Similarity biological

Insulin is available as purified extracts from beef and pork pancreas and is biologically similar to human insulin. However, these animal source insulins are used less frequently today than in years past. They are being replaced by synthetic insulins, including human insulin or insulin analogy. 

Amine hormones include the thyroid hormones and the catecholamines. The thyroid hormones tend to be biologically similar to the steroid hormones. They are mainly insoluble in the blood and are transported predominantly (>99%) bound to proteins. As such, these hormones have longer half-lives (triiodothyronine, t3, = 24 h thyroxine, T4, = 7 days). Furthermore, thyroid hormones cross cell membranes to bind with intracellular receptors and may be administered orally (e.g., synthryoid). In contrast to steroid hormones, however, thyroid hormones have the unique property of being stored extra-cellularly in the thyroid gland as part of the thyroglobulin molecule. 

The catecholamines are biologically similar to protein/peptide hormones. These hormones are soluble in the blood and are transported in an unbound form. Therefore, the catecholamines have a relatively short half-life. Because these hormones do not cross cell membranes, they bind to receptors on the membrane surface. Finally, the catecholamines are stored intracellu-larly in secretory granules for future use. 

Yes, but with caution. Reference has been made several times to the fundamental biological similarities of mammalian species, and to the expected similarities in response to chemical toxicity in animals and human beings. These expectations have been borne out in a large proportion of those cases in which there has been an opportunity to obtain toxicity data in both humans and animals, so that it would be imprudent to ignore the results of cancer bioassays. At the same time these results need to be carefully scrutinized, because they can easily mislead. 

In the context of compound partitioning, it should also be considered that relationships between structural and biological similarity can differ significantly. Much of the current molecular similarity research is based on the fundamental, and rather intuitive, similar property principle (18), which states that compounds with similar structures should generally have similar biologically activity. On the other hand, it is well known that minute structural modifications of active com-... 

These tumors include all T cell neoplasms that are derived from postthymic T cells and, because of immunophenotypic and apparent biologic similarities, include the natural killer (NK) cell lymphomas. 

These calculations generally start with a series of known active compounds that are added as search templates (or bait molecules) to a source database and compounds that are identified as similar to these templates based on VS calculations are selected as candidate molecules for experimental evaluation. Activity-oriented VS typically aims at identifying compounds that structurally differ from known templates but have similar activity. This is often done because known active compounds are difficult to develop, not easily chemically accessible (for examples, natural products), or already covered by other patents. In such cases, VS analysis attempts to identify molecular similarity relationships that balance structural and biological similarity in rather different ways, which is often a non-trivial task. 

In 1994, six novel drimane-type sesquiterpenoids, mniopetals A-F (1-6) (Fig. (1)), were isolated by Anke and Steglich from the fermentation broth of Canadian Mniopetalum sp. 87256 [1, 2]. These natural products are known to inhibit the enzymatic activity of RNA-directed DNA-polymerases (reverse transcriptases) of the human immunodeficiency virus (HIV)-l, avian myeloblastosis virus (AMV), and moloney murine leukemia virus (MMuLV) as shown in Table 1. In addition, mniopetals exhibit moderate antimicrobial and cytotoxic activities. In the following year, a structurally and biologically similar natural product kuehnero-... 

Due to the unique biological similarity of drospirenone (e.g., mild anti-aldosterone and anti-androgenic activity) to the natural progesterone, Yasmin has important advantages over the known oral contraceptives [14]. For example, the use of Yasmin does not initially cause any increase in body weight, and it is also effective in treating mild to moderate acne. Likewise, menstrual cycle control is excellent. 

These principles can be directly applied to chemistry. It is possible to determine similarities in amino acid sequences in myoglobin in a variety of species. The more similar the species, die closer is die relationship chemical similarity mirrors biological similarity. Sometimes die amount of information is so huge, for example in large genomic or crystallographic databases, diat cluster analysis is die only practicable way of searching for similarities. 

Medicinal chemists always followed and still apply the principle of chemical and biological similarity. Whenever they discover an active lead, they modify its chemical structure more or less systematically, to find similar analogs with improved activities, selectivities, ADME (absorption, distribution, metabolism, elimination) properties fewer side effects and less toxic properties. However, as discussed above, structurally closely related analogs may have significantly different specificity or even a completely different mode of action. 

Tanimoto index > 0.9 but may be very different in terms of activity (chemically similar, biologically diverse), while completely different strucmres are known to have the same biological activity (chemically diverse, biologically similar). This intrinsic drawback to the computational screening of virtual libraries should always be considered when interpreting screening results of a computationally designed library, and real data should be used to refine any virtual SAR information based on chemical similarity or dissimilarity. 

BioSter— pairs of biologically similar structures for bioisosterism applications... 

Carcinoids are the most common tumors arising from the diffuse neuroendocrine system of the GI tract and pancreas. Derived primarily from enterochromaffin cells, these tumors are widely distributed in the body but found with greatest frequency in the GI tract (74%) and respiratory tract (25%). Carcinoids are often classified as APUDomas (flmine precursor uptake and decarboxylation) because of the ability of enterochromaffin cells to take up and decarboxylate amino acid precursors of biogenic amines. In this regard, carcinoid tumors share certain pathological and biological similarities with pheochromocytomas. 

Of the actinides, plutonium is potentially a particularly dangerous biological hazard because of the chemical and biological similarities between Pu(IV) and Fe(III). With this similarity in mind, a series of tetracatechol ligands with both linear and cyclic tetramines as backbone were synthesized in accordance with the general scheme outlined above 24,118) (see Fig. 7a and b). The eight-coordinate nature of Pu(IV)... 

Commercial PCB Mixtures. Information on the immunotoxicity of commercial PCBs in orally-exposed animals is available from intermediate- and chronic-duration studies in various species. Findings in nonhuman primates are emphasized in the following summary because monkeys appear to be more sensitive than other species and provide a better animal model due to phylogenetic and biologic similarities to humans (Tryphonas 1994, 1995). 

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