activity in a KARPAS-422 mouse xenograft model. Compound 18 is currently in
phase I clinical trials for B-cell lymphoma treatment [52]. Tazemetostat (EPZ6438,
19, Fig. 2) was developed by means of a follow-up optimization of the Epizyme
scaffold (EPZ005687, 12). It has greater potency and better PK profile than compound 12, including good oral bioavailability [53]. Compound 19 recently entered
the clinical arena and is currently studied for a number of lymphomas in phase II but
also for solid tumors in phase I [54–56]. Very recently Lu et al. published an
optimization study of tazemetostat leading to compound EBI-2511 (20) demonstrating excellent in vivo efficacy in Pfeiffer tumor xenograft mouse [57]. Honma et al.
recently described (R)-OR-S1 21 and (R)-OR-S2 22 (Fig. 2) as dual inhibitors of
EZH1/2 suppressing trimethylation of histone H3K27 in cells more than EZH2
selective inhibitors. They also showed greater antitumor efficacy than EZH2 selective inhibitor in vitro and in vivo against diffuse large B-cell lymphoma as well as
solid cancers, without exhibiting severe toxicity in rats, thus indicating the possibility of EZH1/2 dual inhibitors for clinical applications [58].
1.4.2 PRC2 Disruptors
Even though EZH2 knockdown studies showed that EZH2 is crucial in many tumor
types, small-molecules EZH2 inhibitors proved to be effective in a smaller range of
cancers. This phenomenon could be explained considering the need to target both the
catalytic and the scaffolding activity of EZH2/PRC2 [59] and/or thinking about
selectively targeting PRC2-dependent functions. Thus, both issues call for an alternative way of targeting the PRC2. In this regard, targeting protein-protein interactions
has been considered an interesting strategy to be applied. The first PRC2 disruptors to
be described have been stabilized α-helix of EZH2 peptides (also called SAH-EZH2).
Kim et al. applied all-hydrocarbon stapling to stabilize α-helical structures of their
peptides, leading to an enhanced target binding affinity, protease resistance, and
membrane penetration. Upon treatment with SAH-EZH2, MLL-AF9 leukemia cells
undergo growth arrest and monocyte-macrophage differentiation [60]. Highthroughput screenings led to the identification of the first small-molecule EZH2EED disruptors: astemizole (23, Fig. 3), an old antihistamine drug [61], and
wedelolactone (24, Fig. 3), a natural compound [62]. Between December 2016 and
March 2017, a series of publications proved the growing interest and the huge effort
done in developing EED-targeting agents as an alternative strategy to inhibit the
PRC2 functions [63–68]. In December 2016, Novartis reported the discovery of five
structurally distinct EED binder hits 25–29 (Fig. 3), identified by a high-throughput
screen [69]. Compounds 25–29 displayed low micromolar activities against PRC2,
with similar values in presence of EZH1 or EZH2, and they were quite selective in
inhibition with respect to other HMTs (IC 50 > 100 μM). The co-crystal structure of
compounds 25–29 in complex with EED has been resolved and studied in detail
[63]. This work was followed by three other publications describing the subsequent
development of some of the newly reported scaffolds. An optimization study of
compound 28, through X-ray crystallography-guided fragmentation and regrowth,
Lysine Methyltransferases and Their Inhibitors
133
phase I clinical trials for B-cell lymphoma treatment [52]. Tazemetostat (EPZ6438,
19, Fig. 2) was developed by means of a follow-up optimization of the Epizyme
scaffold (EPZ005687, 12). It has greater potency and better PK profile than compound 12, including good oral bioavailability [53]. Compound 19 recently entered
the clinical arena and is currently studied for a number of lymphomas in phase II but
also for solid tumors in phase I [54–56]. Very recently Lu et al. published an
optimization study of tazemetostat leading to compound EBI-2511 (20) demonstrating excellent in vivo efficacy in Pfeiffer tumor xenograft mouse [57]. Honma et al.
recently described (R)-OR-S1 21 and (R)-OR-S2 22 (Fig. 2) as dual inhibitors of
EZH1/2 suppressing trimethylation of histone H3K27 in cells more than EZH2
selective inhibitors. They also showed greater antitumor efficacy than EZH2 selective inhibitor in vitro and in vivo against diffuse large B-cell lymphoma as well as
solid cancers, without exhibiting severe toxicity in rats, thus indicating the possibility of EZH1/2 dual inhibitors for clinical applications [58].
1.4.2 PRC2 Disruptors
Even though EZH2 knockdown studies showed that EZH2 is crucial in many tumor
types, small-molecules EZH2 inhibitors proved to be effective in a smaller range of
cancers. This phenomenon could be explained considering the need to target both the
catalytic and the scaffolding activity of EZH2/PRC2 [59] and/or thinking about
selectively targeting PRC2-dependent functions. Thus, both issues call for an alternative way of targeting the PRC2. In this regard, targeting protein-protein interactions
has been considered an interesting strategy to be applied. The first PRC2 disruptors to
be described have been stabilized α-helix of EZH2 peptides (also called SAH-EZH2).
Kim et al. applied all-hydrocarbon stapling to stabilize α-helical structures of their
peptides, leading to an enhanced target binding affinity, protease resistance, and
membrane penetration. Upon treatment with SAH-EZH2, MLL-AF9 leukemia cells
undergo growth arrest and monocyte-macrophage differentiation [60]. Highthroughput screenings led to the identification of the first small-molecule EZH2EED disruptors: astemizole (23, Fig. 3), an old antihistamine drug [61], and
wedelolactone (24, Fig. 3), a natural compound [62]. Between December 2016 and
March 2017, a series of publications proved the growing interest and the huge effort
done in developing EED-targeting agents as an alternative strategy to inhibit the
PRC2 functions [63–68]. In December 2016, Novartis reported the discovery of five
structurally distinct EED binder hits 25–29 (Fig. 3), identified by a high-throughput
screen [69]. Compounds 25–29 displayed low micromolar activities against PRC2,
with similar values in presence of EZH1 or EZH2, and they were quite selective in
inhibition with respect to other HMTs (IC 50 > 100 μM). The co-crystal structure of
compounds 25–29 in complex with EED has been resolved and studied in detail
[63]. This work was followed by three other publications describing the subsequent
development of some of the newly reported scaffolds. An optimization study of
compound 28, through X-ray crystallography-guided fragmentation and regrowth,
Lysine Methyltransferases and Their Inhibitors
133