Novel nanostructure improves photothermal therapy of deep tumors

(Nanowerk Spotlight) Photothermal therapy (PTT) is a form of cancer treatment where a therapeutic agent absorbs energy from photons and dissipates it partially in the form of heat. When the therapeutic agents, for instance nanoparticles, are located in close vicinity to the tumor site, the temperature increase can lead to cell damage, i.e. it kills the cancer cell.

MoS 2 nanosheets have shown great prospect as a near-infrared light (NIR) absorbing agent for PTT applications due to their unique photoelectric property, low cost and good biocompatibility.

However, as Dr. Xianwei Meng from the Laboratory of Controllable Preparation and Application of Nanomaterials at the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, who led the research team, explains, the absorbance of nanosheets in the NIR region is not specific and strong, and the photothermal conversion efficiency of MoS 2 based materials need to be enhanced.

In new work, Meng and his team have proposed a novel MoS 2 nanostructure, i.e. layered MoS 2 hollow spheres (LMHSs), for improving their near-infrared absorption and photothermal conversion efficiency.

The LMHSs were synthesized by a chemical aerosol flow process. According to the researchers, the advantages of their synthesis strategy are one-step, continuous, fast, and easy to scale-up.

The team proposes a new strategy for imaging guided PTT on orthotopic transplantation VX2 liver tumor in rabbits. The team has reported their results in Small ("Layered MoS 2 Hollow Spheres for Highly-Efficient Photothermal Therapy of Rabbit Liver Orthotopic Transplantation Tumors").

LMHSs are fabricated by a fast and continuous chemical aerosol flow method. Due to their unique structure, the prepared LMHSs preserve strong absorption in near-infrared (NIR) region and have high photothermal conversion efficiency. High tumor targeting and therapy efficiency are obtained by transarterial administration under the guide of DSA, IR and CT imaging using rabbit liver tumor as model.

The researchers obtained high tumor targeting and PTT efficiency by transarterial administration of the LMHSs to the arterial feeding VX2 liver tumor under the guide of digital subtraction angiography (DSA).

This is the first proof-of-concept study for PTT of tumors located deeply inside the body. The results may greatly promote the development of PTT for clinical cancer treatment.

The low tumor targeting efficiency of nanomaterials is one of the biggest obstacles for their clinical application because they are usually excreted from the blood by the reticuloendothelial system, such as Kupffer cells and macrophage cells. An effective strategy is urgently required to improve the tumor targeting of PTT agents.

In addition, due to the limited penetration depth of NIR, the main studies of PTT only focus on the subcutaneous transplantation tumor in mice. Exploring and in-depth understanding of PTT efficiency on tumors located deeply inside the body is extremely important for the further clinical application.

"We designed and prepared a brand-new layered MoS 2 hollow sphere, which show strong absorption in NIR and high photothermal conversion efficiency," says Meng. "Our method is innovative, simple and fast, and can be easily extended to the synthesis of other transition metal dichalcogenide with hollow and spherical structures."

The size of the as-prepared LMHSs is too large to be efficiently delivered to the tumor site by intravenous injection. The current work resolves this problem by using a new strategy, in which the clinical interventional transarterial administration technique is used to directly deliver PTT agents into the blood vessels that feed the tumor cells.

According to the scientists, over 30% of LMHSs are found in the tumor tissue, confirming that the novel administration technique can deliver theranostic agents to tumors with high efficiency and specificity.

Due to the high photothermal conversion efficiency and outstanding tumor targeting efficacy, the orthotopic transplantation liver tumors of rabbits can be effectively eliminated by the PTT technique.

"The striking results reported in our Small paper represent a significant advance in the area of PTT," concludes Meng. "We believe that this paper will attract a broad readership and provide a viable approach for studying various functional nanomaterials for cancer theranostics."