A new antivirulence drug that can render Methicillin Resistant Staphylococcus Aureus (MRSA) and Streptococcus pyogenes bacteria ineffective by stopping the production of disease causing toxins has been developed by a researcher at Case Western Reserve University.
Menachem Shoham, PhD, associate professor of biochemistry at Case Western Reserve University School of Medicine,
MRSA infections are a growing public health concern, causing thousands of deaths per year. It is the most prevalent bacterial pathogen in hospital settings and in the community at large.
The problem has become increasingly severe as the bacteria have developed a resistance to antibiotics. As result, health care providers are running out of options to treat patients suffering from antibiotic-resistant infections, like MRSA and strep, creating a dire need for alternative treatments and approaches.
"Staph bacteria are ubiquitous and normally do not cause infections, however, occasionally these bacteria become harmful due to their secretion of toxins," said Dr. Shoham.
"We have discovered potential antivirulence drugs that block the production of toxins, thus rendering the bacteria harmless. Contrary to antibiotics, these new antivirulence drugs do not kill the bacteria. Since the survival of the bacteria is not threatened by this approach, the development of resistance, like that to antibiotics, is not anticipated to be a serious problem," the researcher noted.
Dr. Shoham identified a bacterial protein, known as AgrA, as the key molecule responsible for turning on the release of toxins. AgrA, however, needs to be activated to induce toxin production. His goal was to block the activation of AgrA with a drug, thus preventing the cascade of toxin release into the blood that can lead to serious infections throughout the body.
The screening for AgrA inhibitors was initially carried out in a computer by docking libraries of many thousands of "drug-like" compounds and finding out which compounds would fit best into the activation site on AgrA. Subsequently, about 100 of the best scoring compounds were tested in the laboratory for inhibition of the production of a toxin that ruptures red blood cells. Seven of these compounds were found to be active. Testing compounds bearing chemical similarity to the original compounds lead to the discovery of additional and more potent so-called "lead" compounds.
Optimization of the initial "lead" compounds was performed by chemical synthesis of 250 new compounds bearing small but important chemical modifications on one of the initial leads. More than a dozen active compounds have been discovered by this method. The best drug candidate reduces red blood cell rupture by 95 percent without affecting bacterial growth.
Beginning this fall, Dr. Shoham and colleagues will begin testing the drug candidate in animal models.
"It is possible to inhibit virulence of MRSA without killing the bacteria. Such antivirulence drugs may be used for prophylaxis or therapy by themselves or in combination with an antibiotic. Antivirulence therapy may resensitize bacteria to antibiotics that have become ineffective by themselves," added Dr. Shoham.
His promising discovery was presented this week at the Interscience Conference on Antimicrobial Agents and Chemotherapy in San Francisco.