Gold nanoparticle-based theranostics: disease diagnostics and treatment using a single nanomaterial

Abstract

Photodynamic therapy (PDT) is a minimally in- vasive therapeutic modality approved for clinical treatment of several types of cancer and non-oncological disorders. In PDT, a compound with photosensitising properties (pho- tosensitiser, PS) is selectively accumulated in malignant tissues. The subsequent activation of the PS by visible light, preferentially in the red region of the visible spec- trum (λ≥600 nm), where tissues are more permeable to light, generates reactive oxygen species, mainly singlet oxygen (1O2), responsible for cytotoxicity of neoplastic cells and tumour regression. There are three main mecha- nisms described by which 1O2 contributes to the destruc- tion of tumours by PDT: direct cellular damage, vascular shutdown and activation of immune response against tu- mour cells. The advantages of PDT over other conventional cancer treatments are its low systemic toxicity and its abili- ty to selectively destroy tumours accessible to light. There- fore, PDT is being used for the treatment of endoscopically accessible tumours such as lung, bladder, gastrointestinal and gynaecological neoplasms, and also in dermatology for the treatment of non-melanoma skin cancers (basal cell carcinoma) and precancerous diseases (actinic keratosis). Photofrin®, ALA and its ester derivatives are the main compounds used in clinical trials, though newer and more efficient PSs are being evaluated nowadays.