In vitro activities

The basic biology and pharmacology of Epo B (as the most potent and most widely studied natural epothilone) have been summarized in several previous review articles.As indicated in Section 1.1, the biological effects of the compound are based on its ability to bind to microtubules and alter the intrinsic stabihty and dynamic properties of these supramolecular structures. In cell-free in vitro systems, this is demonstrated by the prevention of Ca - or cold-induced depolymerization of preformed microtubule polymers as well as by the promotion of tubuhn polymerization (to form microtubule-like polymers) in the absence of either microtubule-associated proteins (MAPs) and/or guanosine triphosphate (GTP), at temperatures significantly below 37 °C, and in the presence of The latter 

In line with its effects on mbulin polymerization in vitro (i.e., in an excellular context), the prevention of cold-induced depolymerization of micrombules by epothilones has also been demonstrated in cells. Microtubule stabilization in intact cells (as well as cancer cell growth inhibition, vide infra), however, is observed at strikingly lower concentrations than those required for the induction 

Treatment of human cancer cells with low nM concentrations of Epo B leads to profound growth inhibition and cell death (Table 1-1). In line with the effects on tubulin polymerization in vitro, Epo B is a more potent antiproliferative agent than Epo A, which in turn is about equipotent with paclitaxel. As observed for paclitaxel, Epo B treatment produces aberrant mitotic spindles, results in cell cycle arrest in mitosis, and eventually leads to apoptotic cell death. It is often assumed that apoptosis is a direct consequence of G2/M arrest, which in turn would be a prerequisite for growth inhibition and cell death. However, as has been elegantly demonstrated by Chen et al. in a series of recent experiments, the situation is clearly more complex, such that low concentrations of Epo B (and paclitaxel 

TABLE 1-1. ICso Values [nM] for Net Growth Inhibition of Hnman Cancer Cell Lines by Epo A and B in Comparison With Paclitaxel  

In summary, all tubulin mutations identified to date in epothilone-resistant cells are found in regions of the tubulin structure, which are predicted to be important for 

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The investigations of Jensen and Schmith (45) indicate that in vitro activity of 2-sulfanilamido and 4-methyl-2-sulfanilamido selenazoles against pneumonia infections is comparable to that of sulfathiazole or sulfadiazine. Frisk (47) found that the activity of the selenium compounds was much lower than that of sulfathiazole. 

Another important development in the stmcture—activity relationships of quinolone antibacterials came with the introduction of the 1,8-bridged quinolone ofloxacin (6a). In this quinolone, the movement of the ethyl group at the 1-position is restricted by "tying" it to the 8-position in the form of a 1,4-benzoxazine ring. In vitro activity improvements are found that are more or less comparable to the improvements noted with ciprofloxacin (35,41—43). 

The streptovaricins inhibit the reverse transcriptase of some RNA oncogenic vimses that may be involved in the process of viral transformation (see Antiviral agents). The atropisostreptovaricins again have similar activities to the corresponding natural isomers. The streptovals and streptovarone exhibit gready improved activity against reverse transcriptase relative to the streptovaricins (85), but their in vitro activities were low (86). The damavaricins also inhibit reverse transcriptase (4) as well as tumor cell growth (87). 

This antimycotic, which was iatroduced for topical use, shows in vitro activity against dermatophytes, species of Candida Jispergillus Coccidioides immitis Histop/asma capsulatum Cryptococcus neoformans and Madure/h species. Petriellidium (Alkscheria) boydii and Phialophora species are less sensitive. 

Itraconazole. Itraconazole (18) is a highly lipophilic compound with a triazole stmcture. Compared to ketoconazole, itraconazole has a broader spectmm (including yispergillus spp.) (29,30) and an in vitro activity that is 10 times higher than ketoconazole for most species. 

