Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Chitin

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who worked with various substances. The first widely used

drug was 6-Mercaptopurine, synthesized by Elion and

Hitchings in 1952.

Chemotherapy is used alone, in combination, and along

with radiation and/or surgery, with varying success rates,

depending on the type of cancer and whether it is localized or

has spread to other parts of the body. They are also used after

treatment to keep the cancer from recurring (adjuvantther-

apy). Since many of the drugs have severe side effects, their

value must always be weighed against the serious short-and

long-term effects, particularly in children, whose bodies are

still growing and developing.

In addition to the male and female sex hormones andro-

gen, estrogen, and progestins, scientists also use the hormone

somatostatin, which inhibits production of growth hormone

and growth factors. They also use substances that inhibit the

action of the body’s own hormones. An example is Tamoxifen,

used against breast cancer. Normally the body’s own estrogen

causes growth of breast tissues, including the cancer. The drug

binds to cell receptors instead, causing reduction of tissue and

cancer cell size.

Forms of the B-vitamin folic acid were found to be use-

ful in disrupting cancer cell metabolism by the American sci-

entist Sidney Farber (1903–1973) in 1948. Today they are

used on leukemia, breast cancer, and other cancers.

Plant alkaloids have long been used as medicines, such

as colchicine from the autumn crocus. Cancer therapy drugs

include vincristine and vinblastine, derived from the pink peri-

winkle by American Irving S. Johnson (1925– ). They prevent

mitosis (division) in cancer cells. VP-16 and VM-16 are

derived from the roots and rhizomes of the may apple or man-

drake plant, and are used to treat various cancers. Taxol, which

is derived from the bark of several species of yew trees, was

discovered in 1978, and is used for treatment of ovarian and

breast cancer.

Another class of naturally occurring substances are

anthracyclines, which scientists consider to be extremely use-

ful against breast, lung, thyroid, stomach, and other cancers.

Certain antibiotics are also effective against cancer cells

by binding to DNA and inhibiting RNA and protein synthesis.

Actinomycin D, derived from Streptomyces, was discovered

by Selman Waksman and first used in 1965 by American

researcher Seymour Farber. It is now used against cancer of

female reproductive organs, brain tumors, and other cancers.

A form of the metal platinum called cisplatin stops can-

cer cells’ division and disrupts their growth pattern. Newer

treatments that are biological or based on proteins or genetic

material and can target specific cells are also being developed.

Monoclonal antibodies are genetically engineered copies of

proteins used by the immune system to fight disease.

Rituximab was the first moncoclonal antibodyapproved for

use in cancer, and more are under development. Interferons

are proteins released by cells when invaded by a virus.

Interferons serve to alert the body’s immune system of an

impending attack, thus causing the production of other pro-

teins that fight off disease. Interferons are being studied for

treating a number of cancers, including a form of skin cancer

called multiple myeloma. A third group of drugs are called

anti-sense drugs, which affect specific genes within cells.

Made of genetic material that binds with and neutralizes mes-

senger-RNA, anti-sense drugs halt the production of proteins

within the cancer cell.

Genetically engineered cancer vaccines are also being

tested against several virus-related cancers, including liver,

cervix, nose and throat, kidney, lung, and prostate cancers.

The primary goal of genetically engineered vaccines is to trig-

ger the body’s immune system to produce more cells that will

react to and kill cancer cells. One approach involves isolating

white blood cells that will kill cancer and then to find certain

antigens, or proteins, that can be taken from these cells and

injected into the patient to spur on the immune system. A “vac-

cine genegun” has also been developed to inject DNA directly

into the tumor cell. An RNA cancer vaccineis also being

tested. Unlike most vaccines, which have been primarily tai-

lored for specific patients and cancers, the RNA cancer vac-

cine is designed to treat a broad number of cancers in many

patients.

As research into cancer treatment continues, new can-

cer-fighting drugs will continue to become part of the medical

armamentarium. Many of these drugs will come from the bur-

geoning biotechnologyindustry and promise to have fewer

side effects than traditional chemotherapy and radiation.

See also Antibiotic resistance, tests for; Antiviral drugs;

Bacteria and bacterial infection; Blood borne infections; Cell

cycle and cell division; Germ theory of disease; History of

microbiology; History of public health; Immunization

CHICKEN POX•seeANTIBIOTICS

CChitinHITIN

Chitin is a polymer, a repeating arrangement of a chemical

structure. Chitin is found in the supporting structures of many

organisms. Of relevance to microbiology, chitin is present in

fungal species such as mushrooms, where it can comprise

from 5% to 20% of the weight of the organism.

The backbone of chitin is a six-member carbon ring that

has side groups attached to some of the carbon atoms. This

structure is very similar to that of cellulose. One of the side

groups of chitin is known as acetamide, whereas cellulose has

hydroxy (OH) side groups.

Chitin is a noteworthy biological feature because it is

constructed solely from materials that are naturally available.

In contrast, most polymers are man-made and are comprised

of constituents that must be artificially manufactured.

The purpose of chitin is to provide support for the

organism. The degree of support depends on the amount and

the thickness of chitin that is present. In fungisuch as mush-

rooms, chitin confers stability and rigidity, yet allows some

flexibility. This allows the mushrooms to stand and still be

flexible enough to sway without snapping.

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