Characterization of paclitaxel sensitivity in Human glioma- and medulloblastoma-derived cell lines

Overview
This paper examines the sensitivity of a Paclitaxel on gliomas. Paclitaxel is a cytotoxic product that disrupts microtubule integrity and is currently being evaluated for its purpose in killing malignant astrocytic gliomas and medulloblastomas. In the past, methylating agents have been used to form alkyl base adducts in the DNA of the gliomas and medulloblastomas, to prevent growth of these tumors, and induce death. However, because of the processes of evolution most malignant tumors have become resistant to this treatment.

Since damaging the DNA no longer has an effect on malignant tumors, the scientists in this paper have used a different drug that targets the cytoskeleton of the cell, rather than it’s DNA. Experiments with Paclitaxel has shown that the drug works on several malignant tumors including those that are resistant to the effects of methylating agents on tumor DNA. By damaging and preventing cytoskeleton growth and rearrangement, Paclitaxel prevents the cells from undergoing all the steps of mitosis, as the cytoskeleton plays a key role in cell replication and growth. When a cell is prevented from entering or completing mitosis, it will eventually enter apoptosis.

Specificities of Experiment:
Medulloblastoma cells and glioma cell lines were taken from several different sources. They were plated individually on 12 well plates at a cell count of 750cells/well and incubated for 4,8,24, and 48 hours. They tested the sensitivity of Paclitaxel by conducting a clonogenic assay.

Results:
An interesting result was that all cell lines displayed biphasic survival curves. The biphasic survival curves are an indication of subpopulations in the cell line that differed in their sensitivity. These biphasic curves were evident throughout most of the beginning time intervals. At later time intervals (24 hrs) the resistant cell lines were eliminated and cell lines showed a single linear survival curve. This result shows that Paclitaxel is effective in eliminating resistant cells. At 48 hours, Paclitaxel did not eliminate any more differences in the sensitivities between the cell lines.

The differences in sensitivity were attributed to not only the biological nature of the specific subpopulations but also the phase of mitosis they were currently in when the drug was added. Those in the G2 phase were more sensitive to Paclitaxel, because of the necessity for microtubules at this stage. However, cells that were in G1 or S phases had a higher resistance to Paclitaxel because a damaged cytoskeleton at this stage in the cycle does not have as catastrophic effects as in other stages.