Versatile Nanosponges Now Aimed at MRSA Toxins

In successful research, any one path can quickly lead to new paths of even more promising results. This branching out of a research project couldn’t be more true than for a team of researchers at the University of California-San Diego’s Jacobs School of Engineering.

Working under the guidance of nanoengineering professor Liangfang Zhang, UCSD researchers have developed “nanosponges” that were initially designed as a platform for cancer drug delivery and now are being developed to soak up the dangerous pore-forming toxin produced by MRSA (methicillin-resistant Staphylococcus aureus).

The toxin-studded nanosponges have shown promise as a safe and effective vaccine against MRSA, a “staph” germ that is resistant to first-line antibiotics. In tests, the nanosponge vaccine enabled the immune systems of mice to block the adverse effects of the alpha haemolysin toxin from MRSA—both within the bloodstream and on the skin.

The nanosponges are biocompatible particles made of a polymer core wrapped in a red blood cell membrane. The membrane seizes and detains the staph toxin alpha-haemolysin without compromising the toxin’s structural integrity, explained Che-Ming “Jack” Hu, a member of the UCSD development team.

“The work introduces a novel approach in toxoid vaccine preparation, which exploits nanoparticle vectors to detain harmful toxins and in turn use them to train the immune system to develop defenses against the toxins,” Hu said. “The method provides a simple way to produce safe and potent toxoid vaccines that have significant potential in preventing infectious diseases.”

The researchers reported their MRSA findings in Nature Nanotechnology (Dec. 1, 2013) in the paper, “Nanoparticle-detained toxins for safe and effective vaccination,” in which Hu was the lead author. Hu said a primary motivation of the work is to combat the rising threat of antibiotic resistance in bacteria.

“Conventional antibiotics exert a selective pressure on bacteria, which promote mutations toward drug resistance,” Hu said. Our “method is designed to raise innate immunity to defend against bacterial virulence factors. An individual receiving the vaccine would then be less susceptible to bacterial infections, which would reduce the overall need for antibiotics.” 

The researchers found that their nanosponge vaccine was safe and more effective than vaccines made from heat-treated staph toxin. Hu said the nanosponges allow the toxins to be presented to the immune system in their “natural form.”

“Conventionally, toxins need to be cooked, or ‘denatured,’ before they can be safely administered as vaccines. Without this denaturing process, the toxins would be too harmful for administration,” he said.

But the cooking process changes the toxins’ protein structure, “and the subsequent presentation to the immune system is no longer faithful to the initial toxin protein,” he added. “If you cook the toxins for too long, they lose their potency, and if you don’t cook them enough, they are not safe. The nanosponge approach bypasses this hurdle as it enables intact toxins to be safely administered.”

Before this, “there was no way you could deliver a native toxin to the immune cells without damaging the cells,” group leader Liangfang Zhang added.

Zhang and Hu said the nanosponge platform plays a pivotal role in its effectiveness to deliver the toxin.

“The nanosponges have an exterior that is identical to cell membranes,” Hu said. “This biomimetic surface draws many toxins that naturally attack cell membranes. As a result, these toxins become firmly anchored on the particle-stabilized cell membranes, and ‘toxin detainment’ is achieved. The size and spherical morphology of these nanosponges also facilitate the detained toxins to be taken up by immune cells, thereby achieving effective immune stimulation.” 

Hu said the next step is to demonstrate the vaccine’s potency against actual MRSA infections.

“We are currently conducting animal studies to demonstrate the platform’s therapeutic benefit,” he said. “We aim to translate the technology to the clinics.”

Long line of nanosponges

The MRSA work is a twist on a previous UCSD project on a nanosponge that can sop up a variety of pore forming toxins in the body, from bacterial proteins to snake venom. Initially, the platform had been developed for cancer drug delivery.

“We certainly did not expect the many out-branching applications when we first developed the red blood-cell membrane coated nanoparticles in 2011,” Hu explained. “Initially the platform was designed for long-circulating cancer drug delivery. We are more than delighted to find that the biomimetic platform has applications in drug delivery, biodetoxification and vaccine preparation. 

“We are always searching for ways to improve the biocompatibility of nanoparticles to extend their applicability,” Hu added. “We recognize that cell membranes govern the majority of biological interactions found in nature and thus developed the unique platform. We continue to look for new ways to apply the platform.”

The particles “work so beautifully,” Zhang said, that it might be possible to detain several toxins at once on them, creating a “one vaccine against many types of pore-forming toxins,” from staph to snake venom.