Bovine serum albumin-based and dual-responsive targeted hollow mesoporous silica nanoparticles for breast cancer therapy

Highlights

• Chemo-photodynamic combination therapy to enhance the therapeutic effect of breast cancer.

• FA molecules endowed the system with the characteristics of active targeting.

• The drug carrier could achieve pH/redox-responsive drug release.

• BSA molecules served as both a redox-sensitive agent and a gatekeeper for the “on-demand” drug release.

Abstract

Combination therapy is an effective way to alleviate the shortcoming of monotherapy and enhances therapeutic efficacy. Herein, a distinctive hollow mesoporous silica nanoparticle (HMSNs) encapsulated with folic acid-modified bovine serum albumin (BSA-FA), denoted as HBF, was engineered for tumor targeting and dual-responsive release of loaded-therapeutic agents MD (methylene blue (MB) and doxorubicin (DOX)). The BSA molecule as a ‘‘gatekeeper’’ prevents premature drug leakage and actively unloads the cargos through BSA detachment in response to intracellular glutathione (GSH). Folic acid (FA) promotes the specific intracellular delivery of the drug to folate receptor (FR)-expressing cancer cells to improve the efficacy of chemo-photodynamic therapy (PDT). In vitro drug release profiles showed that the drug carrier could achieve pH/redox-responsive drug release from MD@HBF owing to the cleavage of the imine bonds between HMSNs-CHO and BSA-FA and BSA intramolecular disulfide bond. Additionally, a series of biological evaluations, such as cell uptake experiments, toxicity experiments, and in vivo therapeutic assays indicated that MD@HBF possesses the features of accurately targeting FR-expressing 4T1 cells to induce cells apoptosis in vitro, exhibits outstanding tumor cell synergistic killing efficiency of chemo-photodynamic therapy (combination index CI = 0.325), and inhibits tumors growth. These results demonstrated that the strategy of combining HMSNs with stimuli-responsive biodegradable protein molecules could provide a new potential direction toward the ‘‘on-demand’’ drug release for precision chemo-photodynamic therapy in cancer treatment.

Introduction

Cancer, as one of the destructive diseases with complex pathogenesis, seriously endangers human life and health [1]. In terms of cancer treatment, chemotherapy remains one of the most frequently used approaches for clinically combating tumors [2]. However, administering a single drug or exploring single chemotherapy is not successful as expected due to the limited therapeutic effect and poor tumor-targeting ability in current clinical therapy [3], [4]. A combination of multiple anticancer agents or different types of therapy has been widely explored to enhance clinical anticancer efficiencies, such as chemo-photothermal therapy [5], chemo-immunotherapy [6], [7], and chemo-photodynamic therapy [8]. Particularly, photodynamic therapy (PDT), which can produce cytotoxic singlet reactive oxygen species (ROS) to induce cell destruction and tissue damage, has emerged as a new treatment approach for various types of cancers [9]. In PDT, the photochemical sensitizer can absorb and transfer the energy of photons to surrounding oxygen molecules at specific wavelengths and then produce cytotoxic ROS, which induces irreversible damage to biomolecules such as DNA, proteins, and lipids [10]. Therefore, chemo-photodynamic therapy presents significantly decreased side effects and enhanced selectivity due to elevated basal ROS levels compared to normal cells and greatly improve the therapeutic effect against tumor [11], [12], [13], [14].

It is worth noting that the traditional administration way of chemotherapeutic agents faces great limitations of low delivery efficiency and side effects, leading to poor therapy effects [15]. Therefore, extensive studies have focused on developing “intelligent” drug delivery systems (DDSs) for targeted delivery of anticancer drugs to tumor sites and responsive release at the lesion site in recent decades, including MnO₂-based nanomaterials [16], Fe₃O₄-based nanomaterials [17], [18], carbon-based nanomaterials [19] and silica-based nanomaterials [20], [21]. Among the widely investigated nanomaterials, hollow mesoporous silica nanoparticles (HMSNs) are a type of promising vector for drug delivery due to the high specific surface area, large pore volume, and easy surface functionalization [22]. However, the explosive prophase drug release and non-specific targeted therapy of naked HMSNs results in suboptimal antitumor efficacy and undesired side effects [23].

To achieve drug release “on demand” in a specific environment, various “gatekeepers” have been designed to retain the drugs and “intelligently” release cargos by removing clogging segments in response to physical/chemical stimuli [24], [25], [26]. Among the series of stimuli applied for the controlled drug release, glutathione (GSH), unevenly distributed between the cellular cytoplasm (2–10 mM) and the blood concentration (2–20 µM), is emerging as an appealing trigger [27]. Inspired by the characteristic of biodegrading by GSH and existing stably in extracellular fluids, redox-activated DDSs based on disulfide bonds (–SS–) are expected to achieve the “on-demand” drug release. However, most disulfide bonds need a complex reaction process or accompanied by-products, so it is urgent to construct a simple and environmentally friendly redox nanocarrier [28]. Bovine serum albumin (BSA), a bio-safe natural macromolecule, has been widely used in medical and biochemical research owing to its excellent biocompatibility, on-antigenic, and non-toxic properties [29], [30]. Importantly, abundant functional groups and intramolecular disulfide bonds endowed BSA molecules to combine with other materials to construct novel drug carriers for redox reactions with no need for the complicated pyridyl disulfide exchange reaction [28], [31]. To further enhance the specific release ability of drugs, there are multiple response strategies have been applicated in tumor tissues [32], [33], [34]. Typically, tumor tissues have lower extracellular pH values (pH≈6.8) than normal tissues and the bloodstream, moreover, endosomes and lysosomes inside cells exhibit much lower pH values (<5.4) [35]. According to this, the dynamic imine linkage is widely exploited to construct pH-responsive nanocarriers [36]. In addition, folic acid (FA), as one of the most common targeting ligands, was modified on the surface of BSA, which can effectively target tumor cells and accurately deliver anticancer drugs into tumor cells [37]. This would lead to a significant improvement in cancer therapy and decrease toxic side effects on normal cells or tissues [38].

Hence, a pH and redox dual-responsive targeted nanoplatforms based on HMSNs (drug carrier) and bovine serum albumin (gatekeeper) were fabricated (MD@HBF). As shown in Scheme 1A, BSA was attached to HMSNs via imine bonds, which significantly improved the biostability and compatibility of nanoparticles, prevented premature drug leakage, and achieved pH/redox dual-response release from tumor sites. Furthermore, along with the decorated FA molecules, the synthesized NPs can achieve effective accumulation at tumor sites and increase drug availability. Finally, triggered by intracellular acidity and high glutathione concentration, the nanoparticles shell was gradually degraded into fragmented and fell off due to the broken of intramolecular disulfide bonds of BSA and imine bonds in the outer layer of HMSNs, causing drugs release from the nanocarrier and inducing cell apoptosis. Meanwhile, cytotoxic substances-reactive oxygen species (ROS) were effectively produced by the released MB molecules under the irradiation (635 nm), further causing toxicity to target tissues and enhancing the effect of chemotherapy. To further explore the application of vectors, the effects of nanocarriers on inducing apoptosis of 4T1 tumor cells in vitro and treating tumors in vivo were studied. It is expected that the designed nanocarrier is promising for application as a target DDS, and shows combined enhancement in tumor therapy.