Abstract
The purpose of this research was to study the chemical reactivity of a somatostatin analogue octreotide acetate, formulated in microspheres with polymers of varying molecular weight and co-monomer ratio under in vitro testing conditions. Poly(D,L-lactide-co-glycolide) (PLGA) and poly(D,L-lactide) (PLA) microspheres were prepared by a solvent extraction/evaporation method. The microspheres were characterized for drug load, impurity content, and particle size. Further, the microspheres were subjected to in vitro release testing in acetate buffer (pH 4.0) and phosphate buffered saline (PBS) (pH 7.2). In acetate buffer, 3 microsphere batches composed of low molecular weight PLGA 50∶50, PLGA 85∶15, and PLA polymers (≤10 kDa) showed 100% release with minimal impurity formation (<10%). The high molecular weight PLGA 50∶50 microspheres (28 kDa) displayed only 70% cumulative release in acetate buffer with significant impurity formation (∼24%). In PBS (pH 7.4), on the other hand, only 50% release was observed with the same low molecular weight batches (PLGA 50∶50, PLGA 85∶15, and PLA) with higher percentages of hydrophobic impurity formation (ie, 40%, 26%, and 10%, respectively). In addition, in PBS, the high molecular weight PLGA 50∶50 microspheres showed only 20% drug release with ∼60% mean impurity content. The chemically modified peptide impurities inside microspheres were structurally confirmed through Fourier transform-mass spectrometry (FT-MS) and liquid chromatography/mass spectrometry (LC-MS/MS) analyses after extraction procedures. The adduct compounds were identified as covalently modified conjugates of octreotide with lactic and glycolic acid monomers within polymeric microspheres. The data suggest that due to steric hindrance factors, polymers with greater lactide content were less amenable to the formation of adduct impurities compared with PLGA 50∶50 copolymers.
Keywords: somatostatin analogues; octreotide acetate; peptide acylation; peptide stability; poly(D,L-lactide-co-glycolide) (PLGA) microspheres
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References
- 1.Hunter SJ, Shaw JA, Lee KO, Wood PJ, Atkinson AB, Bevan JS. Comparison of monthly intramuscular injections of Sandostatin LAR with multiple subcutaneous injections of octreotide in the treatment of acromegaly: effects on growth hormone and other markers of growth hormone secretion. Clin Endocrinol (Oxf). 1999;50(2):245–251. doi: 10.1046/j.1365-2265.1999.00668.x. [DOI] [PubMed] [Google Scholar]
- 2.Tsai T, Mehta RC, DeLuca PP. Adsorption of peptides to poly(D,L-lactide-co-glycolide). 1. Effect of physical factors on the adsorption. Int J Pharm. 1996;127:31–42. doi: 10.1016/0378-5173(95)04111-7. [DOI] [Google Scholar]
- 3.Tsai T, Mehta RC, DeLuca PP. Adsorption of peptides to poly(D,L-lactide-co-glycolide). 2. Effect of solution properties on the adsorption. Int J Pharm. 1996;127:43–52. doi: 10.1016/0378-5173(95)04112-5. [DOI] [Google Scholar]
- 4.Lucke A, Kiermaier J, Gopferich A. Peptide acylation by poly(alpha-hydroxy esters) Pharm Res. 2002;19(2):175–181. doi: 10.1023/A:1014272816454. [DOI] [PubMed] [Google Scholar]
- 5.Lucke A, Gopferich A. A cylation of peptides by lactic acid solutions. Eur J Pharm Biopharm. 2003;55(1):27–33. doi: 10.1016/S0939-6411(02)00138-8. [DOI] [PubMed] [Google Scholar]
- 6.Rothen-Weinhold A, Oudry N, Schwach-Abdellaoui K, Frutiger-Hughes S, Hughes GJ, Jeannerat D, Burger U, Besseghir K, Gurny R. Formation of peptide impurities in polyester matrices during implant manufacturing. Eur J Pharm Biopharm. 2000;49(3):253–257. doi: 10.1016/S0939-6411(00)00066-7. [DOI] [PubMed] [Google Scholar]
- 7.Jeyanthi R, Thanoo BC, Mehta RC, DeLuca PP. Effect of solvent removal technique on the matrix characteristics of polylactide/glycolide microspheres for peptide delivery. J Control Release. 1996;38:235–244. doi: 10.1016/0168-3659(95)00125-5. [DOI] [Google Scholar]
- 8.Jeyanthi R, Mehta RC, Thanoo BC, DeLuca PP. Effect of processing parameters on the properties of peptide-containing PLGA microspheres. J Microencapsul. 1997;14(2):163–174. doi: 10.3109/02652049709015330. [DOI] [PubMed] [Google Scholar]
- 9.Bodmer D, Kissel T, Traechslin E. Factors influencing the release of peptides and proteins from biodegradable parenteral depot systems. J Control Release. 1992;21:129–138. doi: 10.1016/0168-3659(92)90014-I. [DOI] [Google Scholar]
- 10.Domb AJ, Turovsky L, Nudelman R. Chemical interactions between drugs containing reactive amines with hydrolyzable insoluble biopolymers in aqueous solutions. Pharm Res. 1994;11(6):865–868. doi: 10.1023/A:1018985909777. [DOI] [PubMed] [Google Scholar]
- 11.Kostanski JW, DeLuca PP. A novel in vitro release technique for peptide-containing biodegradable microspheres. AAPS Pharm-SciTech. 2000;1:4–4. doi: 10.1208/pt010104. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Blanco-Prieto MJ, Besseghir K, Orsolini P, Heimgartner F, Deuschel C, Merkle HP, Nam-Tran H, Gander B. Importance of the test medium for the release kinetics of a somatostatin analogue from poly(D,L-lactide-co-glycolide) microspheres. Int J Pharm. 1999;184(2):243–250. doi: 10.1016/S0378-5173(99)00118-0. [DOI] [PubMed] [Google Scholar]