Image by Difu Wu
Targeting a pair of transcription factors might improve the treatment of chronic myeloid leukemia (CML), according to researchers.
The team found that p53 and c-MYC have “defining roles” in the survival of leukemia stem cells (LSCs) in CML.
And by targeting these transcription factors with a pair of investigational drugs, the researchers were able to kill LSCs.
The team described this work in Nature.
“This collaborative study combined proteomics, transcriptomics, and systems biology to identify a novel, precision medicine-based approach for eradicating leukemic stem cells,” said study author Tony Whetton, PhD, of the University of Manchester in the UK.
Dr Whetton and his colleagues first discovered that p53 and c-MYC are “central hubs” in a CML network of deregulated proteins. The team also found that CML cells express increased c-MYC and decreased p53 levels.
So the researchers theorized that simultaneously activating p53 and inhibiting c-MYC could be a method for treating CML.
To that end, the team tested 2 drugs—RITA (or NSC652287), which binds p53 and blocks its degradation, and CPI-203, a BET inhibitor that hinders transcription by disrupting chromatin-dependent signal transduction.
The researchers found that CPI-203 successfully downregulated c-MYC but also reduced p53, while RITA increased p53.
Treating CML CD34+ cells with RITA or CPI-203 for 72 hours reduced cell viability and induced significant apoptosis, the team said. Combining the drugs enhanced these effects.
The researchers also found evidence to suggest that c-MYC inhibition induces differentiation of CML CD34+ cells. The team said that labelling with the cell-division tracker carboxyfluorescein succinimidyl ester (CFSE) and CD34 antibody showed that, as CML cells divided in the presence of CPI-203, there was a clear and rapid loss of CD34 expression that was not seen in the presence of RITA.
The researchers did not observe any differences in the effects of RITA and CPI-203 when they were tested in CML CD34+ cells pretreated with imatinib.
Furthermore, RITA and CPI-203, either alone or in combination, had no significant effects on normal CD34+ cells when tested at lower concentrations. However, when CPI-203 was used alone at higher concentrations (2 or 5 μ M) or with RITA at the highest concentrations tested (RITA at 25 nM, CPI-203 at 5 μ M), apoptosis did occur.
In CML cells, the researchers observed “significant apoptosis” with all concentrations of CPI-203 and RITA tested.
The team also exposed CML LSCs, defined as either CFSEmax or CD34+CD38− cells, to CPI-203 and RITA as well as a pair of tyrosine kinase inhibitors.
The CFSEmax population persisted despite 5 days of treatment with dasatinib or nilotinib, but the cells were “significantly reduced” after 5 days of treatment with CPI-203 alone and in combination with RITA.
Similarly, 72 hours of treatment with RITA with CPI-203 eliminated residual CD34+CD38− cells.
The researchers also assessed LSC engraftment after treatment with RITA and/or CPI-203, as well as dasatinib. They exposed CML CD34+ cells to the drugs for 48 hours before transplanting the cells into sublethally irradiated NSG mice.
The team said dasatinib had no significant effect on NSG-repopulating CML LSCs. However, RITA, CPI-203, and the drugs in combination reduced engraftment, as indicated by decreased CD45+, CD34+, CD33+, CD11b+, CD19+ and CD14+ cells.
