Polymer Amphiphiles for Photoregulated Anticancer Drug Delivery

Abstract

We report the synthesis of amphiphilic polymers featuring lipophilic stearyl chains and hydrophilic poly(ethylene glycol) polymers that are connected through singlet oxygen-cleavable alkoxyanthracene linkers. These amphiphilic polymers assembled in water to form micelles with diameters of ∼20 nm. Reaction of the alkoxyanthracene linkers with light and O₂ cleaved the ether C-O bonds, resulting in formation of the corresponding 9,10-anthraquinone derivatives and concomitant disruption of the micelles. These micelles were loaded with the chemotherapeutic agent doxorubicin, which was efficiently released upon photo-oxidation. The drug-loaded reactive micelles were effective at killing cancer cells in vitro upon irradiation at 365 nm, functioning through both doxorubicin release and photodynamic mechanisms.

Keywords: amphiphilic polymers; doxorubicin; drug delivery; light-responsive materials; self-assembly.

Figure 1

a) Photooxidation and cleavage reaction of the amphiphilic polymer 9,10-C₁₈PEG. b) Schematic depiction of micelle disruption upon anthracene photooxidation. c) Intracellular DOX release.

Figure 2

Pseudo-first-order kinetics of reaction of four reported ¹O₂-cleavable groups upon irradiation of methylene blue in CH₂Cl₂; k_rel = 1 for 9,10-diphenylanthracene.

Figure 3

Left: Distribution of hydrodynamic diameters of 9,10-C₁₈PEG and 3,9-C₁₈PEG micelles in water (1.0 mg/mL), determined by dynamic light scattering. Right: Negative stain TEM images of 9,10-C₁₈PEG and 3,9-C₁₈PEG micelles (1.0 mg/mL and 0.5 mg/mL respectively).

Figure 4

Sequences of spectra recorded over the course of titrating a 7.0 μM solution of eosin Y with a solution of 9,10-C₁₈PEG (top) or 3,9-C₁₈PEG (bottom): spectrum of eosin Y prior to the addition (thick black line); spectrum after the addition of polymer (thick blue line). The inset shows titration profiles at 542 nm and determination of CMCs.

Figure 5

Aromatic region of ¹H NMR spectra in CDCl₃ of a) 9,10-C₁₈PEG before and b) after one hour UV irradiation and c) 3,9-C₁₈PEG before and d) after 12 hours UV irradiation.

Figure 6

Release of DOX from micelles in water upon exposure to light (λ = 365 nm) and in the dark at room temperature. The amount of DOX removed from the solubilizing environment of the micellar cores upon irradiation of 9,10-C₁₈PEG micelles is greater than the amount released from 3,9-C₁₈PEG and C₁₈PEG micelles. Error bars show standard errors of three replicates.

Figure 7

Cell viability of HeLa cells upon exposure to micelles that are either: i) loaded with DOX (YES) or not loaded (No), and ii) irradiated at 365 nm in the presence of the cells (Light) or not irradiated (Dark). Error bars show standard deviations of four replicates. The irradiation time for all “light” experiments was 60 minutes.

Scheme 1

Synthesis of the amphiphilic polymers 9,10-C₁₈PEG and 3,9-C₁₈PEG, and chemical structure of commercially available, unreactive amphiphile C₁₈PEG. In each case, the molecular weight of PEG was 2 kDa.