Pharmaceuticals and fermentation: from molecule to medicine: Enzymes, biologics and the economics

5.1 Enzymes and biocatalysis: one clean step at a time

Enzymes are protein catalysts made by living cells. Kent stresses their attractions: they are highly specific, so they make few by-products; they work at ambient temperature and near-neutral pH; they can be made by fermentation from sugar; and they can be engineered. The world market for "Industrial enzymes" exceeded $3.5 billion in 2010, growing 5 to 8% a year. Over half of sales are proteases for detergents, dairy and leather; carbohydrases such as amylases are nearly 40%. Novozymes and Genencor (now DuPont) lead.

An enzyme is expensive and fragile in solution, so the key industrial trick is immobilisation: fixing it to a solid support so it can be reused. Shreve lists adsorption, covalent bonding and entrapment in a polymer. Kent's glucose isomerase example shows the payoff. Over 500 t of immobilised enzyme are made each year, mostly by binding whole cells into a clay-based granule. In a packed column above 60°C its half-life exceeds a year, and one kilogram makes 20,000 kg of high-fructose syrup.

Biocatalysis now does steps in drug manufacture. Penicillin G acylase, immobilised on a resin, snips the side chain off penicillin G to make 6-aminopenicillanic acid (6-APA), the nucleus from which ampicillin and amoxicillin are built. Kent gives productivities over 2,000 kg of product per kg of catalyst and reuse for over 1,000 cycles; the reaction is held at pH 7.5 to 8 against the phenylacetic acid it releases. Enzymes similarly make 7-aminocephalosporanic acid (7-ACA) from cephalosporin C. Worldwide output of semisynthetic penicillins is around 10,000 t a year. These are the "Antibiotic intermediates (6-APA, 7-ACA)" tile.

• Kent (2012), Ch 31 Industrial Enzymes and Biocatalysis · pdf pp. 1184-1185, 1208, 1213, 1215-1218
• Shreve (1984), Ch 31 Fermentation Industries · pdf pp. 618-619

5.2 Biologics: proteins made by living cells

Biologics are protein drugs: insulin, growth hormone, erythropoietin, monoclonal antibodies. Kent's biotechnology chapter puts biopharmaceutical sales at about $45 billion, 10% of the pharmaceutical market, with 25% of new drugs now biologics. Kent's pharmaceutical chapter notes biologics went from none to eight of the top 20 US drugs between 2006 and 2009.

Small proteins can be made by bacteria. Kent describes human insulin made in E. coli as a precursor, proinsulin, in an 18 to 24 hour fermentation at 37°C. The protein piles up inside the cells as insoluble clumps called inclusion bodies, 10 to 30% of dry cell mass, which protect it and ease recovery. It is then refolded and trimmed with enzymes.

Larger proteins need mammalian cells, because bacteria cannot fold them correctly or attach the sugar chains (glycosylation) that many need to work. Kent states that 60 to 70% of recombinant protein drugs are made in cultured mammalian cells, mostly Chinese hamster ovary (CHO) cells. These are delicate: 37°C, pH 7.0 to 7.4, tight control of dissolved oxygen and osmolality, and protection from bubble damage. Batch culture runs 3 to 5 days and gives under 0.5 g/L. Fed-batch, the industrial norm, runs one to two weeks and gives over 1.5 g/L, with the best reaching about 4 g/L. Perfusion, a continuous mode that keeps cells in the vessel, gives roughly ten times the volumetric productivity. Production bioreactors hold 10,000 to 20,000 L.

Purification follows a sequence of capture, intermediate purification and polishing, mainly by chromatography. For antibodies, Protein A affinity resin captures the product in one step with purification of several thousandfold, then ion-exchange steps remove host-cell protein, DNA and viruses.

• Kent (2012), Ch 30 Industrial Biotechnology: Discovery to Delivery · pdf p. 1180
• Kent (2012), Ch 11 Chemistry in the Pharmaceutical Industry · pdf p. 422
• Kent (2012), Ch 32 Industrial Production of Therapeutic Proteins · pdf pp. 1229, 1239-1245
• Pollak (2011), Fine Chemicals · pdf pp. 66-67

5.3 Where the cost of a medicine sits

Pull the module together and the cost structure of a medicine looks nothing like that of a commodity chemical. Pollak, using data from European generic producers and IMS Health, splits the price of a drug product into four parts: cost of goods (API, formulation and packaging) about 20%, R&D 15 to 20%, marketing and administration 35 to 40%, and profit about 25%. The API alone is usually under 10% of the selling price. Within a fine chemical company the API's own price is about 35% raw materials and 55% conversion cost, the rest margin.

Two consequences follow. Originators price by the daily cost of treatment, not the cost of the molecule; Pollak notes 100 Lipitor tablets cost the same at 20, 40 or 80 mg. And after patent expiry the arithmetic reverses: generic producers chase every gram of yield.

Batch versus continuous follows from scale. Most APIs are needed in 10 to 1,000 t a year, so multipurpose batch plants win; Kent adds that batch suits cGMP because each lot is accepted or rejected on its own. Continuous operation pays where volumes are large and the catalyst is robust, as the glucose isomerase figures show.

Regulation is a cost at every stage: years of trials, validation of each process, batch release testing, and inspected plants. Pollak counts more than 2,000 producers of APIs for generics worldwide, but fewer than 10% meet the highest GMP and regulatory standards for the regulated markets. China has become the main source of large-volume generic APIs such as penicillins, and Pollak lists Indian firms such as Cipla, Divi's Laboratories, Dishman, Hikal and Ranbaxy among the fine chemical producers serving the industry, a position built on the process skills Dryden describes.

• Pollak (2011), Fine Chemicals · pdf pp. 75, 185-187, 225, 239-240
• Kent (2012), Ch 11 Chemistry in the Pharmaceutical Industry · pdf p. 425
• Dryden (1997), IVH Pharmaceutical Industry · pdf pp. 566-567

See it in the table

Check your understanding

Immobilised penicillin G acylase gives over 2,000 kg of 6-APA per kg of enzyme. Why does immobilisation matter so much for cost?

Which bioreactor mode is the industrial norm for mammalian cell culture, and why?

Pollak puts cost of goods at about 20% of a drug product's price. What is the largest single element?