Insights on metal-free type I photosensitizers for photodynamic therapy

Non-invasive treatment techniques have drawn a lot of interest due to the rising need for precise and secure cancer treatment. One such treatment method is photodynamic therapy (PDT), which uses the light irradiation of photosensitizers (PSs) to produce reactive oxygen species (ROS), which kill cancer cells. Most of the conventional photosensitizers used in the PDT process rely on molecular oxygen to produce cytotoxic ROS, known by the name of type II PSs. Because type II PSs requires oxygen to produce ROS, their full potential is not realized in hypoxic tumor tissues. On the other hand, type I PSs can increase the effectiveness of PDT in hypoxic tumor tissues since they rely less on oxygen to produce ROS. Consequently, it has become increasingly crucial to develop type I PSs to treat hypoxic malignancies. Numerous type I PSs of inorganic origin have been developed so far. Nonetheless, certain issues like poor biodegradability and persistent toxicity exist. Type I PSs based on organic compounds were developed in response to these concerns since they are comparatively more biocompatible and biodegradable. Therefore, in this article, we describe recent developments in the development of organic type I PSs for the PDT.