Cancer Research · us
Keeping Immunotherapy Drugs Inside Tumors: Rice-Grain-Sized Biodegradable Implant Eliminates 60% of Tumors in Mice
A nanofiber drug seed slowly releases two immune-stimulating agents inside tumors and, when combined with radiation therapy, shows potential for localized drug control. However, the findings remain limited to mice with triple-negative breast cancer, with manufacturing and safety hurdles still to be cleared before human trials.
One challenge with systemic immunotherapy is that drugs may reach and stimulate not only tumors but also other tissues, causing toxicity. Although injecting drugs directly into tumors can limit the area of exposure, uneven distribution or rapid leakage can reduce their effectiveness. A Houston Methodist research team therefore designed a biodegradable implant about the size of a grain of rice in an effort to turn the tumor into a small reservoir that continuously supplies drugs.
This “biodegradable nanofiber drug-eluting seed” (b-NDES) is made from electrospun polymers and allows immune-stimulating drugs to diffuse gradually after implantation in the tumor. The material breaks down over time, so in theory it does not require another surgery for removal. Barium sulfate is also added to the formulation, making the implant visible on imaging so its position can be confirmed.
After testing different material ratios, the researchers selected a formulation with a 1-to-4 ratio of polycaprolactone to poly(lactic-co-glycolic acid). Surface modification reduced the permeable porosity from about 19% to 2.74% and, in vitro, lowered the release rate of rhodamine used as a tracer from about 163 micrograms per hour to 31 micrograms per hour. In a six-month degradation test, the implants lost an average of about 46% of their mass, indicating that they break down slowly but do not disappear completely over the short term.
In a 4T1 triple-negative breast cancer mouse model, the team loaded the implants with a CD40 agonist antibody and a STING agonist, then combined them with stereotactic radiation therapy. According to the paper, tumors were completely eliminated in 60% of the animals, the drugs remained mainly localized within the tumors, and no systemic adverse effects were observed. The result supports the possibility that “localized, sustained release” could both activate the immune system and reduce off-target exposure, but it cannot by itself establish whether the therapeutic effect came from the implant, the two drugs, or the radiation therapy.
The potential applications of this design are not limited to breast cancer. The research team believes that solid tumors such as pancreatic cancer and lung cancer could also be candidates for testing, provided the lesions can be reached through image-guided or interventional procedures. However, implantation difficulty, intratumoral drug diffusion, material degradation rates, and local inflammatory responses may vary among organs, and the current findings in mice cannot be directly extrapolated to patients.
The research remains a preclinical proof of concept. Next steps include repeating the tests in additional tumor models, clarifying the contributions of the dose and treatment combination, and completing studies on manufacturing consistency, long-term degradation, and safety. In particular, “no systemic adverse effects were observed” reflects only this group of animals under the specified observation conditions and cannot yet be considered a guarantee of safety in humans.