Transdermal Delivery of Biopharmaceuticals Using Dissolving Microneedles Patch

 SEQ CHAPTER \h \r 1TRANSDERMAL DELIVERY OF BIOPHARMACEUTICALS USING DISSOLVING MICRONEEDLES PATCH

Jeong Woo Lee¹, Seong-O Choi¹, Eric I. Felner^1,2, Mark R. Prausnitz¹

¹School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332

²Division of Pediatric Endocrinology, Hughes Spalding Children's Hospital, Emory University School of Medicine,

 Atlanta, GA 30332

Introduction

            The delivery of biopharmaceuticals via the oral route is not practically possible due to enzymatic degradation in the gastrointestinal tract, low absorption through mucous membranes of intestine, and hepatic degradation due to the first-pass effect in the systemic circulation. Hypodermic injection can ensure higher bioavailability; however, it has low patient compliance because of fear and pain caused by hypodermic needles and it often requires patients to visit a clinic for correct injection, disposal of used needles and maintaining the integrity of biopharmaceuticals in the cold chain. As an alternative, transdermal delivery with a dissolving microneedles patch can address these problems associated with oral and injection delivery. Here, we present a dissolving microneedles patch loaded with human growth hormone (hGH) by examining the functional activity of hGH and in vivo pharmacokinetics of hGH to assess transdermal delivery of biopharmaceuticals with a dissolving microneedles patch and ultimately for the self-administration of biopharmaceuticals.

Methods and Materials

   Dissolving microneedles patches as shown in Figure 1A were prepared using microfabrication technologies, molding techniques, and modified solvent-casting methods.^[1] First, microneedle master structures were fabricated using UV photolithography processes and an inverse mold was made by casting master structures in polydimethylsiloxane (PDMS). To fabricate dissolving microneedles patches, carboxymethylcellulose (CMC) was dissolved in deionized water and then dehydrated to form a viscous hydrogel. In the case of CMC/trehalose microneedles, CMC and trehalose were dissolved in deionized water at a ratio of 1:1. Then, recombinant hGH (Genotropin, Pfizer) was added to the concentrated hydrogel, which contains hGH and matrix at a mass ratio of 1:9 on a dry basis. Finally, the hydrogel containing hGH was cast onto the mold and dried under centrifugation used to fill the microneedle cavities.

Figure 1. Brightfield micrograph of (A) CMC/trehalose dissolving microneedles patch encapsulating hGH. Scanning electron micrographs of (B) CMC microneedles patch and (C) CMC/trehalose microneedles patch after 24 h application to rat skin.

hGH functional activity was determined by measurement of hGH-stimulated growth of Nb2 rat lymphoma cells.^[2] Nb2 cells in stationary culture medium will resume replication when stimulated by hGH. The viable Nb2 cell population at 3 days after the addition of hGH was measured using a cell viability analyzer (Vi-CELL, Beckman Coulter). Five different hGH solutions were added to the Nb2 cell culture; (i) CMC placebo solution (negative control), (ii) hGH solution (Genotropin, positive control), (iii) hGH solution mixed with CMC reconstituted from dissolved placebo microneedles, (iv) a reconstituted CMC microneedles patch encapsulating hGH, and (v) a reconstituted CMC microneedles patch encapsulating hGH after 3 months storage at ambient conditions (23±2^oC and 38±5% relative humidity).

The pharmacokinetic study was performed with wild-type male hairless rats with approval by the Institutional Animal Care and Use Committee of Georgia Tech. Four groups were involved; Group 1 - subcutaneous injection of hGH from the manufacturer (positive control), Group 2 - CMC microneedles patch encapsulating hGH, Group 3 - CMC/trehalose microneedles patch encapsulating hGH, and Group 4 - subcutaneous injection of a reconstituted CMC/trehalose microneedle patch encapsulating hGH Rat blood was drawn from the tail vein at various time points up to 24 h after administration and collected in a CAPIJECT tube (T-MG, Terumo Medical). The collected blood was spun to isolate serum, which was stored at -70^oC until hGH concentration was determined by enzyme-linked immunosorbent assay (ELISA). Areas under the serum hGH concentration curve were computed to calculate bioavailability.

