BACKGROUND: Triple-negative breast cancer (TNBC) is a recurrent, heterogeneous, and invasive form of breast cancer. The treatment of TNBC patients with paclitaxel and fluorouracil in a sequential manner has shown promising outcomes. However, it is challenging to deliver these chemotherapeutic agents sequentially to TNBC tumors. We aim to explore a precision therapy strategy for TNBC through the sequential delivery of paclitaxel and fluorouracil.
METHODS: We developed a dual chemo-loaded aptamer with redox-sensitive caged paclitaxel for rapid release and non-cleavable caged fluorouracil for slow release. The binding affinity to the target protein was validated using Enzyme-linked oligonucleotide assays and Surface plasmon resonance assays. The targeting and internalization abilities into tumors were confirmed using Flow cytometry assays and Confocal microscopy assays. The inhibitory effects on TNBC progression were evaluated by pharmacological studies in vitro and in vivo.
RESULTS: Various redox-responsive aptamer-paclitaxel conjugates were synthesized. Among them, AS1411-paclitaxel conjugate with a thioether linker (ASP) exhibited high anti-proliferation ability against TNBC cells, and its targeting ability was further improved through fluorouracil modification. The fluorouracil modified AS1411-paclitaxel conjugate with a thioether linker (FASP) exhibited effective targeting of TNBC cells and significantly improved the inhibitory effects on TNBC progression in vitro and in vivo.
CONCLUSIONS: This study successfully developed fluorouracil-modified AS1411-paclitaxel conjugates with a thioether linker for targeted combination chemotherapy in TNBC. These conjugates demonstrated efficient recognition of TNBC cells, enabling targeted delivery and controlled release of paclitaxel and fluorouracil. This approach resulted in synergistic antitumor effects and reduced toxicity in vivo. However, challenges related to stability, immunogenicity, and scalability need to be further investigated for future translational applications.

We have previously employed cyclization of a linear peptide as a strategy to modulate peptide function and properties, but cleavage to regenerate the linear peptide left parts of the linker structure on the peptide, interfering with its activity. Here, we focused on cyclization of a linear peptide via a \"traceless\" disulfide-based linkage that would be cleaved and completely removed in a reducing environment, regenerating the original linear peptide without any linker-related structure. Thus, the linker would serve as a redox switch that would be activated in the intracellular environment. We applied this strategy to a lysine-specific demethylase 1 (LSD1) inhibitor peptide 1. The resulting cyclic peptide 2 exhibited approximately 20 times weaker LSD1-inhibitory activity than peptide 1. Upon addition of reducing reagent, the linker was completely removed to regenerate the linear peptide 1, with full restoration of the LSD1-inhibitory activity. In addition, the cyclic peptide was far less susceptible to proteolysis than the linear counterpart. Thus, this switch design not only enables control of functional activity, but also improves stability. This approach should be applicable to a wide range of peptides, and may be useful in the development of peptide pharmaceuticals.