Nanotechnology Provides an Armory of Imaging and Therapeutic Applications

Built on a simple-to-construct polymer base, these particles can be utilized as contrast agents to illuminate tumors for magnetic resonance imaging (MRI) and PET scans or deliver chemo and other therapies to kill tumors. Furthermore, the particles are biocompatible and have shown no toxicity.

The study’s finding were published online August 26, 2014, in Nature Communications. “These are amazingly useful particles,” noted co-first author Dr. Yuanpei Li, a research faculty member in the laboratory of Dr. Kit Lam and colleagues from the University of California (UC) Davis (Sacramento, USA). “As a contrast agent, they make tumors easier to see on MRI and other scans. We can also use them as vehicles to deliver chemotherapy directly to tumors; apply light to make the nanoparticles release singlet oxygen (photodynamic therapy) or use a laser to heat them (photothermal therapy)—all proven ways to destroy tumors.”

Jessica Tucker, program director of Drug and Gene Delivery and Devices at the US National Institute of Biomedical Imaging and Bioengineering, which is part of the National Institutes of Health (NIH; Bethesda, MD, USA), stated that this strategy has the capability to combine both imaging and therapeutic applications in a single platform, which has been problematic to achieve, particularly in an organic, and therefore biocompatible, vehicle. “This is especially valuable in cancer treatment, where targeted treatment to tumor cells, and the reduction of lethal effects in normal cells, is so critical,” she added.

Though these are not the first constructed nanoparticles, these may be the most versatile. Other particles are suitable for some tasks but not others. Non-organic particles, such as quantum dots or gold-based materials, work well as diagnostic tools but have safety problems. Organic probes are biocompatible and can deliver drugs but do not have any imaging or phototherapy applications.

Constructed on a porphyrin/cholic acid polymer, the nanoparticles are simple to make and perform well in the body. Porphyrins are common organic compounds. Cholic acid is produced by the liver. The basic nanoparticles are 21-nm wide. To further stabilize the particles, the researchers added the amino acid cysteine (creating CNPs [carbon nanotube–polymers]), which prevents them from prematurely releasing their therapeutic payload when exposed to blood proteins and other barriers. At 32 nm the CNPs are ideally sized to penetrate tumors, accruing among cancer cells while sparing healthy tissue.

In the study, the scientists evaluated the nanoparticles, both in vitro and in vivo, for a wide range of tasks. On the therapeutic side, CNPs effectively transported anti-cancer drugs, such as doxorubicin. Even when kept in blood for many hours, CNPs only released small amounts of the drug; however, when exposed to light or agents such as glutathione, they readily released their payloads. The ability to precisely control chemotherapy release inside tumors could greatly reduce toxicity. CNPs carrying doxorubicin provided excellent cancer control in animals, with minimal side effects.

CNPs also can be configured to respond to light, producing singlet oxygen, reactive molecules that destroy tumor cells. They can also generate heat when hit with laser light. Significantly, CNPs can perform either task when exposed to a single wavelength of light.

CNPs offer a number of advantages to enhance imaging. They readily chelate imaging agents and can remain in the body for long periods. In animal studies, CNPs congregated in tumors, making them easier to read on an MRI. Because CNPs accumulated in tumors, and not so much in normal tissue, they dramatically enhanced tumor contrast for MRI and may also have potential for PET-MRI scanning applications.

This versatility provides multiple options for clinicians, as they mix and match applications. “These particles can combine imaging and therapeutics,” said Dr. Li. “We could potentially use them to simultaneously deliver treatment and monitor treatment efficacy.”

“These particles can also be used as optical probes for image-guided surgery,” said Dr. Lam. “In addition, they can be used as highly potent photosensitizing agents for intraoperative phototherapy.”

Even though the early findings are promising, there is still a long way to go before CNPs can enter the clinic. The researchers and its collaborators will pursue preclinical studies and, if all goes well, proceed to human trials. Meanwhile, they are thrilled about these capabilities. “This is the first nanoparticle to perform so many different jobs,” concluded Dr. Li. “From delivering chemo, photodynamic and photothermal therapies to enhancing diagnostic imaging, it’s the complete package.”

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