A thermoresponsive hydrogel system for long-acting corticosteroid delivery into the paranasal sinuses

Abstract

Delivering localized treatment to the paranasal sinuses for diseases such as chronic rhinosinusitis (CRS) is particularly challenging because of the small natural openings leading from the sinuses that can be further obstructed by presence of inflammation. As such, oral steroids, topical nasal sprays or irrigation, and surgery can be utilized to treat persistent sinonasal inflammation, but there exists a need for post-operative options for long-term steroid delivery to prevent disease recurrence. In the present study, a Thermogel, Extended-release Microsphere-based-delivery to the Paranasal Sinuses (TEMPS) is developed with the corticosteroid mometasone furoate. Specifically, the bioactive steroid is released for 4 weeks from poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a poly(N-isopropylacrylamide) (p-NIPAAm)-based hydrogel. The temperature-responsive system undergoes a reversible sol-gel transition at 34-35 °C such that it can be applied as a liquid at ambient temperature, conforming to the sinonasal epithelium as it gels. In a rabbit model of CRS, TEMPS was maintained in rabbit sinuses and effectively reduced sinonasal inflammation as characterized by micro-computed tomography and histopathology analysis. Ultimately, the combination of controlled release microspheres with a thermoresponsive hydrogel provides flexibility for encapsulating therapeutics in a reversible and conforming system for localized delivery to the sinuses.

Keywords: Hydrogel; Microsphere; Sinusitis; Steroid; Sustained release; Thermoresponsive.

Fig. 1.

Bioactive mometasone furoate can be released from TEMPS for 4 weeks in vitro. (A) Size distribution and (inset) representative scanning electron micrograph, scale bar = 10 μm, of drug-loaded MSs showing a smooth, spherical morphology with mean diameter of 7.8 μm. (B) Cumulative release of mometasone furoate from MSs (n = 3) and (C) TEMPS, MSs embedded in thermogel (n = 5). Error bars represent mean ± cumulative S.D. (D) Drug released from TEMPS after 28 days of aqueous incubation at 37 °C displays activity (EC50 = 0.33 pM) similar to a control, drug prepared the day of the assay (EC50 = 0.31 pM).

Fig. 2.

TEMPS is compatible for reversible apposition with the sinonasal epithelium. (A) Absorbance measurements at 415 nm as a function of increasing temperature for samples (n = 4) of thermogel and TEMPS showing that both undergo phase transition at 34–35 °C. (B) The reversible temperature-responsive phase change of TEMPS demonstrated by repeated absorbance measurements at ambient temperature and 37 °C over 28 days. (C) Cytocompatibility of the thermogel with RPMI 2650 cells showing that viability is maintained after 24-h incubation with gel. Cell viability was measured using PrestoBlue reduction and % viability was calculated relative to positive (+) and negative (−) controls.

Fig. 3.

MicroCT imaging showed reduced opacification of the right maxillary sinus following application of m-TEMPS compared to v-TEMPS. (A) Disease was induced by creating a reversible obstruction of the left ostiomeatal complex for 2 weeks. Over the subsequent 11 weeks (disease induction) or 8 weeks (disease re-induction) chronic disease phenotype developed [16]. Subjects were divided into 4 groups for bilateral treatment and monitored for 4 weeks. (B) Representative coronal microCT images of the maxillary sinuses in soft tissue and bone (center) windows. Using the bone window, opacification was measured in a defined region of interest and the median CT # of that region was recorded for 3 consecutive sections. (C) Change in CT # between the disease state and treatment timepoints on the right side. Error bars represent the mean ± S.D. for each group: no treatment (n = 5), v-TEMPS (n = 5), m-TEMPS (n = 5), and daily nasal drops (n = 3). Statistical significance was determined by one-way ANOVA with post hoc Wilcoxon Method testing, ***p < 0.001, **p < 0.020, ns = not significant.

Fig. 4.

Evidence of iatrogenic trauma due to application of TEMPS was observed in right histopathology sections, but damage was reversed by local steroid delivery. Two sections from each subject were stained with H&E and scored by a blinded veterinary pathologist for (A–D) severity and involvement of (A) epithelial cell damage, (B) cilia damage, (C) inflammation of the submucosal glands, and (D) subepithelial edema, and (E–G) presence (1) or absence (0) of (E) granulocyte infiltrate, (F) granulocytes in the lumen, (G) involvement of the basement membrane, and (H) severity of epithelial hyperplasia. Individual symbols represent the score for each section and error bars represent the mean ± S.D. for treatment groups: no treatment (n = 4), v-TEMPS (n = 3), m-TEMPS (n = 4), and daily nasal drops (n = 3). Statistical significance was determined by Chi-square test using Pearson’s p-value, * p < 0.050, ns = not significant.

Fig. 5.

Intraocular pressure was not affected by 4 weeks of local steroid delivery from the retained system. (A) Mean bilateral IOP measurements for each subject are represented as individual symbols and error bars represent the group mean ± S.D. for: before treatment application (n = 18), no treatment (n = 5), v-TEMPS (n = 5), m-TEMPS (n = 5), and daily nasal drops (n = 3). Solid and dotted lines denote the mean and range, respectively, of healthy New Zealand rabbit IOP values [17]. (B) A foreign material (yellow arrow) was recovered during post-mortem analysis from a subject treated with TEMPS. (C) The recovered material was visualized by SEM and spherical MSs were observed, scale bar = 10 μm. (D) Representative H&E section of a subject treated with TEMPS showed a foreign material in the lumen and apposed to the epithelium that contains spherical holes, which are consistent with the expected appearance of TEMPS (40× magnification). (E) Percentage of subjects in each treatment group where TEMPS material was observed in H&E sections. Statistical significance was determined by repeated measures ANOVA with Tukey post-hoc testing, *p < 0.050, ns = not significant.