Chemie | Biochemie | Medizin
Daria Diethelm, 2001 | Grenchen, SO
This project deals with the effect of the known chemotherapeutic cytarabine on HSV-2- and VSV-infected Vero cells. The percentage of infection was measured with a plaque assay after the cells were treated with different concentrations of cytarabine. Additionally, the toxicity of cytarabine on healthy cells was evaluated with an MTT assay. The results show that the drug has an antiviral effect on HSV-2- as well as VSV-infected cells, whereas the EC50 value lies at 10.81nM for HSV-2 and at 1.924µM for VSV. In the MTT assay, no sign of toxicity was detected.
From the discovery of a new drug until its approval on the market it normally takes 10–17 years. This period can be shortened by repurposing a drug. This means that another effect of an already approved drug is discovered and can be used. This fact led me to the drug cytarabine. It is a known chemotherapeutic that consists of a cytosine base and an arabinose sugar. Its structure is similar to the human deoxycytidine triphosphate. Different reports show that the drug is also able to inhibit the DNA replication of viruses. In light of this, I developed my central question: Does the chemotherapeutic cytarabine have an antiviral effect on HSV-2- and VSV-infected cells? The exact mechanism of cytarabine is not fully discovered yet, but the common hypothesis at the moment is that the compound inhibits, via the competition with deoxycytidine triphosphate, the DNA polymerase. For the experiment, the DNA virus HSV-2 and the RNA virus VSV were chosen, to see the effect of cytarabine on both kinds of genetic material.
To answer my central question, a plaque assay was performed. In the first experiment, the cells were infected with one virus each and then treated with a 1:2 serial dilution of cytarabine starting at 100 µM. For the second experiment, this was repeated with a 1:3 serial dilution starting at 50 µM. For VSV, this experiment was done in the supernatant. The third and last experiment was only performed for HSV-2 with a 1:5 serial dilution starting at 5 µM. For the MTT assay, a serial dilution (ratio 1:2) starting at 1000 µM was added to the healthy cells. The percentage of viability was then calculated with the help of the Prism software.
In the first experiment using HSV-2, the percentage of infection decreased the higher the concentration of cytarabine was. In the first three concentrations, the percentage was 0%. For VSV, the rate of infection was very high (above 65%) in every concentration and no clear sign of an increase or decrease was detectable. The results of the second experiment with HSV-2 were similar to the previous ones. Again, there was a percentage of 0% in the first three concentrations. However, the percentages in the following concentrations were approximately twice as high as in the first experiment. The results with VSV show that the rate of infection increases exponentially the higher the concentrations are, from approximately 8% to around 100%. In the last experiment using HSV-2, the rate of infection in the three lowest concentrations of cytarabine was at 0% again. In the following ones, the percentage increased exponentially to approximately 80%. In the MTT assay, the percentage of viability of the treated cells was between 80% and 100% in every concentration.
Cytarabine has an antiviral effect on both viruses, as the rate of infection decreases significantly with the addition of the drug. The higher the concentration of the compound, the lower the rate of infection. Thus, cytarabine probably has an effect on the DNA as well as the RNA replication. Additionally, the results of the toxicity test show that the drug has no impact on the viability of the healthy cells, as over 80% survived in all of the concentrations.
Even if the results of these experiment are really promising, it is not possible to start clinical trials. The experiments were only performed once and then adapted to find an efficient concentration of cytarabine and to calculate the EC50 value. To answer my central question completely, the experiments have to be repeated with the right concentrations many more times. Nevertheless, this project suggests that further research on this topic could be profitable.
Würdigung durch den Experten
Prof. Dr. Cornel Fraefel
Mit dieser Maturarbeit hat Frau Diethelm ein sehr hohes Niveau an Wissenschaftlichkeit bewiesen. Frau Diethelm hat eine Hypothese gestellt, diese experimentell geprüft und die Resultate schliesslich analysiert und kritisch diskutiert. Der praktische Teil wurde an der Universität Genf durchgeführt und dort auch professionell begleitet. Frau Diethelm musste sich in mehrere Methoden einarbeiten, was auch bei professioneller Betreuung konzentrierte Laborarbeit, Hartnäckigkeit, und Engagement erfordert.
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Lehrerin: Christina Tardo-Styner