Tumor‐Specific Drug Release and Reactive Oxygen Species Generation for Cancer Chemo/Chemodynamic Combination Therapy

Abstract The combination of chemotherapeutic drugs and reactive oxygen species (ROS) is a promising strategy to achieve improved anticancer effect. Herein, a nanomedicine (LaCIONPs) that can achieve tumor‐specific chemotherapeutic drug release and ROS generation is developed for cancer chemo/chemodynamic combination therapy. The LaCIONPs are constructed by encapsulation of iron oxide nanoparticles (IONPs) and β‐lapachone (La) in nanostructure assembled by hydrogen peroxide (H2O2)‐responsive polyprodrug and pH‐responsive polymer. Through the enhanced permeability and retention effect, the nanosized LaCIONPs can accumulate in tumor tissue. After the LaCIONPs are internalized by tumor cells, the structure of LaCIONPs is disintegrated in acidic intracellular environment, leading to rapid release of La and iron ions. Then the released La generates massive H2O2 through tumor specific catalysis. On the one hand, H2O2 further reacts with iron ions to produce highly toxic hydroxyl radicals for chemodynamic therapy. On the other hand, H2O2 also activates the release of camptothecin from the polyprodrug for chemotherapy. The potent antitumor effect of the LaCIONPs is demonstrated by both in vitro and in vivo results. Therefore, the LaCIONP is a promising nanomedicine for tumor‐specific chemo/chemodynamic combination therapy.

2 solution (9.1 mmol). After 1 h of reaction, the mixture was filtered and the solvent was evaporated under reduced pressure. Then the concentrated mixture was allowed to afford chromatographic separation (silica gel, dichloromethane/ethyl acetate (2:1, v/v)) to yield CPTMA prodrug monomer as a pale yellow solid.

Synthesis of PEG-PCPT
PEG-PCPT (Scheme S2) The mixture was precipitated into an excess of ethyl acetate to generate PEG-PCPT.
Bromotrimethylsilane (1.3 mL) was added in a dropwise manner, and the mixture was stirred at room temperature for 12 h. After evaporation of the solvent, methanol (5 mL) was added and the mixture was stirred at room temperature for another 12 h. The solvent was evaporated and the BiBEP was obtained after washing with ether.

°C
The mixture was precipitated into methanol/water to generate P-PDPA.

Characterizations
The morphology of the HRNMs was observed by Tecnai TF30 transmission electron microscope (TEM) (FEI, Hillsboro, OR). The effective particle diameters and zeta potential of the samples were determined by a SZ-100 nano particle analyzer (HORIBA Scientific, USA) at room temperature. UV-vis-NIR absorption spectra were measured by Genesys 10S UV-Vis spectrophotometer (Thermo Scientific, Waltham, MA).

In vitro drug release
The in vitro drug release behaviors of the samples were evaluated by a dialysis method. The samples were dispered in 2 mL of media and added to dialysis bags (MWCO: 1000 Da) and placed in 20 mL of environmental media. At appropriate time points, 2 mL of the medium was taken out and replaced with the same amount of fresh medium. The amounts of the released La and CPT were measured by HPLC. The amount of the released Fe was measured by inductively coupled plasma mass spectrometry (ICP-MS).

In vitro cell experiments
The in vitro cell cytotoxicity, ROS generation study and antitumor activity study were assessed on A549 cell line, which was purchased from American type culture collection (ATCC).
To mice. An Inveon small-animal PET scanner (Siemens, Erlangen, Germany) was used for the scanning at indicated time points after injection. At 48 h post-injection, the mice were sacrificed and the major organs were collected and assayed for radioactivity using a gamma counter. The percent of injected dose/gram of tissue (%ID/g) was then calculated.

In vivo therapy
A549 tumor-bearing mice were randomly divided into 6 groups (n = 5): control group, free CPT group, LaDUCNPs group, LaDIONPs group, LaCUCNPs group and LaCIONPs group.
When the tumors reached about 80 mm 3 , the mice were treated with samples (3 mg CPT kg -1 ) via intravenous injection every 3 days for 5 times. Tumor volume and body weight were monitored every 3 days. Tumor volume was calculated as (major axis) × (minor axis) 2 /2.
Mice were euthanized when major axis of tumor exceeded 20 mm or when mouse weight lost by over 20%.