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Combined LSD1 and ATRA in AML
inhibition were determined for each cell line. GSK2879552 inhibited cell growth with a potent average EC50 value of 137±30 nM across 20 cell lines. The average maximum inhibition was 62±5% suggesting complete cytostasis is not achieved by ten days with LSD1 inhibition alone. By comparing 6-day to 10-day proliferation assay results (Online Supplementary Figure S1A and B), it is evident that an increase in maximum inhibition can be achieved with
longer treatment, indicating that the biological conse- quences of LSD1 inhibition, including growth effects, may require time to be fully revealed. Several studies were con- ducted to determine if the lag in inhibition of cancer cell line growth is due to a delayed effect on all cells or involves some cell death. Cell cycle evaluation of MOLM- 13 cells treated with a titration of GSK-LSD1 for six days revealed an increase in cells in G1 phase with a concomi-
AB
C
D
Figure 4. The addition of all-trans retinoic acid (ATRA) enhances GSK2879552 induced differentiation effects on acute myeloid leukemia (AML) cells. (A) Representative histograms of CD11b surface marker expression on MOLM-13 cells (left) and OCI-AML3 cells (right) treated with dimethyl sulfoxide (DMSO) (green), 1000 nM GSK2879552 (orange), 100 nM ATRA (blue), or 1000 nM GSK2879552 plus 100 nM ATRA (red) for two days. (B) Dose response curves of CD11b surface marker expression on MOLM-13 cells (left) and OCI-AML3 cells (right) treated with a titration of GSK2879552 + 0, 0.1, 1, 10, 100, or 1000 nM ATRA for two days. (C) Percent CD11b+ expression (blue bars, ±Standard Error) on MOLM-13 cells (top) and OCI-AML3 cells (bottom) treated with the indicated concentrations of GSK2879552 and ATRA for two days. The value representing the predicted additive effect at each combination concentration is indicated with a red circle. (D) Shading represents percent CD11b+ expression relative to additive threshold on AML cells treated with the indicated concentrations of GSK2879552 and ATRA for two days. Dark green shading indicates >10% above additive threshold, light green indicates >5-10% above additive threshold, and light brown indicates 0-5% above additive threshold.
haematologica | 2019; 104(6)
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