Imidazoquinolines Inhibit Cell Growth and Induce Apoptosis in Human Prostate Cancer Cell Lines.
Huixian Liu, Michael J. Schwartz, Eric Kauffman, and Douglas S. Scherr
Purpose: Toll-like receptors 7 and 8 (TLR7/8) are expressed in both murine and human bladder cancer cells. Imidazoquinolines, TLR7/8 agonists, are able to inhibit bladder cancer cell growth in vitro and in vivo. In an attempt to expand the clinical utility of imidazoquinolines, we investigate TLR7/8 expression in human prostate cancer cell lines and characterize the effects of imidazoquinolines on cell growth, apoptosis, tumorigenesis and related gene expressions in these cell lines in vitro.
Experimental Design: Prostate cancer cell lines PC-3 and LNCap were cultured in normal culture medium or medium supplemented with imidazoquinolines. TLR7/8 expression was detected with western blot. Effects of imidazoquinolines on proliferation were measured with methylthiazoletetrazolium (MTT) assay, and effects on apoptosis were evaluated by DNA fragmentation ELISA and immunohistochemistry. Gene expression was investigated by RT-PCR and confirmed at the translational level by western blot. Tumorigenesis experiements were carried out with soft agar assay.
Results:While TLR8 was equally expressed in both cell lines, TLR7 was much more abundant in LNCap line compared with PC-3. The expression of both TLR7/8 is not regulated by imidazoquinolines. With imidazoquinoline treatment, cell proliferation was reduced by 27.44% and 24.15%, and apoptosis was increased by 179.03% and 79.26% in PC3 and LNcap cell lines, respectively. The expression of related gene Bcl-2 and E2F1 was significantly suppressed in PC3 cell line, but only Bcl-2 was suppressed in LNcap cell line. Consistently, the colony formation in in vitro tumorigenesis experiment was completely inhibited in both cell lines at 100μg/ml of imidazoquinolines.
Conclusions: Human prostate cancer cell lines abundantly express TLR7/8. In addition, imidazoquinolines, TLR7/8 agonists, can efficiently inhibit proliferation and induce apoptosis in human prostate cancer cell lines. The drug effects may be mediated through different pathways in these two cell lines, given the observed differential gene expression. Further investigation into the application of imidazoquinolines in prostate cancer therapy is warranted.