Displaying In Vivo “Assembly–Disassembly” Cascade with “Off–On–Off” Magnetic Resonance Imaging Signals in Tumor

"Assembly-Disassembly" cascade has been utilized as a highly effective approach for tumor theranostics, but its real-time in vivo monitoring remains challenging. Current strategies face a fundamental trade-off between penetration depth and real-time nature, while there is still no report on integrating both features to display this dynamic cascade in a living organism. In this work, we develop a gadolinium (Gd) probe Cys(StBu)-Asp-Asp-Asp-Asp-Lys-Lys(DOTA(Gd))-CBT (Gd-AD) to display an in vivo "Assembly-Disassembly" cascade via T₁-weighted "Off-On-Off" ¹H magnetic resonance imaging (MRI) signals. Under reduction conditions, Gd-AD undergoes a CBT-Cys click reaction to assemble into a Gd nanoparticle, with enhanced ¹H MRI signals of 59.3% and 25.4% in cells and in tumors, respectively ("Off-On"). Upon enterokinase (ENTK) cleavage, the nanoparticle disassembles, rendering decreased ¹H MRI signals of 23.4% and 15.2% in cells and in tumors, respectively ("On-Off"). A scrambled control probe Asp-Asp-Asp-Asp-Lys-Cys(StBu)-Lys(DOTA(Gd))-CBT (Gd-A), which responds to reduction and ENTK to assemble into a Gd nanoparticle with "Off-On" ¹H MRI signals, is designed and studied in parallel. During 1 h tumor imaging, while Gd-A only displays "Off-On" ¹H MRI signals, Gd-AD clearly shows "Off-On-Off" signals to reflect the "Assembly-Disassembly" cascade of Gd nanoparticles in tumor. We expect that our strategy of real-time display of in vivo "Assembly-Disassembly" cascade could help people to optimize their nanodrug-based tumor theranostics in the near future.