Instructor: Instructor:

Dr. Marinella SandrosDr. Marinella Sandros

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NanochemistrNanochemistryy

NAN 601NAN 601

Lecture 23: Drug Design

A substance used in the diagnosis, treatment, or prevention of a disease.

A drug is any chemical or biological substance, synthetic or non-synthetic

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A Drug….

http://www.detox-center.com/images/3.jpg

A drug is anything that affects the way an organism works.

Drugs can be taken to enhance function, such as a student drinking caffeine to enhance alertness.

For now we only consider drugs which are used to cure a disease.

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Discovery of Drugs

Man has found, by trial and error, which berries, roots, leaves and barks could be used for “medicinal purposes” to alleviate symptoms of illness.

All ancient civilisations made discoveries in this field

Chinese herbal remedies are probably the most well known

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A disease is often thought of as an infection, where a bacteria, virus, or other living thing invades the body.

However, a disease is anything which affects the proper functioning of the body.

It can be an infection, a genetic disorder, or the result of environmental conditions such as malnourishment, poisoning, or stress.

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Discovery of Drugs

Engineers often find it easy to see the body as a factory.

Individual organs can be seen as machinery. The actual nuts, bolts, screwdrivers, and wrenches that make up all the machinery are the equivalent of proteins, little chunks of organic material that move things around in the body and attach them together.

Most of the work in our body is done by proteins.

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Discovery of Drugs

The body contains thousands of different kinds of proteins.

The construction of each is determined by the DNA in the nucleus of each cell.

DNA may be thought of as long strings of instructions which code for how each protein is too be built.

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Discovery of Drugs

The DNA is just a long string of acids that serves as a message about how to make proteins.

http://www.labgrab.com/files/science-news/images/LabGrab/CentralDogma_0.jpg?1286382362

Transcription, Translation and Protein Synthesis

The processes of new drug discovery and development are long, complicated and dependent upon the expertise of a wide variety of scientific, technical and managerial groups.

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Today there are at least 120 distinct chemical substances derived from plants that are considered important drug and are currently in use in one or more countries in the world

Some of these drugs are simply a chemical or chemicals extracted from plant materials and put into a capsule, tablet or liquid.

Eg. In Germany a Cynarin drug is manufactured and sold to treat hypertension, liver disorders and highly cholesterol levels.

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The cynarin drug is simply an Artichoke liquid extract, that has been concentrated and chemically manipulated to contain a specific amount of this one chemical ; such a preparation is called a standardized extract.

However in the U.S artichoke extracts are available as natural products and sold in health food stores as “dietary supplements”

Some –U.S artichoke products are even standardized to contain a specific amount of cynarin, yet they can still be purchased here as a natural product without a prescription.

There may be little to no difference between the Cynarin drug produce in Germany and the artichoke standardized herbal supplements made in the U.S considering that the same amount of Cynarin is being delivered, dose for dose

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Consumers find it very frustrating to sort through a lot of ambiguous information put out by natural product manufacturers who cannot legally label their goods with condition-specific.

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http://www.nlm.nih.gov/medlineplus/images/pills5.jpg

While many drugs have originated from medicinal plants, medicine uses can be attributed to various active chemicals found in them, there is a distinct difference between using a medicinal plant and a chemical drug.

The difference is one that scares most conventionally trained doctors with no training in plants.

Drugs usually consist of a single chemical, whereas medicinal plants can contain 400 or more chemicals.

It’s relatively easy to figure out the activity and side effects of a single chemical.

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Rev Edward Stone (1760s) searched along a riverbank (i.e. a cold and wet place) for a plant-based cure for the fevers associated with influenza.

Found that the bark of the willow was effective in reducing fever.

Native American Cherokees used willow bark for such purposes for centuries.