Results and Discussion

We assessed the stability of hGH in dissolving microneedles patches by determining the level of cell proliferation of each group at the saturation level of hGH stimulation. As shown in Figure 2A, unprocessed hGH (positive control) stimulated cell growth resulting in almost 750% of initial population. Addition of CMC to unprocessed hGH stimulated cell growth to the statistically same level as the positive control, and reconstituted CMC microneedles (containing no hGH, placebo) did not stimulate cell growth, suggesting that CMC had no effect on hGH activity or cell proliferation, further indicating that CMC was inert. The cell population increase by reconstituted hGH in a CMC microneedles patch was not statistically different from the positive control, showing that the fabrication and reconstitution of hGH microneedles patches were not detrimental to hGH stability. Moreover, storage of hGH microneedles patches for 3 months in air at ambient temperature (23°) and relative humidity (~40%), caused only a 15% loss of hGH activity. This hGH functional activity study demonstrates the suitability of the formulation and process to fabricate hGH dissolving microneedles patches.

We next administered hGH into hairless rats and measured plasma concentration of hGH to assess bioavailability of hGH from a dissolving microneedles patch. As shown in Figure 2B, hGH administered by any group quickly had a peak hGH plasma concentration (C_max) at t_max ≈ 0.7 h (ANOVA, p > 0.05) and then decreased over the next 6 hours. Subcutaneous injection of hGH was used as the positive control corresponding to 100% bioavailability. A reconstituted microneedles patch injected subcutaneously had the statistically same pharmacokinetic profile and bioavailability in comparison with the positive control, implying that the fabrication process of hGH microneedles patch did not degrade hGH integrity.

We next studied hGH administration using microneedle patches prepared with two different formulations. The first formulation contained only CMC as the microneedle material. In this case, the hGH serum concentration profile was significantly lower than the positive control, showing a C_max value that was 20% of the positive control (Student's t-test, p < 0.05) and a bioavailability of 13%. We hypothesized that this low bioavailability can be attributed to slow and incomplete dissolution of the CMC microneedle matrix in the limited amount of interstitial fluid in the skin. To examine this, we prepared microneedles formulated with a mixture of CMC and trehalose, which can dissolve more quickly with less fluid than CMC. Consistent with this hypothesis, CMC/trehalose microneedles achieved four times higher C_max and five times higher bioavailability than CMC microneedles (Student's t-test, p < 0.05).

                                   (A)                                                                                    (B)

Figure 2. (A) Stability of hGH in a dissolving microneedles patch. Asterisk indicates statistical comparison with positive control. (two-way ANOVA, P>0.05 for * and P<0.05 for **) (B) Pharmacokinetic profile of hGH in rat serum after administration.

Scanning electron micrographs and the measurement of remaining hGH in the patch could support the difference between the two formulations. As shown in Figure 1B, CMC microneedles were partially dissolved, leaving much of the microneedle shaft. In contrast, CMC/trehalose microneedles (Figure 1C) were mostly dissolved with just short stubs remaining behind. These microneedle patches were then dissolved in vitro after application and analyzed to determine residual hGH content, which was measured as 69±3% of the initial dose in CMC microneedles patch and 17±3% of the initial dose in CMC/trehalose microneedles patch. In future studies, microneedle design needs to be modified to improve insertion more deeply into the skin, to incorporate more soluble matrix materials and/or to localize active therapeutics more toward the tip.

Conclusion

This study addresses transdermal delivery of hGH with a dissolving microneedles patch designed for safe and simple self-administration by patients. Microneedle patches were fabricated to encapsulate and deliver hGH without loss of functional activity. The dissolving microneedles patches made of CMC and trehalose demonstrated 71% bioavailability of hGH; the loss of bioavailability was mostly accounted for by incomplete dissolution of microneedles. Overall, this study demonstrates the feasibility of a dissolving microneedles patch for transdermal delivery of hGH and other biopharmaceuticals.

Reference

[1]        J. W. Lee, J. H. Park, M. R. Prausnitz, Biomaterials 2008, 29, 2113-2124.

[2]        P. W. Gout, C. T. Beer, R. L. Noble, Cancer Research 1980, 40, 2433-2436.