Table 1.
Binding profile of clinical progestins to progesterone, glucocorticoid, and androgen receptors
| Progestins | PR
|
GR IC50 (nm) | AR IC50 (nm) | Selectivity (PR/GR) | Selectivity (PR/AR) | Selectivity (AR/GR) | |
|---|---|---|---|---|---|---|---|
| IC50 (nm) | RBA (%) | ||||||
| P4 | 9.01 | 100 | 6.51 | 119.30 | 4.78 | 87.72 | 0.05 |
| MPA | 6.20 | 145.30 | 1.42 | 4.53 | 0.23 | 0.73 | 0.31 |
| Nestorone | 5.07 | 177.70 | 8.71 | NB | 1.72 | NA (+∞) | NA (−∞) |
| NET | 14.32 | 62.90 | 97.84 | 18.02 | 6.83 | 1.26 | 5.43 |
| NETA | 38.92 | 23.20 | 202.70 | 876.90 | 5.21 | 22.53 | 0.23 |
| Norethynodrel | 67.76 | 13.30 | 1306.00 | 196.70 | 19.27 | 2.90 | 6.64 |
| LNG | 5.46 | 165.20 | 16.73 | 2.90 | 3.07 | 0.53 | 5.77 |
| Norgestimate | 482.80 | 1.87 | 287.10 | 5021.00 | 0.59 | 10.40 | 0.06 |
Fluorescence polarization-based competitive binding assays were conducted to determine the binding profile of test progestins to PR, GR, and AR. IC50 refers to the concentration of test progestins resulting in a half-maximal shift in polarization value, which was determined from the binding curve by a nonlinear least-squares analysis. The relative binding affinity (RBA) of test progestins is expressed as percent of the binding affinity of progesterone (RBA = 100%). Selectivity was calculated as the ratio between the binding IC50. NA, Not applicable; NB, no binding.