Combretastatin is a

dihydrostilbenoid Dihydrostilbenoids (bibenzyls) are natural phenols formed from the dihydrostilbene ( bibenzyl) backbone. Examples Dihydro-resveratrol is a natural phenol with a bibenzyl structure found in wine. It is also a metabolite of trans-resveratrol forme ...

found in ''

Combretum caffrum ''Combretum caffrum'' is the Eastern Cape South African bushwillow tree. Biochemistry In ''C. caffrum'', combretastatins A-1, A-4 and B-1 can be found.natural phenol In biochemistry, naturally occurring phenols are natural products containing at least one phenol functional group. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenolic compounds in response to eco ...

s. A variety of different natural combretastatin molecules are present in the bark of ''

Combretum caffrum ''Combretum caffrum'' is the Eastern Cape South African bushwillow tree. Biochemistry In ''C. caffrum'', combretastatins A-1, A-4 and B-1 can be found.statins Statins, also known as HMG-CoA reductase inhibitors, are a class of lipid-lowering medications that reduce illness and mortality in those who are at high risk of cardiovascular disease. They are the most common cholesterol-lowering drugs. Low- ...

, a family of cholesterol lowering drugs.

Natural combretastatins

Molecules that fall into the combretastatin family generally share 3 common structural features: a trimethoxy "A"-ring, a "B"-ring containing substituents often at C3' and C4', and ftenan

ethene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene is ...

bridge between the two rings which provides necessary structural rigidity. Molecules with such an ethene bridge are also

stilbenoid Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with chalcones. Most stilbenoids are prod ...

s, molecules with a non-ethene bridge are

s. Molecules with C3'

amino In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent s ...

and

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

substituents are very active, and molecules with C4' hydroxyl or

methoxy In organic chemistry, a methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula . On a benzene ring, the Hammett equation classifies a methoxy substituent at the ''para'' position as ...

substituents are also cytotoxic. Of the natural products presently known

combretastatin A-4 Combretastatin A-4 is a combretastatin and a stilbenoid. It can be isolated from '' Combretum caffrum'', the Eastern Cape South African bushwillow tree or in '' Combretum leprosum'', the mofumbo, a species found in Brazil. Function Tubulin repre ...

is the most potent in regards to both

tubulin Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoske ...

binding ability and

cytotoxicity Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa''). Cell physiology Treating cells ...

Combretastatin A-1 Combretastatin A-1 is a combretastatin and a stilbenoid. It can be found in '' Combretum caffrum'', the Eastern Cape South African Bushwillow tree. Biological effects in mammals It is an antiangiogenic agent acting by destabilizing tubulin, which ...

is also a potent cytotoxic agent. Another molecule is

combretastatin B-1 Combretastatin B-1 is a combretastatin and a dihydrostilbenoid Dihydrostilbenoids (bibenzyls) are natural phenols formed from the dihydrostilbene ( bibenzyl) backbone. Examples Dihydro-resveratrol is a natural phenol with a bibenzyl structure ...

Biological function

In the plants that make it

It is thought to help protect the plant from pests and parasites.

In mammalian tumours

Members of the combretastatin family possess varying ability to cause

vascular The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...

disruption in

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

s. Combretastatin binds to the β-subunit of

at what is called the colchicine site, referring to the previously discovered

vascular disrupting agent A vascular-targeting agent (VTA) or vascular disrupting agent (VDA) is a drug designed to damage the vasculature (blood vessels) of cancer tumors causing central necrosis. VTAs can be small-molecule or ligand-based. Small-molecule VTAs include: * ...

colchicine Colchicine is a medication used to treat gout and Behçet's disease. In gout, it is less preferred to NSAIDs or steroids. Other uses for colchicine include the management of pericarditis and familial Mediterranean fever. Colchicine is taken ...

. Inhibition of tubulin

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are ...

prevents

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

cells from producing

microtubules Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 an ...

. Microtubules are essential to

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

production, intercellular movement, cell movement, and formation of the

mitotic spindle In cell biology, the spindle apparatus refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a pr ...

used in chromosome segregation and

cellular division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there are ...

. The anti-cancer activity from this action results from a change in shape in vasculature

endothelial cells The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...

. Endothelial cells treated with combretastatin rapidly balloon in shape causing a variety of effects which result in

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

of the tumor core. The tumor edge is supported by normal vasculature and remains, for the most part, unaffected. As a result it is likely that any therapeutic use will involve a combination of drugs or treatment options.

Chemical synthesis

A variety of possible routes to the combretastatin skeleton are possible. One reasonably easy synthesis is as follows: * 1-Bromomethyl-3,4,5-trimethoxybenzene undergoes an S_N2 reaction with

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists a ...

, which yields a

phosphonium In polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, or halide group). These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions. Types of phosphonium ...

salt. * This compound, through an

ylide An ylide or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms h ...

intermediate, is coupled to a

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. ...

-derived B-ring possessing the desired substituents using a Wittig olefination. * The Wittig reaction produces varying amounts of ''E'' and ''Z''

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

depending mainly on solvent polarity, temperature, metal cation coordination effects, and the electronic effect of substituents on either the triphenylphosphine salt or the benzaldehyde. Generally cis-combretastatin possesses significantly improved ability to inhibit tubulin polymerization as well as

. To directly generate the cis forms a Perkin condensation reaction can be used.

Clinical studies

Combretastatin A-4 Combretastatin A-4 is a combretastatin and a stilbenoid. It can be isolated from '' Combretum caffrum'', the Eastern Cape South African bushwillow tree or in '' Combretum leprosum'', the mofumbo, a species found in Brazil. Function Tubulin repre ...

, the most potent naturally occurring combretastatin known, its phosphate

prodrug A prodrug is a medication or compound that, after intake, is metabolized (i.e., converted within the body) into a pharmacologically active drug. Instead of administering a drug directly, a corresponding prodrug can be used to improve how the drug ...

( CA-4-P), and other analogs of CA-4 such as

ombrabulin Ombrabulin was an experimental drug candidate discovered by Ajinomoto and further developed by Sanofi-Aventis. Ombrabulin is a combretastatin A-4 derivative that exerts its antitumor effect by disrupting the formation of blood vessels needed for t ...

are currently being investigated in a number of

clinical trials Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...

References

{{Dihydrostilbenoid