Apoptosis has always been an interesting subject to me regarding the cell cycle and cell function. The body seems to have some form of response to nearly any change or situation that it undergoes, even if that means sending cells to their death. Apoptosis is a critical process in cell cycle regulation and efficiency, and sets up two pathways: Intrinsic and Extrinsic. As a cell undergoes the phases of mitosis, important checkpoints are in place to ensure that the DNA is not damaged or malfunctioned. Vital proteins work alongside each other to keep this process in check. If DNA is damaged, a key histone (Gamma-H2AX) alerts another major protein of the injury. This protein is p53, which will halt the cell cycle until the DNA is repaired, or carries the cell towards apoptosis. P53 also acts as a tumor suppressor, inhibiting cells from proliferating in a rapid manner. (TP53 gene3: tumor protein p53, 2018). P53 is activated by Ck-1a via phosphorylation, which is also responsible for the phosphorylation of proto-oncogene B-Caratin. This halt in the cell cycle also triggers the caspase cascade, which finalizes apoptosis. Caspase 3 is the most critical in the outcome of apoptosis, degrading DNA until it is no longer useful. Other factors involved in cell cycle progression and transcription are CDK 7 and CDK 9. CDK 7 participates in transcriptional initiation, while CDK 9 is involved in transcriptional elongation.
The function of the p53 gene and apoptosis also happen to play a crucial role in many types of cancer, including Acute Myeloid Leukemia. Acute Myeloid Leukemia forms from the accumulation of pre-cursor white blood cells in the bone marrow and blood. (Minzel et al., 2018) Although p53 has not been mutated, its activity is suppressed by the activation of MDM2. Other problematic mechanisms are activated to increase leukemia cell proliferation. These activations can occur when Ck-1a fails to phosphorylate B-Caratin. When this occurs, B-Caratin will not degrade, and continues to accumulate until it translocates into the nucleus and act as a transcription factor.
In this article, Israeli researchers developed small-molecule inhibitors to target specific inhibitors and lead to the killing of AML cells. The two main inhibitors that were targeted were Ck-1a, and CDK 7/9. By targeting Ck-1a alongside CDK 7/9, p53 could be activated and stabilized, depleting support for super-enhancing oncogenes responsible for the proliferation of Leukemia cells. The targeting of Ck-1a is also expected, as kinases are vital in drug treatment due to their role in signal transduction. (Schittek, B., and Sinnberg, T., 2014) By re-activating p53, apoptosis can take place, killing Leukemia cells specifically while avoiding normal, healthy blood cells. In order to test this, researchers developed six different drugs and examined their ability to bind with and inhibit crucial proteins involved in apoptosis and cell cycle regulation. They administered these medications orally to mice afflicted with AML, and tracked how the mice without treatment fared compared to those who did receive treatment. They also examined isolated leukemia cells from the bone marrow of these mice to compare the number of cells present. Of the six medications that were used, A51 was shown to be the most efficient.
In figure 1F, a western blot is used to depict the concentration of specific proteins in the control group and in those treated with the different medications. The darker and larger the bands, the higher the concentration of that protein. If the bands darken and grow larger from right to left, then the medication is dose-dependent. When looking at this chart, A51 is shown to have a loss in phosphorylated serine 45 on B-Catenin when Ck-1a is present. This increases B-Catenin stability, which will ultimately inhibit transcription and decrease proliferation.
In figure 4D, A51 is shown to have the greatest binding capability to CDK 7 and CDK 9. In figure 4E, drugs A51 and A86 are shown to inhibit both CDK 7 and CDK 9, which will then inhibit transcription and decrease proliferation. In figure 2C, A51 increased concentration in the proteins p53, Gamma-H2Ax, and Caspase 3. These proteins are crucial in the process of apoptosis, and would be essential in killing AML cells. This is shown further in figure 2A, where the presence of Annexin V (used to detect apoptosis since it flips to the outside of the cell) is compared between the different medications used. A51 and A86 were shown to have caused the most apoptosis.
A51 also showed great improvement in mice lifespan and survival rate, as well as the histology of treated mice. In figure 3D, the lifespan between the control mice and the treated mice were compared. While all control mice died, half of the treated mice survived. In figure 2D, the abnormal appearance of the enlarged spleen and pale bone marrow in the afflicted mice were drastically different from the mice treated with A51. The bone marrow darkened and appeared healthier, while the spleen decreased in size. In figure 2F, dramatic improvement in the appearance of tissue samples from the bone marrow, spleen, liver, and a blood smear were witnessed sixteen hours post administration of A51.
In conclusion, the results from the experiment supports the goals of the research group. Through the administration of A51, apoptosis was activated by targeting proteins that are vital to the detection of damaged DNA, cell cycle regulation, and transcription inhibition. From analyzing the figures and information within the article, I believe that there is potential for this medication. I can not say that they could cure AML, as there is no way to “cure” any form of cancer. Some mice that were treated with the medication died regardless of receiving treatment or not. Nonetheless, this is a huge step forward for AML treatment, and I believe that human testing could be carried out based on the results from this article.