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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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Competition of exogenous steroids (concentration 50 µM) and haloperidol (50 µM) with 11C-SA4503 binding to C6 cells in normal culture medium and in steroid-free medium (expressed as a percentage of the binding to untreated cells in normal culture medium). All treatments resulted in a statistically significant effect on tracer binding, with exception of the DHEA-S effect in normal culture medium
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Fig1: Competition of exogenous steroids (concentration 50 µM) and haloperidol (50 µM) with 11C-SA4503 binding to C6 cells in normal culture medium and in steroid-free medium (expressed as a percentage of the binding to untreated cells in normal culture medium). All treatments resulted in a statistically significant effect on tracer binding, with exception of the DHEA-S effect in normal culture medium

Mentions: The growth medium of C6 cells (DMEM-high) contains steroid hormones since it is supplemented with FCS (7.5% v/v). This medium also contains the indicator phenol red which may interact with hormone binding sites, particularly oestrogen receptors [31]. Yet, the addition of non-radioactive steroids to normal growth medium (50 µM of progesterone, allopregnanolone, testosterone or androstanolone) resulted in measurable competition with the radioligand 11C-SA4503 for binding to cellular sigma receptors (Fig. 1). In contrast, the administration of 50 µM DHEA-S had no statistically significant effect.Fig. 1


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)

Competition of exogenous steroids (concentration 50 µM) and haloperidol (50 µM) with 11C-SA4503 binding to C6 cells in normal culture medium and in steroid-free medium (expressed as a percentage of the binding to untreated cells in normal culture medium). All treatments resulted in a statistically significant effect on tracer binding, with exception of the DHEA-S effect in normal culture medium
© Copyright Policy
Related In: Results  -  Collection

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

Fig1: Competition of exogenous steroids (concentration 50 µM) and haloperidol (50 µM) with 11C-SA4503 binding to C6 cells in normal culture medium and in steroid-free medium (expressed as a percentage of the binding to untreated cells in normal culture medium). All treatments resulted in a statistically significant effect on tracer binding, with exception of the DHEA-S effect in normal culture medium
Mentions: The growth medium of C6 cells (DMEM-high) contains steroid hormones since it is supplemented with FCS (7.5% v/v). This medium also contains the indicator phenol red which may interact with hormone binding sites, particularly oestrogen receptors [31]. Yet, the addition of non-radioactive steroids to normal growth medium (50 µM of progesterone, allopregnanolone, testosterone or androstanolone) resulted in measurable competition with the radioligand 11C-SA4503 for binding to cellular sigma receptors (Fig. 1). In contrast, the administration of 50 µM DHEA-S had no statistically significant effect.Fig. 1

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