We are all well known of the fact that cancer has become the first killer of human health, and anticancer therapy has attracted more attention of researchers from all over the world. Currently, four main methods are clinically applied in cancer treatments but every kind of treatment has its own limitations which are the major challenges for cancer treatment.
Being developed as a novel promising noninvasive approach, Sonodynamic Therapy (SDT) is derived from photodynamic therapy (PDT). The major difference between Sonodynamic Therapy and Photodynamic Therapy is the energy source used to activate the sensitizers. Photodynamic therapy is not effective for the treatment of deep-seated tumors due to its short penetration depth of light. However, the significant advantage of Sonodynamic Therapy over Photodynamic Therapy is that ultrasound can be tightly focused with penetration in soft tissue up to several tens of centimeters.
Anticancer effect of Sonodynamic Therapy
With an evolving methodology, sonodynamic therapy offers the possibility of non-invasively eradicating solid tumors in a site-directed manner. A high therapeutic efficacy of sonodynamic therapy in cancers is resulting from the comprehensive functions. According to several investigations, it is confirmed that the production of a large amount of intracellular Reactive Oxygen Species (ROS) induced by sonodynamic therapy can produce direct cytotoxicity in cancer cells. The sonodynamic therapy can also possess the modulation effects on cancer microenvironment, e.g., the suppression effect on tumor vasculature and the stimulation effect on the tumor immunity, which inhibit the growth of cancers.
Role of sonosensitizers
Sonosensitizer is considered as an important element in sonodynamic therapy, which can maximize the effects of ultrasonic irradiation. Sonosensitizers have achieved rapid development in the past decades, based on the known mechanisms of cell apoptosis or cell death induced SDT. Moreover, the selection of a suitable sonosensitizer in carrying out SDT on cancers has become an important issue in current investigations.
Modulation effects of SDT on Cancer microenviroment
Cancer microenvironment describes cellular environments in which the tumor exists. It includes surrounding blood vessels, fibroblasts, immune cells, bone marrow-derived inflammatory cells, signaling molecules, lymphocytes, and the extracellular matrix. The surrounding microenvironment and the tumor are intimately related and interact constantly. While the tumor microenvironment provide the support for the growth and metastasis of cancer cells, the tumors can influence the microenvironment by releasing extracellular signals, promoting tumor angiogenesis and inducing peripheral immune tolerance,. Recently, several investigations have showed that sonodynamic therapy can efficiently modulate the tumor microenvironment.
A significant body of data has demonstrated therapeutic effectiveness of sonodynamic therapy in cancer treatment. In view of the significant depth that ultrasound penetrates tissue, sonodynamic therapy provides an advantage over photodynamic therapy, in which less penetrating light is employed. More work needs to be done before sonodynamic therapy is accepted as an adjuvant or replacement method for traditional cancer treatment. More data necessary to ascertain the actual anticancer activities of sonodynamic therapy will be acquired in the near future.