15 nM, respectively) in proliferation arrest of MV4–11 cells. Overall, 40–43 are all
exciting new non-nucleoside-based potent and selective DOT1L inhibitors, being
useful tools for cellular and in vivo studies with high potential to achieve a clinical
trial setting.
1.6 The H3K4 Histone Methyltransferases SET1/MLL
Family: MLL1–4 and SETD1A and 1B
The human SET1 family includes MLL1 (KMT2A), MLL2 (KMT2D), MLL3
(KMT2C), MLL4 (KMT2B), SET1A (KMT2F), and SET1B (KMT2G). MLL1
(also known as KMT2A or TRX1) is a multidomain histone methyltransferase
specific for mono-, di-, and trimethylation of H3K4 [92]. MLL1 undergoes several
types of chromosomal rearrangements, and all of them have been associated with
different leukemias [92]. A number of nonsense, frameshift, or coding mutations in
the MLL protein family have been identified, but their physiological role is not yet
fully understood [92]. The crystal structure of MLL1 SET domain, together with
biochemical data, showed that MLL1 itself displays a poor methyltransferase activity [93]. Indeed, an optimal catalytic activity is achieved within the MLL complex
including at least three evolutionary conserved subunits: WDR5 (WD repeatcontaining protein 5), RBBP5 (retinoblastoma-binding protein 5), and ASH2L
(ASH2 like histone lysine methyltransferase complex subunit) [93]. Selective
MLL inhibitors have not been described so far; however, considering the relevance
of MLL interactions with its partners [94, 95], a number of PPI disruptors have been
identified. These compounds can be divided in two classes: on the one hand the
WDR5 inhibitors and on the other the menin-MLL PPI disruptors.
1.6.1 WDR5 Inhibitors
In 2013, Karatas et al. reported novel peptidomimetic antagonists of WDR5-MLL
interaction, among them MM-102 (44, IC 50 : 400 nM, Fig. 5) was the most potent
and effective in cells, and it became a starting point for the development of cyclic
peptidomimetic derivatives. First, in 2014, Cao et al. reported compound MM-401
(45, Fig. 5). Despite the cyclization, compound 45 proved to be a tight binder (K D :
0.9 nM) and potent (IC 50 : 320 nM) and selective inhibitor [96]. Interestingly, in
MLL-AF9 cells, compound 45 (at 20 μM) specifically reduced H3K4me2 and
H3K4me3 across 5
0 HoxA loci, after 48 h of treatment, while selectively inducing
cell-cycle arrest, apoptosis, and differentiation in murine leukemia cells MLL1AF9, MLL1-ENL, and MLL1-AF1. Moreover, it efficiently inhibited cell growth
in human blasts derived from AML patients with MLL1 rearrangements [96]. In
2017, in a follow-up study on the same scaffold, the authors determined the optimal
linker length and discovered a number of promising analogues, being MM-589 (46,
138
G. Stazi et al.
exciting new non-nucleoside-based potent and selective DOT1L inhibitors, being
useful tools for cellular and in vivo studies with high potential to achieve a clinical
trial setting.
1.6 The H3K4 Histone Methyltransferases SET1/MLL
Family: MLL1–4 and SETD1A and 1B
The human SET1 family includes MLL1 (KMT2A), MLL2 (KMT2D), MLL3
(KMT2C), MLL4 (KMT2B), SET1A (KMT2F), and SET1B (KMT2G). MLL1
(also known as KMT2A or TRX1) is a multidomain histone methyltransferase
specific for mono-, di-, and trimethylation of H3K4 [92]. MLL1 undergoes several
types of chromosomal rearrangements, and all of them have been associated with
different leukemias [92]. A number of nonsense, frameshift, or coding mutations in
the MLL protein family have been identified, but their physiological role is not yet
fully understood [92]. The crystal structure of MLL1 SET domain, together with
biochemical data, showed that MLL1 itself displays a poor methyltransferase activity [93]. Indeed, an optimal catalytic activity is achieved within the MLL complex
including at least three evolutionary conserved subunits: WDR5 (WD repeatcontaining protein 5), RBBP5 (retinoblastoma-binding protein 5), and ASH2L
(ASH2 like histone lysine methyltransferase complex subunit) [93]. Selective
MLL inhibitors have not been described so far; however, considering the relevance
of MLL interactions with its partners [94, 95], a number of PPI disruptors have been
identified. These compounds can be divided in two classes: on the one hand the
WDR5 inhibitors and on the other the menin-MLL PPI disruptors.
1.6.1 WDR5 Inhibitors
In 2013, Karatas et al. reported novel peptidomimetic antagonists of WDR5-MLL
interaction, among them MM-102 (44, IC 50 : 400 nM, Fig. 5) was the most potent
and effective in cells, and it became a starting point for the development of cyclic
peptidomimetic derivatives. First, in 2014, Cao et al. reported compound MM-401
(45, Fig. 5). Despite the cyclization, compound 45 proved to be a tight binder (K D :
0.9 nM) and potent (IC 50 : 320 nM) and selective inhibitor [96]. Interestingly, in
MLL-AF9 cells, compound 45 (at 20 μM) specifically reduced H3K4me2 and
H3K4me3 across 5
0 HoxA loci, after 48 h of treatment, while selectively inducing
cell-cycle arrest, apoptosis, and differentiation in murine leukemia cells MLL1AF9, MLL1-ENL, and MLL1-AF1. Moreover, it efficiently inhibited cell growth
in human blasts derived from AML patients with MLL1 rearrangements [96]. In
2017, in a follow-up study on the same scaffold, the authors determined the optimal
linker length and discovered a number of promising analogues, being MM-589 (46,
138
G. Stazi et al.