Abstract
BackgroundThe use of targeted agents to impel dual inhibition of anti-apoptotic mechanisms and mTOR-mediated pro-survival signaling in colorectal carcinoma (CRC) cell lines with KRAS or BRAF mutation has been shown to induce apoptosis, a timely result given CRC entities harboring such mutations are in need of new therapies. Since CRC comprises heterogeneous tumors with predominant hypoxic components, we investigated effects of an inhibitor of anti-apoptotic Bcl-2 family proteins (ABT-737) in combination with an mTOR inhibitor (AZD8055)—collectively referred to as combo-Rx, in hypoxic CRC cell lines.MethodsCell viability measures, expression of proteins implicated in apoptosis and MAPK/PI3K-AKT/mTOR pathway signaling, and profiling of composite kinase activities were undertaken in a panel of 14 cell lines.ResultsIn hypoxic conditions, combo-Rx suppressed viability of 13 of the cell lines, albeit ABT-737 did not significantly potentiate the inhibitory effect of single-agent AZD8055 in six of the models. Hypoxic KRAS/PIK3CA-mutant HCT-116 and HCT-15 cell lines (both with low endogenous expression of the anti-apoptotic Mcl-1 protein and showing augmented inhibition of viability following the addition of ABT-737 to AZD8055) responded to combo-Rx by induction of apoptosis but with the simultaneous strong Mcl-1 up-regulation and activation of MAPK/PI3K-conducted signaling. In contrast, in hypoxic KRAS-mutant LoVo (devoid of PIK3CA mutation), BRAF/PIK3CA-mutant RKO, and wild-type Colo320DM cell lines (all with high endogenous Mcl-1 expression and being resistant to the additional effect of ABT-737 to AZD8055), combo-Rx did not elicit apoptotic or pro-survival responses.ConclusionsThe concurrent inhibition of anti-apoptotic proteins and mTOR-mediated signaling in hypoxic KRAS/PIK3CA-mutant CRC cell lines resulted in pro-survival responses in parallel with the intended anti-proliferative effects, a finding that should be of note if considering combinatory targeting of multiple pathways in this CRC entity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2600-y) contains supplementary material, which is available to authorized users.
Highlights
The use of targeted agents to impel dual inhibition of anti-apoptotic mechanisms and mTORmediated pro-survival signaling in colorectal carcinoma (CRC) cell lines with KRAS or BRAF mutation has been shown to induce apoptosis, a timely result given CRC entities harboring such mutations are in need of new therapies
Since no information is available regarding the concurrent inhibition of anti-apoptotic proteins and mTORmediated pro-survival signaling under CRC tumor hypoxia, we investigated response to treatment with ABT-737 and AZD8055, in this report referred to as combo-Rx, in a panel of hypoxic CRC cell lines harboring various typical mutations
Since Faber and co-workers found that the combination of ABT-263, a structurally related compound to ABT-737, with AZD8055 at concentrations of 50–500 nM for 72 h caused apoptosis in CRC cell lines with KRAS or BRAF mutation [9], we investigated inhibitory effects on cell viability when combining AZD8055 at 0.10 μM with ABT-737 for 72 h
Summary
The use of targeted agents to impel dual inhibition of anti-apoptotic mechanisms and mTORmediated pro-survival signaling in colorectal carcinoma (CRC) cell lines with KRAS or BRAF mutation has been shown to induce apoptosis, a timely result given CRC entities harboring such mutations are in need of new therapies. Mutations in genes such as KRAS, BRAF, and PIK3CA commonly result in constitutive activation of cellular signaling mediated by mitogen-activated protein kinases (MAPK) and phosphatidylinositol 3-kinase–protein kinase B (PI3K–AKT) [4, 5] These pathways converge at the mechanistic target of rapamycin (mTOR), which regulates cell growth and survival [6] and makes the mTOR complex an attractive target for CRC therapy. Recent findings showed that the combination of the mTOR inhibitor AZD8055 with ABT-263, an inducer of apoptosis, promoted cell death in CRC cell lines with KRAS or BRAF mutation [9], a timely result given CRC entities harboring these mutations are refractory to current targeted therapies. Hypoxia has been shown to promote ABT-737-mediated apoptotic cell death in small-cell lung carcinoma, CRC, and hematologic cell lines via down-regulation of Mcl-1 [15,16,17]
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