Exploration of New Sensitizers for Photodynamic Therapy Targeting Deep Cancer Treatment

Abstract

Despite its advantages, photodynamic therapy (PDT) has one major drawback: penetration depth. This limits the use of conventional PDT methods to skin (surface) tumors only, making it ineffective for deep tumors. There are four possible solutions for the light delivery for deep tumor treatment: particles activated by near-infrared (NIR) light, up-conversion of nanoparticles that absorb NIR light and emit visible light for other photosensitizers (PSs), fiber optics and ionizing X-rays. Of these options, the best is X-rays. Near-infrared light can penetrate only 5[Formula: see text]mm in tissue while retaining enough energy to activate the PSs. The use of fiber optics is neither convenient nor efficient as it cannot effectively and evenly activate the photosensitizers. It is also almost impossible for the treatment of metastatic sites or lymph nodes involved with this disease, unless they are located in the region where light delivery is feasible. In contrast with the other methods, X-rays can easily penetrate as deeply as necessary into the patients, and are convenient as they are commonly used in cancer therapy. The use of novel copper–cysteamine (Cu–Cy) nanoparticles is a good solution for overcoming these issues because Cu–Cy nanoparticles can be effectively activated by X-rays to produce singlet oxygen, which makes it very efficient for deep cancer treatment. Here, I will discuss the use of copper–cysteamine nanoparticles to enhance radiation therapy in combination with PDT and targeting therapies.