Gold Nanotubes Are Novel Agents for Cancer Diagnosis and Treatment

Cancer researchers have produced a highly defined class of gold nanotubes that are suitable for use in animals as in vivo imaging nanoprobes, photothermal conversion agents, and drug delivery vehicles.

Investigators at the University of Leeds (United Kingdom) developed a method for length-controlled synthesis of gold nanotubes (NTs) with well-defined shape (i.e., inner void and open ends), high crystallinity, and tunable NIR (near infrared) surface plasmon resonance. A coating of poly(sodium 4-styrenesulfonate) (PSS) endowed the nanotubes with colloidal stability and low cytotoxicity.

Details published in the February 12, 2015, online edition of the journal Advanced Functional Materials revealed that the PSS-coated gold NTs had the following characteristics: 1) cellular uptake by colorectal cancer cells and macrophage cells, 2) photothermal ablation of cancer cells using single wavelength pulse laser irradiation, 3) excellent in vivo photoacoustic signal generation capability and accumulation at the tumor site, and 4) clearance from the body within 72 hours of injection.

A primary use for the gold nanotubes is in photoacoustic imaging, a hybrid biomedical imaging modality based on the aforementioned photoacoustic effect. In photoacoustic imaging, non-ionizing laser pulses are delivered into biological tissues. Some of the delivered energy is absorbed and converted into heat, leading to transient thermoelastic expansion with wideband ultrasonic emission. The generated ultrasonic waves are then detected by ultrasonic transducers to form images. The optical absorption in biological tissues can be due to endogenous molecules such as hemoglobin or melanin, or exogenously delivered contrast agents. Since blood usually has orders of magnitude larger absorption than surrounding tissues, there is sufficient endogenous contrast for photoacoustic imaging to visualize blood vessels. Recent studies have shown that photoacoustic imaging can be used in vivo for tumor angiogenesis monitoring, blood oxygenation mapping, functional brain imaging, and skin melanoma detection.

Senior author Dr. Steve Evans, professor of physics and at the University of Leeds, said, “Human tissue is transparent for certain frequencies of light – in the red/infrared region. This is why parts of your hand appear red when a torch is shone through it. When the gold nanotubes travel through the body, if light of the right frequency is shone on them they absorb the light. This light energy is converted to heat, rather like the warmth generated by the sun on skin. Using a pulsed laser beam, we were able to rapidly raise the temperature in the vicinity of the nanotubes so that it was high enough to destroy cancer cells. The nanotubes can be tumor-targeted and have a central "hollow" core that can be loaded with a therapeutic payload. This combination of targeting and localized release of a therapeutic agent could, in this age of personalized medicine, be used to identify and treat cancer with minimal toxicity to patients.”

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