Activation in Vitro

There are several examples of activation of xenobiotic-metabolizing enzymes by compounds other than the substrate. This differs from induction (described in Chapter 9) in that it is an immediate effect on a preexisting enzyme, occurring in an enzyme preparation in vitro, that does not involve de novo protein synthesis. The occurrence and significance of such stimulation in vivo is not apparent. 

CYP-mediated microsomal oxidations may be stimulated by the addition of any of a rather heterogeneous group of compounds, including ethyl isocyanide, acetone, 

2 -bipyridyl, and, under certain conditions, the inhibitor metyrapone. The effect is not uniform, however, because acetone, for example, stimulates aniline hydro-xylation but has no effect on the /V-demethylation of A-methylanilinc, N,N-dimethylaniline, or ethylmorphine, or the O-demethylation of p-nitroanisole. 2,2 -Bipyridyl, on the other hand, stimulates both aniline hydroxylation and N-demethylation of /V-mcthyl- and /V,/V-dimethylaniline but, at the same time, inhibits the A-dealkylation of ethylmorphine and aminopyrine. Presumably, these differences are related to isoform specificity for the activator and/or the substrate. 

The activation of another membrane-bound enzyme of interest in biochemical toxicology, UDP glucuronyltransferase, is probably due to effects on the membrane. In this case, significant stimulation is brought about by aging the enzyme preparation, by sonication, and by such agents as dilute detergents and proteolytic enzymes. 

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A second class of herbicides primarily affects ( -carotene desaturase. These herbicides are apparent feedback inhibitors of PD as well. This class of compounds includes dihydropyrones like LS 80707 [90936-96-2] (56) and 6-methylpyridines (57,58). The third class consists of the ben2oylcyclohexane-diones, eg, 2-(4-chloro-2-nitroben2oyl)-5,5-dimethyl-cyclohexane-I,3-dione. This class of atypical bleaching herbicides induces phytoene accumulation when appHed either pre- or post-emergence. However, it does not inhibit phytoene desaturase activity in vitro (59). Amitrole also has been considered a bleaching herbicide, though its main mode of action is inhibition of amino acid synthesis. 

In the parvodicin and teicoplanin series (Table 3) the nature and length of the fatty acid portion of the glycoHpid moiety only slightly influence the activity in vitro. Dalbaheptides are bactericidal against actively growing, but not against resting, bacteria (33). 

The discovery and biological properties of lincomycin (1, R = OH, R = H) were described ia 1962 (1). This antibiotic is active in vitro and in vivo against most of the common gram-positive pathogens. Resistance by Staphylococci is developed slowly ia a stepwise manner, based on in vitro serial subculture experiments, and its activity is not iafluenced by body fluids up to concentrations of 50% ia the assay medium (2). 

Antibacterial activity of clindamycin is found both in urine and feces after adrninistration of clindamycin. This activity is a consequence of the presence of both clindamycin and its metaboUte, de- /V-methy1c1indamycin [22431-45-4] (6, R = R = H). Unlike de-/V-methy11incomycin, the de-Ai-methyl analogue is as active in vitro as clindamycin. The analogue has been isolated from the urine of humans who had received clindamycin, and its presence in semm has been detected (65). 

Fluconazole. This substance (19) is a water-soluble bis-triazole tertiary alcohol (33). Fluconazole [86586-75-4] h.3.s a broad spectmm, but has httie activity in vitro. However, animal experiments reveal a broad spectmm and a potent effect. 

There are no hiUy effective therapeutic agents for the treatment of thederiasis. Chlorotetracycline (20) and oxytetracycline (3) have therapeutic activity duting the iacubation period. Pamaquiae (68) was reported to have a specific effect on the erythrocyctic forms. Other dmgs with limited efficacy are imidocarb (19) on T annulata halofugiaone (45) on both T annulata and T parva and the naphthoquiaones menoctone (76), parvaquone (88), and buparvaquone (89) on T parva. Methotrexate (90) has been found to be active in vitro (Table 9). 

The harmol derivatives (type C), in which R ranged from ethyl to w-dodecyl, proved active in vitro, and reached a peak of activity at 0-n-nonylharmol, and in a second series in which R was modified by the inclusion of a dialkylamino-residue, activity was further increased and reached a maximum at 0-A-di-n-butylaminoundecylharmol (tvpe C R = (C4H9),N(CH,)ii-). 

Anti-mycobacterium avium activity in vitro of 3-carboxy-7-methyl-6-nitro-l-ethyl-l,8-naphthyridin-4(lH)-one (6-nitro derivative of nalidixic acid) was demonstrated (93MI1). 

All of the acids prepared in (74JAP(K)4, 79CPB1) were tested for their antimicrobial activities in vitro 2-Thiazolone derivatives showed far higher activity... 

Cefpimizole (51) appears to be less active in vitro than cefotaxime and cefoperazone and to have a somewhat narrower activity spectrum although some strains of Pseudomonas are susceptible. It is not orally active, but its performance in vivo appears superior to what would be expected from its in vitro data. Its synthesis begins by acylation of cephaloglycin (48) with the bis acid chloride of imidazole-4,5-dicarboxylic acid (49) to give amide 50. The acetyl moiety at C-3 of this intermediate is displaced with 4-pyridineethanesulfonic acid and sodium iodide to give cef-pimazole (51) [16]. 

C. Evaluation of Biological Activity In Vitro Superoxide Release from Cultured Cells... 

RGD analogs have been shown to inhibit the attachment of osteoclasts to bone matrix and to reduce bone resotptive activity in vitro. The cell surface integrin, av 33, appears to play a role in this process. RGD analogs may rq resent a new approach to modulating osteoclast-mediated bone resorption and may be useful in the treatment of osteoporosis [9]. 

Larson, J.S., Schuetz, T.J., Kingston, R.E. (1988). Activation in vitro of sequence specific DNA binding by a human regulatory factor. Nature 335, 372-375. 

Cooke CM (2002) Effect of organotins on human aromatase activity in vitro. Toxicoiogy Letters, 126 121-130. 

HCV-796 is a non-nucleosidic NS5B polymerase inhibitor with potent antiviral activity in vitro. A phase lb study was performed to determine the antiviral activity, pharmacokinetics, and safety of HCV-796 in patients with chronic HCV infection. Maximum antiviral effects were achieved after 4 days of treatment with a mean reduction of HCV-RNA of 1.4 loglOIU/ml. Combination of HCV-796 with pegylated interferon-a led to a greater reduction of viral RNA load (3.3-3.5 loglO lU/ml) after a 14 days treatment interval. 

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