The development of polypharmacology therapies, able to modulate simultaneously multiple targets involved in the onset of a disease, is considered an attractive approach to treat multifactorial disorders such as cancer. Recent studies revealed an interesting in vitro synergism of the combination of HDACi and EZH2i in cancer. Based on these evidences, we would like to design and synthesize novel dual HDAC/EZH2 inhibitors. Classes I and II HDACs are Zn2+-dependent histone deacetylases, while EZH2, the catalytic subunit of PRC2 complex, is a SAM-dependent histone methyltransferase. For the development of the aforementioned dual inhibitors we will combine the HDACi moieties of approved drugs to the scaffold of MC3707, an EZH2i optimized by us. Our previous results suggested that the phenyl ring bound to the N1-pyrrole of MC 3707 could accept substituents on the meta position. Thus, we will insert the HDAC targeting element in that position. According to the HDACi pharmacophoric model, we have chosen different type of spacer: the aliphatic one (Vorinostat), the benzoic one (Entinostat) and the cinnamic one (Panobinostat and Belinostat). As zinc binding group we will use in turn a hydroxamic acid or an ortho-amino anilide.
EZH2 and HDACs are pivotal enzymes in epigenetic machinery and their over-expression and gain of function are implicated in the initiation and progression of cancer. While the HDACs remove the acetyl group from the ¿-amino group of the lysine of histone and non-histone proteins, EZH2 is the catalytic unit of PRC2 complex that catalyses the addition of three-methyl mark on H3K27. Both events, the histones deacetylation and H3K27 three-methylation, promote a transcriptional silencing. Therefore, the simultaneous inhibition of both enzymes producing the reactivation of numerous genes including ¿tumour suppressor genes¿ could realize some interesting antitumor effects.
In the last few years, various researchers have studied the effects of EZH2i and HDACi combination in diverse cancer cell lines. Natalie Grinshtein et al, for example, have showed that the combination of UNC1999 (a novel SAM-competitive EZH2 inhibitor) and a brain-penetrant class I HDAC inhibitor realized synergy in vitro by augmenting apoptosis and increasing DNA damage in glioblastoma (GBM) brain-tumour initiating cell lines (BTIC).8 According to this study, EZH2 and HDACs are key epigenetic modulators in GBM that regulate BTIC growth and survival.
Additionally, in 2018 Taylor Harding et al. published a study showing that EZH2 inhibitors sensitize myeloma cell line to panobinostat, pan-HDAC inhibitor. In particular, the authors tested the efficacy of EZH2 specific inhibitors in a large panel of human Multiple Myeloma (MM) cell lines (HMCLs) and found that only a subset of HMCLs demonstrate single agent sensitivity despite ubiquitous global H3K27 demethylation. Instead, pre-treatment with EZH2 inhibitors greatly enhanced the sensitivity of HMCLs to panobinostat in nearly all cases regardless of single agent EZH2 inhibitor sensitivity. Combination treatment greatly increased the scale of gene expression change with a large portion of differentially expressed genes being unique to the combination. Transcriptomic analysis demonstrated that combination treatment further perturbed oncogenic pathways and signaling nodes consistent with an antiproliferative/pro-apoptotic state. 9 Therefore, the combination of HDACi and EZH2i is a promising therapeutic strategy to target the epigenetic landscape of aggressive MM.
In the same way, in April 2019 another study supporting the combination of EZH2i and HDACi in EZH2 dysregulated lymphomas has been published. In this case, the authors showed that the simultaneous inhibition of EZH2 and HDAC is synergistic and lead to the dissociation of PRC2 complex.10
Even if many scientific publications reveals a synergistic activity between EZH2 and HDAC inhibitors, until now, dual inhibitors of EZH2 and HDACs have not been described in literature. Therefore, based on the dual inhibitors advantages, the research that we would like to promote point to discover for the first time dual inhibitors of two relevant targets in cancer. Such novel dual inhibitors will be useful both as tools to study the implication of HDACs and EZH2 in cancers, and as starting point for the development of new therapeutic tools. Additionally, obtaining an HDAC isoform selectivity, we will be able to design specific tools to study certain disorders, and will allow better defining the contribution of certain HDACs isoforms in a specific type of cancer. Additionally, the isoform selectivity will help to reduce off-target and undesired side effects.
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