(W0930-12-82) Fabrication of Tip-Loaded Implantable PLGA Microneedles for Sustained Release of a Peptide- Carfilzomib

Purpose: Transdermal drug delivery system (TDDS) is an attractive route of administration, providing several advantages, especially over oral, and parenteral routes. However, transdermal drug delivery is significantly restricted due to the barrier imposed by the uppermost layer of the skin, the stratum corneum. A specific technological advancement in TDDS is the development of polymeric microneedles (MNs), which includes the encapsulation of lipophilic drugs in a biodegradable polymer matrix such as polylactic acid, polyglycolic acid, or poly(lactide-co-glycolide) (PLGA). This efficiently pierces the stratum corneum and deposits its drug cargo into the layers of the skin. Further, it helps in the prolonged release of the drug due to the slow degradation of the polymer matrix following its insertion (1,2). We selected Carfilzomib (CFZ), a small therapeutic peptide (MW: 719.924 g/mol, logP 4.19) as a model drug to fabricate a MN-based sustained delivery technique. CFZ is a potent proteasome inhibitor used for treating relapsed and refractory multiple myeloma and is only available via the intravenous route (3–5). In this study, we fabricated tip-loaded implantable PLGA MNs using different grades of PLGA and determined the feasibility of long-acting transdermal delivery of CFZ.

Methods: We fabricated tip-loaded microneedles using the micro molding technique. Using a pyramidal-shaped master structure, we prepared the molds with poly (dimethyl siloxane) and silicone elastomer base in the ratio of 10:1, followed by oven drying at 60°C. We used the obtained molds to fabricate MNs of two different grades of PLGAs (PLGA 50-5A and PLGA 50-7P). To form the drug-loaded needle tips, we suspended 10 mg CFZ in 20 µL of 20% w/v solution of PLGA in N-methyl pyrrolidone (NMP), followed by vacuum drying (Vacufuge plus, Eppendorf) for 30 mins at 25°C and drying overnight at 60°C in a vacuum oven. We incorporated 20% w/v in NMP of higher molecular weight PLGA grade (50-8A) in the baseplate by following stepwise (200 µL/step) addition followed by overnight drying in a vacuum oven at 60°C till the entire baseplate was formed. We stored the MNs in a -20°C freezer until further use. We performed characterization tests on the MNs including mechanical integrity, insertion capability using skin simulant Parafilm® model, methylene blue staining, histological evaluation, and scanning electron microscopy (SEM). We performed in vitro permeation testing (IVPT) in vertical Franz diffusion cells to test the transdermal permeation of CFZ across dermatomed cadaver human skin. We withdrew samples at predetermined time points up to seven days and analyzed them using a validated UPLC method. Further, we inserted the MN arrays into the skin using the gentle thumb force for 1 min and secured the MN array in place with a 3M tape before mounting the skin pieces onto the Franz cells. Based on the data obtained from the IVPT study, we calculated the cumulative amount of CFZ delivered to the receptor as well as the lag time of transdermal delivery.

Results: We observed that the fabricated MNs had appropriate insertion capability, evidenced by their penetration up to the third layer in the skin simulant Parafilm® model when applied manually. This method has previously been shown to have a reasonable correlation with results obtained from skin studies and indicates ability to efficiently pierce the stratum corneum delivering CFZ into and across the skin (6). Further, we observed disruption of stratum corneum and formation of microchannels in the skin upon treatment with MNs from histological evaluation and methylene blue staining. SEM allowed us to clearly visualize sharp, pyramidal-shaped MNs. Through the IVPT study, we observed that the total amount of CFZ delivered across the skin with PLGA-MNs showed a statistically significant increase in the delivery of CFZ across the skin compared to the passive group which had no permeation. The release of CFZ from the tip-loaded implantable MNs is largely controlled by the presence of PLGA, which forms a matrix from where the drug must dissolve and diffuse into the skin layers before reaching the receptor chamber. We also observed that different PLGA grades had a varied release; transdermal delivery of CFZ was found to be 81.14 ± 15.04 µg/cm² and 40.31 ± 1.83 µg/cm² with lag time 1.05 ± 1.82 h and 5.42 ± 1.03 with grades 50-5A and 50-7P respectively. The lower delivery from 50-7P may be attributed to the presence of hydrophilic polyethylene glycol (PEG) in the polymer. CFZ, being lipophilic in nature, may have thus experienced retarded release from these MNs. Nevertheless, we observed a sustained release of CFZ throughout 7-days with the PLGA grades, suggesting a potentially valuable method for transdermal delivery of lipophilic drug from PLGA-based MNs.

Conclusion: We successfully achieved sustained delivery of a highly lipophilic, small peptide molecule, CFZ across the skin with the PLGA-MNs over 7-days. Thus, this study establishes the feasibility of fabricating tip-loaded implantable PLGA microneedles for sustained release of CFZ.

References: 1. Panda A, Sharma PK, McCann T, Bloomekatz J, Repka MA, Murthy SN. Fabrication and development of controlled release PLGA microneedles for macromolecular delivery using FITC-Dextran as model molecule. J Drug Deliv Sci Technol [Internet]. 2022;68(November 2020):102712. Available from: https://doi.org/10.1016/j.jddst.2021.102712
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Acknowledgements: This project was funded by Merck KGaA, Frankfurter Str. 250, 64293 Darmstadt, Germany. The life science business of Merck KGaA, Darmstadt, Germany, operates as MilliporeSigma in the U.S. and Canada. Product designations of Merck KGaA, Darmstadt, Germany and third parties may appear in this material. For details of the ownership of mentioned trademarks, please refer to publicly available resources such as tmdn.org

Fig 1. Results from IVPT studies with PLGA-MNs (a) Total amount of CFZ delivered across the skin in 7 days (b) Permeation profile of CFZ delivered across the skin in 7 days (c) Lag time (h) (one-way ANOVA with Tukey’s post hoc analysis and unpaired t-test: ns, P > 0.05; *, P ≤ 0.05) ;***; P ≤ 0.001)