Dynamic micelles with detachable PEGylation at tumoral extracellular pH for enhanced chemotherapy

Multistage O2-producing liposome for MRI-guided synergistic chemodynamic/chemotherapy to reverse cancer multidrug resistance

Reduced drug uptake and elevated drug efflux are two major mechanisms in cancer multidrug resistance (MDR). In the present study, a new multistage O₂-producing liposome with NAG/R8-dual-ligand and stimuli-responsive dePEGylation was developed to address the abovementioned issues simultaneously. The designed C-NAG-R8-PTXL/MnO₂-lip could also achieve magnetic resonance imaging (MRI)-guided synergistic chemodynamic/chemotherapy (CDT/CT). In vitro and in vivo studies showed that C-NAG-R8-PTXL/MnO₂-lip enhanced circulation time by PEG and targeted the tumor site. After tumor accumulation, endogenous l-cysteine was administered, and the PEG-attached disulfide bond was broken, resulting in the dissociation of PEG shells. The previously hidden positively charged R8 by different lengths of PEG chains was exposed and mediated efficient internalization. In addition, the oxygen (O₂) generated by C-NAG-R8-PTXL/MnO₂-lip relieved the hypoxic environment within the tumor, thus reducing the efflux of chemotherapeutic drug. O₂ was able to burst liposomes and triggered the release of PTXL. The toxic hydroxyl radical (·OH), which was produced by H₂O₂ and Mn²⁺, strengthened CDT/CT. C-NAG-R8-PTXL/MnO₂-lip was also used as MRI contrast agent, which blazed the trail to rationally design theranostic agents for tumor imaging.

Drug Delivery Systems with a "Tumor-Triggered" Targeting or Intracellular Drug Release Property Based on DePEGylation

Coating nanosized anticancer drug delivery systems (DDSs) with poly(ethylene glycol) (PEG), the so-called PEGylation, has been proven an effective method to enhance hydrophilicity, aqueous dispersivity, and stability of DDSs. What is more, as PEG has the lowest level of protein absorption of any known polymer, PEGylation can reduce the clearance of DDSs by the mononuclear phagocyte system (MPS) and prolong their blood circulation time in vivo. However, the "stealthy" characteristic of PEG also diminishes the uptake of DDSs by cancer cells, which may reduce drug utilization. Therefore, dynamic protection strategies have been widely researched in the past years. Coating DDSs with PEG through dynamic covalent or noncovalent bonds that are stable in blood and normal tissues, but can be broken in the tumor microenvironment (TME), can achieve a DePEGylation-based "tumor-triggered" targeting or intracellular drug release, which can effectively improve the utilization of drugs and reduce their side effects. In this review, the stimuli and methods of "tumor-triggered" targeting or intracellular drug release, based on DePEGylation, are summarized. Additionally, the targeting and intracellular controlled release behaviors of the DDSs are briefly introduced.

pH-triggered small molecule nano-prodrugs emulsified from tryptamine-cinnamaldehyde twin drug for targeted synergistic glioma therapy

Chemotherapy fails to achieve an ideal gliomas therapy due to the limited delivery of chemotherapeutics across the blood brain barrier (BBB), difficult accumulation of drugs in the gliomas area, and off-target toxicity. Herein, the pH-triggered small molecule nano-prodrugs (Try-CA-NPs) emulsified from hydrophobic tryptamine (Try)-cinnamaldehyde (CA) twin drug were successfully prepared through a facile method. Try-CA-NPs exhibited long-term storage and circulation stability. Furthermore, liposoluble Try-CA-NPs could easily cross BBB and efficiently accumulate in brain, selectively target to gliomas cells via Try-mediated cellular uptake, and enhance cytotoxicity through intracellular pH-triggered endosomal escape and efficient drug release, and synergistic effect between CA and Try, therefore achieving the complete destruction of SH-SY5Y multicellular spheroids (MCs). Thus, the pH-triggered small molecule nano-prodrugs emulsified from Try-CA twin drug have the great potential for clinically targeted synergistic glioma therapy.

A sequentially responsive nanogel via Pt(IV) crosslinking for overcoming GSH-mediated platinum resistance

Chemotherapy efficiency of platinum(II) (Pt(II)) is often attenuated owing to the low intracellular drugs concentration and glutathione (GSH)-mediated detoxification. To address these problems, we fabricated a step-by-step responsive nanogel (~160 nm) by copolymerization between four functional monomers. Hydrophilic methoxypolyethylene glycols (mPEG) distributedrandomly on the surface of particles endowed the nanogel with "stealth" property in blood circulation, while the chemical crosslinking inside particles by platinum(IV) (Pt(IV)) linker remarkably increased the stability of nanogel in vivo. These advantages of nanogels leaded to higher accumulation at tumor region (6.4% ID/g), followed by triggering the dePEGylation effect by the cleavage of ortho ester at tumoral extracellular pH. Meanwhile, the exposed phenylboric acid (PBA) could significantly increase cellular uptake and intracellular drugs levels by targteing sialic acid residues on the cells membrane. More importantly, this nanogels could further deplete intracellular glutathione (GSH) by the dual-regulation of platinum(IV) and arylboronic ester, resulting in enhanced platinum(II) toxicity both in vitro and in vivo, eventually achieving superior inhibition rate (79.14%) in A549/DDP tumor. Thus, the sequentially responsive nanogel could be considered as an effective strategy for cancer treatment.