br Introduction br Metastatic breast cancer also
Metastatic breast cancer, also known as metastases, is a stage of breast cancer where tumor cells have diﬀused to distant sites by virtue of blood and lymphatic circulation [1,2]. Distant metastases account for 90% of breast cancer-related deaths . Despite the rapid advances in recent clinical techniques, current treatment only improves the overall survival period by a few months [4–6]. One primary reason is that chemotherapeutic agents cannot eﬀectively capture and eliminate cir-culating tumor cells (CTCs) [7,8].
Nanoparticulate drug delivery systems (NDDS) could eﬀectively target primary tumors by the well-known enhanced permeability and retention eﬀect (EPR) [9–12]. However, when the breast cancer has developed to the advanced stage, the connections between tumors cells are loosened and tumors cells subsequently undergo epithelial-me-senchymal transition . Partially liberated tumor cells could spread into the blood or lymph, in which case they are known as CTCs, which
are capable of forming life-threatening metastases . Therefore, it is necessary not only to deliver the drug cargo specifically to the metas-tases that have already been generated but also to neutralize the CTCs within blood or lymph circulations to prevent the further formation of micrometastases [15,16].
Platelets play an important role in tumor metastasis. Several studies have shown that platelets facilitate tumor metastasis by protecting tumor cells from host immune surveillance by forming platelet-cloaking CTC 85-66-5 and inducing CTCs to adhere to endotheliocytes [17–19]. Platelet-derived cytokines and receptors could bind to CTCs to form large emboli, which are crucial in protecting CTCs from host im-mune attack and physical stress [14,20]. Mechanistically, P-selectin, a protein overexpressed on the platelet membrane, could bind to CD44 receptors overexpressed in breast tumor cells, contributing to the spe-cific association of CTCs with host platelets [18,21–26].
The biomimetic cell membrane-cloaking NDDS strategy is capable of maintaining the surface antigenic diversity of the source cell
∗ Corresponding author. Department of Pharmaceutics, Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, 110016, PR China. ∗∗ Corresponding author. Department of Pharmaceutics, Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, 110016, PR China. E-mail addresses: [email protected]com (Z. He), [email protected] (J. Sun).
membrane and possesses the innate advantages of immune surveil-lance-escaping ability , specific cell-cell interactions and physical barrier-crossing ability, etc. It has been reported that platelet mem-brane (PM) coating poly(lactic-co-glycolic acid) (PLGA) NPs exhibit anticancer eﬀects in the treatment of primary cancer . However, most patients with breast cancer are prone to lymphatic metastasis, based on clinical data . Here, we suppose that PM-camouflaging PLGA NPs, also regarded as nanoplatelets in this study, might be used to enhance the delivery of chemotherapeutic agents to CTCs and micro-metastases via P-selectin-CD44 specific interactions between CTCs and platelets, thus inhibiting tumor metastasis.
In this study, we prepared 3 p.m.-coating PLGA nanoparticles (PMNPs) incorporating a chemotherapeutic agent, doxorubicin (DOX), an FDA-approved photothermal agent, indocyanine green (ICG), and DOX together with ICG, with the three NPs respectively abbreviated as PMDs, PMIs and PMDIs. We used PLGA NPs loaded with DOX plus ICG as a control, referred to as DINPs. Interestingly, the biomimetic nano-platelets combining photothermal treatment and chemotherapy showed high eﬃciency not only in eliminating the primary tumor but also in removing the CTCs from blood and lymphatic circulation and inhibiting breast cancer metastasis in MDA-MB-231 xenograft (the right hind foot and back) and orthotopic breast tumor-bearing nude mice due to smaller particle size (Fig. 1) . Collectively, these findings under-score the clinical application potential of the biomimetic PMDIs in combination therapy, such as chemotherapy and photothermal therapy (PTT), for breast cancer anti-metastasis treatment.
2. Material and methods
Hyaluronic acid (HA), doxorubin (DOX), indocyanine (ICG), DiD, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) were obtained from Dalian Meilun Biotech Co., Ltd. (Dalian, China). Cell culture reagents were purchased from Gibco, DAPI from Vector laboratories, and Hoechst 33342 from BD Biosciences. All
solvents and reagents used were of analytical standard grade.