Polymer-protein and polymer-drug conjugates in cancer therapy.

Polymer conjugates are becoming established as a new approach towards improved cancer therapy. These water-soluble, hybrid constructs fall into two main categories: polymer-protein conjugates (already available as licensed products), and polymer-drug conjugates (currently in clinical development). Polyethyleneglycol conjugation of proteins is accepted as a means to reduce immunogenicity, prolong plasma half-life and enhance protein stability. Polymer-drug conjugation promotes tumor targeting by the 'enhanced permeation and retention' effect, and at the cellular level, allows lysosomotropic drug delivery. Eleven polymer-drug conjugates have entered clinical development and activity has already been observed in chemotherapy refractory patients. Certain compounds have also demonstrated a marked reduction in drug toxicity.