A Potential Treatment For MRSA

Methicillin resistant Staphylococcus aureus (MRSA) is a major public health threat. Currently, there are only a few antibiotics that are effective against it, and resistance is even a problem with these antibiotics. There is a potential treatment that might be effective against MRSA: heteropolymer (HP) antibody therapy.

To explain what HP antibody therapy is, I first want to give a vastly oversimplified explanation of what your immune system does when your bloodstream is infected with MRSA. The immune system, produces two molecules that attach to each other, one of which is an antibody. One of the molecules in this two molecule complex then attaches to a single MRSA bacterium (the antibody). The other molecule then attaches to a red blood cell--red blood cells are involved in bringing oxygen into the body--to yield something like this (obviously, this is a diagram, not a photo):

[MRSA bacterium]---[antibody]---[other immune system protein]----[red blood cell]

When the blood ultimately reaches the liver, the [MRSA]---[antibody]---[other immune system protein] complex is freed from the red blood cell where it is destroyed, killing the MRSA bacterium.

In HP antibody therapy, an HP antibody injected into the bloodstream replaces the two molecule complex:

[MRSA]---[HP antibody]----[red blood cell]

Why is this such a significant breakthrough? Because many MRSA-infected patients, particularly those at risk for MRSA infections like the immunocompromised, have a depleted immune system (also, those who are severely ill might not be able to mount an immune response). As a result, that [antibody]---[other immune system protein] complex isn't formed at high enough number to halt the infection. The HP antibody essentially acts as a surrogate antibody and gives the immune system a boost.

Not only might this therapy be used in the very rare cases of vancomycin resistant S. aureus, it could also function as either a replacement for antibiotics or as a supplement to antibiotic therapy.

(an aside: Typically, antibiotics don't kill all of the infecting bacteria, but, instead, lower their numbers to where the immune system can mount a response. Obviously, if your immune system is shot to hell, that threshold concentration of bacteria will be much lower, making treatment failure more likely even with the appropriate antibiotics).

This therapy is being developed by Elusys. Here's a story about it from the January 12, 2007 edition of ScripNews (no link available):

Pfizer in MRSA deal with Elusys

Pfizer has struck a deal with the US firm Elusys Therapeutics for certain infectious diseases, including met[h]icillin-resistant Staphylococcus aureus (MRSA) infections.

The deal takes the shape of an exclusive collaborative research and licence agreement under which the firms will develop new therapeutics and which includes Elusys' ETI211, an HP antibody with potential to treat MRSA infections.

The partners will collaborate to determine the product profile of ETI-211 and will conduct research into other indications. ETI-211 is a proprietary product developed by Elusys. It says that when ETI-211 is given to mice prophylatically they were completely protected against a lethal MRSA challenge. The company also added that the ETI-211-treated mice survived a second lethal MRSA or S. epidermidis challenge months later with no additional drug treatment.

Elusys will receive an up-front equity investment from Pfizer, R&D funding and near-term research milestone payments. It will also be entitled to royalties on future sales of products from the collaboration.

In the US MRSA treatment and hospitalisation is estimated to cost more than $48,000 on average per patient. MRSA accounts for over half the infections in intensive care units in the US alone, with an estimated 300,000 people contracting the infection each year and resulting in 12,000 deaths.