Exploiting tumour biology to develop novel drug delivery strategies for PDT

Photodynamic therapy (PDT) is a novel modality for cancer treatment that exploits the selective retention of a photosensitizer (PS) in tumour tissues to generate a localized cytotoxic species via light irradiation. While PDT has become an approved treatment method, only a small number of PSs have received regulatory approval for the clinical treatment of a limited number of disease states. Even though much progress has been made in the understanding of the therapeutic mechanisms associated with PDT, several challenges remain to be resolved before PDT can be a major therapeutic option that is clinically viable. Paramount to reaching this objective is the creation of innovative drug delivery strategies that exploit unique characteristics of tumour biology to enhance the selectivity of PSs and improve the therapeutic efficacy. In this review article, recent research will be highlighted that has synthesized novel PS (and chemotherapeutic) conjugates that utilize the over expression of specific extra/intracellular enzymes, membrane receptors and antigens to selectively target and deliver these therapies.