Chronic Heart Failure is characterised by perivascular and interstitial collagen fiber deposition caused by elevated levels of the steroid aldosterone. To negate this remodelling of the heart tissue we have postulated the inhibition of aldosterone

1
Selectivity of Aldosterone Synthase Inhibitors
Luc Roumen BMI, BioModeling
Eveline Ruijters Farmacologie

• Introduction
• Chronic Heart Failure is characterised by
  perivascular and interstitial collagen fiber
  deposition caused by elevated levels of the
  steroid aldosterone. To negate this remodelling
  of the heart tissue we have postulated the
  inhibition of aldosterone synthesis as a
  potential means for treating Chronic Heart
  Failure patients.
• Inhibitor Selectivity
• One of the most important aspects of inhibitor
  design is the target selectivity of the drug. The
  challenge of our research is to design inhibitor
  selectivity between the target enzyme,
  aldosterone synthase (Cyp11B2), and its close
  family member 11?-hydroxylase (Cyp11B1). We
  intend to inhibit only Cyp11B2, keeping the
  activity of Cyp11B1 and hence formation of
  aldosterone precursors intact (scheme 1).

Currently, the models have been used to screen
compound libraries for potential Cyp11B2
inhibitors and predict binding affinity through
ligand docking with the program GOLD
1. Results We have identified several
potential inhibitors from in silico screening and
have compared the most promising lead to the in
vitro selectivity of three known inhibitors
metyrapone, ketoconazole and aminoglutethimide
(table 1, 2a and 2b). A high docking score can be
related to a low IC50, meaning good inhibition.
The GOLD docking score is related to binding data
in V79 cells. Conclusions
For the enantiomers of our lead, the in silico
and in vitro results coincide, with the exception
of the results of the S-enantiomer in Cyp11B1.
Here the docking value is too high meaning the
homology model should be optimised. The
general selectivity trend of metyrapone and
aminoglutethimide in H295R cells is also found by
the docking, although the values may not be
compared. Ketoconazole is too big for the static
models but is expected to bind by induced fit.
The stereoselectivity for Cyp11B2 of the
R-enantiomer of our lead will be further
investigated by derivatisation of the
structure. References 1 Jones, G., Willett,
P., Glen R.C., J. Mol. Biol., 245, 43-53, 1995
Table 1 In silico GOLD docking results Table 1 In silico GOLD docking results Table 1 In silico GOLD docking results
Cyp11B2 Score Cyp11B1 Score
R-enantiomer 54.04 48.15
S-enantiomer 50.87 58.32
Metyrapone 53.34 51.75
Ketoconazole none none
Aminoglutethimide 39.84 44.65
Table 2a In vitro binding assay in H295R cells Table 2a In vitro binding assay in H295R cells Table 2a In vitro binding assay in H295R cells Table 2a In vitro binding assay in H295R cells Table 2a In vitro binding assay in H295R cells
IC50 (nM) Aldosterone Cyp11B2 Cortisol Cyp11B1 Estradiol Cyp19 11-deoxycortisol Cyp21
R-enantiomer 18 33 600 gtgt10000
S-enantiomer 213 259 65 gtgt10000
Metyrapone 290 890 - gtgt90000
Ketoconazole 2850 4150 - 4300
Aminoglutethimide 5300 10000 - 28000
Table 2b In vitro binding assay in V79 cells Table 2b In vitro binding assay in V79 cells Table 2b In vitro binding assay in V79 cells Table 2b In vitro binding assay in V79 cells Table 2b In vitro binding assay in V79 cells
IC50 (nM) Corticosterone Cyp11B2 Corticosterone Cyp11B2 Corticosterone Cyp11B1 Corticosterone Cyp11B1
R-enantiomer 1 1 gt2000 gt2000
S-enantiomer 110 110 23 23
Scheme 1 Aldosterone synthesis catalysed by
CYP11B1 and CYP11B2. The formation of aldosterone
is limited to enzyme CYP11B2