Various human enzyme structures were examined to select one that might be used to develop a marker used to detect imbalance and therefore possible pathology. The enzyme, aromatase, was selected for further study due to the available documented research, its relevance in identified pathologies, and the similarity between known chemicals that inhibit aromatase and hexestrol.
Introduction
Various human pathologies can be detected through initial screening of bloodwork for reduced or elevated levels of human enzymes created or utilized by an organ system. Development and use of efficient, accurate, and cost-effective markers for these enzymes is valuable to medicine.
Aromatase is part of the cytochrome P450 enzyme group created by the liver. Cytochrome P450 is responsible for many aspects of liver function, and inhibition or promotion of these enzymes must be performed selectively for maximum benefit and minimal side-effect.
Aromatase converts testosterone to estrogen. More specifically, aromatase converts androstendione to estrone, thereby stopping the sequential manufacture of testosterone from this precursor and instead starting the eventual production of 17 β-estradiol. The result of this conversion has implications in estrogen and testosterone sensitive pathologies.
While aromatase is currently detectable, the possibility of finding more efficient, accurate and cost-effective detection is a consideration. Perhaps more importantly, development or discovery of a more selective, safe, effective, and affordable aromatase inhibitor may prove valuable.
Aromatase Inhibitors
Since the structure of aromatase is intricate and its complete mechanism of action still not widely agreed upon, study of that which is known to bind with and inhibit aromatase is currently more revealing and promising. Many chemicals are known to have affinity for aromatase, both steroidal and nonsteroidal.
Steroidal inhibitors include the drugs Formestane, Atamestane, and Exemestane. These usually effect an irreversible inhibition.
The somewhat analogous structure of hexestrol to the steroidal inhibitors is evident in the basic structure.
Nonsteroidal inhibitors are many and include flavones, isoflavones, indoles, sesquiterpene lactones and various compounds showing some inhibitory effect with the list of the most promising including azole derivatives Anastrozole, Fadrozole, Liarozole, Letrozole, and Vorozole, and imides including Aminoglutethimide and Rogletimide.
“Nonsteroidal inhibitors possess a heteroatom such as a nitrogen-containing heterocyclic moiety. This interferes with steroidal hydroxylation by binding with the heme iron of cytochrome P-450. These compounds are reversible inhibitors of aromatase. Most nonsteroidal inhibitors are intrinsically less enzyme specific and will inhibit, to varying degrees, other cytochrome P-450 mediated hydroxylations in steroidogenesis. The challenge in developing these types of inhibitors is to improve selectivity for aromatase so as not to interfere with other P-450 enzymes.” 2
“Because many of the nonsteroidal compounds that have been evaluated as inhibitors of aromatase are not potent inhibitors of the enzyme, it seems likely that the nature of the nonheterocyclic moiety is important. This portion of the molecule may interact with aromatase via hydrogen and/or van der Waals bonding. The degree of compatibility or synergism between binding to the heme-iron and interaction with the protein residue may also be crucial.” 3
Similarities exist with the nonsteroidal inhibitors. Of note is that the 3′,4′-dihydroxy-7-methoxyflavanone molecule has been shown to be more than twice as potent as aminoglutethimide. “Using a series of flavanones prepared by cyclisation of 2’-hydroxychalcones, B ring substituted flavanones with a 7-methoxyflavanone group on A ring were shown in almost all cases to exhibit an inhibitory effect on aromatase with potency dependent on their B ring substitution pattern.” 4 It is possible that the presence of the hydroxyl groups is significant with regard to the inhibitors affinity for aromatase, and further investigation into this hypothesis is suggested. Polyhydroxylated derivatives of 7-hydroxyflavone have higher inhibitory potency.
Conclusion
Aromatase inhibition is suggested treatment for estrogen sensitive cancers and male menopause related symptoms, and clearly may be implicated in any pathology in which estrogen manufacture is involved. Therefore, development of selective aromatase inhibitors with high affinity that are cost-effective and without undesirable side-effects would be valuable to medicine. While drugs and OTC substances are currently available which inhibit aromatase, none exist that have high affinity for aromatase, no side-effects, and are cost effective to produce. Clues do exist which may lead to such a chemical, and the most promising appear to lead in the direction of nonsteroidal inhibitors because of their fewer side-effects and reduced cost to manufacture. The race appears to be in the search for nonsteroidal aromatase inhibitors with higher affinity than those currently known.
References:
S. Graham-Lorence, B. Amarneh, R.E. White, J.A. Peterson, and E.R. Simpson, “A Three-Dimensional Model of Aromatase Cytochrome P-450”, Protein Science, 1995, Vol. 4, Issue 6, pp: 1065-1080.
Brodie, A. and Long, B., “Aromatase Inhibition and Inactivation”, American Cancer Research, December 2001, Vol. 7, pp: 43443s-43449s.
IBID
Pouget, C., Fagnere, C., Basly, J.P., et al, “Synthesis and Aromatase Inhibitory Activity of Flavanones”, Pharmaceutical Research, March 2002, Vol. 19(3), pp: 286-291.
T.K. Vinh, P.J. Nicholls, A. J. Kirby, C. Simons, “Evaluation of 7-Hydroxy-Flavones as Inhibitors of Estrone and Estradiol Biosynthesis”, Journal of Enzyme Inhibition, November 2001, Vol. 16(5), pp: 417-424.
M. Recanatini, A. Cavalli, P. Valenti, “Nonsteroidal Aromatase Inhibitors: Recent Advances”, Medicinal Research Reviews, 2002, Vol. 22(3), pp: 282-304.
S. Graham-Lorence, M. Wahid Khalil, M. C. Lorence, C. R. Mendelson, and E. R. Simpson, “Structure-Function Relationships of Human Aromatase Cytochrome P-450 Using Molecular Modeling and Site-Directed Mutagenesis”, The Journal Of Biological Chemistry, June 25, 1991, Vol. 266, No. 18, pp: 11939-11946.