Abstract
Activation of Wnt signalling due to inability to degrade β-catenin is found in >85% of colorectal cancers. Approximately half of colon cancers express a constitutively active KRAS protein. A significant fraction of patients show both abnormalities. We previously reported that simultaneous down-regulation of both β-catenin and KRAS was necessary to induce significant cell death and tumor growth inhibition of colorectal cancer cells. Although attractive, an RNAi-based therapeutic approach is still far from being employed in the clinical setting. Therefore, we sought to recapitulate our previous findings by the use of small-molecule inhibitors of β-catenin and KRAS. We show here that the β-catenin inhibitors PKF115-584 and pyrvinium pamoate block β-catenin-dependent transcriptional activity and synergize with the KRAS inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS, salirasib) in colon cancer cells driven by Wnt and KRAS oncogenic signals, but not in cells carrying BRAF mutations. The combined use of these compounds was superior to the use of any drug alone in inducing cell growth arrest, cell death, MYC and survivin down-modulation, and inhibition of anchorage-independent growth. Expression analysis of selected cancer-relevant genes revealed down-regulation of CD44 as a common response to the combined treatments. These data provide a proof of principle for a combination therapeutic strategy in colorectal cancer.
Highlights
Recent advances in our understanding of tumour biology have shown that, despite their great heterogeneity, cancer cells often remain dependent on a limited subset of genetic defects for their survival
We demonstrated that combined shRNAmediated silencing of b-catenin and KRAS in Colorectal cancer (CRC) cells led to massive induction of apoptosis in vitro and suppression of tumor growth in vivo, while individually targeting either of the two pathways showed modest effects [19]
In order to verify the activity of the two drugs in CRC cells, we characterized their effects in the Ls174T cell line, carrying bcatenin and KRAS activating mutations [30,33]
Summary
Recent advances in our understanding of tumour biology have shown that, despite their great heterogeneity, cancer cells often remain dependent on a limited subset of genetic defects for their survival. Colorectal cancer (CRC) is characterized by well-known genetic defects: the great majority (70–95%) of sporadic CRCs carry mutations that hyper-activate the Wnt pathway, leading to abnormal b-catenin-dependent gene expression [4,5,6,7]. These alterations occur early during tumour development [8] and likely represent addicting lesions for the tumor. Double targeting might be needed in order to achieve important therapeutic effects
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