WP5: Improving in vitro/in vivo correlations – Absorption, Distribution, Excretion
WP5 results, download the entire summary: 
Results WP5.pdf
In WP5 the focus was to investigate the influence of ADE (administration, distribution and elimination) on the kinetics of chemicals using modeling and in vitro testing, with the aim to identify factors that influence the correlation between in vitro toxicity (concentration) and in vivo toxicity (dosage) and to develop an algorithm that accounts for this.
Important factors to be considered have been:
1. The degree and rate of absorption after oral uptake
2. The distribution over the different organs and tissues
3. The elimination of compounds
4. The determination of the concentration of the compound in the in vitro system
To address the points mentioned above the following methodologies have been used:
• Neural network models for oral and blood brain barrier (BBB) passage
• In vitro measurements of BBB passage
• In vitro measurements for determination of oral absorption
• In vitro biokinetics: evaluation of free concentration of a chemical
• Physiologically-based kinetic modeling
In summary, the data obtained in WP5 have been the basis for the biokinetic modeling and development of a system in which input from in vitro data can be used for estimation an LD50 value.
Estimation of LD50 values from in vitro cytotoxicity by introduction of biokinetics:
- Calculation of an apparent volume of distribution (Vd), assuming that the total body water volume of a 250 g rat is 170 ml and correcting for 3 factors: lipophilicity, clearance, and protein binding.
- Calculation of the internal dose (from IC50 values obtained in 3T3 NRU assay or organ specific assays), taking into account the Vd
- Calculation of the external dose (estimated LD50) taking into account the oral absorption (calculated from Caco-2 permeability)
The correlation (in mM) improves from R2 = 0.45 ? R2 = 0.63 when using data from the 3T3/NR uptake assay in order estimate LD50 values.