Low-intensity (< 0.1 mW/cm2) yet long-term (> 2-3 days) photodynamic therapy(PDT), termed metronomic photodynamic therapy(mPDT), is attracting attention because of its superior selectivity for malignant tumors and safety for the surrounding normal tissues.
Because mPDT requires only a feeble light, the light source can be miniaturized and thus fully implantable in the human body by using the technology of wireless electric power supply.
These advantages suggest that mPDT can be applied to the tumors in internal cavities such as the brain, chest, and abdomen. We investigated the anti-tumor effect of mPDT using wirelessly powered fingernail size LED device which was sandwiched by tissue-adhesive nanosheets for suture-free fixation onto the tissue. The devices were implanted subcutaneously beneath small intradermal tumors on the back of mice. Mice moved freely in the cage which was placed on the antenna board for 12 days experimental period.
We used photofrin as the photosensitizer, and applied two separate colors of LED devices, red(λ=630nm) and green(λ=530nm), according to light absorbances by photofrin.
After ten days of treatment, mouse receiving mPDT achieved significant growth suppression of the tumor compared to the control group which carried non-functional device along with being placed on the antenna board. Unlike conventional PDT which is confined to use red light by optical fibers, mPDT employing green light led even stronger anti-tumor effect than red. These results showed that mPDT using implantable optoelectronic device could be applied to cancers in internal organs as a new treatment strategy.