Aptamer modified MoS₂ nanosheets application in targeted photothermal therapy for breast cancer

Abstract

To ensure photothermal nanosheets have high specific recognition and can effectively enrich to tumor cells, controlling the size of nanosheets and lowering the potential toxicity of photothermal nanosheets is the key problem to be solved in the research of tumor photothermal therapy. In this study, MoS₂ nanosheets around 10 nm in size were prepared using the hydrothermal method. The biocompatibility of bovine serum albumin (BSA) and molybdenum disulfide (MoS₂) nanoscale was enhanced by combining bovine serum albumin (BSA) with MoS₂ nanosheets, and then the nucleic acid aptamer (Apt) with high specific recognition was coupled with it. The successfully prepared MoS₂-BSA-Apt nanosheets have excellent photostability and photothermal effect. The in vitro experimental results and cytotoxicity tests indicate that MoS₂-BSA-Apt nanosheets has good biological safety and can target and identify tumor cells. Combined with 808 nm laser irradiation, tumor cells can be effectively ablated. The vivo experimental results also showed that MoS₂-BSA-Apt nanosheets have good biological distribution, and when combined with 808 nm laser irradiation, had an obvious inhibitory effect on the growth of subcutaneous tumors in tumor-bearing mice, with a steady increase in the body weight of mice during the treatment, indicating low toxicity. Therefore, our results confirm that MoS₂-BSA-Apt nanosheets possess certain potentials in the precise and effective treatment of tumors.

Introduction

High cancer incidence and mortality statistics classify it as a serious threat to human life were, incidences of female breast cancer globally is 24.2 %, and is increasing annually [[1], [2], [3]]. Breast cancer is a malignant tumor that occurs in the epithelial tissue of the breast. Because the connection between breast cancer cells is loose and easily detachable, once the cancer cells break off, the free cancer cells can spread to other parts of the body both through the blood vessels or through the lymph, form metastasis, and endanger lives. This has posed a serious threat to women's physical and mental health, hence, it is necessary to develop effective and safe cancer treatment strategies [4]. At this stage, the conventional detection methods of breast cancer include breast color ultrasound examination, molybdenum target examination, ultrasound imaging, and so on. Among them, the accuracy of ultrasound imaging in the diagnosis of women about 30 years old is 80 %–85 %. Molybdenum target examination is mainly used in elderly patients with loose breast tissue, however, there is a certain risk attached to its use-frequent molybdenum target examination will increase the risk of breast cancer [[5], [6], [7]]. The main breast cancer treatments include chemotherapy, radiotherapy, and surgery. However, in surgical treatments, it is more difficult to remove the tumor tissue, easy to relapse, and cause damage to normal tissue around the tumor. Chemotherapy and radiotherapy have greater side effects on patients [8,9]. In recent years, although photothermal therapy has attracted wide attention due to advantages such as simple operation, high level of accuracy, and minimal side effects [10,11], still, photothermal therapy is not perfect in the accurate target recognition of tumor cells. The most widely studied photothermal materials in photothermal therapy are organic nano-photothermal conversion materials, precious metal nanoparticles, metal chalcogenide nanomaterials, and carbon-based photothermal conversion materials [[12], [13], [14], [15]]. Most carbon nanomaterials such as carbon nanotubes and graphene have good photothermal conversion rates, however, since most are hydrophobic, their biocompatibility is poor, hence, they can no longer be degraded in vivo. This increases the risk of poisoning caused by retention in the body [[16], [17], [18]]. Compared with molybdenum disulfide, carbon nanotubes and graphene have lower photothermal conversion rate, lower absorption coefficient and poor metabolism in NIR region [[19], [20], [21]]. Although molybdenum disulfide is also hydrophobic, its water solubility and biocompatibility can be changed by surface modification, and the preparation size is smaller and easier to metabolize from the body. Compared with other cancers in vivo, the thickness of biological tissue in breast cancer is relatively thin and close to the surface of the skin, which is conducive to the transmission of light in photothermal therapy. Thus, accurate detection and treatment is a more effective way to improve the survival rate of breast cancer patients [[22], [23], [24], [25]].

Therefore, it is both imperative and urgent to develop a photothermal nano-therapeutic agent with high biocompatibility and high target properties simultaneously. Molybdenum disulfide (MoS₂) is a typical transition metal disulfide, which has attracted wide attention because of its wide range of raw material sources, simple preparation method, low cost, good chemical stability and high photothermal conversion efficiency [16,17,21,25]. In several studies [[26], [27], [28]], MoS₂ nanosheets have been successfully used in photothermal therapy, which confirmed the photothermal therapeutic characteristics of MoS₂, and the prepared MoS₂ nanosheets have good water dispersibility and biocompatibility. However, size control and the specific recognition of tumor cells need to be improved.

Nucleic acid aptamers are single-stranded oligonucleotides with good binding specificity and high affinity to target molecules screened from synthetic DNA or RNA libraries by in vitro SELEX technique (exponential enrichment ligand phylogeny) [[29], [30], [31], [32]]. At present, a variety of specific nucleic acid aptamers of tumor cells have been screened, and as a new type of tumor-targeted recognition molecules, important achievements have been made in tumor imaging and treatment [[33], [34], [35], [36]]. MS03 aptamer with high specificity and affinity to breast cells is used in this experiment. MS03 aptamer is easy to synthesize and does not have immunogenicity. It is a molecular probe that can distinguish breast CSC-like cells from breast cancer cells. This provides an idea for the construction of targeted functionalized molybdenum disulfide nanosheets [37].

On this basis, MoS₂ nanosheets were synthesized using the hydrothermal method, and bovine serum albumin (BSA) and amino-nucleic acid aptamer (Apt) were modified successively to construct photothermal composite MoS₂-BSA-Apt nanosheets with high specific recognition, good biocompatibility, stable size, and low toxicity. Among them, the size of the MoS₂ nanosheet is about 10 nm and the particle size is small, which is beneficial to the rapid excretion of the material from the body and reduces the toxicity. MoS₂-BSA-Apt nanosheets has good biological safety by cytotoxicity test, and the study of targeting performance proved that MoS₂-BSA-Apt nanosheets has excellent targeting ability to identify tumor cells. Combined with near-infrared 808 nm laser irradiation, it can effectively ablate tumor cells and detect the production of singlet oxygen. The in vivo experimental results also confirmed that MoS₂-BSA-Apt nanosheets had an obvious inhibitory effect on tumors in tumor-bearing mice, with low toxicity and good biological distribution, and could be extracted from the body in about 7 days (Scheme 1). The above results show that MoS₂-BSA-Apt nanosheets are expected to be used in the accurate treatment of tumors.