Proliferative effect of androst-4-ene-3,17-dione and its metabolites in the androgen-sensitive LNCaP cell line

As a therapeutic approach for the treatment of androgen-sensitive diseases, it would be tempting to lower the level of the potent androgens testosterone (T) and dihydrotestosterone (DHT) by using inhibitors of type 3 and type 5 17β-hydroxysteroid dehydrogenases (17β-HSDs). However, the efficiency of such a strategy will be optimal only if androst-4-ene-3,17-dione (Δ4-dione), the precursor of T, does not possess per se agonist activity on the androgen receptor (AR). To determine if the proliferative effect previously observed on AR+ cells for Δ4-dione originates from its direct (per se) action on AR or from its transformation into a metabolite, we started a series of experimentations using the human prostate cancer LNCaP cell line, which expresses a highly sensitive AR. By real-time RT-PCR analysis, we detected type 1 5α-reductase (5α-R), a small amount of type 5 17β-HSD, but not type 2 5α-R nor type 3 17β-HSD. We then studied the transformation of labeled Δ4-dione in LNCaP cells after 1-7 days and the most important metabolite detected was 5α-androstane-3,17-dione (A-dione), which is the product of 5α-R activity. We measured only low levels of androsterone (ADT) and epi-ADT. This result was next confirmed by using an inhibitor of 5α-R that completely inhibited the transformation of Δ4-dione into A-dione, and consequently into ADT and epi-ADT. The proliferative effect of Δ4-dione (carefully purified) on LNCaP (AR+) cells was next determined in presence or absence of the 5α-R inhibitor. Although the cells proliferate in the presence of Δ4-dione only, no cell proliferation was observed with a combination of Δ4-dione and 5α-R inhibitor, suggesting that Δ4-dione is not androgenic per se. We next determined that A-dione and epi-ADT stimulated cell growth with the same pattern and potency as Δ4-dione, whereas ADT had a 3.5-fold lower proliferative activity. In conclusion, Δ4-dione is not in itself an agonist steroid on LNCaP (AR+) cells, and its proliferative activity appears to be mediated by its transformation into A-dione and/or into epi-ADT.