Einfluss endogener und exogener PBR-Liganden auf die tamoxifeninduzierte Apoptose bei Mammakarzinomzellkulturen

Zusammenfassung

Fragestellung

Benzodiazepine binden neben dem zentralen GABA_A-Rezeptor auch an einen in Aufbau, Lokalisation und Funktion unterschiedlichen peripheren Rezeptor. Dieser ubiquitär vorhandene periphere Benzodiazepinrezeptor (PBR) ist ein integraler Bestandteil der Mitochondrienmembran und konnte in Primärtumoren und MCF-7- und BT-20-Mammakarzinomzellkulturen nachgewiesen werden. Zu seinen Liganden zählt neben Isochinolinderivaten und Benzodiazepinen das Neuropeptid DBI (Diazepambindungsinhibitor), das aufgrund seiner Funktion auch Acyl-CoA-Bindungsprotein genannt wird. In der vorliegenden Arbeit wurde der Einfluss der PBR-Liganden auf die durch tamoxifeninduzierte Apoptose der Mammakarzinomzellen untersucht.

Methode

Die Auswertungen der Zellzyklusphasen und des Mitochondrienpotenzials erfolgten durchflusszytometrisch, wobei die Zellen vor Inkubation mit Tamoxifen und den spezifischen PBR-Liganden Ro5-4864, PK11195 und DBI durch Serumentzug synchronisiert wurden.

Ergebnisse

Die exogenen Benzodiazepinliganden Ro5-4864 und PK11195 bewirkten dosisabhängig eine Hemmung der tamoxifeninduzierten Apoptose in beiden Zelllinien. Dagegen verstärkte der endogene Ligand DBI den Effekt des Tamoxifens.

Diskussion

PBR-Liganden greifen in Abhängigkeit von Zelltyp, von der Dosierung und den Bindungseigenschaft der Liganden in das proliferative bzw. apoptotische Geschehen der MCF-7- und BT-20-Zellen ein. So kann die durch Tamoxifen ausgelöste Apoptose in den oben genannten Zellkulturen gehemmt oder verstärkt werden.

Abstract

Purpose

The action of benzodiazepines, clinically used as muscle relaxants, anticonvulsants and sedative hypnotics, is mediated by a central-type GABA_A-receptor located in the brain. In addition, they also bind to an ubiquitous peripheral benzodiazepine receptor (PBR), which is an integral part of the mitochondrial membrane. It has been shown to be present in primary tumors and in the human breast cancer cell lines MCF-7 and BT-20. In addition to the synthetic ligands, e.g. isochinoline derivates and benzodiazepines, there is an endogenous ligand, diazepam-binding inhibitor (DBI), a neuropeptide which is also called acyl-CoA-binding protein. In the present study, the influence of PBR ligands on tamoxifen-induced apoptosis in breast cancer cell lines was investigated.

Material and Methods

Data acquisition was performed in all experiments by flow cytometry. After synchronisation by serum-deprivation, the breast cancer cells were incubated with various concentrations of tamoxifen with or without the addition of PBR ligands Ro5-4864, PK11195 and DBI.

Results

The specific ligands Ro5-4864 and PK11195 inhibited the tamoxifen-induced apoptosis in BT-20 and MCF-7 breast cancer cells in a dose-dependent manner. In contrast, the endogenous ligand DBI amplified the effect of tamoxifen.

Conclusion

These data suggest that PBR ligands are involved in the regulation of cell growth and apoptosis in breast cancer cell lines. Depending on cell-type, dose and ligand binding properties, the tamoxifen-induced apoptosis can be inhibited or enhanced.

Peripherer Benzodiazepinrezeptor - Apoptose - Tamoxifen

Peripheral benzodiazepine receptor - tamoxifen - apoptosis

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