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Novel Histone Deacetylase Class IIa Selective Substrate Radiotracers for PET Imaging of Epigenetic Regulation in the Brain.

Bonomi R, Mukhopadhyay U, Shavrin A, Yeh HH, Majhi A, Dewage SW, Najjar A, Lu X, Cisneros GA, Tong WP, Alauddin MM, Liu RS, Mangner TJ, Turkman N, Gelovani JG - PLoS ONE (2015)

Bottom Line: Histone deacetylases (HDAC's) became increasingly important targets for therapy of various diseases, resulting in a pressing need to develop HDAC class- and isoform-selective inhibitors.PET imaging with [18F]TFAHA can be used to visualize and quantify spatial distribution and magnitude of HDAC class IIa expression-activity in different organs and tissues in vivo.Furthermore, PET imaging with [18F]TFAHA may advance the understanding of HDACs class IIa mediated epigenetic regulation of normal and pathophysiological processes, and facilitate the development of novel HDAC class IIa-specific inhibitors for therapy of different diseases.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Wayne State University, Detroit, MI 48202, United States of America.

ABSTRACT
Histone deacetylases (HDAC's) became increasingly important targets for therapy of various diseases, resulting in a pressing need to develop HDAC class- and isoform-selective inhibitors. Class IIa deacetylases possess only minimal deacetylase activity against acetylated histones, but have several other client proteins as substrates through which they participate in epigenetic regulation. Herein, we report the radiosyntheses of the second generation of HDAC class IIa-specific radiotracers: 6-(di-fluoroacetamido)-1-hexanoicanilide (DFAHA) and 6-(tri-fluoroacetamido)-1-hexanoicanilide ([18F]-TFAHA). The selectivity of these radiotracer substrates to HDAC class IIa enzymes was assessed in vitro, in a panel of recombinant HDACs, and in vivo using PET/CT imaging in rats. [18F]TFAHA showed significantly higher selectivity for HDAC class IIa enzymes, as compared to [18F]DFAHA and previously reported [18F]FAHA. PET imaging with [18F]TFAHA can be used to visualize and quantify spatial distribution and magnitude of HDAC class IIa expression-activity in different organs and tissues in vivo. Furthermore, PET imaging with [18F]TFAHA may advance the understanding of HDACs class IIa mediated epigenetic regulation of normal and pathophysiological processes, and facilitate the development of novel HDAC class IIa-specific inhibitors for therapy of different diseases.

No MeSH data available.


Proposed mechanism of de-trifluoroacetylation by HDAC4.Increased electronegativity of trifluoromethyl moiety of the trifluoroacetyl leaving group increases the susceptibility of the carbonyl carbon to the nucleophilic attack by the water molecule bound to His802 and His803 and enables the catalytic activity of HDACs class IIa. This results in formation of the tetrahedral oxyanion, which is irreversible, thereby releasing the trifluoroacetate.
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pone.0133512.g010: Proposed mechanism of de-trifluoroacetylation by HDAC4.Increased electronegativity of trifluoromethyl moiety of the trifluoroacetyl leaving group increases the susceptibility of the carbonyl carbon to the nucleophilic attack by the water molecule bound to His802 and His803 and enables the catalytic activity of HDACs class IIa. This results in formation of the tetrahedral oxyanion, which is irreversible, thereby releasing the trifluoroacetate.

Mentions: HDAC class IIa enzymes lack a hydrogen bond donor that can bind to the carbonyl oxygen of the leaving acetyl group as a result of the substitution His976 (class IIa) for Tyr306 (class I), which renders the acetyl group inactive (Figs 8 and 9). In HDAC class I, this hydrogen bond increases the electrophilicity of the carbonyl carbon in the acetyl group, which renders it more susceptible to the nucleophilic attack by the activated water molecule, bound to His142 and His143. This leads to the formation of a tetrahedral oxyanion intermediate stabilized by the Zn2+ ion and by the hydroxyl group of Tyr306 of HDAC8. Consecutive replacement of the hydrogen atoms in the methyl moiety of the leaving acetyl group by fluorine atoms reduces the enzymatic activity in HDACs class I. This suggests that increasing the electronegativity of the leaving group is not sufficient to overcome the size increase, which may force the carbonyl carbon to rotate away from the activated water molecule, adding additional distortion to the hydrogen bonding with Tyr306. Increasing the electronegativity should increase the reactivity of carbonyl carbon, but since this is not the case, it is reasonable to assume that the relative increase in the effective size of the leaving group in TFAHA > DFAHA > FAHA may be a determining factor in the decreasing enzymatic activity. In contrast, increasing the number of fluorine atom substitutions in the methyl moiety of the acetyl leaving group increases the electrophilicity of the carbonyl carbon and restores the catalytic activity of HDACs class IIa by facilitating the nucleophilic attack on the carbonyl carbon of the acetyl moiety by activated water molecule bound to His802 and His803. As a result, the formation of the tetrahedral oxyanion is irreversible and releases trifluoroacetate as shown in Fig 10.


