Axially Disubstituted Silicon(IV) Phthalocyanine as a Potent Sensitizer for Antimicrobial and Anticancer Photo and Sonodynamic Therapy

The unique properties of phthalocyanines (Pcs), such as strong absorption, high photostability, effective singlet oxygen generation, low toxicity and biocompatibility, versatile chemical modifications, broad spectrum of antimicrobial activity, and synergistic effects with other treatment modalities, make them a preferred superior sensitizer in the field of antimicrobial photodynamic therapy. The photodynamic and sonodynamic activity of 3-(3-(diethylamino)phenoxy)propanoxy substituted silicon(IV) Pc were evaluated against bacteria and cancer cells. Stability and singlet oxygen generation upon light irradiation and ultrasound (1 MHz, 3 W) were assessed with 1,3-diphenylisobenzofuran. The phthalocyanine revealed high photostability in DMF and DMSO, although the singlet oxygen yields under light irradiation were low. On the other hand, the phthalocyanine revealed excellent sonostability and caused a high rate of DPBF degradation upon excitation by ultrasounds at 1 MHz. The silicon phthalocyanine presented significant bacterial reduction growth, up to 5 log against MRSA and <i>S. epidermidis</i> upon light excitation, whereas the sonodynamic effect was negligible. The phthalocyanine revealed high activity in both photodynamic and sonodynamic manner toward hypopharyngeal tumor (FaDu, 95% and 42% reduction, respectively) and squamous cell carcinoma (SCC-25, 96% and 62% reduction, respectively). The sensitizer showed ca. 30% aldehyde dehydrogenase inhibition in various concentrations and up to 85% platelet-activating factor acetylhydrolase for 0.25 μM, while protease-activated protein C was stimulated up to 66% for 0.75 μM.