Breast cancer is a high incidence of cancer among females around the world [1]. Triple-negative breast cancer is characterized by the absence of expression of the progesterone receptor (PR), estrogen receptor (ER), and human epidermal growth factor receptor 2 (HER2), making it the most aggressive subtype of breast cancer [2]; and poses a significant challenge for successful therapy [3], [4]. Conventional treatment methods include surgery, radiotherapy, and chemotherapy for breast cancer. Chemotherapy is one of the major methods used to treat breast cancer. Nevertheless, traditional chemotherapy limitations, such as non-selectivity and unwanted side effects. Therefore, it is an urgent need to choose a powerful and safe strategy for the therapy of triple-negative breast cancer [5].

Stimuli-responsive nanoparticles have received considerable attention as a smart approach in tumor therapy. The drug nanocarrier can respond to the tumor-specific microenvironment, such as enzyme, pH and redox levels [6], [7]. Further, it leads to facilitating the rapid release of therapeutics in specific tumor sites. For instance, tumor cells present several-fold higher levels of glutathione (GSH) than normal cells [8]. As previously described, disulfide bond-containing polymeric nanocarriers exhibited GSH-responsive drug release [9], [10], [11]. Our group reported the stimuli-sensitive nanoparticles from the conjugate of chondroitin sulfate A-ss-deoxycholic acid (CSSD) [12]. Hydrophilic chondroitin sulfate A (CSA) is a biodegradable and natural glycosaminoglycan, and could specifically bind to cluster determinant 44 (CD44) receptors [13]. Deoxycholic acid (DOCA) which naturally exists in our bodies was used as a hydrophobic group. CSSD can form self-assembled micelles in aqueous media. Doxorubicin-loaded CSSD (CSSD-D) micelles exhibited desirable reduction-sensitivity in drug release and intracellular uptake in vitro. Further, CSSD-D demonstrated higher killing potency in HGC-27 tumor cells than the non-reduction sensitive micelles.

Passive targeting nanocarriers have shown great potential for cancer treatment [14], [15]. These nanoparticles are transported to the tumor sites via the enhanced permeability and retention (EPR) effect. However, actively targeted nanoparticles have emerged as an effective alternative strategy to improve cellular uptake by tumor cells [16], [17]. Active targeting is mediated by specific targets, including receptors such as folate, CD44, P-selectin and integrin [18], [19], [20]. Some types of ligands include polysaccharides, aptamers, peptides, etc [21], [22], [23], [24], [25]. As previously reported, the peptides (CDVEWVDVS sequence) were selected by phage display technology and could inhibit the binding of an established glycoside ligand for P-selectin [26], [27]. P-selectin is a cell adhesion protein and acted as an important role in thrombosis and cancer growth [28]. Some studies reveal that overexpression of P-selectin has been found in lung and breast cancers [29], [30], [31]. It is expected that the conjugation of targeted peptides to the surface of nanoparticles improves the uptake in tumor cells via the P-selectin receptor.

Herein, we aimed to develop dual-targeting and bioresponsive micelles for enhanced drug efficacy against triple-negative breast cancer. We synthesized and characterized a targeted peptide (CDVEWVDVS) modified CSSD (TCSSD) copolymer. Doxorubicin (DOX)-containing TCSSD (TCSSD-D) micelles were prepared. We evaluated the drug release, cytotoxicity and intracellular uptake in triple-negative MDA-MB-231 and non-triple negative MCF-7 breast cancer cells. In addition, we assessed the antitumor activity of TCSSD-D nanoparticles in MDA-MB-231 bearing nude mice.