Platform Technologies

About Photodynamic and Sonodynamic Therapies

Photodynamic Therapy (PDT) is increasingly used in the practice of medicine and is the basis for the pioneering treatment for age-related wet macular degeneration. Other treatment modalities based on PDT have also been approved by the regulators. The principle involves a drug (the photosensitizer) which is relatively harmless until it is illuminated by light of various wavelengths, depending on the photosensitizer. The drug is delivered to the target tissue as selectively as possible and then the target tissue is illuminated. This activates the photosensitizer which then destroys the diseased tissue, predominately through the action of singlet oxygen. The killing effect is a combination of apoptosis (programmed cell death) and necrosis. It is also thought that PDT – mediated destruction of cancerous tissue may also serve to mobilize the immune system to further eliminate cancerous cells, through an ‘uncloaking’ of masked tumor antigens. The main drawback of PDT is the relatively limited penetration of light into human tissue. Even longer wavelength light cannot penetrate more than 5mm. This limits such treatments to surface (topical) applications unless light can be delivered inside the body, as with Quest’s prostate cancer treatment system.

Characteristics of the Ideal Photo/Sonosensitizer

• Absorption and phototoxic activity in the optimum ‘phototherapeutic window’ (560 - 700 nm)
• Excellent sonodynamic activity in the frequency range 1 – 3 MHz
• Low molecular weight (MW 550 – 880)
• Available in pure monomeric form
• Simple pharmacokinetics, rapid serum and skin clearance
• Negligible cytotoxicity in vitro and in vivo
• Excellent photopotentiation (2 orders of magnitude) conferring excellent safety margin
• Phototoxicity mediated via conventional type II reactions as well as type I (indicates utility for hypoxic tumour cells)
• Potent inhibitors of protein kinases
• Confer apoptotic cell death
• No genotoxicity
• Excellent tumor control
• Potential for targeted delivery
• Amenable to nuclear targeting to further augment sono/phototoxicity

Quest believes that its family of Hypocrellin B derived photosynthesizers share more of these desired characteristics than any other photosynthesizer currently in development or in use.