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Page 3
II. Non-viral systems - These methods avoid the hazards of working with viruses, and are easier to prepare. The methods generally rely on normal cellular mechanisms for uptake of large molecules.
A. DNA plasmids. A plasmid is a small circular DNA molecule found in the cytoplasm of the cell instead of in the nucleus. This plasmid is also called "naked DNA", since it is not enclosed in an envelope of protein or other substance. After inserting the transgene in the plasmid, it is delivered by injection into the patient's muscle or by means of a "gene gun". The disadvantage of plasmids is that few (1-3%) cells take up the DNA.
B. Liposomes are small spherical structures with a shell that have two layers of lipid (fatty substance) on their surface. In the laboratory, researchers prepare liposomes with DNA in their interiors. The lipid layer has similarities to the cell membrane, so the liposome can fuse with the cancer cell and release its contents. Although the lipid bilayer protects the DNA from attack by the body's immune system, it lacks specificity and only a relatively few cancer cells take up the DNA.
C.DNA-polypeptide ligand complexes. This is a recent development in delivery systems. It attempts to overcome the problem of non-specificity by combining the DNA with a polypeptide (protein) ligand. This ligand binds with a specific receptor on the cancer cell. Unfortunately, much of the DNA is broken down within the cell before the transgene can be expressed.
In my next article, I will describe current research on the applications of gene therapy for the treatment of cancers.
1. Blau,H. ans Springer, M. Gene Therapy-A Novel Form of Gene Delivery, New England Journal of Medicine, Volume 333, Number 18, pages 1204-1207 (November 2, 1995). 2.CancerNet Questions and Answers About Gene Therapy (search term, gene therapy) 3.In Touch Gene Transfer Systems (search term, cancer gene therapy)
The copyright of the article Cancer Gene Therapy I - Page 3 in Cancer Treatment is owned by . Permission to republish Cancer Gene Therapy I - Page 3 in print or online must be granted by the author in writing.
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