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Binding of [3H]-methyltrienolone (R1881) by human breast cancers
Abstract:
The synthetic radioligand [3H]-R1881 binds to both androgen and progestogen receptors; these two types of receptor activity can be separated by competition experiments with radioinert steroids of defined biological activity. Using two standard tissues, rat prostate and human uterus, which are sources of androgen and progestogen receptors respectively, the optimal conditions for the determination of each type of activity were established. For the purposes of routine assay, androgen receptors were quantified after saturation of progestogen receptor sites with 125 nM radioinert R5020 using [3H]-R1881 and increasing concentrations of radioinert R1881. Progestogen receptor activity could be identified using the same radioligand and competition with radioinert progesterone or R5020, though for routine purposes, progestogen receptors were quantified using the more specific radioligand, [3H]-R5020. The binding of [3H]-R1881 to tumour cytosol was examined in 122 human breast cancers. Seventy-two tumours (59%) showed binding. Androgen receptor activity alone was present in 16 tumours, progestogen receptor activity alone in 30 tumours and both types in 26 tumours. Tumours containing progestogen receptor activity also showed binding to the progestogen [3H]-R5020, whilst those containing androgen receptors alone did not. Androgen receptor concentration varied from 17 to 210 fmol binding sites/mg cytosol protein (mean value 68) and the mean Kd was 2.15 X 10(-9) M. Progestogen receptor concentration varied from 25 to 1350 fmol binding sites/mg cytosol protein (mean value 410) and the mean Kd was 1.35 X 10(-9) M. The biological significance of the presence of these types of receptor in human breast cancers is currently being assessed from clinical follow-up.
Insights
This study quantifies androgen and progestogen receptor activity in human breast cancers using radioligand binding assays. Results show varying receptor levels, with implications for understanding cancer biology and treatment.
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- Androgen and progestogen receptors play roles in various physiological processes.
- Their presence in breast cancer tissues suggests potential involvement in tumor development and progression.
- Distinguishing between these receptor types is crucial for accurate diagnosis and targeted therapy.
Purpose of the Study:
- To establish reliable methods for quantifying androgen and progestogen receptor activity in human breast cancer cytosol.
- To determine the prevalence and levels of these receptors in a cohort of breast cancer patients.
- To investigate the differential binding characteristics of radioligands used for receptor assays.
Main Methods:
- Development of competitive binding assays using synthetic radioligands ([3H]-R1881 and [3H]-R5020) and radioinert steroids.
- Optimization of assay conditions using rat prostate (androgen receptors) and human uterus (progestogen receptors) as standard tissues.
- Analysis of tumor cytosol from 122 human breast cancer specimens to assess receptor binding.
Main Results:
- A reliable method was established to differentiate and quantify androgen and progestogen receptor activity.
- In 122 breast cancers, 72 (59%) exhibited detectable receptor binding.
- Androgen receptor activity was found alone in 16 tumors, progestogen receptor activity alone in 30, and both in 26.
- Mean androgen receptor concentration was 68 fmol/mg protein (Kd 2.15 x 10(-9) M), and mean progestogen receptor concentration was 410 fmol/mg protein (Kd 1.35 x 10(-9) M).
Conclusions:
- The study successfully quantified androgen and progestogen receptor levels in human breast cancers.
- The findings indicate a significant prevalence of these receptors in breast tumors, with distinct patterns of co-occurrence.
- Further clinical follow-up is needed to assess the biological and clinical significance of these receptor findings in breast cancer.