Syntheses of click PEG-dexamethasone conjugates for the treatment of rheumatoid arthritis

Abstract

A novel linear multifunctional polyethylene glycol (PEG)-dexamethasone (Dex) conjugate (click PEG-Dex) was synthesized using facile Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (a click reaction). Dex was conjugated to the click PEG via an acid-labile hydrazone bond to allow the drug release in a pathophysiological environment. To evaluate click PEG's potential as a versatile drug delivery platform, the click PEG-Dex conjugates were tested in an adjuvant-induced arthritis (AA) rat model. In vivo optical imaging data confirmed the arthrotropism of the conjugates in the arthritic rats. A long-term treatment study revealed that a single click PEG-Dex conjugate administration provided sustained (>15 days) amelioration of ankle joint inflammation to the AA rats. Treatment with an equivalent dose of dexamethasone phosphate sodium (free Dex) only provided temporal resolution of the arthritis, which recurred upon treatment withdrawal. Further histological and bone mineral density comparison between the ankle joints from both click PEG-Dex and free Dex treatment groups confirmed the superior anti-inflammatory and disease modifying effects of the novel polymer-drug conjugates.

Figure 1

¹H NMR spectrum of click PEG-Dex. Key structural elements of click PEG-Dex are assigned.

Figure 2

Cumulative in vitro Dex release profiles of click PEG-Dex at pH = 5.0, 6.0 and 7.4. Each sample was measured 3 times. The mean values and standard deviation were calculated with Microsoft Excel.

Figure 3

In vivo NIRF imaging of rats at different time points post injection of IRDye CW 800-labeled click PEG-Dex. Top panels, arthritic rats; bottom panels, healthy controls.

Figure 4

The right ankle joint diameter of the five animal groups (click PEG-Dex, Dex, click PEG, saline, and healthy; 6 rats/group) during the entire experiment.

Figure 5

The articular index (AI) scores of the five animal groups (click PEG-Dex, Dex, click PEG, saline, and healthy; 6 rats/group) during the entire experiment.

Figure 6

The endpoint bone mineral density (BMD) and representative pDEXA images of the right ankle joints of the five animal groups (click PEG-Dex, Dex, click PEG, saline and healthy). One-way ANOVA analysis, p < 0.01.

Figure 7

Histological evaluation of the ankle joint sections from the five animal groups (click PEG-Dex, Dex, click PEG, saline and healthy). One-way ANOVA analysis, p < 0.0001.

Figure 8

Photomicrographs of representative histological sections of the ankle joint from four treatment groups and a healthy control group. A. Click PEG-Dex; B. Healthy; C. Free Dex; D. Saline; E. Click PEG. F. Saline, at higher magnification. Finger-like pannus formation (single arrow), bone destruction (asterisk) and cartilage damage (double arrow) are clearly evident in free Dex, click PEG and saline groups. Bar=0.5 mm in A~E, bar = 0.05mm in F.

Scheme 1

Syntheses of diazide monomers for click copolymerization.

Scheme 2

Synthesis of click PEG-Dex.

Scheme 3

Structure of IRDye 800 CW-labeled click PEG-Dex.