Normal human immune cells are sensitive to telomerase inhibition by Brassica-derived 3,3-diindolylmethane,partly mediated via ERα/β-AP1 signaling.

Scope: Indole-3-carbinol (I3C) and 3,3'-diindolylmethane (DIM) from Brassica plants are regarded as promising anticancer phytochemicals. The enzyme telomerase is a very attractive target for cancer therapeutics; in normal cells such as lymphocytes, it plays a decisive role for cell maintenance. The effect of I3C and DIM on telomerase in normal human immune cells (PBMC) was studied compared to leukaemia cells (HL-60). Signalling of telomerase regulation via estrogen receptor (ER) was addressed.

Methods And Results: Short-term treatment with I3C and DIM inhibited telomerase activity in leukaemia cells (>30 μM I3C; >3 μM DIM). In CD3/CD28 activated PBMC, inhibition was stronger, though (>3 μM I3C; >1 μM DIM). DIM long-term treatment resulted in DNA damage induction and proliferation inhibition in PBMC as determined by the comet assay and CFSE staining, respectively. A relevance of ERα/β-AP1 signaling for telomerase inhibition on enzyme activity, but not transcription level became evident indicating a nonclassical mode for ER regulation of telomerase by DIM.

Conclusion: Although desired in cancer cells, this study identified a potential adverse impact of I3C and DIM on telomerase action in normal human immune cells, partly mediated by an ER-dependent mechanism. These new findings should be considered for potential chronic high-dose chemoprevention strategies using these compounds.