Antiandrogenic and growth inhibitory effects of ring-substituted analogs of 3,3′-diindolylmethane (Ring-DIMs) in hormone-responsive LNCaP human prostate cancer cells

BACKGROUND Cruciferous vegetables protect against prostate cancer. Indole-3-carbinol (I3C) and its major metabolite 3,3′-diindolylmethane (DIM), exhibit antitumor activities in vitro and in vivo. Several synthetic ring-substituted dihaloDIMs (ring-DIMs) appear to have increased anticancer activity. METHODS Inhibition of LNCaP prostate cancer cell growth was measured by a WST-1 cell viability assay. Cytoplasmic and nuclear proteins were analyzed by immunoblotting and immunofluorescence. Androgen receptor (AR) activation was assessed by measuring prostate-specific antigen (PSA) expression and using LNCaP cells containing human AR and an AR-dependent probasin promoter-green fluorescent protein (GFP) construct. RESULTS Like DIM, several ring-substituted dihaloDIM analogs, namely 4,4′-dibromo-, 4,4′-dichloro-, 7,7′-dibromo-, and 7,7′-dichloroDIM, significantly inhibited DHT-stimulated growth of LNCaP cells at concentrations ≥1 μM. We observed structure-dependent differences for the effects of the ring-DIMs on AR expression, nuclear AR accumulation and PSA levels in LNCaP cells after 24 hr. Both 4,4′- and 7,7′-dibromoDIM decreased AR protein and mRNA levels, whereas 4,4′- and 7,7′-dichloroDIM had minimal effect. All four dihaloDIMs (10 and 30 μM) significantly decreased PSA protein and mRNA levels. Immuofluorescence studies showed that only the dibromoDIMs increased nuclear localization of AR. All ring-DIMs caused a concentration-dependent decrease in fluorescence induced by the synthetic androgen R1881 in LNCaP cells transfected with wild-type human AR and an androgen-responsive probasin promoter-GFP gene construct, with potencies up to 10-fold greater than that of DIM. CONCLUSION The antiandrogenic effects of ring-DIMs suggest they may form the basis for the development of novel agents against hormone-sensitive prostate cancer, alone or in combination with other drugs.