Induction of cellular differentiation has been proposed as a unique modality for prostate cancer treatment. However, it is unclear whether or not terminal differentiation, resulting in irreversible growth arrest, can be produced in prostate cancer cells. In this study, the effect of androgen exposure on terminal differentiation in the androgen-sensitive LNCaP human prostate cancer cell line was examined. A 4-day exposure of LNCaP cells to 1 nM of the synthetic androgen R1881 resulted in a G0/G1 growth arrest with no decrease in cell viability compared to untreated control LNCaP cells. LNCaP cells growth arrested by androgen exposure showed a 3.6-fold increase in cell volume, a 1.2-fold increase in intracellular calcium levels, and a significant change in cellular reduction/oxidation status (i.e., a 52% decrease in the GSH/GSSG ratio), consistent with the development of a more differentiated phenotype. In addition, androgen exposed LNCaP cells showed a 2.2-fold increase in cytokeratin 18 protein expression, a marker of differentiated prostate secretory cells. An increase in the secretory activity of R1881 treated LNCaP cells was observed by a 7.1-fold increase in prostate specific antigen release. Also, an increase in intracellular granularity after androgen exposure in LNCaP cells, as determined by flow cytometric side light scatter analysis, was suggestive of increased secretory granules. Using a fluorescence-activated cell sorter, a population of highly granular LNCaP cells was selectively collected and maintained in complete growth medium for 7 days without the addition of androgen. Compared to untreated control LNCaP cells and cells with low intracellular granularity, highly granular cells continued to release high levels of prostate specific antigen and were terminally growth arrested. These data suggest that prostate cancer cells can be induced to terminally differentiate, which may serve as a useful endpoint in identifying novel agents for prostate cancer treatment.
[Proc Amer Assoc Cancer Res, Volume 45, 2004]