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Team:NJU China/Modeling
From 2013.igem.org
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Introduction
Pharmacokinetic Modeling
Parameters
Mass balance equation of exosome
Results and conclusions
After drug administration, what happened within the body is quite complex and all the tissues are involved in the drug metabolism. In order to construct a pharmacokinetic model, we need to first make a few simplification of the body to make a pharmacokinetic model feasible.
Based on the multi-compartmental model, we divide the human body into central compartment (blood circulation) and peripheral compartment (body tissues). Since the exosome is administrated by intravenous injection, we assume that the concentration of exosome within the blood circulation reached its peak soon after injection and there is no variation within different parts of the blood circulation. Inspired by the pharmacokinetic model made by iGEM Slovenia 2012, we subdivide the peripheral compartment into liver (our target organ), kidney, lung, rapidly perfused tissues (such as skin, muscle) and slowly perfused tissues (such as spleen, heart). Each peripheral compartment has blood exchange with the central blood circulation, and during this process, certain percentage of exosome flow through a compartment will be absorbed. Apart from that, some of the exosome get into the kidney will be eliminated. Based on these simplifications, our multi-compartmental model is shown in the figure 1.
Introduction
Pharmacokinetics is the quantitative study of the drug absorption, distribution and metabolism within the body. It shows the fluctuation of the drug concentration within a certain part of the body along the time. For a new drug, we need to first experimentally obtain the pharmacokinetic parameters and then make the pharmacokinetic model to predict the concentration change after drug administration. Thus pharmacokinetic model plays a vital role in new drug development. Since our targeting-exosome is a brand new drug delivery system, we need to make a pharmacokinetic model to check if it can really target the specific site we want and predict the concentration change within that site.
Pharmacokinetic Modeling
After drug administration, what happened within the body is quite complex and all the tissues are involved in the drug metabolism. In order to construct a pharmacokinetic model, we need to first make a few simplification of the body to make a pharmacokinetic model feasible.
Based on the multi-compartmental model, we divide the human body into central compartment (blood circulation) and peripheral compartment (body tissues). Since the exosome is administrated by intravenous injection, we assume that the concentration of exosome within the blood circulation reached its peak soon after injection and there is no variation within different parts of the blood circulation. Inspired by the pharmacokinetic model made by iGEM Slovenia 2012, we subdivide the peripheral compartment into liver (our target organ), kidney, lung, rapidly perfused tissues (such as skin, muscle) and slowly perfused tissues (such as spleen, heart). Each peripheral compartment has blood exchange with the central blood circulation, and during this process, certain percentage of exosome flow through a compartment will be absorbed. Apart from that, some of the exosome get into the kidney will be eliminated. Based on these simplifications, our multi-compartmental model is shown in the figure 1.
Parameters
Mass balance equation of Exosome
A. The concentration change of the exosome within each compartment over time
a .The central compartment-blood circulation
The exosomes are removed from the blood through two main ways: distribution to other compartments and metabolism in the blood. Based on that, the mass balance equation of exosomes goes like follows:
b. The peripheral compartments
There are two main factors affect the concentration fluctuation in peripheral compartments: absorption from the blood and metabolism within the compartments.
For kidney, there is an additional factor, which is the elimination rate of the exosomes by kidney.
Thus the mass balance equations of the peripheral compartments are listed as below:
Liver:
Lung:
Kidney:
Rapidly perfused tissues:
Slowly perfused tissues:
Solving all the mass equations above, we can get the function which show the concentration change within each compartment along the time:
Blood circulation:
Liver:
Lung:
Kidney:
Rapidly perfused tissues:
Slowly perfused tissues:
B. Examine the relationship between the exosome concentration change over time and absorption percentage within liver.
C. Examine the relationship between the exosme concentration change over time and drug half-life within liver.
Kel=
Achievement
Starting from March, our lab work continues for 7 months. During these 7 months, we first came up with the idea of ‘biomissile’ via brainstorming, then carefully designed every component of our biomissile. And the most difficult part was to experimentally prove that every part of the system can work properly. From the hard work of the past 7 months, we have successfully done the following:
We designed and created a new anti-HBV siRNA biobrick(BBa_K1180000), and experimentally validated that it can significantly suppress the HBV viral gene. Apart from that, after transfection of HEK 293T cells with this part, the siRNA can be successfully encapsulated into the exosmes produced by the cells.
We designed and constructed a liver-targeting fusion protein (BBa_K1180003) . After transfecting the HEK 293T cells with this plasmid, we monitored the exosomes with this fusion protein on its surface successfully get into the Hep G2 cell.
We designed and constructed a brain-targeting fusion protein(BBa_K1180002). After transfecting the HEK 293T cells with this plasmid, the exosomes produced by the HEK 293T cells can successfully bring the siRNA contained into the mouse brain.
Combining the targeting module and kill module together, firstly it can target specific sites, apart from that, the siRNA contained within the exosome can specifically destroy the disease related gene. Thus we realize the idea of boimissile by using our engineered exosome for target-destruction of disease.
