Polymer conjugates for tumour targeting and intracytoplasmic delivery. The EPR effect as a common gateway?

Tumour capillaries are frequently hyperpermeable compared with normal vasculature, and thus they offer a much sought-after gateway for targeted delivery of cancer chemotherapy. Phase I clinical trials reported recently describe the first synthetic polymer-drug conjugate to be tested in man. N-(2-Hydroxypropyl)methacrylamide copolymer-doxorubicin (PK1, FCE 28068) displayed antitumour activity in chemotherapy-refractory patients, considerably reduced toxicity compared with doxorubicin, and evidence of tumour-selective targeting. With increasing understanding of the vector- and tumour-related factors that govern vascular permeability, non-viral vectors are being designed for tumour-selective targeting and subsequent intracytoplasmic delivery of macromolecular medicines such as genes, antisense oligonucleotides, proteins and peptides.