Photoactivated drug delivery and bioimaging

Among the various types of diseases, cancer remains one of the most leading causes of mortality that people are always suffering from and fighting with. So far, the effective cancer treatment demands accurate medical diagnosis, precise surgery, expensive medicine administration, which leads to a significant burden on patients, their families, and the whole national healthcare system around the world. In order to increase the therapeutic efficiency and minimize side effects in cancer treatment, various kinds of stimuli-responsive drug delivery systems and bioimaging platforms have been extensively developed within the past decades. Among them, the strategy of photoactivated approach has attracted considerable research interest because light enables the precise control, in a highly spatial and temporal manner, the release of drug molecules as well as the activation of bioimaging agents. In general, several appropriate photoresponsive systems, which are normally sensitive to ultraviolet (UV) or visible light irradiation to undergo the multiple reaction pathways such as photocleavage and photoisomerization strategy etc. have been mainly involved in the light activated cancer therapies. Considering the potential issues of poor tissue penetration and high photoctotoxicity of short wavelength light, the recently emerged therapies based on long-wavelength irradiation, e.g., near-infrared (NIR) light (700-1000 nm), have displayed distinct advantages in biomedical applications. The light irradiation at NIR window indicates minimized photodamage, deep penetration, and low autofluorescence in living cells and tissues, which are of clinical importance in the desired diagnosis and therapy. In this review article, we introduce the recent advances in light-activated drug release and biological imaging mainly for anticancer treatment. Various types of strategies such as photocage, photo-induced isomerization, optical upconversion, and photothermal release by which different wavelength ranges of light can play the important roles in the controlled therapeutic or imaging agents delivery, and activation will be systemically discussed. In addition, the challenges and future perspectives for photo-based cancer theranostics will be also summarized. (C) 2016 Wiley Periodicals, Inc.