calcitonin and Hemolysis

Protein aggregation, which is triggered by various factors, is still one of the most prevalent problems encountered during all stages of protein formulation development. In this publication, we present novel excipients, tryptophan-mPEGs (Trp-mPEGs) of 2 and 5 kDa molecular weight and suggest their use in protein formulation. The synthesis and physico-chemical characterization of the excipients are described. Possible cytotoxic and hemolytic activities of the Trp-mPEGs were examined. Turbidity, 90° static light scatter, intrinsic fluorescence, fluorescence after staining the samples with Nile Red and fluorescence microscopy were used to study the inhibitory effect of the Trp-mPEGs on the aggregation of salmon calcitonin (sCT) in different buffer systems and at various molar ratios. Aggregation of sCT was reduced significantly with increasing concentrations of Trp-mPEG 2 kDa. A 10-fold molar excess of Trp-mPEG 2 kDa suppressed almost completely the aggregation of sCT in 10mM sodium citrate buffer (pH 6) for up to 70 h. Trp-mPEG 5 kDa also reduced the aggregation of sCT, though less pronounced than Trp-mPEG 2 kDa. Low aggregation of sCT was measured after approximately 10 days in 10mM sodium citrate buffer, pH 5, with a 10-fold molar excess of Trp-mPEG 2 kDa. This paper shows that Trp-mPEGs are potent excipients in reducing the aggregation of sCT. Trp-mPEGs are superior to dansyl-PEGs concerning the stabilization of sCT in a harsh environment, wherein sCT is prone to aggregation. Trp-mPEGs might therefore also be used for stabilization of other biopharmaceuticals prone to aggregation.

Topics: Calcitonin; Cell Line; Cell Proliferation; Cell Survival; Drug Compounding; Drug Stability; Erythrocytes; Excipients; Hemolysis; High-Throughput Screening Assays; Humans; Keratinocytes; Microscopy, Fluorescence; Polyethylene Glycols; Protein Stability; Spectrometry, Fluorescence; Tryptophan

Salmon calcitonin (sCT) was conjugated via its N-terminal cysteine to a comb-shaped end-functionalized poly(poly(ethylene glycol) methyl ether methacrylate) (PolyPEG, 6.5 kDa), and to linear PEG (5 kDa). Conjugate molecular weight and purity was assessed by SEC-HPLC and MALDI-TOF MS. Bioactivity of conjugates was measured by cyclic AMP assay in T47D cells. Calcium and calcitonin levels were measured in rats following intravenous injections. Stability of conjugates was tested against serine proteases, intestinal and liver homogenates and serum. Cytotoxicity of conjugates was assessed by lactate dehydrogenase (LDH) assay and by haemolytic assay of rat red blood cells. Results showed that the two conjugates were of high purity with molecular weights similar to predictions. Both conjugates retained more than 85% bioactivity in vitro and had nanomolar EC(50) values similar to sCT. While both sCT-PolyPEG(6.5 K) and sCT-PEG(5 K) were resistant to metabolism by serine proteases, homogenates and serum, PolyPEG (6.5 K) was more so. Although both conjugates reduced serum calcium to levels similar to those achieved with sCT, PolyPEG(6.5 K) extended the T(1/2) and AUC of serum sCT over values achieved with sCT-PEG and sCT itself. None of PolyPEG, PEG or methacrylic acid displayed significant cytotoxicity. PolyPEG may therefore have potential to improve pharmacokinetic profiles of injected peptides.

Topics: Animals; Bone Density Conservation Agents; Caco-2 Cells; Calcitonin; Calcium; Chromatography, High Pressure Liquid; Cyclic AMP; Drug Carriers; Drug Stability; Erythrocytes; Hemolysis; Humans; Intestinal Mucosa; Liver; Methacrylates; Molecular Weight; Polyethylene Glycols; Polymethacrylic Acids; Rats; Rats, Wistar