Abstract
Photodynamic therapy (PDT) has been a routine treatment of tumors and some microvascular diseases, but clinically available photosensitizers are still scarce. Among all kinds of photosensitizers, hypocrellins possess the most characteristics of ideal photosensitizers, such as, high photo-activity but low dark toxicity, fast clearance from tissues. This review is focused on two main topics, drug-delivery problem of hypocrellins and how the environment-sensitive fluorescence of hypocrellins was used for recognition of various biomolecules. Drug-delivery of hypocrellins was mainly achieved in two strategies — preparing the drug-delivery vehicles and finding quantitatively amphiphilic derivatives. Hypocrellin fluorescence originated from the intramolecular proton transfer is very distinct from other kinds of photosensitizers. Recently, it was proved that quantitative hypocrellin fluorescence could not only recognize various biomolecules, including proteins, polysaccharides and lipids, but also distinguish the specific binding from nonspecific binding with some kind of biomolecules. Meantime, hypocrellin fluorescence was pH-sensitive. It is known that tumor cells or tissues have the features of a large amount of lipid, neonatal collagen, over-expression of polysaccharides, and lower pH values compared to normal tissues. According to the relative but not absolute specificity, further studies on quantitative recognition of various biomolecules at a cellular level, may find a new clue to treat tumors by joint usage of photodynamic diagnosis (PDD) and PDT.
Highlights
Photodynamic therapy (PDT) has become a regular methodology to treat various tumors clinically,[1] and recently, it has been successfully used to treat some microvascular diseases, such as port wine stains (PWS), age-related macular degeneration (AMD).[2,3] It is known that light, photosensitizer and oxygen are the three primary factors for PDT but photosensitizer is the key important one
Ultrasonic method was previously used to prepare the liposome of hypocrellin A (HA) and hypocrellin B (HB) which can retain about 70% of PDT activity of HA or HB.[16,17]
It was reported that triton X-100 micelles of HB could maintain most of the photosensitization activity, the sizes of micelles are too large to be used as PDT drugs
Summary
Photodynamic therapy (PDT) has become a regular methodology to treat various tumors clinically,[1] and recently, it has been successfully used to treat some microvascular diseases, such as port wine stains (PWS), age-related macular degeneration (AMD).[2,3] It is known that light, photosensitizer and oxygen are the three primary factors for PDT but photosensitizer is the key important one. It has long been hoped that a photosensitizer might be used for photodynamic diagnosis (PDD) and PDT at the same time,[4] which may be a good strategy to conquer cancers, lack of specic target and °uorescence signal prohibit the program. Hypocrellins, including hypocrellin A (HA) and hypocrellin B (HB) (shown in Fig. 1), exhibit most of the characteristics of ideal photosensitizers mentioned above.[5,6,7] their low absorption in the phototherapeutic window (600–900 nm) makes them not suitable for PDT of solid tumors.[8] In addition, hypocrellins are lipophilic organic compounds, which promotes the cellular uptake[9] but prohibits the drug-delivery and bioavailability.[10] Besides PDD depends on the typical °uorescent signals of a photosensitizer on the targets. Some recent progresses of researches on the drug-delivery and environment-sensitive °uorescence of hypocrellins are concerned
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