Multidrug resistance (MDR) remains the biggest challenge in treating cancers. Herein we propose the intracellular self-assembly of nanodrugs as a new strategy for overcoming MDR. By employing a biocompatible condensation reaction, we rationally designed a taxol derivative Ac-Arg-Val-Arg-Arg-Cys(StBu)-Lys(taxol)-2-cyanobenzothiazole (CBT-Taxol) which could be subjected to furin-controlled condensation and self-assembly of taxol nanoparticles (Taxol-NPs). In vitro and in vivo studies indicated that, compared with taxol, CBT-Taxol showed a 4.5-fold or 1.5-fold increase in anti-MDR effects, respectively, on taxol-resistant HCT 116 cancer cells or tumors without being toxic to the cells or the mice. Our results demonstrate that structuring protease-susceptible agents and assembling them intracellularly into nanodrugs could be a new optimal strategy for overcoming MDR.

Large magnetic nanoparticles or aggregates are advantageous in their magnetic resonance properties over ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles (NPs), but the former are cleared faster from the blood pool. Therefore, the "smart" strategy of intracellular aggregation of USPIO NPs is required for enhanced T2-weighted MR imaging. Herein, employing an enzyme-instructed condensation reaction, we rationally designed a small molecule Ac-Asp-Glu-Val-Asp-Cys(StBu)-Lys-CBT (1) to covalently modify USPIO NPs to prepare monodispersive Fe3O4@1 NPs. In vitro results showed that Fe3O4@1 NPs could be subjected to caspase 3 (Casp3)-instructed aggregation. T2 phantom MR imaging showed that the transverse molar relaxivity (r2) of Fe3O4@1 NPs with Casp3 or apoptotic HepG2 cells was significantly larger than those of control groups. In vivo tumor MR imaging results indicated that Fe3O4@1 NPs could be specifically applied for enhanced T2 MR imaging of tumor apoptosis. We propose that the enzyme-instructed intracellular aggregation of Fe3O4 NPs could be a novel strategy for the design of "smart" probes for efficient T2 MR imaging of in vivo biomarkers.

Bacterial infection poses a massive threat to our society, and bacterial biofilm is a major cause of chronic and recurrent infections. The treatment of bacterial biofilms represents a challenging task, and the development of antibacterial materials that can not only disperse bacterial biofilms but also kill bacteria is of increasing interest. Herein, we report the fabrication of well-defined nitric oxide (NO)-releasing amphiphiles, poly­(ethylene oxide)-b-polyCouNO (PEO-b-PCouNO), where CouNO is an N-nitrosoamine-based NO donor containing a coumarin chromophore, exhibiting visible-light-mediated and self-reporting NO-release behavior. Unlike conventional polymeric NO donors derived from N-diazeniumdiolate (NONOates) or N-nitrosothiol (SNOs) that could be only synthesized via the postmodification procedure due to poor stability, the newly developed N-nitrosoamine-based NO donors can be directly polymerized into amphiphiles using reversible addition-fragmentation chain transfer (RAFT) polymerization. The NO-releasing amphiphiles self-assembled into micelles and selective NO release in aqueous medium was achieved by irradiating the micelle solution with visible light, which was characterized by a remarkable fluorescence turn-on (>185-fold), thereby enabling in situ self-reporting NO release. The photoinduced NO release can efficiently disperse bacterial biofilm of Pseudomonas aeruginosa. Moreover, antibiotics (e.g., Ciprofloxacin, Cip) could be loaded into the NO-releasing micelles, and co-delivery of NO and Cip was achieved, allowing for simultaneous biofilm dispersal and bacterial killing. This work provides a new strategy to fabricate macromolecular NO donors, which can efficiently avoid uncontrolled NO leakage and display promising antibacterial applications.

For cancer diagnosis, 1H magnetic resonance imaging (MRI) is advantageous in sensitivity but lacks selectivity. Endogenous 19F MRI signal in humans is barely detectable and thus 19F MRI has very high selectivity. A combination of 1H and 19F MRI is ideal for precise tumor imaging but a protease‐controlled strategy of simultaneous T2 1H MRI enhancement and 19F MRI “Turn‐On” has not been reported. Here, used is a click condensation reaction to rationally project a dual‐functional fluorine probe 4‐(trifluoromethyl)benzoic acid (TFMB)‐Arg‐Val‐Arg‐Arg‐Cys(StBu)‐Lys‐CBT (1), which is further utilized to functionalize Fe3O4 nanoparticle (IONP) to achieve IONP@1. As such, the IONP aggregation can be activated by furin addition, thereby enhancing the T2 1H MRI signal and switching the 19F NMR/MRI signal “On”. Using this strategy, IONP@1 is successfully applied to detect the activity of the furin enzyme with “Turn‐On” 19F NMR/MRI and T2 1H MRI signals are enhanced. Moreover, IONP@1 is also applied for precise dual‐mode (1H and 19F) MR imaging of tumors in zebrafish under 14.1 T. The current approach, therefore, provides a feasible and robust means to reconcile the dilemma between selectivity and sensitivity of conventional MRI probes. More importantly, it is envisioned that, by substituting the TFMB moiety in 1 with a perfluorinated compound, this “smart” method could be of potential use for precise 1H MR and 19F MR imaging of tumor in mouse or in bigger rodents in near future.

Fatty acid amide hydrolase (FAAH) overexpression induces several disorder symptoms in nerve systems, and therefore long-term tracing of FAAH activity in vivo is of high importance but remains challenging. Current bioluminescence (BL) methods are limited in detecting FAAH activity within 5 h. Herein, by rational design of a latent BL probe (d-Cys-Lys-CBT)2 (1), we developed a "smart" method of intracellular reduction-controlled self-assembly and FAAH-directed disassembly of its cyclic d-luciferin-based nanoparticles (i.e., 1-NPs) for persistent BL imaging of FAAH activity in vitro, in cells, and in vivo. Using aminoluciferin methyl amide (AMA), Lys-amino-d-luciferin (Lys-Luc), and amino-d-luciferin (NH2-Luc) as control BL probes, we validated that the persistent BL of 1 from luciferase-expressing cells or tumors was controlled by the activity of intracellular FAAH. With the property of long-term tracing of FAAH activity in vivo of 1, we envision that our BL precursor 1 could probably be applied for in vivo screening of FAAH inhibitors and the diagnosis of their related diseases (or disorders) in the future.