Switching from Aromatase Inhibitors to Dual Targeting Flavonoid-Based Compounds for Breast Cancer Treatment

Abstract

Despite the significant outcomes attained by scientific research, breast cancer (BC) still represents the second leading cause of death in women. Estrogen receptor-positive (ER+) BC accounts for the majority of diagnosed BCs, highlighting the disruption of estrogenic signalling as target for first-line treatment. This goal is presently pursued by inhibiting aromatase (AR) enzyme or by modulating Estrogen Receptor (ER) α. An appealing strategy for fighting BC and reducing side effects and resistance issues may lie in the design of multifunctional compounds able to simultaneously target AR and ER. In this paper, previously reported flavonoid-related potent AR inhibitors were suitably modified with the aim of also targeting ERα. As a result, homoisoflavone derivatives 3b and 4a emerged as well-balanced submicromolar dual acting compounds. An extensive computational study was then performed to gain insights into the interactions the best compounds established with the two targets. This study highlighted the feasibility of switching from single-target compounds to balanced dual-acting agents, confirming that a multi-target approach may represent a valid therapeutic option to counteract ER+ BC. The homoisoflavone core emerged as a valuable natural-inspired scaffold for the design of multifunctional compounds.

Keywords: ERα ligands; aromatase inhibitors; homoisoflavones; molecular dynamics; multitarget.

Figure 1

Design of the studied flavones and homoisoflavones.

Scheme 1

Reagent and conditions: (i) 48% HBr, reflux, 10 h.

Scheme 2

Reagent and conditions: (i) MOMCl, 60% NaH, THF, 0 °C 1 h, then rt overnight. (ii) benzaldehyde or p-nitrobenzaldehyde, pyridine, 150 °C, 3 h. (iii) a. NBS, benzoyl peroxide, CCl₄, reflux, 5 h. b. imidazole, CH₃CN, N₂, reflux, 6 h. (iv) AcOH, H₂SO₄, reflux, 1 h.

Figure 2

Structure determination of compounds 3b and 4b.

Figure 3

Representative structures as obtained from QM/MM molecular dynamics trajectories of the coordination complex between (a) R-3b, (b) S-3b, (c) R-4a, and (d) S-4a and AR active site. AR structure is displayed in silver new cartons, the heme moiety, Cys437, and the inhibitors are shown in licorice; the residues mostly contributing to the binding are shown in balls and sticks. Labels of residues forming hydrophobic and hydrogen bonding interactions are circled in green and blue, respectively.

Figure 4

Binding poses of (a) R-3b, (b) S-3b, (c) R-4a, and (d) S-4a to the ERα ligand binding cavity as obtained from a representative cluster of 500 ns classical MD trajectory. ERα is shown as white new cartoons. The residues forming aromatic interactions are depicted in green new cartoons and those forming electrostatic interactions are displayed as blue new cartoons. The relative labels are circled in green and blue, respectively.