Valproic acid inhibits proliferation and affects androgen sensitivity in prostatic cancer cells.

Valproic acid (VA), a drug used as an anticonvulsant and mood stabilizer, has been shown to impair cell growth and evoke cell differentiation in several cell types. In the present study, we investigated the effect of VA on the proliferation of both androgen-sensitive (LNCaP) and -insensitive (PC-3) prostate cancer cells. Moreover, we explored the effect of VA on the androgen response of these two models with the aim of establishing whether the drug modulates or induces hormone sensitivity. LNCaP cells were plated at a density of 50,000 cells/ml in RPMI 1640 supplemented with 10% foetal bovine serum (FBS) in 60-mm plastic Petri dishes. Forty-eight h later, the medium was changed with RPMI 1640 supplemented with 5% charcoal-treated FBS (CH-FBS) containing VA (75 Ìg/ml). PC-3 cells were plated at a density of 25,000 cells/ml in Dulbecco Modified Eagle’s Medium (DMEM) supplemented with 5% FBS in 60-mm plastic Petri dishes. Twenty-four h later, the medium was changed with DMEM supplemented with 5% CH-FBS containing VA (75 Ìg/ml). The medium with the drug was renewed every 48 h and cell counts performed after 2, 4 and 6 days of treatment. In experiments performed to evaluate the effect of VA on the androgen sensitivity of LNCaP cells, these cells were pretreated for 48h with VA (75 Ìg/ml) and subsequently exposed to dihydrotestosterone (DHT) at concentrations ranging from 10-11 to 10-5 M. Alternatively, cells were treated with VA combined with the above mentioned DHT concentrations. PC-3 cells were also exposed to VA associated with DHT (10-10, 10-9 and 10-8 M). Our data indicate that VA induced a slight inhibition of LNCaP cell proliferation (about 15% with respect to control). Nevertheless, when used in the sequential modality or in combination with 10-10-10-7 M DHT, it strongly reduced or suppressed the androgenpromoted cell growth. In addition, it generally amplified the inhibitory effect provoked by 10-6-10-5 M DHT. PC-3 cell proliferation was markedly reduced by VA, the maximum inhibition reaching 40% when compared to control. When DHT, which is ineffective on PC-3 cell growth when used alone, was combined with VA, it was able to counteract the inhibitory action of VA, inducing a slight stimulation of cell growth at 10-9 and 10-8 M. Our findings show that VA reduces the cell growth of prostate cancer cells and may interfere with the androgen receptor machinery. Of particular interest is the effect observed in PC-3 cells, in which VA seems to induce androgen sensitivity. It is worth noting that, in our experience, PC-3 cells show very low levels of androgen receptors (AR). Work is in progress to verify whether alterations in AR expression are involved in the modulation or induction of androgen sensitivity by VA.