The biological therapeutics play an significant role in cancer treatment. Although the number of naked antibodies with clinical efficacy increases with the R & D of protein therapeutic discovery, their functions are also limited by simple working mechanism, and one popular way to enhance therapeutic potential of antibodies is to conjugate them to small molecule drugs, to combine the benefits of highly potent drugs and selective binders of specific tumor antigens. However, design and optimization of the Antibody-Drug Conjugates (ADC) is more complicated, requiring more comprehensive consideration of antibody, linker and drugs.
The ADC can be taken as a pro-drug, connecting the cytotoxic warhead (drug) to the chosen antibody (serving as targeted delivery system to the tumor expressing the antigen/target recognized by the antibody) via a linker. So it’s important to figure our Drug-to-Antibody Ratio (DAR), an critical quality attribute of an ADC as it determines the amount of drugs that can be delivered to the tumor cell, and directly affect both safety and efficacy of the tested ADC.
These two attitudes, DAR and drug load distribution, are essential characteristics of ADCs as they can determine the exact drug quantity to which the patient is exposed after administration; meanwhile various drug-loaded forms may differ in their PK/PD performance.
Drug load distribution(%)
=(peak area of Ab with drug load n/sum of all peak areas)* 100 % [where n is number of drug load]
=∑(drug load distribution (%)of each Ab with drug load n)*n/100
Because of the diversity of the linkers, our tech staff in Creative Proteomics can provide different analytical workflows. Hydrophobic Interaction Chromatography (HIC), and Reversed Phase High-Performance Liquid Chromatography (RP-HPLC) are often used to separate the ADCs with different drug loads, while UV/Vis spectroscopy and mass spectrometry are often applied for ADC detection. LC-ESI-MS platform in Creative Proteomics is widely utilized when accurate determination of DAR and Drug Load Distribution is needed and Lysine-linked ADCs are especially suitable for use with the denaturing RP-HPLC mobile phases typically used in LC-ESI-MS analysis. ESI can ionize the ADCs without dissociate the multiple protonated ADCs, and the collected MS spectra by high resolution MS would be processed with professional bioinformatic tools for deconvolution, to show the ADC peaks with different drug loads. Based on the accurate molecular weight of antibody and the small molecule drug, the numbers of loaded drugs of each peak can be calculated correctly.