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Steroid hormones affect binding of the sigma ligand 11C-SA4503 in tumour cells and tumour-bearing rats.

Rybczynska AA, Elsinga PH, Sijbesma JW, Ishiwata K, de Jong JR, de Vries EF, Dierckx RA, van Waarde A - Eur. J. Nucl. Med. Mol. Imaging (2009)

Bottom Line: Tumour-bearing male rats were repeatedly treated with pentobarbital (a condition known to result in reduction of endogenous steroid levels) or injected with progesterone.Binding of (11)C-SA4503 to C6 cells was increased (approximately 50%) upon removal and decreased (approximately 60%) upon addition of steroid hormones (rank order of potency: progesterone > allopregnanolone = testosterone = androstanolone > dehydroepiandrosterone-3-sulphate, IC(50) progesterone 33 nM).The binding of (11)C-SA4503 is sensitive to steroid competition.

View Article: PubMed Central - PubMed

Affiliation: Nuclear Medicine and Molecular Imaging, University of Groningen Medical Center, University of Groningen, Hanzeplein 1, 9713GZ, Groningen, The Netherlands. a.rybczynska@ngmb.umcg.nl

ABSTRACT

Purpose: Sigma receptors are implicated in memory and cognitive functions, drug addiction, depression and schizophrenia. In addition, sigma receptors are strongly overexpressed in many tumours. Although the natural ligands are still unknown, steroid hormones are potential candidates. Here, we examined changes in binding of the sigma-1 agonist (11)C-SA4503 in C6 glioma cells and in living rats after modification of endogenous steroid levels.

Methods: (11)C-SA4503 binding was assessed in C6 monolayers by gamma counting and in anaesthetized rats by microPET scanning. C6 cells were either repeatedly washed and incubated in steroid-free medium or exposed to five kinds of exogenous steroids (1 h or 5 min before tracer addition, respectively). Tumour-bearing male rats were repeatedly treated with pentobarbital (a condition known to result in reduction of endogenous steroid levels) or injected with progesterone.

Results: Binding of (11)C-SA4503 to C6 cells was increased (approximately 50%) upon removal and decreased (approximately 60%) upon addition of steroid hormones (rank order of potency: progesterone > allopregnanolone = testosterone = androstanolone > dehydroepiandrosterone-3-sulphate, IC(50) progesterone 33 nM). Intraperitoneally administered progesterone reduced tumour uptake and tumour-to-muscle contrast (36%). Repeated treatment of animals with pentobarbital increased the PET standardized uptake value of (11)C-SA4503 in tumour (16%) and brain (27%), whereas the kinetics of blood pool radioactivity was unaffected.

Conclusions: The binding of (11)C-SA4503 is sensitive to steroid competition. Since not only increases but also decreases of steroid levels affect ligand binding, a considerable fraction of the sigma-1 receptor population in cultured tumour cells or tumour-bearing animals is normally occupied by endogenous steroids.

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Dose-response plot of progesterone competition with 11C-SA4503 binding to C6 cells in steroid-free medium. Specific binding was defined as total binding minus the residual binding observed in the presence of an excess of haloperidol (50 µM)
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Fig2: Dose-response plot of progesterone competition with 11C-SA4503 binding to C6 cells in steroid-free medium. Specific binding was defined as total binding minus the residual binding observed in the presence of an excess of haloperidol (50 µM)

Mentions: When the steroid supplementation experiment was repeated in steroid-free medium, a stronger effect of exogenous steroids was observed than in the normal growth medium. Even 50 µM DHEA-S caused now a significant decrease of cellular 11C-SA4503 binding (Fig. 1). Both in normal and in steroid-depleted medium, the observed rank order of potency was: progesterone > androstanolone = testosterone = allopregnanolone > DHEA-S. A dose-response plot was made for the most potent steroid competitor, progesterone. The IC50 value of this compound for inhibition of cellular 11C-SA4503 binding was 33 nM (Fig. 2).Fig. 2


Steroid hormones affect binding of the sigma ligand 11C-SA4503 in tumour cells and tumour-bearing rats.

