Carbon-Spaced Tandem-Disulfide Bond Bridge Design Addresses Limitations of Homodimer Prodrug Nanoassemblies: Enhancing Both Stability and Activatability.

Redox-responsive homodimer prodrug nanoassemblies (RHPNs) have emerged as a significant technology for overcoming chemotherapeutical limitations due to their high drug-loading capacity, low excipient-associated toxicity, and straightforward preparation method. Previous studies indicated that α-position disulfide bond bridged RHPNs exhibited rapid drug release rates but unsatisfactory assembly stability. In contrast, γ-disulfide bond bridged RHPNs showed better assembly stability but low drug release rates. Therefore, designing chemical linkages that ensure both stable assembly and rapid drug release remains challenging. To address this paradox of stable assembly and rapid drug release in RHPNs, we developed carbon-spaced double-disulfide bond (CSDD)-bridged RHPNs (CSDD-RHPNs) with two carbon-spaces. Pilot studies showed that CSDD-RHPNs with two carbon-spaces exhibited enhanced assembly stability, reduction-responsive drug release, and improved selective toxicity compared to α-/γ-position single disulfide bond bridged RHPNs. Based on these findings, CSDD-RHPNs with four and six carbon-spaces were designed to further investigate the properties of CSDD-RHPNs. These CSDD-RHPNs exhibited excellent assembly ability, safety, and prolonged circulation. Particularly, CSDD-RHPNs with two carbon-spaces displayed the best antitumor efficacy on 4T1 and B16-F10 tumor-bearing mice. CSDD chemical linkages offer novel perspectives on the rational design of RHPNs, potentially overcoming the design limitations regarding contradictory assembly ability and drug release rate.