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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.


A) Substrate affinity of FAHA, DFAHA, and TFAHA to different recombinant HDACs in vitro. The substrate affinity is expressed as Kcat. B) Maximum catalytic rate of FAHA, DFAHA, and TFAHA for different recombinant HDACs in vitro, expressed as vmax. C) The concentration required for half of the maximal catalytic activity for all recombinant HDACs expressed as km.
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pone.0133512.g005: A) Substrate affinity of FAHA, DFAHA, and TFAHA to different recombinant HDACs in vitro. The substrate affinity is expressed as Kcat. B) Maximum catalytic rate of FAHA, DFAHA, and TFAHA for different recombinant HDACs in vitro, expressed as vmax. C) The concentration required for half of the maximal catalytic activity for all recombinant HDACs expressed as km.

Mentions: Evaluation of substrate affinity of FAHA, DFAHA, and TFAHA in a panel of recombinant HDACs demonstrated the selectivity of these compounds for HDACs class IIa (HDACs 4, 5, 7, and 9), especially for HDACs 4 and 5. The kcat values in HDACs class IIa were two orders of magnitude higher than those for other classes of HDACs (Fig 5a). The higher kcat values of TFAHA, as compared to DFAHA and FAHA demonstrates the increasing ability of HDACs class IIa to cleave the trifluoro acetyl moiety, as compared to both difluoroacetyl and fluoroacetyl moieties. The HDAC class IIa enzymes also have lower km values and higher vmax values for TFAHA than the other HDACs enzymes (Fig 5b and 5c). There is a significant change in the vmax value of TFAHA from those of FAHA or DFAHA for HDAC8, demonstrating the decreased cleavage efficiency of HDAC class I with the addition of fluorine atoms (Fig 5b). Also, these results are consistent with previous reports demonstrating that HDACs class IIa enzymes exhibit higher catalytic efficiency for Boc-L-Lys(ɛ-trifluoroacetyl)-MCA, as compared to Boc-L-Lys(ɛ-acetyl)-MCA, which is not an efficient substrate to class IIa HDACs [37]. This explains, at least in part, why [11C]6-acetamido-1-hexanoicanilide (11C-AHA) demonstrated significantly lower uptake and more uniform distribution in the brain in the regions of high accumulation of 18F-FAHA [19].


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)

A) Substrate affinity of FAHA, DFAHA, and TFAHA to different recombinant HDACs in vitro. The substrate affinity is expressed as Kcat. B) Maximum catalytic rate of FAHA, DFAHA, and TFAHA for different recombinant HDACs in vitro, expressed as vmax. C) The concentration required for half of the maximal catalytic activity for all recombinant HDACs expressed as km.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0133512.g005: A) Substrate affinity of FAHA, DFAHA, and TFAHA to different recombinant HDACs in vitro. The substrate affinity is expressed as Kcat. B) Maximum catalytic rate of FAHA, DFAHA, and TFAHA for different recombinant HDACs in vitro, expressed as vmax. C) The concentration required for half of the maximal catalytic activity for all recombinant HDACs expressed as km.
Mentions: Evaluation of substrate affinity of FAHA, DFAHA, and TFAHA in a panel of recombinant HDACs demonstrated the selectivity of these compounds for HDACs class IIa (HDACs 4, 5, 7, and 9), especially for HDACs 4 and 5. The kcat values in HDACs class IIa were two orders of magnitude higher than those for other classes of HDACs (Fig 5a). The higher kcat values of TFAHA, as compared to DFAHA and FAHA demonstrates the increasing ability of HDACs class IIa to cleave the trifluoro acetyl moiety, as compared to both difluoroacetyl and fluoroacetyl moieties. The HDAC class IIa enzymes also have lower km values and higher vmax values for TFAHA than the other HDACs enzymes (Fig 5b and 5c). There is a significant change in the vmax value of TFAHA from those of FAHA or DFAHA for HDAC8, demonstrating the decreased cleavage efficiency of HDAC class I with the addition of fluorine atoms (Fig 5b). Also, these results are consistent with previous reports demonstrating that HDACs class IIa enzymes exhibit higher catalytic efficiency for Boc-L-Lys(ɛ-trifluoroacetyl)-MCA, as compared to Boc-L-Lys(ɛ-acetyl)-MCA, which is not an efficient substrate to class IIa HDACs [37]. This explains, at least in part, why [11C]6-acetamido-1-hexanoicanilide (11C-AHA) demonstrated significantly lower uptake and more uniform distribution in the brain in the regions of high accumulation of 18F-FAHA [19].

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.