As a result, we are investigating many plants and animals as sources of new medicines. Ticks and bat saliva could provide anticoagulants, and poison-arrow frogs might be a source of new painkillers. A fungus produces a novel, antioxidant enzyme that is a particularly efficient at mopping up free radicals known to encourage tumor growth. ByettaTM (exenatide), an incretin mimetic, was chemically copied from the venom of the gila monster and approved in early 2005 for the treatment of diabetes. PRIALT® (ziconotide), a recently approved drug for pain relief, is a synthetic version of the toxin from a South Pacific marine snail.
The ocean presents a particularly rich habitat for potential new medicines. Marine biotechnologists have discovered organisms containing compounds that could heal wounds, destroy tumors, prevent inflammation, relieve pain and kill microorganisms. Shells from marine crustaceans, such as shrimp and crabs, are made of chitin, a carbohydrate that is proving to be an effective drug-delivery vehicle.
REPLACING MISSING PROTEINS
Some diseases are caused when defective genes don't produce the proteins (or enough of the proteins) the body requires. Today we are using recombinant DNA and cell culture to produce the missing proteins. Replacement protein therapies include
factor VIII-a protein involved in the blood-clotting process, lacked by some hemophiliacs.
insulin-a protein hormone that regulates blood glucose levels. Diabetes results from an inadequate supply of insulin.
USING GENES TO TREAT DISEASES
Gene therapy presents an opportunity using DNA, or related molecules such as RNA, to treat diseases. For example, rather than giving daily injections of missing proteins, physicians could supply the patient's body with an accurate instruction manual-a nondefective gene-correcting the genetic defect so the body itself makes the proteins. Other genetic diseases could be treated by using small pieces of RNA to block mutated genes.
Only certain genetic diseases are amenable to correction via replacement gene therapy. These are diseases caused by the lack of a protein, such as hemophilia and severe combined immunodeficiency disease (SCID), commonly known as the "bubble boy disease." Some children with SCID are being treated with gene therapy and enjoying relatively normal lives, although the therapy has also been linked to leukemia. Hereditary disorders that can be traced to the production of a defective protein, such as Huntington's disease, may be best treated with RNA that interferes with protein production.
Medical researchers also have discovered that gene therapy can treat diseases other than hereditary genetic disorders. They have used briefly introduced genes, or transient gene therapy, as therapeutics for a variety of cancers, autoimmune disease, chronic heart failure, disorders of the nervous system and AIDS.
In late 2003, China licensed for marketing the first commercial gene therapy product, Gendicine, which delivers the P53 tumor suppressor gene. The product treats squamous cell carcinoma of the head and neck, a particularly lethal form of cancer. Clinical trial results were impressive: Sixty-four percent of patients who received the gene therapy drug, in weekly injections for two months, showed a complete regression and 32 percent attained partial regression. With the addition of chemotherapy and radiation, results were improved greatly, with no relapses after three years.
Approximately 18 people die each day waiting for organs to become available for transplantation in the United States. To circumvent this problem, scientists are investigating ways to use cell culture to increase the number of patients who might benefit from one organ donor. Liver cells grown in culture and implanted into patients kept them alive until a liver became available. In one study of patients with type 1 diabetes, researchers implanted insulin-producing cells from organ donors into the subjects' livers. Eighty percent of the patients required no insulin injections one year after receiving pancreatic cells; after two years, 71 percent had no need for insulin injections. In another study, skeletal muscle cells from the subject repaired damage to cardiac muscle caused by a heart attack.
Drugs for suppressing the immune response must be given if the transplanted cells are from someone other than the patient. Researchers are devising new ways to keep the immune system from attacking the transplanted cells. One method being used is cell encapsulation, which allows cells to secrete hormones or provide a specific metabolic function without being recognized by the immune system. As such, they can be implanted without rejection. Other researchers are genetically engineering cells to express a naturally occurring protein that selectively disables immune system cells that bind to it.
Other conditions that could potentially be treated with cell transplants are cirrhosis, epilepsy and Parkinson's Disease.
STIMULATING THE IMMUNE SYSTEM
The immune system is made up of different branches, each containing different types of "soldiers" that interact with each other in complex, multifaceted ways.