Convenient and Controllable Synthesis of Poly(2-oxazoline)-Conjugated Doxorubicin for Regulating Anti-Tumor Selectivity

Polyethylene glycol (PEG)–doxorubicin (DOX) conjugation is an important strategy to improve toxicity and enhance clinically therapeutic efficacy. However, with the frequent use of PEG-modified drugs, the accumulation of anti-PEG antibodies has become a tough issue, which limits the application of PEG–drug conjugation. As an alternative solution, poly(2-oxazoline) (POX)−DOX conjugation has shown great potential in the anti-tumor field, but the reported conjugation process of POX with DOX has drawbacks such as complex synthetic steps and purification. Herein, we propose a convenient and controllable strategy for the synthesis of POX−DOX conjugation with different chain lengths and narrow dispersity by N-boc-2-bromoacetohydrazide-initiated 2-ethyl-oxazoline polymerization and the subsequent deprotection of the N-Boc group and direct reaction with DOX. The DOX−PEtOx conjugates were firstly purified, and the successful conjugations were confirmed through various characterization methods. The synthetic DOX−PEtOx(n) conjugates reduce the toxicity of DOX and increase the selectivity to tumor cells, reflecting the promising application of this POX−DOX conjugation strategy in drug modification and development.