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The growth and survival of many tumors rely upon aberrant sustained signaling from certain signaling pathway in the cell. One of these pathways is the Hedgehog (HH) / Patched (PTCH) pathway. PTCH signaling is an important regulator of embryonic stem cell patterning, tissue regeneration, stem cell renewal, and cancer growth. PTCH regulates the membrane protein Smoothened (SMO), and SMO in turn promotes the expression of HH target genes through the action of the GLI family of transcription factors. Aberrant HH pathway activation is associated with the formation of several types of cancer, including small-cell lung cancer, breast cancer, prostate cancer, gastric carcinoma, and pancreatic carcinoma. Given the importance of HH signaling in tumorigenesis and stem cell regulation and the central role of SMO in HH pathway activation, specific targeting of HH/SMO signaling may therefore offer a highly effective therapeutic strategy for the treatment of a variety of HH pathway dependent cancers and manipulation of stem cell population. We hypothesized that SMO peptides could inhibit the growth of human cancer cells through inhibiting HH pathway activation. Thus, we synthesized several peptide analogs corresponding to transmembrane domains and intracellular loops of SMO, and characterized the inhibitory effects of these peptides on prostate cancer cells DU-145, PC3, and LnCap, and gastric cancer cells AGS. We found that the synthetic analogs of second and third intracellular loops (I2-1 and I3-1) of SMO inhibited growth of DU-145, LnCap and AGS cells. Treatment of I2-1 and I3-1 reduced the growth of DU-145 cells up to 79%, LnCap cells up to 30%, and AGS cells up to 56% in a dose-and time dependent manner compared with non-treatment control. The growth of PC3 cells was inhibited 20-27% by I3-1 only, but no effect of I2-1 on PC-3 cells and I3-1 on LnCap cells were observed. The modified synthetic analogs of the second intracellular loop (I2-8) were potentited by adding palmitic acid to the terminus. Moreover, the expression level of GLI and PTCH genes, indicators of HH pathway activity, was significant inhibited by I2-1 and I3-1 in Du145 cells. The synthetic analogs of transmembrane domains had no inhibitory effect on either cell proliferation or HH pathway gene expression. In conclusion, the present study showed that synthetic analogs of intracellular loops of SMO inhibited cell growth of prostate cancer cells and gastric cancer cells, and suppressed expression level of HH pathway genes. The observed inhibitory effects of SMO peptides were more effective than currently available cyclopamine and likely work via a different molecular mechanism. This result offers a new rationally-designed anticancer approach to treat common malignancies in which HH activation is important, including breast, metastatic prostate, lung, and gastrointestinal cancers.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA