Abstract
The cancer incidence world-wide has caused an increase in the demand for effective forms
of treatment. One unconventional form of treatment for cancer is photodynamic therapy (PDT).
PDT has 3 fundamental factors, namely a photosensitiser (PS) drug, light and oxygen. When a PS
drug is administered to a patient, it can either passively or actively accumulate within a tumour site
and once exposed to a specific wavelength of light, it is excited to produce reactive oxygen species
(ROS), resulting in tumour destruction. However, the efficacy of ROS generation for tumour damage
is highly dependent on the uptake of the PS in tumour cells. Thus, PS selective/targeted uptake and
delivery in tumour cells is a crucial factor in PDT cancer drug absorption studies. Generally, within
non-targeted drug delivery mechanisms, only minor amounts of PS are able to passively accumulate
in tumour sites (due to the enhanced permeability and retention (EPR) effect) and the remainder
distributes into healthy tissues, causing unwanted side effects and poor treatment prognosis. Thus, to
improve the efficacy of PDT cancer treatment, research is currently focused on the development
of specific receptor-based PS-nanocarrier platform drugs, which promote the active uptake and
absorption of PS drugs in tumour sites only, avoiding unwanted side effects, as well as treatment
enhancement. Therefore, the aim of this review paper is to focus on current actively targeted or
passively delivered PS nanoparticle drug delivery systems, that have been previously investigated
for the PDT treatment of cancer and so to deduce their overall efficacy and recent advancements.