Tamoxifen administration to mice
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One of the uses of tamoxifen in the lab is the activation of enzymes deactivated via an estrogen-binding domain, like Cre-ERT (Cre-LBD). Tamoxifen is an estrogen analogue that binds with higher affinity than estrogen to altered estrogen binding domains.
Tamoxifen is administered to mice in 2 main ways: via the drinking water or in an oily mix given via a feeding needle. Administration via the drinking water is easier but somewhat less reliable.
Chemical data for tamoxifen
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Tamoxifen citrate
| molecular weight | pKa' | equilibrium solubility in water at 37°C |
| 563.62 g/mol | 8.85 | 0.5 mg/mL |
see [1] and PubChem entry: tamoxifen citrate
4-hydroxytamoxifen (OHT)
Tamoxifen is metabolised to 4-hydroxytamoxifen (often abbreviated OHT).
| molecular weight | pKa' | equilibrium solubility in water at 37°C |
| 563.65 g/mol | ? | ? mg/mL |
see [2] and PubChem entry: 4-hydroxytamoxifen
Tamoxifen administration via the drinking water
- dissolve 100mg tamoxifen in 100µl pure ethanol (10mg/100µl = 100mg/ml tamoxifen)
- dilute 100-200x in distilled water to final concentration of 1-0.5mg/ml
- use 1% ethanol in distilled water as a negative control
- replace water in drinking bottles with tamoxifen solution; let mice drink at will
compare Gail et al 1999, PMID 10547390, p355: treatment of mice
Tamoxifen administration via a feeding needle
- 100 mg Tamoxifen-free base (Sigma, T5648) was suspended in 100 μl Ethanol and solved in 900 μl peanut oil (Sigma). This 10 mg/100 μl tamoxifen solution was shaken rigorously at 55°C (Tamoxifen precipitates at RT) and divided in aliquots of 50 μl (1 daily dose = 5mg). Store at -20°C.
- Heat to 37°C before administration. Verify that tamoxifen is properly dissolved.
- Feed orally to mice with a feeding needle. Fix the mice at their neck and ridge so that the belly is directed to the floor. Hold the mouse tightly so that it can not move the head, but not too tight to avoid choking. Carefully introduce the feeding needle in the mouth behind the tongue (max. 1 cm). It is helpful to mark 1 cm on the needle with an edding pen in order to see how deep you have inserted the needle.
- Introduce slowly 50 μl of the Tamoxifen solution with the syringe. Make sure that they swallow (can be seen).
- Repeat this procedure for 5 days once a day.
(protocol: Stefan Glaser)
see also Metzger and Chambon, 2001, PMID: 11327805
