Airflow obstruction caused by a malignant tracheal tumor may be managed with a uniquely designed, 3-dimensional (3D) drug-eluting tracheal stent that, at least in animal models so far, works well and may soon be ready for human trials, Chinese investigators are reporting.
The research was published online Jan. 29 in Materials Today Chemistry.
The problems with currently available stents used to treat airflow obstruction are considerable, corresponding author Shengrong Guo, PhD, professor of pharmaceutics, Shanghai Jiao Tong University, China, and colleagues observe. “Tracheal stents physically open up stenosis, recover airway patency, and promptly relieve symptoms, but [they] cannot treat the tumor,” they explain.
“Thus, tracheal restenosis always occurs soon [after], due to progressive tumor growth after stent placement,” they add. Moreover, implanted stents cover the entire tracheal mucosa, thus preventing mucus and sputum discharge, causing airway blockage, the investigators also note. Compounding these flaws is the unalterable fact that delivery of chemotherapy to a malignant tracheal tumor is inefficient, and systemic chemotherapy is always associated with systemic side effects.
All of these issues make it very challenging to treat these tumors, Dr. Guo noted. On the other hand, if there were a means to deliver a chemotherapeutic agent more directly to the disease site – as is done with drug-eluting beads, for example, in other tumor types – then at least drug delivery would be much more efficient. “In this study, a novel tracheal stent was designed with features of a C-shaped and trilayered wall,” the researchers explain.
The gap angle of the newly developed stent is 72°; the inner diameter is 0.5 cm, and it is 2.0 cm in length. The trilayered wall consists of an inner layer of poly (ε-caprolactone) (PCL), which is a biodegradable and implantable material used alone or compounded with other ingredients to print implants. The middle layer consists of magnetic nanoparticle (MNP)–loaded PCL. The authors explain that MNPs have been approved in the U.S. as contrast agents in MRI.
Combined with temperature-responsive materials, MNPs can serve as a source of magnetic thermotherapy as well, which can be used to control drug release and facilitate drug penetration into deeper tissues. The outer layer of the stent contains a paclitaxel-loaded ethylene-vinyl acetate copolymer layer.
“The C-shaped tracheal stents are easily fabricated on a roller by using a self-made specific three-dimensional printer,” the authors explain. They point out that the C-shaped tracheal stents do not cover the entire tracheal wall, and the uncovered gap in that wall allows for normal mucus and sputum discharge.
In vivo evaluation
Once the stents were printed, the researchers evaluated the biosafety and applicability of their C-shaped tracheal stents. Small rabbits weighing 2.5 to 3.0 kg were used as experimental models and were prepared for surgery. The stent was implanted in the rabbits’ tracheas through the use of a simple stent delivery device. During follow-up, the rabbits recovered well without any sign of infection or respiratory complications.
The animals were also eating well within about 5 days of the surgery, and their weight gradually increased, suggesting that the implantation of a stent with intermittent magnetic heating did not lead to any prominent systemic toxicities. “All rabbits were [euthanized] 30 days after the placement of the tracheal stents” and the stent was removed from the rabbits’ trachea, the researchers report.
Close observation of the trachea indicated that the gap left by the C-shaped stent could keep the airway patent without blocking either mucus or sputum discharge. “The stents have good biosafety in rabbits and keep airway patency for 1 month without the occurrence of mucus/sputum blockage after implantation in rabbit trachea,” Dr. Guo and colleagues conclude.
“These results provide a scientific basis for the development of novel self-expandable C-shaped tracheal stents with combinatorial tracheal support and local chemotherapy,” they affirm.