Rybczynska AA, Elsinga PH, Sijbesma JW, Ishiwata K, de Jong JR, de Vries EF, Dierckx RA, van Waarde A - Eur. J. Nucl. Med. Mol. Imaging (2009)

Dose-response plot of progesterone competition with 11C-SA4503 binding to C6 cells in steroid-free medium. Specific binding was defined as total binding minus the residual binding observed in the presence of an excess of haloperidol (50 µM)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2691528&req=5

Fig2: Dose-response plot of progesterone competition with 11C-SA4503 binding to C6 cells in steroid-free medium. Specific binding was defined as total binding minus the residual binding observed in the presence of an excess of haloperidol (50 µM)
Mentions: When the steroid supplementation experiment was repeated in steroid-free medium, a stronger effect of exogenous steroids was observed than in the normal growth medium. Even 50 µM DHEA-S caused now a significant decrease of cellular 11C-SA4503 binding (Fig. 1). Both in normal and in steroid-depleted medium, the observed rank order of potency was: progesterone > androstanolone = testosterone = allopregnanolone > DHEA-S. A dose-response plot was made for the most potent steroid competitor, progesterone. The IC50 value of this compound for inhibition of cellular 11C-SA4503 binding was 33 nM (Fig. 2).Fig. 2

Bottom Line: Tumour-bearing male rats were repeatedly treated with pentobarbital (a condition known to result in reduction of endogenous steroid levels) or injected with progesterone.Binding of (11)C-SA4503 to C6 cells was increased (approximately 50%) upon removal and decreased (approximately 60%) upon addition of steroid hormones (rank order of potency: progesterone > allopregnanolone = testosterone = androstanolone > dehydroepiandrosterone-3-sulphate, IC(50) progesterone 33 nM).The binding of (11)C-SA4503 is sensitive to steroid competition.

View Article: PubMed Central - PubMed

Affiliation: Nuclear Medicine and Molecular Imaging, University of Groningen Medical Center, University of Groningen, Hanzeplein 1, 9713GZ, Groningen, The Netherlands. a.rybczynska@ngmb.umcg.nl

ABSTRACT

Purpose: Sigma receptors are implicated in memory and cognitive functions, drug addiction, depression and schizophrenia. In addition, sigma receptors are strongly overexpressed in many tumours. Although the natural ligands are still unknown, steroid hormones are potential candidates. Here, we examined changes in binding of the sigma-1 agonist (11)C-SA4503 in C6 glioma cells and in living rats after modification of endogenous steroid levels.

Methods: (11)C-SA4503 binding was assessed in C6 monolayers by gamma counting and in anaesthetized rats by microPET scanning. C6 cells were either repeatedly washed and incubated in steroid-free medium or exposed to five kinds of exogenous steroids (1 h or 5 min before tracer addition, respectively). Tumour-bearing male rats were repeatedly treated with pentobarbital (a condition known to result in reduction of endogenous steroid levels) or injected with progesterone.

Results: Binding of (11)C-SA4503 to C6 cells was increased (approximately 50%) upon removal and decreased (approximately 60%) upon addition of steroid hormones (rank order of potency: progesterone > allopregnanolone = testosterone = androstanolone > dehydroepiandrosterone-3-sulphate, IC(50) progesterone 33 nM). Intraperitoneally administered progesterone reduced tumour uptake and tumour-to-muscle contrast (36%). Repeated treatment of animals with pentobarbital increased the PET standardized uptake value of (11)C-SA4503 in tumour (16%) and brain (27%), whereas the kinetics of blood pool radioactivity was unaffected.

Conclusions: The binding of (11)C-SA4503 is sensitive to steroid competition. Since not only increases but also decreases of steroid levels affect ligand binding, a considerable fraction of the sigma-1 receptor population in cultured tumour cells or tumour-bearing animals is normally occupied by endogenous steroids.

Show MeSH
Related in: MedlinePlus