Nanocarrier of α-Tocopheryl Succinate Based on a Copolymer Derivative of (4,7-dichloroquinolin-2-yl)methanol and Its Cytotoxicity against a Breast Cancer Cell Line

Abstract

In order to improve the water solubility and, therefore, bioavailability and therapeutic activity of anticancer hydrophobic drug α-tocopherol succinate (α-TOS), in this work, copolymers were synthesized via free radicals from QMES (1-[4,7-dichloroquinolin-2-ylmethyl]-4-methacryloyloxyethyl succinate) and VP (N-vinyl-2-pirrolidone) using different molar ratios, and were used to nanoencapsulate and deliver α-TOS into cancer cells MCF-7. QMES monomer was chosen because the QMES pendant group in the polymer tends to hydrolyze to form free 4,7-dichloro-2-quinolinemethanol (QOH), which also, like α-TOS, exhibit anti-proliferative effects on cancerous cells. From the QMES-VP 30:70 (QMES-30) and 40:60 (QMES-40) copolymers obtained, it was possible to prepare aqueous suspensions of empty nanoparticles (NPs) loaded with α-TOS by nanoprecipitation. The diameter and encapsulation efficiency (%EE) of the QMES-30 NPs loaded with α-TOS were 128.6 nm and 52%; while for the QMES-40 NPs loaded with α-TOS, they were 148.8 nm and 65%. The results of the AlamarBlue assay at 72 h of treatment show that empty QMES-30 NPs (without α-TOS) produced a marked cytotoxic effect on MCF-7 breast cancer cells, corresponding to an IC₅₀ value of 0.043 mg mL^-1, and importantly, they did not exhibit cytotoxicity against healthy HUVEC cells. Furthermore, NP-QMES-40 loaded with α-TOS were cytotoxic with an IC₅₀ value of 0.076 mg mL^-1, demonstrating a progressive release of α-TOS; however, the latter nanoparticles were also cytotoxic to healthy cells in the range of the assayed concentrations. These results contribute to the search for a new polymeric nanocarrier of QOH, α-TOS or other hydrophobic drugs for the treatment of cancer or others diseases treatable with these drugs.

Keywords: anticancer; biomedical applications; copolymers; nanoparticles; radical polymerization; self-assembly.

Figure 1

Schematic representation illustrating the preparation of α-TOS loaded QMES-VP copolymer nanoparticles, chemical structure of copolymer and nanoparticles internalization in breast cancer cell.

Scheme 1

Synthesis of the QMES monomer.

Scheme 2

Synthesis of the poly(QMES-co-VP) copolymers.

Figure 2

¹H NMR spectrum of QMES in DMSO-d₆.

Figure 3

¹H NMR spectrum of poly(QMES-co-VP) 30:70 in CDCl₃ (composition of comonomers in the copolymer).

Figure 4

(A) DSC Thermograms of poly(QMES-co-VP) copolymer series, and (B) application of Fox’s equation to the T_g values experimentally determined by means of DSC.

Figure 5

DLS size distribution curves of: (A) unloaded NP-QMES-30, NP-QMES-40 and NP-QMES-51. (B) α-TOS loaded NP-QMES-30 and NP-QMES-40.

Figure 6

SEM micrographs of α-TOS loaded nanoparticles dried from aqueous solution at room temperature. Scale bars: 500 nm.

Figure 7

Confocal micrographs of cellular uptake of c6-loaded NP-QMES-30 in MCF-7 cells.

Figure 8

Co-localization of c6 loaded NP-QMES-30 into (A) the lysosomes and (B) the mitochondria of MCF-7 cells by confocal microscopy.

Figure 9

MFC-7 cells viability exposed to different concentrations of NP-QMES-30 (green bars) or NP-QMES-40 (orange bars): loaded with α-TOS and 24 h (A) or 72 h (C) of treatment; or “unloaded” and 24 h (B) or 72 h (D) of treatment. The diagrams include the mean, the standard deviation (n = 8), and Kruskal–Wallis test or ANOVA results. The asterisk (*) denotes a statistically significant difference (p < 0.05) compared to the control (M + PBS).

Figure 10

HUVEC cells viability exposed to different concentrations of NP-QMES-30 (blue bars) or NP-QMES-40 (red bars): loaded with α-TOS and 24 h (A) or 72 h (C) of treatment; or “unloaded” and 24 h (B) or 72 h (D) of treatment. The diagrams include the mean, the standard deviation (n = 6), and Kruskal–Wallis test or ANOVA results. The asterisk (*) denotes a statistically significant difference (p < 0.05) compared to the control (M + PBS).