Methotrexate coated AZA-BODIPY nanoparticles for chemotherapy, photothermal and photodynamic synergistic therapy

Abstract

Multifunctional chitosan-based nanoparticles were designed and synthesized by photosensitizer (PS) AZA-BODIPY grafting water-soluble chitosan as nanoshells and then loaded drug methotrexate (MTX) into the nanoshells, which generated chemotherapy, photothermal therapy (PTT), photodynamic therapy (PDT) and imaging into one system for synergistic therapy in vitro. The nanoshells in this designed nanostructure can serve as drug carriers to increase solubility, reduce toxicity and enhance the efficacy of synergistic PTT and PDT. Cell-viability indicated the low toxicity and safety of chitosan-based AZA-BODIPY nanoshells as carrier materials and the low-drug dosage of chitosan-based nanoparticles (half-maximal inhibitory concentration, IC₅₀ = 34.5 μg/mL) is lower than that of pure drug MTX (IC₅₀ = 56.9 μg/mL). Under light irradiation, photothermal temperature and MTT studies show that nanoparticles produce reactive oxygen species and exhibit photothermal conversion efficiency (38.3%). Thus, this study provides a multifunctional nanoparticle with chemotherapy, photothermal, photodynamic and imaging, synergistic therapy and diagnose for cancer treatment.

Introduction

Cancer, a malignant tumor, is the second most deadly factor in the world [1]. Compared with traditional methods of cancer treatment, in recent years, some new therapeutic methods such as photothermal therapy (PTT), photodynamic therapy (PDT), gene-targeted therapy, and immunotherapy have gradually became good complements to traditional treatments for cancer [[2], [3], [4], [5]]. Among these therapies, PDT and PTT have received extensive attention due to theirselves non-invasive, rapid therapeutic process, good cell killing effect, and reproducible operation. As for PTT, it refers to achieving therapeutic effects by illuminating the nanomaterials to generate heat, increasing the temperature of the tumor region, destroying the function of the cancer cells to induce their apoptosis or thermally ablating the tumor [[6], [7], [8], [9]]. PDT involves the conversion that the PS molecules absorb light energy and transter to an excited state after the PS molecules are excited by light. Due to the unstable excited state, the PS molecules transfer energy to the surrounding oxygen molecules or matrix during the return to the ground state, producing reactive oxygen species (ROS), such as singlet oxygen, hydroxyl radicals, and superoxide anion. Excessive ROS can interact with biomolecules (proteins, nucleic acids, etc.) in cancer cells, destroying their structures, thereby affecting their functions, ultimately inducing cancer cell death and achieving cancer treatment [10]. Some of the PS molecules, which are mostly composed of near-infrared fluorescent dyes. BODIPY as one of them, has significant photophysical properties, such as long excitation/emission wavelength, high molar absorption coefficient and fluorescence quantum yield. In recent years, researchers are interested in transferring the maximum absorption value of related fluorescent dyes to near infrared (NIR) region [11,12]. One of the most effective methods to obtain the maximum absorption red shift is to replace methoxy bridge carbon atoms with nitrogen, which obtaining AZA-boron dipyrrolide (AZA-BODIPY). Compared with similar derivatives of BODIPY, the red shift of wavelength is usually about 90 nm [13,14]. Herein, a photosensitizer (ABDP-SI) based on AZA-BODIPY with high absorption efficient and good photo-stability was designed and synthesized.

Most PS molecules are hydrophobic and readily aggregate in aqueous solution, which can affect biological activity, water solubility and singlet oxygen generation (SOG) [15]. Moreover, the accumulation of non-selective PS may have an adverse effect on normal cells. By stabilizing PS into target delivery carries comprising polymer nanoparticles, liposomes, and polymer micelles, the water stability and selective accumulation of PS can be improved in the targeted tissue [[16], [17], [18], [19], [20]]. Therefore, a hydrophilic chitosan chain was introduced to AZA-BODIPY to construct a hydrophilic unit of nanoparticle structure, and in which a water-insoluble drug methotrexate was entrapped. In vitro experiments have shown that Methotrexate coated AZA-BODIPY nanoparticles (MTX@CABS) with absorption in the NIR region has great photothermal and photodynamic effects (Scheme 1). In the light irradiation below, MTX@CABS exhibits excellent photodynamic performance, and the particle conversion effectively increases while increasing the irradiation power. Cellular uptake of MTX@CABS was studied by confocal laser scanning microscopy (CLSM). In addition, studies have been conducted on phototoxic and cytotoxic (HeLa) cell lines of human cervical cancer, indicating a obvious inhibitory effect on cancer cells.