Computational Approaches Elucidate the Allosteric Mechanism of Human Aromatase Inhibition: A Novel Possible Route to Small-Molecule Regulation of CYP450s Activities?

Abstract

Human aromatase (HA) is a P450 cytochrome (CYP) with an essential role in estrogen biosynthesis. Since more than 70% of breast cancers are positive for estrogenic receptor (ER), the reduction of estrogen physiological concentrations through HA inhibition is one of most important therapeutic strategies against this cancer type. Recently, experimental evidence showed that selected taxmoxifen metabolites, which are typically used as estrogen receptor modulators (SERMs), inhibit HA through an allosteric mechanism. In this work, we present a computational protocol to (i) characterize the structural framework and (ii) define the atomistic details of the determinants for the noncompetitive inhibition mechanism. Our calculations identify two putative binding sites able to efficiently bind all tamoxifen metabolites. Analysis of long-scale molecular dynamics simulations reveal that endoxifen, the most effective noncompetitive inhibitor, induces significant enzyme rigidity by binding in one of the possible peripheral sites. The consequence of this binding event is the suppression of one of the functional enzymatic collective motions associated with breathing of the substrate access channel. Moreover, an internal dynamics-based alignment of HA with six other human cytochromes shows that this collective motion is common to other members of the CYP450 protein family. On this basis, our findings may thus be of help for the development of new (pan)inhibitors for the therapeutic treatment of cancer, targeting and modulating the activity of HA and of estrogen receptor, and may also stimulate the development of new drug design strategies for chemoprevention and chemoprotection via allosteric inhibition of CYP450 proteins.

A Dehydrogenase Dual Hydrogen Abstraction Mechanism Promotes Estrogen Biosynthesis: Can We Expand the Functional Annotation of the Aromatase Enzyme?

“…An equilibrated HA model was taken from our previous work, and, by using the CHARMMGUI webserver, it was embedded in a 1‐palmitoyl‐2‐oleoyl‐ sn ‐glycero‐3‐phosphocholine (POPC) membrane containing 6 wt % cholesterol, as reported for the composition of the endoplasmic reticulum membrane . Physiological protonation states were calculated with the webserver H ++ .…”

Theoretical Study of the Mechanism of Exemestane Hydroxylation Catalyzed by Human Aromatase Enzyme

“…41,48 In recent times, the aromatase inhibition has been studied by means of different computational techniques, where several AIs have been tested. 10,43,51,[53][54][55][56][57] In this paper, we have focused in particular on the EXE compound (6-methylene-androsta-1,4-diene-3,17-dione) because of the resemblance it has with the natural substrate ASD (androst-4-ene-3,17-dione). EXE shares the steroidal backbone with ASD, however, the main differences that exist between them are: i) a C 6 -substitued methylidene group located at the B-ring of EXE, and ii) a double bond between C 1 and C 2 carbons which is present at the A-ring of the EXE but not in the ASD (see Scheme 3 for comparison).…”

Dynamics Insights Into the Gain of Flexibility by Helix-12 in ESR1 as a Mechanism of Resistance to Drugs in Breast Cancer Cell Lines

“…It has been reported that 70% of BC cases diagnosed after menopause are Estrogen Receptor (ER) positive (ER+). The human aromatase (HA) enzyme produces estrogens (17-β-estradiol or estrone) (Magistrato et al, 2017) mainly after menopause, and its inactivity increases the level of estrogens in malignant tissues (Liang and Shang, 2013;Sgrignani et al, 2014Sgrignani et al, , 2015Sgrignani et al, , 2016Magistrato et al, 2017). These hormones have a pro-oncogenic effect by either stimulating cell proliferation or decreasing apoptosis when binding to ERα as an agonist (Liang and Shang, 2013).…”