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silver bullet

A silver bullet is a term used a lot in medicine. It is used to describe a perfect drug that cures a disease with no danger of side effects.

The term silver bullet was first used in this context by the German physician and scientist Paul Ehrlich who received the Nobel Prize in 1908. The story goes that he was sitting on a train thinking about medical matters when the Bavarian fairy tale of The Silver Bullet kept interrupting his train of thought. The silver bullet was a magic bullet that would only kill its intended victim. This led to the first antibiotic.

Germany was the world leader in the chemical and dye industry and Ehrlich tested many chemicals against the syphilis microbe. Syphilis was a widespread, serious infection, mercury salts were the only effective treatment for syphilis. However, these had serious side effects and treatments often led to the death of patients. After much testing Ehrlich found compound 606 was found to be highly effective at killing the microbe while having very few negative effects on the body. It was re–named Salvarsan and was the first antibiotic to be discovered, it was Ehrlich’s best known silver bullet.

The concept of a “silver bullet” continues. Science has harnessed the effectiveness of the body’s own immune system to produce silver bullets. The development of antibody-drug compounds means that antibodies against various cells, compounds and toxins can be made. The monoclonal antibody can then deliver a drug to that specific cell (e.g. a cancer cell). Until recently chemotherapy for cancer consisted of  toxic substances that attacked rapidly dividing cells more than other cells; although cancers cells generally divide rapidly so do other cells in the body (e.g. gut and skin cells) so chemotherapy was associated with severe side effects such as nausea and hair loss.

monoclonal anntibodies

 

Some monoclonal antibodies trigger the immune system to attack and kill cancer cells. Although cancer cells are abnormal, they develop from normal cells so they can be difficult for the immune system to spot. Some monoclonal antibodies simply attach themselves to cancer cells, making them easier for the cells of the immune system to find them.

Pembrolizumab has been approved for use. It is a drug that targets malignant melanoma, a skin cancer. Pembrolizumab has shown enormous promise in shrinking tumours in most people and eradicating them completely in some. Other monoclonal antibodies can block signals telling cancer cells to divide and as mentioned earlier toxic drugs can be attached and delivered to cancer cells by targeting the part of the genome that has mutated.

Gene editing

genetic engineering

On the day before her first birthday, Layla Phillips parents’ were told that all treatments for her leukaemia had failed and she was going to die. In desperation her parents agreed for her to be given a highly experimental treatment -a tiny vial filled with genetically engineered immune cells that were designed to kill her cancer – it succeeded. https://medicalschoolinterviewstheknowledge.wordpress.com/2015/11/11/genetically-modified-super-immune-cells-new-treatment-to-fight-cancer/

Researchers at Duke University in the US used a system known as CRISPR-Cas9 to delete DNA in mice that was preventing cells from producing a protein essential for muscle function which causes a human equivalent disease called Duchenne’s Muscular Dystrophy. A virus was used to deliver DNA alterations into the cells of mice.When they injected the therapy direct into the legs of adult mice, it resulted in improved muscle strength. When they injected it into the bloodstream – tests showed improvements in muscles responsible for heart and lung function.

Earlier this year, a group in China announced it was the first to successfully edit the genome of a human embryo. The breakthrough at Sun Yat-sen University in Guangdong showed the errors in DNA that led to a blood disorder, beta thalassaemia, could be corrected in embryos. Gene editing has been used to make mosquitoes resistant to the malaria parasite which they transmit to humans and to make pig organs genetically similar to human organs.

CRISPR-Cas9 is a gene editing technique that uses the Cas9 protein and a strand of RNA to make breaks in strands of DNA. Then new genetic code is then placed inside the breaks. This can allow the genetic code to be rewritten. It is powerful and reliable, quick and very cheap. CRISPR-Cas 9 “components” can be bought or $30.  Possible applications are numerous, this is why Science Magazine declared the technique its ‘Breakthrough of the Year!’

The first GM humans will probably soon arrive. Is it ethical to go down this path which leads to the alteration of the design of human genomes? Is unethical not to and to leave people suffering and dying from potentially curable diseases? What do you think?

 

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