Firstgeneration tissue plasminogen activator

Although tPA was first studied in the late 1940s, its extensive characterization was hampered by the low levels at which it is normally synthesized. Detailed studies were facilitated in the 1980s after the discovery that the Bowes melanoma cell line produces and secretes large quantities of this protein. This also facilitated its initial clinical appraisal. The tPA gene was cloned from the melanoma cell line in 1983, and this facilitated subsequent large-scale production in CHO cell lines by recombinant DNA technology. The tPA cDNA contains 2530 nucleotides and encodes a mature protein of 527 amino acids. The glycosylation pattern was similar, though not identical, to the native human molecule. A marketing licence for the product was first issued in the USA to Genentech in 1987 (under the tradename Alteplase). The therapeutic indication was for the treatment of acute myocardial infarction. The production process entails an initial (10 000 l) fermentation step, during which the cultured CHO cells produce and secrete tPA into the fermentation medium. After removal of the cells by sub-micrometre filtration and initial concentration, the product is purified by a combination of several chromatographic steps. The final product has been shown to be greater than 99 per cent pure by several analytical techniques, including HPLC, SDS-PAGE, tryptic mapping and N-terminal sequencing.

Alteplase has proven effective in the early treatment of patients with acute myocardial infarction (i.e. those treated within 12 h after the first symptoms occur). Significantly increased rates of patient survival (as measured 1 day and 30 days after the initial event) are noted when tPA is administered in favour of streptokinase, a standard therapy (see later). tPA has thus established itself as a first-line option in the management of acute myocardial infarction. A therapeutic dose of 90-100 mg (often administered by infusion over 90 min) results in a steady-state alteplase concentration of 3-4 mg T1 during that period. However, the product is cleared rapidly by the liver, displaying a serum halflife of approximately 3 min. As is the case for most thrombolytic agents, the most significant risk associated with tPA administration is the possible induction of severe haemorrhage.

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