Curcumin encapsulated zeolitic imidazolate frameworks as stimuli responsive drug delivery system and their interaction with biomimetic environment

Abstract

Metal organic frameworks (MOFs) exhibit unique features of finely tunable pore structures, excellent chemical stability and flexible surface structural functionality, making them advantageous for a wide range of applications including energy storage, compound separation, catalysis, and drug delivery. The present work enlightens a novel approach of single step fabrication of CCM-ZIF-8 as a drug carrier and its application as stimuli responsive drug delivery systems via external stimuli involving change in pH and in presence of biomimetic cell membrane like environment using liposomes and SDS micelles. The methodology is devoid of any post synthesis drug loading steps. The synthesized curcumin encapsulated ZIF-8 frameworks demonstrate ultrahigh drug encapsulation efficiency (ca. 83.33%) and good chemical stability. In vitro drug release of curcumin was three times higher in acidic medium than in physiological pH. Cytotoxicity results demonstrated enhanced therapeutic effect of CCM-ZIF-8 than free curcumin. Confocal microscopy results confirmed the easy cellular internalization of CCM-ZIF-8 in HeLa cells. Intracellular distribution studies at various incubation times confirmed the clathrin-mediated endocytosis to lysosomal pathway of CCM-ZIF-8, but without mitochondria being an intracellular fate. The results signify that CCM-ZIF-8 is an efficient drug carrier for passive tumor therapy in future for cancer treatments.

Figure 1

(a) TEM image of CCM-ZIF-8 (b) AFM image of CCM-ZIF-8 (c) PXRD spectra and (d) TGA thermograms of CCM, ZIF-8 and CCM-ZIF-8.

Figure 2

(a) UV-Vis absorption spectra of curcumin, ZIF-8 and CCM-ZIF-8. (Inset optical images of (a) CCM-ZIF-8, (b) Curcumin and (c) ZIF-8), (b) Photoluminescence spectra, (c) FTIR spectra, (d) Pore size distribution, (e) linear absorption desorption isotherm and (f) Percentage cumulative curcumin release in PBS solutions (0.5% Tween 20 at pH 5 and 7.4) at selected time intervals.

Figure 3

Fluorescence emission spectra of CCM-ZIF-8 in three SDS micelles solutions at concentration of 3, 8 and 30 mM with varying time from 1 to 130 minutes and comparison of ratio of percentage fluorescence quenching of emission peak.

Figure 4

Fluorescence intensity emission spectra of CCM-ZIF-8 in three liposomes solutions of DMPC, DMPG, and DMPC: DMPG (9:1) at selected time intervals from 1 to 130 minutes and comparion of ratio of percentage fluorescence quenching of emission peak.

Figure 5

Confocal laser scanning microscopy (CLSM) images of HeLa cells incubated with free CCM and CCM-ZIF-8 at relative concentrations after 0.5, 2 and 12 hrs of incubation time. The right panel shows bright field fluorescence images, middle panel shows DAPI (blue fluorescence, stained by DAPI) and FITC channel (green fluorescence from CCM and CCM-ZIF-8) and left panel shows overlay merged fluorescence images of all channels on the same cells. (Scale Bar = 50 μm).

Figure 6

Co-localization of CCM-ZIF-8 and LysoTracker Red: HeLa cells were incubated for 0.5, 2 and 12 hrs with CCM-ZIF-8 (green), 0.5 h with Lysosome tracker (red) and the nuclei were stained by DAPI (for 15 min). CLSM images of HeLa cells with merged and individual images of DAPI, CCM-ZIF-8 and Lysosome tracker red, respectively (Scale bar = 20 µm). The scatter plot shows overlap between green and red channels and Pearson’s coefficient for the different time points are mentioned below the plot. Pearson coefficient is described with the maximum overlap between two channels, giving the value 1 and minimum overlap showing the value 0.

Figure 7

Co-localization of CCM-ZIF-8 and MitoTracker Red: HeLa cells were incubated for 0.5, 2 and 12 hrs with CCM-ZIF-8, MitoTracker Red (0.5 h), the nuclei were stained by DAPI (15 min). CLSM images shown are of HeLa cells with merged and individual images of DAPI, CCM-ZIF-8 and MitoTracker Red. (Scale bar = 20 µm). The Pearson Colocalization coefficient value is written below the scatter plot at individual time points.

Figure 8

In vitro biocompatibility of ZIF-8 and cytotoxicity of free CCM and CCM-ZIF-8 against HeLa cell lines at various concentrations for 24 hrs (A), 48 hrs (B) and 72 hrs (C) of incubation time as assayed by MTT.