Page 187 - Haematologica April 2020

EZH2 inhibition synergies with CDK9 inhibition
tive response rate of 17 % further provides a strong ration- ale for the inhibition of H3K27me3 to be a useful thera- peutic strategy in DLBCL. Therefore, we used EZH2i for investigating their synergistic effect with CDK9i. As expected, EPZ6438/GSK126 reversed the elevated H3K27me3 triggered by CDK9i and reactivated the tran- scription of target genes, which was suppressed by H3K27me3. Also, apoptosis induced by the co-treatment was remarkable without reaching the dosages that induce obvious apoptosis by CDKI-73 or EZH2i alone, indicating
strong efficacy with less toxicity at the same time. In addi- tion, combination therapy also improved DNA damage compared to the single treatments alone and synergistical- ly restrained DLBCL growth. More importantly, other CDK9 inhibitors in combination with EZH2i also resulted in a strong synergistic effect in all cases. By expanding our studies with this combination therapy to other solid tumors, in which EZH2i alone do not show any effect, we also demonstrated an impressive synergistic effect. Both preclinical and clinical evidences suggest that only very
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CD
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Figure 5. The combined effect of CDKI-73 and EPZ6438/GSK126 on apoptosis and DNA damage. (A-B) Quantitative assessment of apoptosis and the expression of apoptosis-related proteins in Pfeiffer and Karpas-422 cells pretreated with EPZ6438/GSK126 alone for 48 hours (h) and then together with CDKI-73 for another 24 h. (C) The level of apoptosis-related proteins detected in Pfeiffer xenografts at the end of the in vivo experiment. (D) γ-H2AX detection in Pfeiffer and SU-DHL-4 cells pretreated as mentioned in Figure 4A. (E) Comet assay. Cells were pretreated with EPZ6438/GSK126 alone for 24 h and then in combination with CDKI-73 for additional 24 h (scale bar, 25 μm). C: CDKI-73; E: EPZ6438; G: GSK126. All data are representative of at least three independent experiments. ***P<0.001, **P<0.01, *P<0.05.
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