Harmony in Synchrony
S-phase Inhibition
Mitotic Inhibition
- Aphidicolin (APH) is a secondary metabolite of the fungus Nigrospora oryzae used in cell culturing to block the cell cycle at early S phase. It is a specific inhibitor of DNA polymerase A,D in eukaryotic cells and in some viruses and an apoptosis inducer in HeLa cells.
- Hydroxyurea (HU) is another DNA replication inhibitor used to block the cell cycle in S-phase. HU causes deoxyribonucleotide depletion and results in DNA double strand breaks near replication forks via inhibition of the enzyme ribonucleotide reductase by scavenging tyrosyl free radicals as they are involved in the reduction NDPs
Mitotic Inhibition
- Nocodazole inhibits microtubule polymerization. Cells treated with nocodazole arrest with a G2- or M-phase DNA content when analysed by flow cytometry. Microscopy of nocodazole-treated cells shows that they do enter mitosis but cannot form metaphase spindles because microtubules (of which the spindles are made) cannot polymerise. The absence of microtubule attachment to kinetochores activates the spindle assembly checkpoint, causing the cell to arrest in prometaphase. For cell synchronization experiments, nocodazole is usually used at a concentration of 40-100 ng/mL of culture medium for a duration of 12-18 hrs. Prolonged arrest of cells in mitosis due to nocodazole treatment typically results in cell death by apoptosis.