Category: Formulation and Quality
Purpose: A spray-drying approach, alternative to solvent evaporation, was investigated to encapsulate luteinizing hormone-releasing hormone agonist (LHRHa), leuprolide acetate, in injectable biodegradable long-acting release microspheres. Spray-drying process parameters may affect the heat/mass transfer and other thermodynamic behaviors, and lead to variations in physicochemical properties of microspheres produced. The current understanding of these aspects is lesser known relative to the solvent evaporation method and a deeper knowledge of their relationships is needed . Processing parameters considered for microparticle formation engineering included: inlet air temperature (Tinlet), polymer (i.e., PLGA) concentration (Cfeed), airflow in nozzle (AFnozzle), Ratio (RatioA/L) between inlet atomization air flow and the liquid mass flow rate, nozzle size (Snozzle) and initial sample (feedstock) temperature (Tfeed) at different levels. Critical processing variables were identified during spray-drying encapsulation of leuprolide into PLGA microsphere formulations under conditions that mimic precisely the composition of the one-month Lupron DepotÒ (LD).
Methods: The water phase consisted of a suitable amount of leuprolide and 300 bloom type B gelatin in 1 mL of water and was maintained at 60°C. PLGA 75/15 (acid capped, Mw ~ 13 kDa) was dissolved in methylene chloride (DCM) at a final concentration of 50–300 mg/mL. The water phase and the oil phase were mixed by vortexing for 20 s and then emulsified for 2 min using a homogenizer at a speed of 15000 rpm to form a W/O emulsion. The obtained W/O emulsion was cooled in an ice-bath for 1 min and then subjected to spray-drying by a ProCepT 4M8-TriX spray dryer. The spray-dried crude powder was rinsed three times with 50 mL of cold water at 4°C and centrifuged at a speed of 4000 rpm to wash off unencapsulated drug from the microsphere surface. The microspheres were freeze-dried under reduced pressure for at least 48 h. Preparation processes can be seen in Fig. 1. Particle size was determined by laser diffraction using a Master Sizer 2000. Drug loading was determined after extracting the peptide and analysis by UPLC. Amino acid analysis was used to determine gelatin content. Long-term release of leuprolide from microspheres was conducted in PBS + 0.02%Tween 80 + 0.02% sodium azide at 37 °C while monitoring drug content by UPLC after solution replacement. During this period, Molecular weight (Mw) decline, water uptake, mass loss, and dry/hydrated Tg were also determined by GPC, gravimetry, and modulated DSC, respectively.
Results: Microencapsulation was highly efficient for leuprolide ranging from 70-90% encapsulation efficiency (EE) and 9.0-11.0% drug loading. Gelatin loss was negligible (EE = 80% to 100 %) with loading ~1.7% similar to the LD. The highest Cfeed (30%) caused a serious decline in the yield (~33.4%) and a significant increase in particle size and irregular morphologies. Cfeed displayed a pronounced impact on the drug loading (p< 0.001), and the lower the Cfeed, the lower the drug loading. Altering Tinlet from 80°C to 50°C seemed to have less of an effect on the microsphere size distributions were similar under different Tinlet values. Generally, most spray-dried, drug-loaded microspheres had higher residual DCM or water content than commercial products or empty microspheres. Spray-dried microspheres resulted in similar Tg values, around 47.5-48.5°C, which were significantly lower than the commercial product (p< 0.001). The LD generally displayed a slightly a higher long-term release than that of spray-dried microspheres. It is obvious that Tfeed 13°C, 25°C and 37°C (especially 25°C) had relatively lower overall release rates. The mass losses and Mw changes were similar among spray-dried microspheres and were slower compared to the commercial product. Upon incubation with release media, all microsphere Tg values similarly increased (~50°C) before declining to differing values (42-46°C) through day 42.
Conclusion: Spray-drying can be used to efficiently prepare leuprolide-PLGA microspheres with highly similar composition and release behavior to the 1-month LD. The current study provides a systematic investigation of the influence of spray-drying parameters on the composition and physical-chemical properties of PLGA microspheres loaded with a LHRHa-based peptide.
Jia Zhou– Student, University of Michigan, Ann Arbor, Michigan
Jenna Walker– Graduate Student, n/a, West Bloomfield, Michigan
Jie Tang– Assistant Research Scientist, University of Michigan, Ann Arbor, Michigan
King-Yeung Hong– Ann Arbor, Michigan
Anna Schwendeman– University of Michigan, Ann Arbor, Michigan
Steven Schwendeman– Professor, Department of Pharmaceutical Sciences and the Biointerfaces Institute, University of Michigan, Ann Arbor, Michigan