Specific targeting of insulin-like growth factor 1 receptor signaling in human estrogen dependent breast cancer cell by a novel tyrosine-based benzoxazepine derivative

The present study sought to investigate the in vitro and in vivo effects of a tyrosine-based benzoxazepine, 4-[4-(toluene-4-sulfonyl)-2,3,4,5-tetrahydro-benzo[f][1,4]oxazepin-3-ylmethyl]-phenol) [THBP] in human breast cancer cells, with a focus on determining its molecular target. THBP had growth inhibitory effect on MCF-7 and MDA-MD-231 cells. At IC50 value (∼20 μM), THBP resulted in G1 arrest, decrease in cyclin D1 levels and induction of apoptosis of MCF-7 cells. Mechanistically, activation of caspase 8 contributes critically to the induction of apoptotic cell death as copresence of selective inhibition of caspase 8 effectively abrogates the cytotoxic effect of THBP in MCF-7 cells. Further, THBP increased pro-apoptotic protein, Bax; decreased anti-apoptotic protein, Bcl-2; and decreased mitochondrial membrane potential in MCF-7 cells, indicating involvement of an intrinsic pathway of apoptosis following caspase 8 activation. Out of the various growth factors/hormones, THBP selectively abrogated increased viability of MCF-7 cells by insulin-like growth factor 1 (IGF-1). Molecular docking studies revealed that THBP occupied the ATP binding pocket of IGF-1 receptor (IGF-1R). Accordingly THBP was found to inhibit IGF-1-induced phosphorylation of IGF-1R and insulin receptor substrate-1 (IRS-1) without inhibiting insulin signaling in MCF-7 cells. In athymic nude mice, compared with vehicle, THBP treatment significantly reduced the growth of MCF-7 xenograft tumors through inhibition of cancer cell proliferation as well as promotion of cell death that correlated with reduced phospho-IGF-1R levels. We suggest that interfering with the IGF-1R signaling by the benzoxazepine THBP offers a novel and selective therapeutic strategy for estrogen receptor-positive, postmenopausal breast cancer patients.

4-[4-(Toluene-4-sulfonyl)-2,3,4,5-tetrahydro-benzo[f][1,4]oxazepin-3-ylmethyl]-phenol) [THBP] selectively abrogated signaling of insulin-like growth factor 1 receptor (IGF-1R) in estrogen receptor expressing human breast cancer cells (MCF-7), demonstrated by molecular docking and biochemical studies. THBP inhibits phosphorylation of IGF-1R, which results in inhibition of insulin receptor substrate (IRS1) phosphorylation. IRS1 interacts with the cytoplasmic protein phosphatidylinositol 3-kinases (PI3K) and leads to downregulation of AKT and cyclinD1 levels. THBP also induces caspase-8 activation and BID cleavage, which in turn trigger mitochondrial pathway to amplify cell death by increasing Bax to bcl-2 ratio leading apoptosis. In athymic nude mice, compared with vehicle, THBP treatment significantly reduced the growth of MCF-7 xenograft tumors through inhibition of cell proliferation as well as promotion of cell death that correlated with reduced phospho-IGF-1R levels. THBP represents a new class of IGF-1R inhibitors for future preclinical and clinical studies. Blue color indicates the signaling molecules which has not been studied.Figure optionsDownload high-quality image (66 K)Download as PowerPoint slideHighlights
► We evaluated the effect of a novel benzoxazepine (THBP) on human breast cancer cells.
► THBP caused G1 arrest, downregulation of cyclin D1 and apoptosis of cancer cells.
► THBP did not affect the viability of normal human cells.
► THBP mediated cytotoxic effect by blocking insulin growth factor receptor signaling.
► THBP arrested the growth of xenograft breast tumor in athymic nude mice.