PT  - JOURNAL ARTICLE
AU  - Sharad Sharma
AU  - Zhe Li
AU  - David Bussing
AU  - Dhaval K. Shah
TI  - Evaluation of Quantitative Relationship Between Target Expression and ADC Exposure Inside Cancer Cells
AID  - 10.1124/dmd.119.089276
DP  - 2020 Jan 01
TA  - Drug Metabolism and Disposition
PG  - dmd.119.089276
4099  - http://dmd.aspetjournals.org/content/early/2020/02/21/dmd.119.089276.short
4100  - http://dmd.aspetjournals.org/content/early/2020/02/21/dmd.119.089276.full
AB  - Antibody-drug conjugates (ADCs) employ overexpressed cell surface antigens to deliver cytotoxic payloads inside cancer cells. However, the relationship between target expression and ADC efficacy remains ambiguous. In this manuscript we have addressed a part of this ambiguity by quantitatively investigating the effect of antigen expression levels on ADC exposure within cancer cells. Trastuzumab-vc-MMAE was used as a model ADC, and four different cell lines with diverse levels of human epidermal growth factor receptor 2 (HER2) expression were used as model cells. The PK of total trastuzumab, released MMAE, and total MMAE were measured inside the cells and in the cell culture media following incubation with two different concentrations of ADC. In addition, target expression levels, target internalization rate, and cathepsin B and MDR1 protein concentrations were determined for each cell line. All the PK data was mathematically characterized using a cell-level systems PK model for ADC. It was found that SKBR-3, MDA-MB-453, MCF-7, and MDA-MB-468 cells had ~800,000, ~250,000, ~50,000, and ~10,000 HER2 receptors per cell, respectively. A strong linear relationship (R2>0.9) was observed between HER2 receptor count and released MMAE exposure inside the cancer cells. There was an inverse relationship found between HER2 expression level and internalization rate, and cathepsin B and MDR1 expression level varied slightly among the cell lines. The PK model was able to simultaneously capture all the PK profiles reasonably well, while estimating only 2 parameters. Our results demonstrate a strong quantitative relationship between antigen expression level and intracellular exposure of ADCs in cancer cells.SIGNIFICANCE STATEMENT In this manuscript we have demonstrated a strong linear relationship between target expression level and ADC exposure inside cancer cells. We have also shown that this relationship can be accurately captured using the cell-level systems PK model developed for ADCs. Our results indirectly suggest that the lack of relationship between target expression and efficacy of ADC may stem from differences in the pharmacodynamic properties of cancer cells.