Dual aromatase–sulfatase inhibitors based on the anastrozole template: synthesis, in vitro SAR, molecular modelling and in vivo activity

Abstract

The synthesis and biological evaluation of a series of novel Dual Aromatase-Sulfatase Inhibitors (DASIs) are described. It is postulated that dual inhibition of the aromatase and steroid sulfatase enzymes, both responsible for the biosynthesis of oestrogens, will be beneficial in the treatment of hormone-dependent breast cancer. The compounds are based upon the Anastrozole aromatase inhibitor template which, while maintaining the haem ligating triazole moiety crucial for enzyme inhibition, was modified to include a phenol sulfamate ester motif, the pharmacophore for potent irreversible steroid sulfatase inhibition. Adaption of a synthetic route to Anastrozole was accomplished via selective radical bromination and substitution reactions to furnish a series of inhibitory aromatase pharmacophores. Linking these fragments to the phenol sulfamate ester moiety employed S(N)2, Heck and Mitsunobu reactions with phenolic precursors, from where the completed DASIs were achieved via sulfamoylation. In vitro, the lead compound, 11, had a high degree of potency against aromatase (IC(50) 3.5 nM), comparable with that of Anastrozole (IC(50) 1.5 nM) whereas, only moderate activity against steroid sulfatase was found. However, in vivo, 11 surprisingly exhibited potent dual inhibition. Compound 11 was modelled into the active site of a homology model of human aromatase and the X-ray crystal structure of steroid sulfatase.

Hybrid Dual Aromatase-Steroid Sulfatase Inhibitors with Exquisite Picomolar Inhibitory Activity

“…One obvious route to take would be to repeat the two aforementioned strategies for designing a DASI and apply them to other reported aromatase and STS inhibitors. However, repetitive application of the same strategies lacks some novelty and so pursuing a new design approach seemed more desirable and challenging .On reviewing computational docking studies of leading DASIs and other related molecules performed with a homology model of aromatase, 19,23,25 we noticed that the molecules docked in different orientations with unoccupied space available within the enzyme site. This observation suggested that further interactions with available amino acid residues might be exploited in principle if additional functionality could be built into the docked molecule in a complementary manner.…”

“…On reviewing computational docking studies of leading DASIs and other related molecules performed with a homology model of aromatase, 19,23,25 we noticed that the molecules docked in different orientations with unoccupied space available within the enzyme site. This observation suggested that further interactions with available amino acid residues might be exploited in principle if additional functionality could be built into the docked molecule in a complementary manner.…”

“…This has been a characteristic observed in our previous work. [18][19][20]21,23,24,28,29 The most potent inhibitor against STS in the series is the brominated 15, whose IC 50 value is 0.13 nM, which is two orders and one order of magnitude more potent than the 4-((4-bromobenzyl)-[1,2,4]-triazol-4-ylamino)benzonitrile-based DASI 3 (IC 50 : 39 nM) and the biphenyl-based DASI 9 (IC 50 : 5.5 nM), respectively. This further demonstrates the productive contribution of the additional phenyl ring to inhibitory activity and the advantage of hybrid structure.…”

“…[7][8][9][10][11][12][13][14][15][16][17] We have pioneered this approach to augment our strategy directed at the first-in-class clinical target of STS inhibition and successfully developed three series of single agent dual aromatase and sulfatase inhibitors (DASIs) that are sulfamate derivatives of the nonsteroidal aromatase inhibitor (AI) 4-((4-bromobenzyl)-[1,2,4]-triazol-4-ylamino)benzonitrile (1) (e.g., 2 and 3), 18-20 letrozole 4 (e.g., 5), 21,22 and anastrozole 6 (e.g., 7) (Figure 1). 23 The design of these DASIs shares a common principle of engendering the irreversible STS inhibitory pharmacophore (ie. an aryl sulfamate ester, ArOSO 2 NH 2 ) into a clinical or experimental AI with minimal structural change incurred on the original scaffold in order to retain and maximize aromatase inhibition.…”

“…23 The design of these DASIs shares a common principle of engendering the irreversible STS inhibitory pharmacophore (ie. an aryl sulfamate ester, ArOSO 2 NH 2 ) into a clinical or experimental AI with minimal structural change incurred on the original scaffold in order to retain and maximize aromatase inhibition.…”