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.

Compared to (1)H MRI, (19)F MRI provides higher selectivity but lower sensitivity. Therefore, the need to inject high doses of the (19)F probe to improve its sensitivity for in vivo diagnosis remains a challenge. A "smart" strategy is needed that could locally concentrate a low-dose (19)F probe while avoiding the fast transverse relaxation of the probes. Locally self-assembling and disassembling (19)F nanoparticles may be an optimal measure to achieve this goal. Herein, we report a dual-functional probe 1 for glutathione (GSH)-controlled self-assembly and subsequent caspase 3/7 (Casp3/7)-controlled disassembly of formed nanoparticles (i.e., 1-NPs). Consecutive assembly and disassembly of 1-NPs translate to "off" and "on" (19)F magnetic resonance (MR) signal states, respectively. Employing this smart strategy, we successfully used 1 for the consecutive detection of GSH and Casp3/7 activity in vitro and in cells and imaging Casp3/7 activity in cells and in zebrafish at low doses with a 14.1 T magnetic field.

(19)F MRI has higher selectivity but lower sensitivity than (1)H MRI for in vivo diagnosis. Therefore, to avoid using a high injection dose of the (19)F probe while, in the meantime, maintaining the high sensitivity of (19)F MRI has remained challenging. Local self-assembly and disassembly of (19)F nanoparticles could be one of the "smart" strategies to achieve this goal. Herein, we report a dual-functional probe 1 for glutathione (GSH)-controlled self-assembly and subsequent legumain (Lgmn)-controlled disassembly of its nanoparticles (i.e., 1-NPs). Self-assembly and disassembly of 1-NPs confer (19)F magnetic resonance (MR) signals "off" and "on", respectively. Employing this strategy, we successfully applied 1 for consecutive detections of GSH and Lgmn in vitro and in cells, imaging Lgmn activity in HEK 293T tumors in zebrafish at a low dosage under 14.1 T.

Lanthipeptides represent a large class of cyclic natural products defined by the presence of lanthionine (Lan) and methyllanthionine (MeLan) cross-links. With the advances in DNA sequencing technologies and genome mining tools, new biosynthetic enzymes capable of installing unusual structural features are continuously being discovered. In this study, we investigated an O-methyltransferase that is a member of the most prominent auxiliary enzyme family associated with class I lanthipeptide biosynthetic gene clusters. Despite the prevalence of these enzymes, their function has not been established. Herein, we demonstrate that the Omethyltransferase OlvS A encoded in the olv gene cluster from Streptomyces olivaceus NRRL B-3009 catalyzes the rearrangement of a highly conserved aspartate residue to a β-amino acid, isoaspartate, in the lanthipeptide OlvA(BCS A ). We elucidated the NMR solution structure of the GluC-digested peptide, OlvA(BCS A ) GluC , which revealed a unique ring topology comprising four interlocking rings and positions the isoaspartate residue in a solvent exposed loop that is stabilized by a MeLan ring. Gas chromatography−mass spectrometry analysis further indicated that OlvA(BCS A ) contains two DL-MeLan rings and two Lan rings with an unusual LL-stereochemistry. Lastly, in vitro reconstitution of OlvS A activity showed that it is a leader peptideindependent and S-adenosyl methionine-dependent O-methyltransferase that mediates the conversion of a highly conserved aspartate residue in a cyclic substrate into a succinimide, which is hydrolyzed to generate an Asp or isoAsp containing peptide. This overall transformation converts an α-amino acid into a β-amino acid in a ribosomally synthesized peptide, via an electrophilic intermediate that may be the intended product.