S100A4 as a Potential Target - Therapeutic Strategies in Cancer Biology and Pathology - page 59

The status of β-catenin was uncertain in early work. For instance Kimura et al. (2000)
and Moriyama-Kita et al. (2005) reported a downregulation of β-catenin in a background
of reduced S100A4 expression. However this would not be compatible with the opera-
tion of active Wnt signalling. With the avowed heterogeneity of tumours, it seems pos-
sible that this might have occurred in a subpopulation not directly linked with metastatic
ability. Indeed, Stein et al. (2006) identified TCF binding sites in the S100A4 promoter
and noted that β-catenin/TCF complex directly bound to the promoter and enhanced its
activity. This β-catenin/TCF-mediated regulation of S100A4 has been amply confirmed
recently. Stein et al. (2011) intrasplenically xenografted colon cancer cells overexpress-
ing S100A4 and treated the host animals with sulindac. This treatment seems to have
interfered with Wnt signalling, reduced β-catenin expression, the formation of β-catenin/
TCF transcription complex and importantly here in the downregulation of S100A4 pro-
moter activity and expression. The tumour that formed in the spleen and its metastases
in the liver both had reduced levels of β-catenin and S100A4. High S100A4 expression
together with reduced β-catenin expression has been linked significantly with tumour
growth, invasion and clinical stage of gastric cancers (Yoon et al., 2008).
The inhibitory effects of the Ca2+ ionophore calcimycin (A23187) on the expres-
sion of S100A4 were studied in human and murine hematopoietic cell lines some
years ago by Grigorian et al. (1994) who showed that it markedly reduced the
expression of S100A4 mRNA in the treated cells. This they suggested to be a result
of the degradation of mRNA since it was preventable by cycloheximide treatment,
possibly by blocking nucleases. Sack et al. (2011a) have reiterated and consider-
ably amplified the earlier findings with the demonstration that calcimycin inhibits
the transcription of S100A4. Treatment of colon (HCT116, SW620, LS174T and
SW480) cancer cells with calcimycin reduced S100A4mRNA and protein levels.
Calcimycin reduced S100A4 promoter activity in a concentration-dependent man-
ner. Typically, it inhibited cell proliferation and motility. The treatment also reduced
β-catenin expression suggesting that the effects of the ionophore might have been
brought about by inhibition of Wnt signalling. Among other Wnt effectors affected
were Dkk-1 and cell cycle related proteins. Sack et al. (2011a) also showed that
tumours developing from calcimycin treated HCT116 cells xenografted into intras-
plenic location showed markedly reduced metastatic spread to liver.
Sack et al. (2011b) have used a similar experimental regime to show that the
antihelminth drug Niclosamide also downregulated S100A4 expression with paral-
lel inhibition of cell proliferation, migration and metastatic spread of colon cancer
cells in xenograft tumour models. Of much interest in relation to the S100A4 linkup
with Wnt signalling is the finding that Niclosamide promoted the degradation of Wnt
co-receptor LRP6. It also induced apoptosis of prostate and breast cancer cells at
IC 50 of 1 μM. This dosage was comparable with that which inhibited Wnt signalling
(Lu et al., 2011b). Osada et al. (2011) also reported the inhibition of cell prolifer-
ation of colon cancer cell lines and that oral administration of the drug controlled
the growth of xenografts of tumours. Inhibition of Wnt signalling here seemed to be
due to the downregulation of DVL2. Other suggested routes of functioning include
NF-κB mediation in AML cells, where Niclosamide seems to inhibit the transcrip-
tion and DNA binding of NF-κB. It blocked TNF-induced IκB phosphorylation,