Plasmids (Part 1)

Pharmaceutical compounds

Proteins are produced through recombinant technology for the treatment of numerous diseases - cancer, allergies, autoimmune disease, neurological disorders, heart attacks, blood disorders, infections, wounds and genetic disorders (Watson et al, 1992).

Human insulin

The first licensed drug produced through genetic engineering was human insulin. This hormone is produced in the pancreas and released into the bloodstream. An inability to produce insulin results in diabetes, but daily injections of insulin are sufficient to reverse or at least quell the debilitating effects of the disease. Prior to production of the recombinant molecule, insulin for the treatment of diabetes was obtained from the pancreases of pigs and cows. Although this insulin is biologically active in humans, the amino acid sequences are not identical to that of the human molecule. Thus, some patients produce antibodies against injected insulin, occasionally resulting in serious immune reactions. But, because recombinant insulin is identical to the natural product, immunogenicity is not a problem. Here, the plasmid used is a pBR322-type vector, in which a lacZ' reading frame is present (Brown,1990).

Factor VIII

Factor VIII plays a central role in blood clotting, which is, of course, essential to prevent drastic injuries occurring through haemorrhaging. The commonest form of haemophilia in humans results from an inability to synthesise Factor VIII. Haemophiliacs are treated by injection of purified Factor VIII obtained from human blood provided by donors. Purification is complex and expensive, and this source exposes patients to the risk of viral infections such as hepatitis B and AIDS. Human Factor VIII has been obtained from a gene cloned in recombinant hamster cells. Such Factor VIII should be free of contamination (Burnett, 1985).

Somatostatin - Anti-growth hormone

This was the first human protein to be synthesised in E.coli. It is a small peptide hormone that acts in conjunction with a second protein, somatotropin, to regulate human growth. Somatostatin is important in the treatment of a variety of human growth disorders, including acromegaly, a condition characterised by uncontrolled bone growth. For the synthesis of somatostatin, the strategy used is the same as that for insulin, involving insertion of the artificial gene into a lacZ' vector (Brown,1990).

Somatotropin - Human-growth hormone (HGH)

HGH is the complement of somatostatin and is also used in the treatment of human growth disorders, notably dwarfism. Unlike the situation with insulin, here animal-derived growth hormones are ineffective. Only the human protein works and for many years it was painstakingly extracted from the pituitaries of cadavers. Production

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