Degradation of Folic Acid in the Composition of a Conjugate with Polyvinylpyrrolidone and Fullerene C60 Under UV and E-Beam Irradiation

Abstract

Folic acid (FA) is used as a targeting ligand for targeted drug delivery to tumor cells, some types of which overexpress folate receptors on their surface. However, while the preparation of conjugates containing FA may comprise a multi-step process, FA presents low photostability under UV irradiation. In addition, FA undergoes radiolysis under the action of ionizing radiation, which is utilized for drug sterilization. In this study, we investigate the stability of FA in a conjugate (FA-PVP-C₆₀) with fullerene C₆₀ and polyvinylpyrrolidone under the action of UV (205-400 nm) and electron irradiation (doses from 2 to 8 kGy) at different pH (4.5, 7.2, 10.7). The degradation of FA is studied using fluorescence and UV-Vis spectroscopy. It is found that the fullerene C₆₀ in the FA-PVP-C₆₀ conjugate suppresses the degradation of FA during both photolysis and radiolysis, which is confirmed by the decrease in the quantum yield of fluorescence and the radiation chemical yield of FA destruction accompanied by increasing fullerene content in the conjugate (from 2.8 to 10 wt.%).

Keywords: UV irradiation; folic acid; fullerene; photodegradation; radiation chemical yield; radiolysis.

Figure 1

UV (orange arrows) and radio (blue arrows) FA degradation pathways.

Figure 2

Absorption spectra of the FA-PVP-C₆₀ conjugate, intermediate synthesis products FA-PVP, PVP-C₆₀, PVP, and FA at pH 4.5 (A), pH 7.2 (B) and pH 10.7 (C).

Figure 3

Absorption spectra of C₆₀-PVP conjugates with fullerene content of 2.8, 5 or 10 wt.% before and after 1 h of UV irradiation at pH 4.5 (A), pH 7.2 (B) and pH 10.7 (C).

Figure 4

(A) Time evolution of the absorption spectra of the FA-PVP-C₆₀ conjugates in air-equilibrated aqueous solutions (pH 7.2) under UV irradiation (240–400 nm). Arrows indicate the isosbestic points. (B) Experimental difference (ED) spectra obtained by subtracting the spectrum after 5–60 min of photolysis from the FA-PVP-C₆₀ conjugates initial spectrum.

Figure 5

Fluorescence QYs (Φ_x) of air-equilibrated aqueous solutions of non-irradiated and UV-irradiated FA-PVP-C₆₀ conjugates at pH 4.5 (A), pH 7.2 (B) and pH 10.7 (C).

Figure 6

(A) Time evolution of the absorption spectra of the FA-PVP-C₆₀ conjugates in air-equilibrated aqueous solutions (pH 4.5) under UV irradiation (240–400 nm). Arrows indicate the isosbestic points. (B) Experimental difference (ED) spectra obtained by subtracting the spectrum after 5–60 min of photolysis from the FA-PVP-C₆₀ conjugates initial spectrum.

Figure 7

(A) Time evolution of the absorption spectra of the FA-PVP-C₆₀ conjugates in air-equilibrated aqueous solutions (pH 10.7) under UV irradiation (240–400 nm). Arrows indicate the isosbestic points. (B) Experimental difference (ED) spectra obtained by subtracting the spectrum after 5–60 min of photolysis from the FA-PVP-C₆₀ conjugates initial spectrum.

Figure 8

(A) Absorption spectra of unirradiated and irradiated (2–8 kGy) FA-PVP-C₆₀ conjugates in 7.2 pH buffer. (B) Experimental difference (ED) spectra were obtained by subtracting the spectra of conjugates irradiated with a dose of 2–8 kGy from the initial spectrum of FA-PVP-C₆₀.

Figure 9

(A) Absorption spectra of unirradiated and irradiated (2–8 kGy) FA-PVP-C₆₀ conjugates in 4.5 pH buffer. (B) Experimental difference (ED) spectra were obtained by subtracting the spectra of conjugates irradiated with a dose of 2–8 kGy from the initial spectrum of FA-PVP-C₆₀.

Figure 10

(A) Absorption spectra of unirradiated and irradiated (2–8 kGy) FA-PVP-C₆₀ conjugates in 10.7 pH buffer. (B) Experimental difference (ED) spectra were obtained by subtracting the spectra of conjugates irradiated with a dose of 2–8 kGy from the initial spectrum of FA-PVP-C₆₀.

Figure 11

Fluorescence QYs (Φ_x) of air-equilibrated aqueous solutions of non-irradiated and irradiated with doses of 2–8 kGy FA-PVP-C₆₀ conjugates at pH 4.5 (A), pH 7.2 (B) and pH 10.7 (C).

Figure 12

Radical scavenging activity of FA-PVP-C₆₀ and intermediate conjugates FA-PVP and PVP-C₆₀. (A) DPPH radical scavenging activity; (B) hydroxyl radical scavenging activity. The data are presented as mean values ± SD (n = 3 independent experiments).