Photodynamic Therapy Could be Made Easier With NIR Light Absorbing Molecule

The clinical application of photodynamic therapy (PDT) could be enhanced through the use of a novel class of molecules. The carbazole-substituted BODIPY (Car-BDP) molecule has an intense, broad NIR absorption band (600–800 nm) with a high singlet oxygen quantum yield (ΦΔ = 67%). When researchers from UMass Medical School (UMMS) encapsulated Car-BDP with biodegradable PLA–PEG-FA polymers, Car-BDP formed uniform organic nanoparticles that were water-soluble and tumor-targetable.

Lead researcher Gang Han said that when used in conjunction with a low-power-density incoherent lamp light, rather than the coherent high power laser light that is used in current PDT therapy, the molecules could be tracked as they spread through the body, deep into the tissue, to identify and kill cancerous tumors. The organic nanoparticles were found to have an extremely long circulating time and could be removed from the body.

UMass Medical School scientist Gang Han. Courtesy of UMass Medical School.

Rather than using laser light, such nanoparticles could offer an unprecedented deep-tissue, tumor targeting photodynamic therapeutic effect using an exceptionally low-power-density and cost-effective lamp light (12 mW cm–2). In addition, the nanoparticles could be simultaneously traced in vivo due to their excellent NIR fluorescence.

The research into Car-BDP indicates that its use in PDT therapy could make the therapy a simpler, more effective and more cost-efficient process.

Tissue penetration depth, a challenge in PDT, traditionally involves the patient receiving a nontoxic light-sensitive drug, which is absorbed by all the body's cells, including cancerous ones. A red laser light specifically tuned to the drug molecules is then selectively turned on in the tumor area. When the red light interacts with the photosensitive drug, it produces a highly reactive form of oxygen (singlet oxygen) that kills the malignant cancer cells while leaving most neighboring cells unharmed.

"This study signals a major step forward in photodynamic therapy by developing a new class of NIR-absorbing biodegradable organic nanoparticles for a highly effective targeting and treatment of deep-tissue tumors," Han said.

The study could lead to a potential platform for precise tumor-targeting theranostics. Additionally, use of a low power lamp light could allow for more affordable clinical cancer treatment; treatment that patients may be able to manage in their homes; and treatment that is accessible in resource deficient areas.

The research was published in Journal of the American Chemical Society (doi: 10.1021/jacs.6b05390).