August 2017 Newsletter – Aptamers in Bioanalysis of Antibody-Drug Conjugates

In This Issue:

• Base Pair Opens New Facility
• Aptamers in Bioanalysis of Antibody-Drug Conjugates
• Complete the Intracellular Analysis Survey and Enter to Win a $50 Visa Gift Card

 

Base Pair Moves to New Facility

​We are excited to announce the opening of our new 5,000+ sq. ft. facility. Still in Pearland, TX, our new site is just a mile from our original location, convenient to Houston’s biomedical hub and clinical research institutions including MD Anderson, Rice University and Baylor College of Medicine.

 

Aptamers in Bioanalysis of Antibody-Drug Conjugates

In an effort to improve drug efficacy and reduce side effects, the latest anti-cancer agents combine toxicity with cell targeting, delivering toxic drug only to cells displaying specific, cancer-related cell surface markers. One method of targeted drug delivery is the antibody-drug conjugate, or ADC. Several ADCs have been FDA-approved and many more are in the pipeline. While ADCs offer unique advantages in cancer treatment, they have created unique challenges in drug development and bioanalysis as well.

Antibody-Drug Conjugates

Antibody-drug conjugates consist of three critical elements: a cell-specific antibody, a cytotoxic drug, and a linker. The antibody must be highly selective for the cell type (typically a cancer cell) being targeted and poorly immunogenic. The drug must be cytotoxic only upon release from the linker. The linker must be stable in circulation to avoid general toxicity and achieve delivery to the target site, but must release the cytotoxic drug within the tumor or cancer cell environment. Non-cleavable linkers rely on antibody degradation within the cell for release of cytotoxic drug, while cleavable linkers often utilize pH-dependent or reduction-dependent release. Ideal linkers are stable in the bloodstream, then cleaved upon entry into cellular compartments. (3)

Bioanalysis of Antibody-Drug Conjugates

Bioanalysis refers to the quantitative measurement of a compound, or drug, and its metabolites in biological fluids. (4) Bioanalysis of an antibody-drug conjugate (ADC) combines traditional testing for both antibody drugs and small molecule drugs. One challenge is testing antibody-drug conjugates with varying drug-to-antibody ratios, as some ligand binding assays have difficulty detecting low ratios. The application of site-specific conjugation is improving ADC homogeneity, but in vivo processing can yield a wide range of breakdown products. Understanding the in vitro and in vivo catabolism and / or metabolism of ADCs is important for proper determination of optimal dose, safety, and efficacy. The small molecule component of ADCs can form several breakdown products, including the drug molecule, linker, linker+ drug, and drug metabolite(s). Antibody breakdown products can include unconjugated antibody, peptides, and whole antibody/antibody fragments with varying degrees of conjugation. While there are complex methods for determining ADC catabolism / metabolism and required analysis will vary from one ADC to another, bioanalysis of all ADCs includes tracking of total antibody, antibody-drug conjugate, and unconjugated drug. (5)

Multiplex Aptamer Selection for Bioanalysis of ADCs

Bioanalysis of ADCs requires assessment of the ADC molecule as well as individual components. Developing selective reagents to toxic small molecules, antibodies with low immunogenicity, and small metabolites and catabolites within a tight time frame is a huge challenge. (2) Aptamers are easily selected against toxic, non-immunogenic, and very small targets. With Base Pair’s patented multiplex selection process, aptamers to the antibody-drug complex, unconjugated antibody, unconjugated drug, and other key catabolites / metabolites can be selected in a single SELEX process. Base Pair’s VENNmultiplex™ SELEX can be utilized to identify selective and pan binders for multiple ADC species for assay development. While traditional bioanalysis methods differ for large (antibody) and small (drug) molecules, aptamer-based assays for both large and small molecules can be developed on a single platform. Aptamers can have high affinity and selectivity in complex samples without the interference of heterophilic antibodies, anti-animal antibodies, and other molecules that can be problematic in antibody-based assays, reducing the need for sample pre-treatment(1).

Base Pair Biotechnologies has experience selecting aptamers to small molecule drugs, antibodies, and many other targets. Contact Base Pair for more information on custom aptamer selection and assay development for bioanalysis.

​References:
 
1. Chandola, C. et al. Application of aptamers in diagnostics, drug-delivery and imaging. J. Biosci. 2016. DOI: 10.1007/s12038-016-9632-y.

2. Halford, A. et al. Meeting challenges for analysis of antibody-drug conjugates. BioPharm International.  2012. 25:10.

3. Lu, J. et al. Linkers having a crucial role in antibody–drug conjugates. Int J Mol Sci. 2016. 17(4): 561.

4. Pandley, S. et al. Bioanalysis in drug discovery and development. Pharmaceutical Methods. 2010. 1(1):14-24.

5.  Saad, O.M., e al. Bioanalytical approaches for characterizing catabolism of antibody-drug conjugates. Bioanalysis. 2015. 7(13)1583-1604.

 

Tell us what you’d like to learn about your cells and enter to win a $50 Visa gift card!

Base Pair scientists are currently working on a new aptamer-based intracellular analysis method that will enable detection of intracellular events within live cells without the addition of a dye, fluorescent label, or fluorescent protein. There are many potential applications for this new method, from confirmation of transfection to monitoring of protein expression. We’d like to determine which applications will have the greatest impact. Take our brief, 10-question survey and let us know what types of intracellular analysis are of most interest to you. One lucky respondent will receive a $50 Visa gift card.  Vote Now!