Safer anti-coagulants: Kicking out the pig.

Synopsis by Audrey Moores and Wendy Hessler, Feb 29, 2012

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An approach combining chemistry and biology improves the process to make important anti-clotting drugs known as heparins. The heparin medicines prevent dangerous blood clots from forming in veins and are needed for surgery and kidney dialysis.

The technique provides easier access to safer drugs that are now either processed from pigs and cows or synthesized in a long, costly lab process. The novel method described in the journal Science provides a realistic alternative to livestock for heparins and is likely to drop the cost of such pharmaceuticals.

The process is not yet ready for large-scale commercial use, but its product yields are impressive.

 

Context

Many pharmaceutical drugs are processed from plants or animals rather than made in a laboratory. While such a strategy may seem more natural, animal-sourced drugs are susceptible to contamination.

Heparins are a family of drugs used for more than 50 years to prevent blood clots in people. These complex molecules come from three main sources. They can be collected from pig intestines or cow lungs, synthesized in a laboratory or collected from animals and then modified in a lab.

The sizes and uses of the three types vary. The animal-sourced drug is the largest. It degrades rapidly in the body and is used for kidney dialysis and surgery. The chemically-altered animal heparin and the synthetic varieties are smaller, longer-lived molecules. Patients with venous thrombosis – the tendency for blood clots to form in veins – take these to prevent the clots.

Safety is an issue with the animal-sourced heparin, the cheapest and most accessible available. In 2007, drug contamination resulted in at least 200 deaths in the United States and raised concerns over the source of heparin.

GlaxoSmithKline synthesizes the smaller-sized heparin under the brand name Arixtra. Their process requires about 50 steps and yields very low amounts of material– around 0.1 percent. As a consequence, this molecule cannot currently replace animal-based heparins for all applications because of its high price.

The risk of contamination and current cost of synthesizing heparin is driving the quest to find a more efficient and cheaper way to make heparin drugs.

 

What did they do?

A team of chemists from the United States applied a strategy called chemoenzymatic synthesis to fabricate the heparin molecule. The method borrows from both chemistry and biology fields.It is an attractive way to synthesize heparin medicines. The drug contamination in 2007 occurred because the heparin collected from animals had an unusual chemical structure. People became allergic and hypersensitive. These side-effects would be avoided using a chemoenzymatic system because the series of chemical and enzymatic reactions needed to produce the drug are much better controlled than those in the animal gut where many proteins can alter the drug-to-be molecule.

In this study, the researchers mimicked the process animals use to make heparins. They chemically synthesized a starting material then added enzymes that lengthened and built the whole heparin molecule. In other words, they transferred what happens in the pig gut into a beaker. This approach is superior to collecting directly from an animal because the reactions are controlled.

To see if the manufactured drugs were effective, the researchers tested them in two different ways in the lab. First, they put them with two key proteins responsible for coagulating blood. Then, they injected rabbits with them and collected the animal blood. The interactions with the proteins alone in a culture and in the blood from the rabbit were measured and compared with the activity of the commercial heparin Arixtra.

 

What did they find?

The researchers discovered they could produce two heparin molecules with the impressive yield of 45 and 37 percent, in 10 and 12 steps respectively. They were able to make several milligrams of the product.

The two newly synthesized heparin molecules were similar in size to as the current Arixtra drug. They also proved as active as Arixtra. The efficacy of the interaction between the drugs and coagulating proteins were similar to Arixtra.

The same was true when the newly developed heparins were tested with rabbits. The drugs interacted with the same proteins as Arixtra.

 

What does it mean?

A more streamlined method to make anti-coagulant drugs may provide a realistic alternative to the animal-sourced pharmaceuticals, which are susceptible to contamination. The new process also produces more heparin product in shorter time and for less money than current synthetic preparations.

This means that the newly made heparins could be used in a wider range of applications than the current synthetic heparin Arixtra, because the reduced cost may open new markets.

This technique isolated 3.5 milligrams of heparin. The obvious next step will be to scale up this process to demonstrate that it is commercially feasible. It is estimated that 10 to 20 tons of heparin drugs are sold every year in the world.

The new drugs must also be tested and properly certified before they can be used commercially. However, the preliminary results of this research effort show that these two heparin molecules should be active anti-coagulant drugs with similar properties as the most popular synthetic version on the market today.

The type of synthesis – which merges chemistry techniques and biological enzyme actions – profiled here may be transferable to the manufacture of other drugs. Read more science at Environmental Health News.