Novel Histone Deacetylase Class IIa Selective Substrate Radiotracers for PET Imaging of Epigenetic Regulation in the Brain.

Bonomi R, Mukhopadhyay U, Shavrin A, Yeh HH, Majhi A, Dewage SW, Najjar A, Lu X, Cisneros GA, Tong WP, Alauddin MM, Liu RS, Mangner TJ, Turkman N, Gelovani JG - PLoS ONE (2015)

Proposed mechanism of de-trifluoroacetylation by HDAC4.Increased electronegativity of trifluoromethyl moiety of the trifluoroacetyl leaving group increases the susceptibility of the carbonyl carbon to the nucleophilic attack by the water molecule bound to His802 and His803 and enables the catalytic activity of HDACs class IIa. This results in formation of the tetrahedral oxyanion, which is irreversible, thereby releasing the trifluoroacetate.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526562&req=5

pone.0133512.g010: Proposed mechanism of de-trifluoroacetylation by HDAC4.Increased electronegativity of trifluoromethyl moiety of the trifluoroacetyl leaving group increases the susceptibility of the carbonyl carbon to the nucleophilic attack by the water molecule bound to His802 and His803 and enables the catalytic activity of HDACs class IIa. This results in formation of the tetrahedral oxyanion, which is irreversible, thereby releasing the trifluoroacetate.
Mentions: HDAC class IIa enzymes lack a hydrogen bond donor that can bind to the carbonyl oxygen of the leaving acetyl group as a result of the substitution His976 (class IIa) for Tyr306 (class I), which renders the acetyl group inactive (Figs 8 and 9). In HDAC class I, this hydrogen bond increases the electrophilicity of the carbonyl carbon in the acetyl group, which renders it more susceptible to the nucleophilic attack by the activated water molecule, bound to His142 and His143. This leads to the formation of a tetrahedral oxyanion intermediate stabilized by the Zn2+ ion and by the hydroxyl group of Tyr306 of HDAC8. Consecutive replacement of the hydrogen atoms in the methyl moiety of the leaving acetyl group by fluorine atoms reduces the enzymatic activity in HDACs class I. This suggests that increasing the electronegativity of the leaving group is not sufficient to overcome the size increase, which may force the carbonyl carbon to rotate away from the activated water molecule, adding additional distortion to the hydrogen bonding with Tyr306. Increasing the electronegativity should increase the reactivity of carbonyl carbon, but since this is not the case, it is reasonable to assume that the relative increase in the effective size of the leaving group in TFAHA > DFAHA > FAHA may be a determining factor in the decreasing enzymatic activity. In contrast, increasing the number of fluorine atom substitutions in the methyl moiety of the acetyl leaving group increases the electrophilicity of the carbonyl carbon and restores the catalytic activity of HDACs class IIa by facilitating the nucleophilic attack on the carbonyl carbon of the acetyl moiety by activated water molecule bound to His802 and His803. As a result, the formation of the tetrahedral oxyanion is irreversible and releases trifluoroacetate as shown in Fig 10.

Bottom Line: Histone deacetylases (HDAC's) became increasingly important targets for therapy of various diseases, resulting in a pressing need to develop HDAC class- and isoform-selective inhibitors.PET imaging with [18F]TFAHA can be used to visualize and quantify spatial distribution and magnitude of HDAC class IIa expression-activity in different organs and tissues in vivo.Furthermore, PET imaging with [18F]TFAHA may advance the understanding of HDACs class IIa mediated epigenetic regulation of normal and pathophysiological processes, and facilitate the development of novel HDAC class IIa-specific inhibitors for therapy of different diseases.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Wayne State University, Detroit, MI 48202, United States of America.

ABSTRACT
Histone deacetylases (HDAC's) became increasingly important targets for therapy of various diseases, resulting in a pressing need to develop HDAC class- and isoform-selective inhibitors. Class IIa deacetylases possess only minimal deacetylase activity against acetylated histones, but have several other client proteins as substrates through which they participate in epigenetic regulation. Herein, we report the radiosyntheses of the second generation of HDAC class IIa-specific radiotracers: 6-(di-fluoroacetamido)-1-hexanoicanilide (DFAHA) and 6-(tri-fluoroacetamido)-1-hexanoicanilide ([18F]-TFAHA). The selectivity of these radiotracer substrates to HDAC class IIa enzymes was assessed in vitro, in a panel of recombinant HDACs, and in vivo using PET/CT imaging in rats. [18F]TFAHA showed significantly higher selectivity for HDAC class IIa enzymes, as compared to [18F]DFAHA and previously reported [18F]FAHA. PET imaging with [18F]TFAHA can be used to visualize and quantify spatial distribution and magnitude of HDAC class IIa expression-activity in different organs and tissues in vivo. Furthermore, PET imaging with [18F]TFAHA may advance the understanding of HDACs class IIa mediated epigenetic regulation of normal and pathophysiological processes, and facilitate the development of novel HDAC class IIa-specific inhibitors for therapy of different diseases.

No MeSH data available.