FIAC also strongly inhibits HCMV and Epstein-Barr vims (EBV) in vitro the two vimses known not to induce a specific viral thymidine kinase for their repHcation. However, HCMV may stimulate cellular kinases that can anabolize FIAC to its 5 -triphosphate, which specifically inhibits the HCMV-encoded DNA polymerase. This selective activity suggests that FIAC should be evaluated against HCMV infections. FIAC-ttiphosphate incorporated into DNA has shown strong in vitro activity against the DNA polymerases of human hepatitis B vims (HBV) and of woodchuck hepatitis vims (WHV) (37). 

An azole nucleoside stmcturaHy related to ribavirin is tiazofutin [60084-10-8] (2-P-D-ribofuranosylthiazole-4-carboxamide, 57) (Fig. 8). It was synthesized ia 1977 (132). Tiazofuria, showa good activity agaiast tomato-spotted wilt vims and good in vitro activity against several... 

Although the precise mechanism of plasminogen activation is unknown, three principal theories have developed based on studies of the in vitro activation of native human plasminogen. Activation of native Glu-plasminogen in the absence of any plasmin inhibitor yields Lys —plasmin plus the so-called pre-activation peptides (PAP) formed by cleavage at LySg2 S E3 Activation takes place by a two-step mechanism in... 

There is thus obtained bishydroxycoumarin (3). Subsequent pharmacologic and clinical work revealed this compound to be an effective anticoagulant drug in humans. It is of note that none of the synthetic anticoagulants shows in vitro activity. Rather, these compounds owe their effect to inhibition of synthesis by the liver of one of the co-factors necessary for coagulation. 

Vanadate (sodium orthovanadate or peroxovanadate) exhibits insulin-like effects in vitro (activation of insulin receptor tyrosine kinase, PI 3-kinase, Akt) and in vivo (diabetic rats, humans). These effects can be explained at least in part by the inhibition of phosphotyrosine phosphatases which deactivate the INSR tyrosine kinase. 

Mosser, D.D., Kotzbauer, P.T., Sarge, K.D., Morimoto, R.I. (1990). In vitro activation of heat shock transcription factor DNA binding by calcium and biochemical conditions that affect protein conformation. Proc. Natl. Acad. Sci. USA 87, 3748-3752. 

Rituximab is a recombinant mouse/human chimeric monoclonal antibody whose in vitro activity varies with the number of terminal galactose moieties glycosylated to the peptide backbone at residue asparagine 301 [8]. The ability to monitor the levels of each discrete species present would allow the manufacturing process to... 

Redwood City, California, and Roche) and two clones have been selected for their improved in vitro activity relative to human IFN-a. One of them has been pegylated but its development has been halted because of strong immune reaction. 

There have been notable successes in the replacement of individual peptide residues by peptoid monomers with retention of in vitro activity and enhancement of specificity. Unfortunately, attempts to completely transform those bioactive peptides that function via specific peptide-protein binding events into entirely pep-toid-based ohgomers have so far proven successful only at short chain lengths (e.g. [23]). It remains to be seen whether any general strategy can be developed in... 

A necessary condition for a compound to exhibit in vivo efficacy is in vitro activity. By activity, we mean that the compound is able to demonstrate binding to the protein target of interest. At constant pressure and temperature, the protein (P) and ligand (L) binding free energy is given by... 

Roxithromycin has similar in vitro activity to erythromycin but enters leucocytes and macrophages more rapidly with higher concentrations in the lysosomal component of the phagocytic cells. It is likely to become an important drug against Legionella pneumophila. Clarithromycin is also of potential value. 

Evans, P.H., Brown, R.C. and Poole, A. (1983). Modification of the in vitro activities of amosite asbestos by surface derivati-zation. J. Toxicol. Environ. Health 11, 535-543. 

Maker, H.S. Weiss, C. and Brannan. Amine-mediated toxicity The effects of dopamine, norepinephrine, 5-hydroxytryptamine, 6-hydroxy-dopamine, ascorbate, glutathione and peroxide on the in vitro activities of creatine and adenylate kinases in the brain of the rat. 

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