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SAR or Quantitative Structure-Activity Relationships are mathematical relationships linking chemical structure and pharmacological activity in a quantitative manner for a series of compounds. Methods, which can be used in QSAR, include various regression and pattern recognition techniques.

Randomization: the process by which patients in a clinical trial are randomly assigned to different treatments Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms.

Randomized Trial: a trial in which the participants are randomly assigned to receive one of the treatments under study or a placebo. See Randomization

Receptor is a molecule or a polymeric structure in or on a cell that specifically recognizes and binds a compound acting as a molecular messenger (neurotransmitter, hormone, lymphokine, lectin, drug, etc.).

Receptor mapping is the technique used to describe the geometric and/or electronic features of a binding site when insufficient structural data for this receptor or enzyme are available. Generally the active site cavity is defined by comparing the superposition of active to that of inactive molecules.

Recombinant DNA (deoxyribonucleic acid) molecules with different origins that have been joined to form a new chimeric chain. It also refers to compounds (proteins) produced by laboratory or industrial cultures of genetically engineered Iiving cells. The cells. genes have been altered to give the capability of producing large quantities of the desired compound for use as a medical treatment.

Rectum: the terminus of the large intestine including the anus.

Refractory: severe disease that is resistant to treatment.

Remission: a period when the signs of a disease have been eliminated through treatment or the immune response. A disease may be in remission without a complete cure having been effected.

Renal: of or relating to the kidneys.

Resistance: reduction in the sensitivity to a particular drug, common for antimicrobial, antiviral or anticancer drugs. Resistance can arise by production of enzyme that destroy the drug, changes in the permeability of the cell membrane or bacterial wall; aleration of the structure of the target for the drug, altered metabolic pathways, by pass of the target of the drug. Resistance detected by searching a pathogen. genetic makeup for mutations thought to confer lower susceptibility is called genotypic resistance. Resistance found by successfully growing laboratory cultures of the pathogen in the presence of a drug is called phenotype resistance.

Retina: the multilayered, light-sensitive membrane lining the inner eyeball that sends visual images to the brain via the optic nerve.

Retinal Detachment: a condition in which a portion of the retina becomes separated from the inner wall of the eye. Retinal detachment can result from retinal disease such as CMV retinitis (see). The condition can rapidly lead to vision loss, but is treatable by adding silicone to the eye.s vitreous humor (see) to increase the pressure on the retina.

Retinitis: inflammation of the retina, usually caused by infections such as CMV. If left untreated, it can lead to blindness.

Retrovirus: a type of virus that, when not infecting a cell, stores its genetic information on a single-stranded RNA molecule instead of the more usual double-stranded DNA. HIV is an example of a retrovirus. After a retrovirus penetrates a cell, it constructs a DNA version of its genes using a special enzyme, reverse transcriptase. This DNA then becomes part of the cell.s genetic material.

Ribozyme is a recombinant RNA/enzyme combination designed to fit onto and cleave specific viral or cancerous genetic sequences from a cell.s DNA.

Rule-of-five is a rule that establishes that poor absorption or permeation of drugs are more likely when there are 5 or more hydrogen bond donors, 10 or more hydrogen bond acceptors, logP is over 5 and the molecular weight is over 500.

Salvage Therapy: the final possible treatment for people who are nonresponsive to or cannot tolerate other available treatments for a particular condition.

Sarcoma: a malignant tumor of the skin and soft tissue.

Scatchard equation or Scatchard plot is a method to extract binding data. Rearranging into a linear form the equilibrium constant and expressing it in terms of the fraction of sites occupied by the drug. The slope of the equation provides the reciprocal of the binding constant, while the intercept of the abscissa is the number of binding sites.

Second messenger is an intracellular metabolite or ion increasing or decreasing as a response to the stimulation of receptors by agonists, considered as the .first messenger.. This generic term usually does not prejudge the rank order of intracellular biochemical events.

Septicemia: a serious condition caused by large numbers of bacteria in the blood. This condition can be fatal. Symptoms are a sudden drop in blood pressure and changes in heart rate and temperature.

Serum is the clear portion of the blood from which cellular components have been removed

Single nucleotide polymorphisms SNPs (pronounced .snips.) are minute genetic variations that occur throughout human DNA. Their value as genetic markers resides in their simplicity, frequency, and relatively even distribution throughout the genome. Of the roughly 3-billion nucleotide pairs (i.e., the .letters.) that make up the genetic code, it is estimated that a SNP.a single letter variation in the code from one person to the next.occurs every thousand or so nucleotide pairs.

Sinusitis is an inflammation of the nasal cavity and sinuses.

Site-specific delivery is an approach to target a drug to a specific tissue, using prodrugs or antibody recognition systems.

Sphingolipid is a complex lipid found in membranes of nerve and brain tissue which contains three components, a sphingosine (long chain amino alcohol) or one of its derivatives, a fatty acid and a polar head group.

Spleen: a large lymphatic organ in the upper left of the abdominal cavity with several functions: 1) trapping of foreign matter in the blood, 2) destruction of degraded red blood cells and foreign matter by macrophages, 3) formation of new lymphocytes and antibody production, and 4) storage of excess red blood cells.

Soft drug is a compound that is degraded in vivo to predictable non-toxic and inactive metabolites, after having achieved its therapeutic role.

Southern Blot or DNA blot transfer is a series of techniques that allow the visualization of specific DNA fragments. In the case where the procedure is carried out on RNA, the technique is named a Northern Blot.

Stem Cell: the precursor of all blood cells, which lives in the bone marrow. Clones of stem cells may become any one of the repertoires of immune cells depending upon what cytokines and hormones they are exposed to.

Steroids are compounds based on the steran skeleton, a fully hydrogenated cyclopentane phenantrene. Steroids are classified according to their substitution patterns in Sterols, bile acids, estrogens, gestagens, androgens, corticoids, cardenolids, sapogenins and steroid alkaloids. [See figure]

Stomatitis: inflammation of the mucous membranes in the mouth.

Structure-activity relationship (SAR) is the relationship between chemical structure and pharmacological activity for a series of compounds.

Structure-based design (SAR) is a drug design strategy based on the 3D structure of the target obtained by X-ray or NMR.

Structure-property correlations refers to all statistical mathematical methods used to correlate any structural property to any other property (intrinsic, chemical or biological), using statistical regression and pattern recognition techniques.

Subcutaneous: injected directly under the skin.

Superoxide Dismutase is one of the major cellular antioxidant enzymes. It removes surplus peroxide, an oxidizing free radical (see). Superoxide dismutase comes in two forms, one containing zinc and the other containing manganese.

Surrogate Marker A measurement of a drug.s biologic activity that substitutes for a clinical endpoint such as death or pain relief.

Suicide Substrate or Kcat substrate is an irreversible enzyme inhibitor that binds covalently.

Symptomatology: the collected symptoms of a particular disease.

Synergy: the interaction of two or more treatments such that their combined effect is greater than the sum of the individual effects observed when each treatment is administered alone.

Systemic means relating to or affecting the whole body. A systemic therapy is one that the entire body is exposed to, rather than just the target tissues affected by a disease.