The stability of recombinant human growth hormone in poly(lactic-co-glycolic acid) (PLGA) microspheres.
OBJECTIVE
The development of a sustained release formulation for recombinant human growth hormone (rhGH) as well as other proteins requires that the protein be stable at physiological conditions during its in vivo lifetime. Poly(lactic-co-glycolic acid) (PLGA) microspheres may provide an excellent sustained release formulation for proteins, if protein stability can be maintained.


METHODS
rhGH was encapsulated in PLGA microspheres using a double emulsion process. Protein released from the microspheres was assessed by several chromatrographic assays, circular dichroism, and a cell-based bioassay. The rates of aggregation, oxidation, diketopiperazine formation, and deamidation were then determined for rhGH released from PLGA microspheres and rhGH in solution (control) during incubation in isotonic buffer, pH 7.4 and 37 degrees C.


RESULTS
rhGH PLGA formulations were produced with a low initial burst (< 20%) and a continuous release of rhGH for 30 days. rhGH was released initially from PLGA microspheres in its native form as measured by several assays. In isotonic buffer, pH 7.4 and 37 degrees C, the rates of rhGH oxidation, diketopiperazine formation, and deamidation in the PLGA microspheres were equivalent to the rhGH in solution, but aggregation (dimer formation) occurred at a slightly faster rate for protein released from the PLGA microspheres. This difference in aggregation rate was likely due to the high protein concentration used in the encapsulation process. The rhGH released was biologically active throughout the incubation at these conditions which are equivalent to physiological ionic strength and pH.


CONCLUSIONS
rhGH was successfully encapsulated and released in its fully bioactive form from PLGA microspheres over 30 days. The chemical degradation rates of rhGH were not affected by the PLGA microspheres, indicating that the internal environment of the microspheres was similar to the bulk solution. After administration, the microspheres should become fully hydrated in the subcutaneous space and should experience similar isotonic conditions and pH. Therefore, if a protein formulation provides stability in isotonic buffer, pH 7.4 and 37 degrees C, it should allow for a safe and efficacious sustained release dosage form in PLGA microspheres.
Cleland
J L
JL
Department of Pharmaceutical Research & Development, Genentech, Inc., South San Francisco, California, USA. cleland@gene.com
Mac
A
A
Boyd
B
B
Yang
J
J
Duenas
E T
ET
Yeung
D
D
Brooks
D
D
Hsu
C
C
Chu
H
H
Mukku
V
V
Jones
A J
AJ
D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D004355:Drug Stability; D019382:Human Growth Hormone / Q000737:chemistry* / Q000302:isolation & purification; D006801:Humans; D019344:Lactic Acid; D008863:Microspheres; D011100:Polyglycolic Acid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification
D011108:Polymers; D011994:Recombinant Proteins; D019382:Human Growth Hormone; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid