Developing a new and better chemotherapy for cancer treatment


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For more than a decade, biomedical researchers have been looking for better ways to deliver cancer-killing medication directly to tumors in the body. If successful, it could render chemotherapy as a more effective and efficient treatment for cancer that doesn't leave patients suffering from the current typical adverse side effects.


Getting the right look

Scientists can now use tiny capsules, called nanoparticles, to transport chemotherapy medicine through the bloodstream directly to the site of cancerous tumors. But how can the nanoparticles gain access to the tumor once it gets there? That's the obstacle Drexel University researchers believe they may be close to overcoming. The team believes that giving the nanoparticles a new look may just do the trick.

Targeted cancer therapy is most effective when the medication is released as close as possible to the interior of a tumor, to increase its odds of penetrating and killing off cancerous cells. You need a delivery vehicle that is not only sturdy enough to get the medication through the bloodstream to the tumors, but also lithe enough to squeeze through the tumor's dense extra cellular space.

In research recently published in the journal Nano Letters, lead author Hao Cheng, PhD — an assistant professor with an appointment in Drexel's College of Engineering, and affiliation with School of Biomedical Engineering, Science and Health Systems — reports that the way to get past the tumor's front door has everything to do with how the tiny particle is suited up for the journey.

"What we've reported here is a strategy to overcome biological barriers that plague delivery of medication, such as nonvehicle clearance in the bloodstream by the host immune system, and ineffective diffusion in the extracellular matrix of tumor cells," Cheng said. "It's a unique strategy that involves the decoration of nanovehicles with enzymes known to break down hyaluronic acid, which is a main barrier in the extracellular space, and the addition of an extra layer of polyethylene glycol to partially cover the enzymes."

In the paper entitled "Hyaluronidase Embedded in Nanocarrier PEG Shell for Enhanced Tumor Penetration and Highly Efficient Antitumor Efficacy," the group reports that its method is four times more effective at sending nanoparticles into a solid tumor than one of the best strategies currently in use. When cancer medication is loaded in the tiny particle, it has been shown to inhibit the growth of a type of aggressive breast cancer.


Dressing in layers

The team, which also included researchers Wilbur Bowne, MD, an associate professor in Drexel's College of Medicine; Dimitrios Arhontoulis, an undergraduate in Drexel's School of Biomedical Engineering, Science and Health Systems; lead author Hao Zhou and Zhiyuan Fan, doctoral candidates, Junjie Deng, PhD, postdoctoral researchers, and Pelin Lemons, a graduate student, all in the Materials Science and Engineering Department in the College of Engineering, created its nanoparticle suit by starting with one that is common in this area of cancer research and making some key alterations.

"In the general design of nanoparticles, bioactive molecules — not limited to enzymes — were attached on the outermost layer of particles," Cheng said. "These enzymes can degrade the extra cellular matrix and enhance the nanoparticle's ability to penetrate solid tumors."

But in the body, this extra cargo can cause problems. One issue is that attaching enzymes to nanoparticles could cause them to come up short of the tumor and be cleared by the bloodstream before delivering the medication. There's also a chance that the trip through the bloodstream could render the enzymes inert.

To counter these issues and keep the nanoparticles on course, the team decided to add an extra layer that not only protects the precious payload, but also positions the enzymes for maximum effect.

"The novelty of our design is that we partially embedded the hyaluronidase enzymes in a second polyethylene glycol layer to form the outer shell of the nanoparticle," Cheng said. "This design dramatically reduces the enzymes' effect on slowing the particle's circulation and allows enzymes to maintain their function after the particle diffuses into the tumor."


Tricking the immune system

Embedding the enzymes in the layers of polyethylene glycol (PEG) ensures that the nanoparticle's appearance tricks the immune system into leaving it alone during its trip to the tumor, yet still allow the particle to deal with any hyaluronic acid it encounters on its penetration of the tumor.

Other researchers have tested a theory that exposes tumors to the enzymes first, and then to nanoparticles, but this is not nearly as effective as Cheng's method, because the nanoparticles developed at Drexel retain the enzymes through the duration of their diffusion into tumors, minimizing unnecessary hyaluronic acid degradation, Cheng explains.

"The degradation of hyaluronic acid removes the barrier for nanoparticles to diffuse and allows them to access more cancer cells," Cheng said. "The enhanced diffusion also increases the accumulation of nanoparticles in tumors, and the more nanoparticles that get into tumors the more effective they are at reducing its size."

As part of the research, the team tested their nanoparticle against competitors that did not have a second layer of polyethylene glycol and ones that did not have the ECM-degrading enzymes. The team reports that its nanoparticle performed better in both penetrating tumors and accumulating in the cancerous cells.

"This exciting, novel nanoparticle drug delivery system will improve delivery of anti-cancer agents, enhancing anti-cancer activity to improve patient outcomes," said Bowne. He foresees enormous potential for this strategy in the neoadjuvant and adjuvant setting for a number difficult to treat cancers such as locally advanced breast, pancreatic and mucin-producing gastrointestinal cancers.