Cell experiment:

Phenol red is dissolved in 0.1% ethanol. To determine the effect of phenol red on cell proliferation, MCF-7 cells grown for 1 week before experiments in phenol red-free MEM supplemented are harvested and seeded into T-25 flasks (ca. 1.5 x 105 cells per flask). The following day, cells from three flasks are harvested and counted with a Coulter Counter. Then the medium is changed to phenol red- and insulin-free MEM, which contains various concentrations of dextran-coated charcoal-treated calf serum, phenol red (0-300 μM), tamoxifen, hydroxytamoxifen, estradiol, or ethanol vehicle (0.1%), and cell number is monitored as a function of time[1]. Phenol Red sodium salt is dissolved in distilled water as a 10 g/L stock solution[2].

Phenol Red sodium salt is a water soluble pH indicator used in the 6.8 (yellow) to 8.2 (red) range.

Phenol Red sodium salt is commonly employed as a cell tissue culture pH marker. Under normal conditions, phenol red added to the growth medium will have a pink-red color. Dying cells or overgrowth of contaminants will cause a change in pH resulting in a change in indicator color. Phenol red bears a structural resemblance to some nonsteroidal estrogens and has significant estrogenic activity at the concentrations (15-45 μM) at which it is found in tissue culture media. Phenol red binds to the estrogen receptor of MCF-7 human breast cancer cells and stimulates the proliferation of estrogen receptor-positive MCF-7 breast cancer cells in a dose-dependent manner but has no effect on the growth of estrogen receptor-negative MDA-MB-231 breast cancer cells[1]. Phenol red is a simple, rapid and inexpensive method for the measurement of hydrogen peroxide produced by cells in culture. The assay is based on the horseradish peroxidase-mediated oxidation of phenol red by hydrogen peroxide which results in the formation of a compound demonstrating increased absorbance at 610 nm[2].

[1]. Berthois Y, et al. Phenol red in tissue culture media is a weak estrogen: implications concerning the study of estrogen-responsive cells in culture. Proc Natl Acad Sci U S A. 1986 Apr;83(8):2496-500. [2]. Pick E, et al. A simple colorimetric method for the measurement of hydrogen peroxide produced by cells in culture. J Immunol Methods. 1980;38(1-2):161-70.