Background: The androgen-dependent model states that testosterone concentration is directly proportional to prostate cancer growth. However, some experts argue that testosterone stimulates prostate cancer growth until androgen receptor saturations are saturated, resulting in a growth plateau. This refinement led to the development of the saturation model. However, there is limited in vitro evidence underpinning this.
Aims: To investigate the growth response of LNCaP (androgen-sensitive prostate cancer cell line), PC3 (androgen-insensitive prostate cancer cell line) cells and PNT2/C2 (cloned normal prostate cell line) cells to varying testosterone concentrations in vitro, and determine if this receptor is dependent.
Methodology: Each cell line was seeded at a concentration of 1x105 using trypan blue exclusion assay in multiple 96-well plates. Testosterone was pipetted down all 12 columns of the plates using doubling dilutions starting with 230nmol/L and reaching 0.11nmol/L. MTT assay determined the residual viable biomass in each well after treatment by measuring the amount of formazan crystals generated by the cell mitochondria. To determine the role of the androgen receptor, the cell lines were treated with equal concentrations of testosterone and flutamide, a selective androgen receptor antagonist.
Results: LNCaP cells incubated with testosterone showed an inverted “U” relationship. At testosterone concentrations between 0.11 and 0.90nmol/L, cell residual viable biomass increased significantly compared to controls (p<0.05). However, between 0.9 and 1.8nmol/L growth plateaus, and then begins a gradual decline in growth all the way to 230nmol/L of testosterone (p<0.05). PC3 cells showed no response to testosterone alone until 57.50nmol/L where growth declined until 230nmol/L (p<0.05). PNT2/C2 cells mirrored the LNCaP growth kinetics. LNCaP and PC3 cells treated with flutamide showed significant reductions in growth compared to controls.
Conclusion: These data suggest that the response of LNCaP and PNT2/C2 cells to testosterone is saturation dependent to a degree. The cells are exquisitely sensitive to low concentrations of testosterone (<1.0nmol/L). PC3 cells are not effected by testosterone either at normal or sub-physiological doses. However, high dose testosterone diminished both LNCaP and PC3 cell growth adding to the growing body of evidence suggesting high dose testosterone may be of value in the management of advanced prostate cancer.
