Recent Progress in Polymer Therapeutics as Nanomedicines - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 78

architecture of polymer-drug conjugates: a polymeric spacer, drug
attached via a hydrolytically or enzymatically cleavable spacer
and a targeting group complementary to a receptor/antigen at
the target cell. Since then, most of the polymer-drug conjugates
have been designed and developed according to Ringsdorf's model
(Figure 4.1A). Most of the earlier systems rarely advanced beyond
in vitro testing. However, over the last 15 years, a growing number
of polymer therapeutics have been synthesized and characterized.
In particular, PEG-protein conjugates have reached the market, and
polymer-drug conjugates and polymeric micelles entered clinical
trials mainly as anti-cancer agents.
Figure 4.1 Structures of polymer therapeutics: (A) Modified Ringsdorf's
model, (B) polymeric drug, (C) polymeric micelle, (D) polymersome, and
(E) dendrimer. See also Color Insert.