Improving SDS-PAGE method for monoclonal antibodies: The advantages of Tris-Acetate over Tris-Glycine SDS-PAGE system and comparison with CE-SDS method.

Present study compares two different buffer systems for the electrophoretic separation of the IgG1 and IgG2 Monoclonal Antibodies using SDS-PAGE method. A modified Tris-acetate system was shown to be superior for separation of these proteins in a 6-20% gradient gel as compared with the traditionally used Tris-glycine method. This modified Tris-acetate buffer system showed sharper bands, more accurate determination of molecular weight, higher resolution, and better estimation of sub-fragments with closer results to those obtained by Capillary Gel Electrophoresis. Also in a parallel experiment, effect of IgG deglycosylation by PNGase-F enzyme was investigated and revealed no significant improvement on the SDS-PAGE results.

Multivariate Optimization of the Refolding Process of an Incorrectly Folded Fc-Fusion Protein in a Cell Culture Broth.

BACKGROUND: Protein misfolding is a common problem in large-scale production of recombinant proteins, which can significantly reduce the yield of the process. OBJECTIVE: In this work, we aimed at treating a cell culture broth containing high levels (>45%) of incorrectly folded Fc-fusion proteins by a simple redox buffer system in order to increase the proportion of the protein with correct conformation. METHODS: Multi-variable process optimization was firstly conducted at a small scale (25 mL), employing an experimental design methodology. After identifying the key variables using a resolution IV Fractional Factorial Design (FFD), the process was then optimized by the Central Composite Design (CCD). RESULTS: The optimal conditions for the refolding reaction were 340 mM Tris-base, 6.0 mM L-cysteine, 0.5 mM L-cystine, a buffer pH of 9.0, a reaction temperature of 8.5ºC and a reaction time of 24 h. Based on the treatment conditions obtained at a small scale, the process was further scaled up to 4500- L. The misfolded content was always less than 20%. The reaction can proceed well in the absence of chemical additives, such as chaotropic agents, aggregation suppressors, stabilizers and chelators. CONCLUSION: The refolding process increases the fraction of active protein in the original broth reducing the burden on downstream purification steps markedly.

Elimination of ghost peaks by optimization of anion exchange chromatography method for determination of gamma-carboxyglutamic acid (Gla)-domainless impurity in recombinant activated clotting factor VII drug products.

Secreted recombinant activated clotting factor VII activated (rFVIIa) in cell culture media missing gamma-carboxyglutamic acid (Gla) domain as a result of failure in gamma-carboxylation or cell lysis is called Gla-domainless impurity which has less negative charge compared to native rFVIIa. Based on risk assessment, this type of impurity is considered as critical drug product quality attribute of rFVIIa and its quantitative analysis in product batches is a critical issue in quality control laboratories. Analysis of Gla-domainless impurity is accomplished by Strong Anion Exchange Chromatography (SAX) in recombinant factor VIIa using Tris and Bis-Tris propane salt buffers as equilibrating buffers and high concentration ammonium acetate as an eluent. Appearance of ghost peaks with notable intensity during elution time of Gla-domainless impurity caused distortion of the related peak and interference with robust and accurate quantification of this impurity. Subsequently, the ghost peak was analyzed by LC-ESI-MS to determine the structure which showed the m/z values at 905.27, 623.53 and 341.60 and 563.73. To find the source of these ghost peaks, quality of water, buffer salts and Chelex-100 together with ionic strength of mobile phase A (addition of 25 mM NaCl) were considered as affecting parameters and several experiments designed with DOE software to optimize the best condition of highest quality the method with lowest signal of ghost peak noises. By interpretation of DOE result, it is concluded that high grade water and buffer salt along with high quality Chelex-100 resins are important factors to achieve a method with lowest ghost peaks. However, addition of 25 mM NaCl to mobile phase A with either lower quality buffer salts or lower water grade yields high quality chromatogram peak with acceptable ghost peaks. LC/MS analysis indicates that macrostructures of Bis-Tris propane made up as a result of hydrogen bonds with each other or Tris molecules can be the source of ghost peaks.

Determination of residual poly diallyldimethylammonium chloride (pDADMAC) in monoclonal antibody formulations by size exclusion chromatography and evaporative light scattering detector.

