X-Message-Number: 18328
Date: Thu, 10 Jan 2002 09:52:42 -0800 (PST)
From: Doug Skrecky <>
Subject: phenylalanine/arginine phosphate looks interesting

Title
  Formulation of proteins in
  vacuum-dried glasses. II. Process and
  storage stability in sugar-free amino acid systems.
Source
  Pharmaceutical Development & Technology.  4(2):199-208, 1999 May.
Abstract
  The purpose of this research was to investigate the freeze- and
  vacuum-drying behavior of L-amino acids of current/potential
  use as adjuvants for formulating proteins. The analytical
  methods used were wide-angle x-ray diffraction, differential scanning
  calorimetry, and scanning electron microscopy. Protein analysis was performed
  either as an activity assay (lactate dehydrogenase [LDH]) or by
  size-exclusion chromatography (granulocyte colony-stimulating factor
  [rhG-CSF]). After samples were freeze-dried, only the four
  basic amino acids (arginine, lysine, histidine, and citrulline) formed
  amorphous solids, which, however, were partially crystalline. The remaining
  amino acids all formed fully crystalline solids. After samples were
  vacuum-dried, (20 degrees C, 0.1 mbar, 1 ml
  fill volume in 2-ml vials) fully crystalline solids were formed by all of the
  amino acids. For arginine, the addition of either HCl, H3PO4, or H2SO4
  sufficient to form the respective salt produced amorphous solids after
  vacuum-drying, but they had high residual water contents and
  low glass transition temperatures (Tg). Addition of phenylalanine to arginine
  base inhibited crystallization of the latter at low concentrations during
  vacuum-drying procedure, leading to formation of a pure
  rubbery solid. At higher concentrations the phenylalanine crystallized,
  producing dry products with glass transition temperatures of > 60 degrees C.
  The process and storage stability of LDH and rhG-CSF in the
  vacuum-dried phenylalanine/arginine glasses
  was greatly improved at temperatures up to 40 degrees C compared with the
  unprotected proteins. Uptake of moisture during storage was,
  however, a complicating factor, reducing Tg, promoting crystallization, and
  leading to decreased protein stability. The PO4 salt of arginine produced
  especially high glass transition temperatures after it was
  vacuum-dried. These sugar-free amino acid
  formulations thus are potential stabilizes for
  proteins.

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