* willow bark contains salicin

* metabolized in vivo to the active agent salicylic acid

* salicylic acid and more tolerable “prodrug” aspirin made in late 19th century

* mechanism of action not discovered until the1970s www.dermaxime.com/willow-bark.htm

• Analgesic (pain reliever)

• Antipyritic (fever reducer)

• Anti-inflammatory

• Anticoagulent

Inhibits production of prostaglandins (pain messengers)

History of Aspirin- Hippocratus: powder made from the

bark and leaves of the willow tree to help heal headaches, pains and fevers

- Henri Leroux & Raffaele Piria: purification of active ingradient from the plant

- 1899 Hoffman: formulation and patent

The synthesis involves the reaction of salicylic acid and acetic anhydride in the presence of a catalyst, phosphoric acid, H3PO4.

wwwchem.csustan.edu/.../aspirincons.htm

Once the aspirin is prepared it must be isolated from the reaction solution and purified. The aspirin is insoluble in cold water, and can be isolated by filtering the chilled reaction solution.

Purification is necessary to remove any unreacted salicylic acid and acetic anhydride, as well as the acetic acid product and phosphoric acid. Acetic anhydride is caused to decompose by the addition of water once the formation of aspirin is complete:

(CH3CO)2O + H2O → 2 CH3CO2H

Powdered dried bark of the cinchona tree, a native of South America, was made into a drink and used by the Quechua Indians of Peru to treat fevers.

“Discovered” by Jesuit priests in the 1620s, Barnabé de Cobo takes cinchona bark to Europe in 1632 to treat malaria.

http://www.mhhe.com/biosci/pae/botany/botany_map/articles/images/bm_08-02.gif

Quinine isolated in 1820 by Pierre Joseph Pelletier and JosephCaventou

First Total Synthesis (1943) RB Woodward and WE von Doering

Kills parasites causing malaria.

Mode of action complex

http://en.wikipedia.org/wiki/File:Quinine.svg

The so-called 'father of modern chemotherapy‘.

Original proponent of the “magic bullet” he aimed to use chemicals to treat disease.

In 1910 the first fully synthetic drug was made: ‘Salvarsan’ which contained arsenic!

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Used for treating sleeping sickness (trypanosomiasis) and syphilis (caused by Treponema pallidum).

The Nobel Prize for Medicine 1908

http://en.wikipedia.org/wiki/File:Salvarsan-montage.png

A bio(macro)molecule may be involved in a disease process, but to be a drug target it has to be validated.

In other words shown to be critical in the disease process.

Useful techniques available are to validate a target are:

Gene knockout: does removal of the gene that encodes the target protein result in, for example, the death of a pathogen (disease causing microorganism)?

RNA interference (RNAi): involves double-stranded ribonucleic acid (dsRNA) interfering with the expression of genes with sequences complementary to the dsRNA. Results in a reduction of the production of the protein (target) in question.

How specific does the interaction between a drug molecule and its target have to be?

A rough and ready ‘back of the envelope’ calculation shows:

Consider: an active compound MW 200 g mol-1

1 mole = 6×1023

Therefore 1 mg substance gives (6×1023)×(10-3/200) = 3×1018 molecules

A human has approximately 3×1013 cells giving……3 ×1018/3×1013 = 1×105 molecules of active substance per cellAn erythrocyte (a typical cell) contains approx 1010 molecules∴1 molecule of active substance per 100,000 cellular molecules

The isolation of many bioactive products from natural sources has led to the systematic screening of plant and animal extracts for activity.

80% of the world’s population uses drugs exclusively from natural sources.

35% of drugs contain ‘principles’ (key structure elements) of natural origin.

Less than 5% of the 500,000 higher plant species have undergone biological pharmacological screening.

Each plant has potentially 10,000 different constituents.

Research based pharmaceutical companies, on average, spend about 20% of their sales on research and development (R&D).

This percentage is significantly higher than in most other industries, including electronics, aerospace, automobiles, and computers.

Since 1980 US pharmaceutical companies have practically doubled spending on R&D every 5 yrs.

Prodrugs are biologically inactive derivative of an active drug intended to permeate certain barriers in the parent drug such as toxicity, instability, minimal solubility and non-targeting capabilities.

The majority of drugs for cardiovascular diseases undergo first-pass metabolism resulting with drug inactivation and generation of toxic metabolites, which makes them appealing targets for prodrug design.

Numerous therapeutic drugs for treating cardiovascular ailments suffer from undesirable properties after metabolism leading to drug inactivation causing pharmacological, pharmaceutical and pharmacokinetic barriers in their clinical drug application.

To minimize these undesirable drug properties while maintaining the drug therapeutic activity, the prodrug approach was developed by covalently linking the active drug to a chemical moiety thus offering the utmost flexibility and at the same time enhancing the drug efficacy.

The universally accepted definition for a prodrug is a pharmacologically inert chemical drug that can be converted in vivo to the active drug molecule enzymatically or non-enzymatically while retaining its therapeutic effect.

It is also worth noting that despite the fact that prodrugs and anologs take on similar structures, there are still some inherent differences.

Mini Reviews in Medicinal Chemistry 2005, 5, 893-914.

Therapeutic drugs for cardiovascular diseases development soared because scientists were able to investigate complex molecular interactions that occur in the onset of disease and overcome pharmacological barriers by adapting to the prodrug approach.

In turn, the amalgamation of these two developments provided a way to identify genetic alterations and to screen for a wider range of new drugs.

Venous thromboembolism is a joint term for deep vein thrombosis and pulmonary embolism, where a blood clot is formed in a vein leading to major organs.

Thrombin plays an intricate role in the development of venous thromboembolism; for that reason scientists were instigated to formulate drugs that can block thrombin formation.

Platelets get promoted at the site of vascular injury by thrombin and fibrinogens which are converted to fibrins to offer stability for the surrounding platelets

Ximelagatran is quickly taken up in the gastrointestinal tract and biologically converted to melagatran.

Melagatran is known to inhibit the production and the activity of human -thrombin with a high binding affinity.

There are several differences between ximelagatran and melagatran.

One ximelagatran contains an ethyl group at the carboxylic end and a hydroxyl group at the amidine end.

Furthermore, at physiological pH melagatran is highly charged whereas ximelagatran is inert and favor more lipopholic environments.

Melagatran can be broken down further in the body therefore it is removed via the renal route.

BIBR 1048 is also rapidly absorbed after oral administration and converts to dabigatran (BIBR 953) which is potent and selective for inhibiting thrombin.

Circulation 2000, 101, (6), e76-80

Monoclonal antibody c7E3 (abciximab), epitifibatide and tirofiban.

Although these inhibitor drugs are effective in lowering platelet aggregation, they can only be administered intravenously and cannot be given orally.

An oral active prodrug was developed by Boehringer Ingelheim, by the name of lefradafiban which is converted to an inhibitor drug fradafiban in the digestive system.

A clinical pharmacology phase I study revealed that lefradafiban was able to inhibit platelet aggregation.

After percutaneous coronary intervention (PCI), coronary stenting is performed to reduce restenosis. Followed coronary stenting, patients are given an antiplatelet drug clopidogrel which has shown superior efficacy in comparison to aspirin to inhibit stent thrombosis.

Clopidogrel is inactive prodrug that is oxidized in the liver by cytochrome P450 to 2-oxo-clopidogrel leading to an active acid derivative metabolite

The acid derivative of clopidogrel releases its antiplatelet effect by generating a disulfide bond with the platelet P2Yac adenosine diphosphate (ADP) receptors.

Platelet aggregation is interceded by P2Yac (P2Y12) ADP receptor by blocking adenyl cyclase.

Biochemical Pharmacology 1992, 44, (3), 527-532.

17 -estradiol which is the most common estrogen hormone found in humans, has been linked to stop the initiation and the development of atherosclerosis in animal models.

Once inside the body, 17 -estradiol is metabolized to 2-methoxyestradiol (2-ME) through methylation.

2-ME can block rat and human vascular smooth muscle cells migration and proliferation.

2-ME inhibits cell division by blocking the expression and activation of cyclin and cyclin-dependent kinases (Cyclin-D1/cdk4), the expression of cdk inhibitor p27, tubulin polymerization and the expression of cyclooxygenase-2

http://www.jove.com/video/2846/method-for-novel-anti-cancer-drug-development-using-tumor-explants-of-surgical-specimens