Abstract
Sorafenib has been recently used for the treatment of patients with advanced colorectal cancer (CRC) and is recognized for its therapeutic value. However, the continuous use of sorafenib may cause resistance in the treatment of cancer patients. In this study, we investigated whether sorafenib exerts an enhanced anticancer effect on CRC cells via the calcium-mediated deactivation of the focal adhesion kinase (FAK) signaling pathways. The appropriate dose of sorafenib and lactate calcium salt (CaLa) for a combination treatment were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Then, cell cycle analysis was performed following treatment with 2.5 μM sorafenib and/or 2.5 mM CaLa. CRC cells were found to be in the G1 phase by sorafenib treatment, and they accumulated in the sub-G1 phase with CaLa treatment. Western blots and enzyme-linked immunosorbent assays were performed to analyze the elements of the recombinant activated factor (RAF) and focal adhesion kinase (FAK) signaling cascades. Sorafenib-inhibited RAF-dependent signaling in CRC cells, however, either did not affect the expression of Akt or increased it. As the upstream signaling of FAK was suppressed by CaLa, we observed that the expression of the sub-signaling phospho (p) AKT and p-mammalian target of rapamycin was also suppressed. Treatment with a combination of sorafenib and CaLa enhanced the antitumor activity of CRC cells. The % viability of CRC cells was significantly decreased compared to the single treatment with sorafenib or CaLa, and the accumulation of Sub G1 of CRC cells was clearly confirmed. The migration ability of CRC cells was significantly reduced. The findings of this study indicate that sorafenib will show further improved antitumor efficacy against CRC due to overcoming resistance through the use of CaLa.
Highlights
Many tyrosine kinase receptors are located upstream of mitogen-activated protein kinase (MAPK)pathways in colorectal cancer (CRC) cells, and the MAPK signaling pathway was found to be related to oncogenic processes [1]
In quantitative analysis, when the viability of the control group was defined as 100%, the viability of CRC cells at concentrations of 0.5, 1.0, and 2.5 μM decreased to 92.8 ± 3.2, 58.1 ± 8.9, and 48.4 ± 7.8% in HCT116 and to 96.8 ± 3.5, 52.1 ± 7.4, and 48.6 ± 5.3% in HT29, respectively (Figure 1B)
The anticancer efficacy of sorafenib was related to the inhibition of cell growth pathways of steroid receptor coactivator (Src)/focal adhesion kinase (FAK)/Akt/mammalian target of rapamycin (mTOR)
Summary
Many tyrosine kinase receptors are located upstream of mitogen-activated protein kinase (MAPK)pathways in colorectal cancer (CRC) cells, and the MAPK signaling pathway was found to be related to oncogenic processes [1]. Sorafenib is an oral kinase inhibitor that has activity in patients with advanced solid tumors, and it is the most successful multi-kinase inhibitor targeting the RAF/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway [1,3]. The abnormal activation of epithelial growth factor receptor (EGFR) and overexpression of its ligands due to the genetic heterogeneity of cancer was reported to lower the antitumor effect of sorafenib [8]. The phosphoinositide 3-kinases (PI3K)/Akt pathway regulates many molecules involved in most aspects of cancer growth and cross-talks with the RAF/MEK/ERK pathway [9]. In acquired resistance, the expression of the phosphorylated PI3K/Akt pathway is maintained by sorafenib, and downstream factors, such as mammalian target of rapamycin (mTOR), are activated to act as a potential compensation mechanism [3,9]
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