In a new article, published in the October 6, 2019 edition of Biotechnology Progress, Travis Gates, Yaqi Fara Lyu, Xin Fang and Xiaoli Liao at the Department of Biochemistry, Augustana College, Rock Island, IL, describes how ultrafiltration (UF) and diafiltration (DF) by tangential flow filtration (TFF) are frequently used for removal of solvents and small molecule impurities and for buffer exchange for biopharmaceutical products.
The biggest technical challenge in the manufacturing process of any pharmaceutical agent is to provide consistently efficacious drug product, with the required purity that is safe from environmental and process related contamination.
This is especially important in the manufacturing of antibody-drug conjugates, requiring subsequent purification of the required ADC sub-population from the post conjugation reaction mixture. Such a reaction mixture includes ADC variants with a range of Drug to Antibody Ratio (DAR), unincorporated drug, spacer derivatives and organic solvents.
When compared to the parent mAb process UF/DF purification requires optimization since the addition of hydrophobic drug moieties to the mAb may result in reduced stability or solubility and an increased propensity to aggregate. Additional purification can be achieved using conventional chromatography modalities, with cation exchange having the potential to resolve both mAb-derived aggregates and ADC species showing extremes of DAR.
In contrast to standard antibody preparation, antibody‐drug conjugates carry unique solvents and small molecule impurities into the final UF/DF step. In their article. Gates et al, specifically describe the diafiltration (DF) step in the clearance of these solvents and small molecules by UF/DF.
In their study the authors observe that rates of clearance for all the impurities in this study are close to the ideal clearance with no apparent interaction with either the protein or the TFF membrane and system.
Gates et al. describes the effect of process variables during diafiltration, such as pH, temperature, membrane loading, transmembrane pressure and cross flow rate, has also been evaluated and found to have minimal impact on the clearance rate.
Their final processing stages the authors describes included further TFF (UF/DF) to adjust final formulation and conventional sterile filtration to meet regulatory guidelines.
These results demonstrate efficient clearance of solvents and small molecule impurities related to the ADC process by the diafiltration process and provide a general data package to facilitate risk assessments based on the sieving factors and program specific needs.
Based on these results, the authors conclude that efficient clearance of solvents and small molecule impurities related to the ADC process by the diafiltration process is possible. They provide a general overview designed to facilitate risk assessments based on the sieving factors and program specific needs.
 Gates T, Lyu YF, Fang X, Liao X. Clearance of Solvents and Small Molecule Impurities in Antibody Drug Conjugates via Ultrafiltration and Diafiltration Operation.Biotechnol Prog. 2019 Oct 6:e2923. doi: 10.1002/btpr.2923. [Pubmed][Article]
 Scanlan C, Zhao J, Rogers M, Waghmare R, Xu S, Cross S, Katz VA Antibody-Drug Conjugates: Manufacturing Challenges and Trends J.ADC Fenruary 20, 2017. DOI: 10.14229/jadc.2017.21.03.001 [Article]