Lysosome-oriented, dual-stage pH-responsive polymeric micelles for β-lapachone delivery

Abstract

β-Lapachone (β-lap), a novel anticancer agent, is bioactivated by NADP(H):quinone oxidoreductase 1 (NQO1), an enzyme over-expressed in numerous tumors, including lung, pancreas, breast, and prostate cancers. Fast renal clearance and methemoglobinemia/hemolytic side-effects from the clinical formulation (β-lap-hydroxyl propyl-β-cyclodextrin complex) hindered its clinical translation. Here, we investigated dual-model pH-responsive polymers for β-lap delivery. Three pH-sensitive linkages, including acylhydrazone, ketal and imine bonds for β-lap prodrug syntheses result in an aryl imine linkage as the most optimal linkage. The conversion to β-lap was 2.8%, 4.5% and 100% at pH 7.4, 6.5 and 5.0 in 8 h, respectively. The β-lap aryl imine prodrug conjugated ultra-pH-sensitive (UPS) polymer reached high β-lap loading density (8.3%) and exhibited dual-stage responsiveness to pH variation. In pHs under pH_t, at stage I, micelles immediately dissociate and subsequently, entering stage II, micelles start to quickly release β-lap. An in vitro release study showed that the micelles constantly release β-lap (14.9 ± 0.1%) at pHs above pH_t in 72 h, whereas there was a boosted release of β-lap (79.4 ± 1.2%) at pH 5.0. The micelles’ intracellular distribution being predominantly in the lysosome organelle guaranteed their pH-responsive dissociation and subsequently β-lap controlled release. The M–P micelles retained NQO1-dependent cytotoxicity in A549 lung cancer cells, similar to the free drug in both efficacy and mechanism of cell death. The lysosome-oriented dual-stage ultra-pH-responsive β-lap prodrug micelles potentially offer an alternative nanotherapeutic strategy for lung cancer, as well as other NQO1+ cancer therapies.