Photodynamic therapy (PDT) is a promising method for treating several cancers that uses photosensitizers. The photosensitizer accumulates in target tissue and is excited using light, generating reactive oxygen species that induce cell death. To enter the target area PDT drugs need to be lipophilic, however this presents problems: lack of solubility in the physiological conditions experienced en route to the target means that they usually take at least 24 hours to get to the tumour. Baowei Fei, Clemens Burda and co-workers have synthesized a PDT drug complex that significantly decreases the delivery time and enables quantitative monitoring of the process. Polyethylene glycol (PEG; a compound approved for human intravenous applications) is attached to gold nanoparticles functionalized with the PDT drug, silicon phthalocyanine-4. Chains of PEG wrap around the drug allowing the system to disperse in aqueous conditions. Free silicon phthalocyanine-4 takes 1-2 days to accumulate in a tumour site; using the new complex this is reduced to less than two hours in vivo in cancer-bearing mice with the tumour reducing in size within one week of treatment.
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