Preclinical evaluation of antitumor activity of acid-sensitive PEGylated doxorubicin.

The acid-sensitive PEGylated doxorubicin (DOX) with exact chemical structure was designed and prepared as a potential tumor intracellular microenvironment-responsive drug delivery system. First, the insensitive succinic anhydride-functionalized DOX (i.e., SAD) and acid-sensitive cis-aconitic anhydride-modified DOX (i.e., CAD) were synthesized through the ring-opening reaction. Subsequently, the insensitive and acid-sensitive PEGylated DOX (i.e., mPEG-SAD and mPEG-CAD) was prepared by the condensation reaction between the terminal hydroxyl group of mPEG and the carboxyl group in SAD and CAD, respectively. The obtained mPEG-SAD and mPEG-CAD could spontaneously self-assemble into micelles in phosphate-buffered saline at pH 7.4 with diameters of about 100 nm. The DOX release of mPEG-CAD micelle could be accelerated by the decrease of pH from 7.4, 6.8, to 5.5 in relation to that of mPEG-SAD micelle. On the other hand, the result of the cellular proliferation inhibition test indicated that mPEG-CAD micelle exhibited favorable antiproliferative activity in vitro. In addition, the selective intratumoral accumulation and antitumor efficacy of mPEG-CAD micelle were significantly better than those of free DOX and mPEG-SAD. More importantly, the prodrug micelles exhibited upregulated security in vivo as compared to free DOX. Overall, the mPEG-CAD micelle with enhanced antitumor efficacy and decreased side effects was a fascinating prospect for the clinical chemotherapy of malignancy.