Analysis of the sono-photodynamic effects using Protoporphyrin IX (PpIX): in vitro and in vivo studies
Sono-photodynamic therapy (SPDT) is a relatively new and promising approach to cancer treatment, based on the combination of photodynamic therapy (PDT) and sonodynamic therapy (SDT). PDT is a well-established anticancer technique for certain types of skin cancer, while SDT is another non-invasive anticancer method capable of reaching tumors located in deeper regions of the body. This study aims to analyze the action mechanisms and effects on rat liver of SPDT using Protoporphyrin IX (PpIX) as a sono-photosensitizer. In vitro, a series of 5 μM PpIX solutions were irradiated with red light (635 nm, 30-50 mW/cm2), ultrasound (1 MHz, 1-2 W/cm2, 50%) and both sources simultaneously. The PpIX absorption spectra recorded during each process, showed that the PpIX decay rate (k) induced by the irradiation of both sources was approximately the sum of those induced by the irradiation of light and ultrasound alone (k_SPDT ≈ k_SDT + k_PDT). In vivo, rats were intraperitoneal injected with 5-aminolevulinic acid (ALA) at dose of 500 mg/kg body weight to load the rat liver with a high concentration of PpIX. At 3 hours (time to optimum PpIX concentration in the liver) after injection, livers were irradiated with red light (635 nm, 180±10 J/ cm2), ultrasound (1.0 MHz, 1.5 W/cm2, 50%) and both sources simultaneously. For these procedures, it was built a single probe capable of irradiating both light and ultrasound. After 30 hours, animals were sacrificed, the livers were surgically removed and histologically processed. Scanned histological slides showed that SPDT induced greater depth and area of necrosis than SDT or PDT alone. These results suggest that SPDT could generate a greater amount of ROS than either PDT or SDT alone, which results in the increment of the drug decay rate, as well as the scope in a homogeneous biological tissue.
Erika Toneth Ponce Ayala
São Carlos Institute of Physics