Abstract A026: Overactivation of histone deacetylases and EZH2 in Wilms tumorigenesis
Authors: Liu Hongbing 
Published: August 2023

Abstract
Wilms tumor (WT) is the most common childhood kidney cancer. Altered epigenetics is central to oncogenesis in many pediatric cancers. The critical contribution of epigenetic dysregulation to pediatric tumors provides a compelling rationale for the therapeutic potential of epigenetic drugs. Histone deacetylases (HDACs, especially HDAC1/2) and Enhancer of Zeste Homolog 2 (EZH2), a histone H3K27 methyltransferase, have been demonstrated to play a critical role in self-renewal and differentiation of mouse nephron progenitor cells (NPCs). WT was considered as the arrest of NPC differentiation at a pre-epithelialized cell state. Altered expression and mutations of HDACs and EZH2 have been linked to many human cancers, including WT. Thus, they are among the most promising therapeutic targets for cancer treatment. The treatment of Panobinostat, an FDA-approved pan-HDAC inhibitor, leaded to apoptosis and growth suppression of WT cells. EZH2 is highly expressed in WT and has been demonstrated to be associated with WT progression. We reasoned that WT results from unrestrained proliferation of progenitor cells due to overactive HDAC1, HDAC2, and EZH2. To prove it, we collected 5 human WT specimens. Immunostaining demonstrated dramatically higher level of HDAC1, HDAC2, SIX1, and SIX2 in the tumor tissues compared with adjacent normal tissues, strongly suggesting a critical role for the overactive HDAC1/2 in the SIX1/2 activation to promote cell proliferation in WT. SIX1 and SIX2 are associated with the high-risk blastemal subtype and with the presence of undifferentiated blastema in WT. In addition, knockdown of HDAC1/2 by siRNAs or CRISPR gene editing resulted in downregulation of SIX1/2 in human embryonic kidney 293 cells. Our study in mouse model also revealed that deletion of Hdac1/2 resulted in deletion of progenitor pool and downregulation of key progenitor genes. We also demonstrated that Ezh2 is the dominant H3K27 methyltransferase in Six2+ NPCs and required for NPC proliferation. Based on these findings, we reason that SIX1/2 upregulation by HDAC1/2 and EZH2 overactivation may play an important role in Wilms tumorigenesis. Concomitant inhibition of HDACs and EZH2 has proven to be highly synergistic and very potent for the treatment of many types of human cancers. Promisingly, combined treatment benzamide-based HDAC1/2-selective inhibitor Merck60 and Tazemetostat (an FDA-approved EZH2 inhibitor) synergistically suppressed cell growth in a wide range of dose combinations in G401 kidney cancer cells. In summary, our studies demonstrated the overactivation of HDAC1/2 in WT, positive regulation of SIX1/SIX2 by HDAC1/2 during tumorigenesis, and synergic effect of HDAC1/2 and EZH2 inhibition in suppressing tumor cell proliferation. Thus, targeting HDAC1/2 and EZH2 may provide a promising therapeutic approach to treat WT and other pediatric kidney cancer with low toxicity and low side effects. Furthermore, availability of epigenetic drugs will facilitate the translation of this research into effective therapies.
Citation Format: Hongbing Liu. Overactivation of histone deacetylases and EZH2 in Wilms tumorigenesis [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr A026.