Nanoscale photodynamic agents for colorectal cancer treatment: A review

Colorectal cancer is the most common form of gastroenteric cancer worldwide. Photodynamic therapy is emerging as an attractive method to treat cancers. Candidate targets of photodynamic therapy include epidermal growth factor receptors, cholesterol and low-density lipoprotein, estrogen receptors, the nucleus and DNA, folic acid receptors, cholecystokinin A receptors, lectin saccharide receptors, and tumor-specific antibodies. Specifically, in colorectal tumors, anti-DR5 antibody and cancer-specific antibody moieties are involved. Cancer cells incorporate greater quantities of sugars, and glycoconjugated photosensitizer has remarkable internalization and cytotoxicity in colon/colorectal cancer cells. Simultaneously, to circumvent the bio-distribution limitation, other molecules, including lectins, Hyaluronic acid, and peptides, have also been considered for colorectal cancer. Other novel strategies indirectly targeting colorectal cancer include pH-responsive PS, enzymatically activated photosensitization, and cancer-suppressing immune cells, mainly macrophages. Recently, nanoparticles have gained attention as a versatile platform for multi-functional photodynamic therapy. In this review, we summarize the targeting strategies investigated and highlight the potential of nanoparticles for target photodynamic therapy in colorectal cancer.