The cationic polyelectrolyte pDADMAC is widely used in biopharmaceutical industry as a flocculating agent to enhance clarification throughput and downstream filtration operations. Due to the possible toxicity, pDADMAC should be assessed for an acceptable residual level to ascertain the safety of the product to patients. The strong protein-polyelectrolyte interaction, however, can negatively affect sensitivity and accuracy of measurements. This paper reports on the application of size exclusion (SE) chromatography coupled to evaporative light scattering detector (ELSD) to the quantitative determination of pDADMAC in monoclonal antibody formulations and in process intermediates during downstream purification. The SE chromatography was performed under isocratic condition with a mobile phase consisting of 0.1% TFA in water (90%) and acetonitrile (10%) at a flow rate of 0.4 ml/min. A quantification limit (S/N = 10) of 0.85 ppm was achieved in sample matrix, which is sufficiently low for the trace analysis of this compound in protein-containing samples.

Targeted Delivery of Cabazitaxel by Conjugation to Albumin-PEG-folate Nanoparticles Using a Cysteine-acrylate Linker and Simple Synthesis Conditions.

BACKGROUND: Cabazitaxel (CBZ) is a new taxane approved by FDA for treatment of castration- resistant prostate cancer not responding to docetaxel. However, CBZ is not a suitable substrate for p-glycoprotein 60, an efflux pump which transports anticancer drugs out of malignant cells and is therefore a promising drug for treatment of multidrug resistant tumors. Similar to other taxanes, the presence of Tween 80 in the CBZ formulation shows that it is insoluble in water. METHODS: In order to increase the solubility and circulation time of this drug, CBZ-human serum albumin (HSA) conjugate was synthesized. The designed linker was composed of methacrylic acid and N-acetyl cysteine to increase the solubility of CBZ and to increase the efficiency of conjugation. Targeting was performed by poly(ethylene glycol)-folic acid amide bound formation with carboxyl groups of HSA during in the step of nanoparticle formation. Cytotoxicity of nanoparticles was evaluated in vitro on HT-29, as a folate negative cell line, and MDA-MB-231, as a folate positive cell line. RESULTS: H-NMR, Gel Permeation Chromatography, High Pressure Liquid Chromatography and UV spectrophotometry analysis confirmed the composition of conjugates. The resulting nanoparticles had a spherical shape, narrow size distribution and mean diameter of 138 nm. The efficiency of conjugation was 41.6 %. The IC50 of CBZ in targeted nanoparticles was 10.1 and 17.4% lower than that of the free CBZ for HT-29 and MDA-MB-231 cells, respectively. CONCLUSION: This designed drug delivery system was more water-soluble and had enhanced in vitro characteristics and higher cytotoxic activity on cancer cells.

Enhanced Cytotoxicity to Cancer Cells by Codelivery and Controlled Release of Paclitaxel-loaded Sirolimus-conjugated Albumin Nanoparticles.

Recently, it is suggested that mTOR signaling pathway is an important mediator in many cancers especially breast cancer. Therefore, effects of sirolimus as a mTOR inhibitor in breast cancer have been studied in combination with paclitaxel with or without controlled release effect. In this work, we prepared a water-soluble formulation of sirolimus-conjugated albumin nanoparticles loaded with paclitaxel, to study the effects of sirolimus concentration when it releases more later than paclitaxel in comparison with sirolimus-paclitaxel-loaded albumin nanoparticles. Also effects of paclitaxel loading on cytotoxic properties of nanoparticles were studied. Sirolimus was succinylated at 42-OH with enzymatic reaction of Candida antarctica lipase B, and then its carboxylic group was activated with EDC/NHS and conjugated to the lysine residues of albumin. Paclitaxel was loaded on albumin surface by nab technique in concentration range of 0-10 µg/mL. Sirolimus-conjugated nanoparticles with 0.01 µg/mL paclitaxel showed lowest cell viability of 44% while it was 53% for non-conjugated nanoparticles in MDA-MB-468 cell lines after 48 h (p-value = 0.003). In MCF-7 cell lines, sirolimus-conjugated nanoparticles with 0.1 µg/mL paclitaxel showed lowest cell viability of 35.69% while it was 48% for non-conjugated nanoparticles after 48 h (p-value = 0.03). We guess that when cancer cell lines arrest in G2-M by anticancer drugs like paclitaxel, Akt activates mTOR to make cells continue living, then inhibiting mTOR can enhance anticancer effects.