnitrosourea. Pregnant mice were injected with various doses of this potent teratogen on day 16 of gestation, a time of differentiation of numerous cell types of the mouse retina. Histological examination of retinas from offspring exposed to 20-, 10- and 5 mg kg-1 doses demonstrated retinal rosettes, a pathology similar to retinal dysplasia. The 1 mg kg-1 dosage did not produce rosettes; in fact, retinas appeared morphologically normal early in life. Control and treated animals were studied at specific age intervals: 2-, 4-, 6-, 8-, 12-, 16-, 20-, 36-, 52 weeks. Measurements of the overall retinal width and five retinal layers were made to quantify the degeneration. Results indicate a thinning of the retina begins at 4 weeks and worsens with age. These results are discussed with respect to the potential of low-level exposure to environmental toxins as a possible cause of retinal degeneration.

Alkali lability and rapid initiation of excision repair following photoaffinity damage by ethidium azide.

DNA damage and repair provoked by ethidium azide (EA) photoaffinity labeling in mouse leukemia cells was studied by measuring sedimentation properties of nucleoids in neutral sucrose gradients, and it was found that the strand opening step was faster than that which followed damage of cells by ultraviolet (UV) light. The two insults were compared at levels of damage which gave the same overall rates of repair synthesis in intact cells and which required the same length of time to complete repair, as judged by the restoration of supercoiling of the isolated nucleoids. In the case of UV, single-strand breaks in DNA were detectable at 30 min, maximum at 2 h, and the superhelical properties restored at 21 h. With photoaffinity labeling, single-strand breaks were prominent immediately, even when photolabeling of cells was done on ice, but restoration of DNA supercoiling still required 21 h. Photolabeling of isolated nucleoids or isolated viral DNA with EA failed to introduce DNA strand breaks. However, it was discovered that photoaffinity labeling of DNA with EA resulted in alkali labile sites shown by single strand breaks produced on alkaline sucrose sedimentation or by alkali exposure followed by sedimentation on neutral formamide gradients. These results suggest that the drug attachment sites should be identifiable by the location of such single strand breaks.

DNA damage and repair in epithelial (mucous) cells and crypt cells from isolated colon.

Colon epithelium is made up of two general classes of cells, surface cells which are post-mitotic and crypt cells which contain the proliferative population. Their relative vulnerability to environmental damage and ability to perform DNA repair are important issues in colon carcinogenesis. DNA damage and repair was studied by the nucleoid sedimentation method in freshly isolated crypt cells for comparison with previous studies of post-mitotic surface epithelial cells. Suspensions of crypt cells were isolated from preparations of mouse colon by a series of sequential incubations in buffer containing 1.5 mM EDTA. Treatment of crypt cells for 30 min with 1.2 X 10(-6) M methyl methane sulfonate (MMS), photoaffinity labeling with 1 X 10(-6) M ethidium monoazide, lithocholic acid (2.5 X 10(-4) M) treatment for 1 h or X-irradiation at 1500 rads resulted in single-strand breaks in the DNA, which were repaired after 2 h of additional incubation. Interestingly, X-rays at 1000 rads and lithocholic acid (LA) (2.5 X 10(-6) M) after 30 min incubation failed to produce the detectable shift in nucleoid sedimentation characteristic of single-strand breaks, perhaps due to rapid repair by these proliferative cells. UV-irradiation failed to provoke strand incision as was also observed for the superficial post-mitotic cells in the previous studies. These studies showed the feasibility of studying DNA damage and repair processes in these two classes of colon epithelial cells in response to specific carcinogenic insult.

Subcellular localization of photoreactive ethidium analogs in Trypanosoma brucei by fluorescence microscopy.

To identify the in vivo targets of the trypanocide, ethidium bromide, the fluorescent staining of T. brucei was examined for a series of ethidium analogs using fluorescence microscopy. Determination of the biological targets for most drugs is limited by the reversible nature of their interactions. To overcome this limitation, photoaffinity (azido) analogs of ethidium, which are capable of covalent attachment with photoactivation, were used to identify the ethidium binding sites within the parasites. Two of these compounds, when covalently attached, demonstrated an enhancement of fluorescent staining and were selective for the kinetoplast at low drug concentrations. These compounds were also those found previously to have the highest trypanocidal activity. Propidium, a phenanthridinium analog identical to ethidium except for a larger, more ionic substitution at R5, showed more nonspecific binding as determined by its general staining of the cytoplasm.