Effects of Palbociclib on leukemia cells
Leukemia is a cancer of white blood cells and is classified according to maturation stage and cell lineage. Acute Lymphoblastic Leukemia (ALL) is the most common type of leukemia in children and Acute Myeloid Leukemia (AML) is the second most common. The survival rate for children with ALL is about 80-90% and 70% in children with AML. Mortality in pediatric patients with leukemia is due to relapse of disease and toxicity from chemotherapy agents. Improved treatment is needed to help prevent these deaths. A drug sensitivity and resistance assay was previously performed on 9 ALL and 16 AML cell lines against 56 different compounds. This functional screen determined that four cell lines: HL-60, NB-4, Nalm-6, and Kasumi-1 were sensitive to the Cyclin-Dependent Kinase-6 and 4 (CDK) inhibiting drug Palbociclib. Palbociclib has been approved for use for treatment of a subset of breast cancer and is generally safer when compared to current therapies being used to treat leukemia.
In order to assess the efficacy of Palbociclib on leukemia cells, several cell-based assays were used. Drug Dose Response (DDR) assays were performed to validate the results from the functional screen and identify the most effective dose of Palbociclib. Results demonstrated that Palbociclib had a cytotoxic effect on the four cell lines tested with EC50 values ranging from 416 - 2561 nM, The AML cell line HL-60 was the most sensitive to Palbociclib with an average EC50 value of 416 nM. Western blot analysis was utilized to evaluate the expression of CDK-6 and indicated that the Nalm-6 and Kasumi-1 cell lines expressed the highest amount of CDK-6 compared to the other leukemia lines and control cells. A cell cycle assay was performed on the NB-4 and Kasumi-1 cell lines treated with Palbociclib to determine its impact on the cell cycle.
The results showed cell cycle arrest in the G1 growth phase in both the cell lines consistent with the mechanism of action of Palbociclib suggesting that Palbociclib may be effective as an alternate form of therapy to help treat individuals with leukemia.