Tissue Plasminogen Activator: A Case Study In Pharming

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Tissue Plasminogen ActivatorA Case Study
InPharming

• Timothy G. Standish, Ph. D.

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What is Tissue Plasminogen Activator (t-PA)?

• t-PA is an enzyme that serves in the cascade of
  events leading to dissolution of blood clots

Damaged Tissues
Plasminogen
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t-PA Has Been Developed As A Drug By Genentech

• The biotechnology company Genentech has cloned
  human t-PA for use in treating unwanted or life
  threatening blood clots
• Activase (Alterplase recombinant) is the trade
  name of Genentechs t-PA
• Activase is useful in treating heart attacks and
  strokes when administered within 5 hours of
  thrombosis formation or embolism lodging in the
  heart or brain
• The FDA approval in 1987 and medical use of
  Activase has a very interesting history

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Production of t-PA

• Scientists at Genetech took human mRNA coding for
  t-PA from a human myloloma cell line
• The mRNA was converted into cDNA
• Human t-PA coding cDNA was inserted it into
  Chinese hamster ovary cell lines
• When grown in culture the CHO cells excrete human
  t-PA into their growth medium
• Activase is produced by isolating t-PA from the
  growth medium
• This is an expensive and difficult process

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Growing t-PA In CHO Cells
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Pharming

• Because production of t-PA in cell culture is a
  difficult and expensive process, t-PA is an
  expensive drug
• t-PAs main competition in the thrombolytic (clot
  busting) market is streptokinase
• Streptokinase costs 1/10th the price of t-PA and
  seems to do an equivalent job
• A cheaper way to produce t-PA would be beneficial
  (unless you are a streptokinase manufacturer)
• Pharming offers the promise of cheap production
  of a wide variety of proteins including t-PA
• T-PA was the first viably produced protein using
  pharming

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What Is Pharming?

• Pharming is the use of recombinant domestic
  animals to produce proteins and other bioactive
  compounds
• One of the most common strategies in pharming
  involves engineering mammals to produce desired
  proteins in their milk
• This strategy was first used to produce t-PA in
  the milk of goats
• It is not coincidental that this work was done at
  the Roslin Institute in Scotland, the same
  institute that cloned Dolly.

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Making Recombinant Goats 1Vector Construction

• The murine (mouse) way acid protein promoter
  signals for expression of the gene in mammary
  cells as part of milk
• LAtPA cDNA codes for a point mutated form of tPA
  (asn-gtglu at AA 117) that is glycosylated
  differently resulting in longer acting (LA) tPA
• SV40 is a virus that provides the poly A signal
  telling cells mRNA is ready for expression

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Making Recombinant Goats 2Vector Insertion
Zygote
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Making Recombinant Goats 2Vector Insertion
Zygote
Nucleus
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Making Recombinant Goats 2Vector Insertion
Zygote
Most copies of the vector are broken down
Nucleus
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Making Recombinant Goats 2Vector Insertion
Nucleus
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Making Recombinant Goats 2Vector Insertion
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Making Recombinant Goats 3Making Kids
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The 1987 Trials Of Genentech

• March
• Japanese patent for tPA awarded to Genentich
• Several companies file objections
• June
• FDA refuses to license tPA - Genentech stock
  loses 1,000,000,000 or 11.50 per share
• Wellcome challenges Genentechs UK tPA patent

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The 1987 Trials Of Genentech

• July
• Genentech looses to Wellcome but appeals - Stock
  loses 1.375
• tPA is on the market in New Zealand, The
  Philippines, and France
• November
• FDA approves tPA for human use
• tPA is on the market in Austria, West Germany and
  South Korea
• December
• In the last 6 weeks of 1987, US sales of tPA
  total 58,000,000

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Genentech Stock Prices 1987
Loss of patent Infrigngment suit
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The 1988 Trials Of Genentech

• January
• 20,000,000 in US tPA sales
• March
• Genetech stock is listed on the NYSE
• A study reveals tPA reduces mortalitiy two weeks
  after acute myocardial infarction
• Sales of tPA drop to 11,000,000 for February
  and March
• 2,000 patients a week are treated with tPA
• April

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The 1988 Trials Of Genentech

• April
• Ontario Medical Association recommends using
  streptokinase instead of tPA because of the
  expense of tPA
• Medicare refuses to pay for tPA
• Genentech stock drops 18 in two weeks
• June
• US patent for tPA is granted to Genentech, but
  only covers the purified form and does not
  exclude others from filing patents
• In a suing-o-rama, Genentech sues Burroughs
  Welcome and Genetics Institute for their tPA
  collaboration, Abbott sues Genentech for patent
  infringement, Genentech fails to win a
  restraining order to prevent clinical trials of
  tPA produced by Toyobo under license from
  Integrated Genetics in Japan

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The 1988 Trials Of Genentech

• September
• Genentech is issued a US patent on its human
  recombinant version of tPA
• On the basis of the new patent Burroughs Wellcome
  and Genetics Institute are sued again
• November
• Genentech looses its appeal of a lower court
  decision to void its patent for being to broad in
  scope

1990

• March
• An Italian study shows streptokinase to be
  equally effective as tPA for long term survival
  of heart attacks

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Genentech Stock Prices 1988
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Current Genentech Stock Prices
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Ethical Issues

• Is production of recombinant organisms ethical?
• Do the risks of recombinant organism production
  outweigh the benefits of recombinant products?
• Is use of organisms as tools to make products
  purely for human benefit ethical?
• Is introduction of animal products into humans
  for therapeutic purposes ethical?
• Is the cost of making recombinant products the
  most productive use of health care resources?
• Is it ethical to withhold treatment using
  expensive recombinant products from the poor so
  that investment can be recouped and reinvested?

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Ethical Issues Cont.

• Is it ethical to produce high tech/high cost
  health care products that are only marginally
  better than lower tech lower cost products?
• Is it possible to own (patent) a naturally
  occurring human gene?
• Is it product infringement when another company
  produces a comparable product that has identical
  activity and other properties, but differs
  structurally from the original?

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