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Analogs of the novel phytohormone, strigolactone, trigger apoptosis and synergize with PARP inhibitors by inducing DNA damage and inhibiting DNA repair.

ABSTRACT: Strigolactones are a novel class of plant hormones produced in roots that regulate shoot and root development. We previously reported that strigolactone analogs (SLs) induce G2/M cell cycle arrest and apoptosis in a variety of human cancer cells and inhibit tumor growth of human breast cancer xenografts in mice. SLs had no significant influences on non-transformed cells. Here we report for the first time that SLs induce DNA damage in the form of DNA double-strand breaks (DSBs) and activate the DNA damage response signaling by inducing phosphorylation of ATM, ATR and DNA-PKcs and co-localization of the DNA damage signaling protein, 53BP1, with ?H2AX nuclear foci. We further report that in addition to DSBs induction, SLs simultaneously impair DSBs repair, mostly homology-directed repair (HDR) and to a lesser extent non-homologous end joining (NHEJ). In response to SLs, RAD51, the homologous DSB repair protein, is ubiquitinated and targeted for proteasomal degradation and it fails to co-localize with ?H2AX foci. Interestingly, SLs synergize with DNA damaging agents-based therapeutics. The combination of PARP inhibitors and SLs showed an especially potent synergy, but only in BRCA1-proficient cells. No synergy was observed between SLs and PARP inhibitors in BRCA1-deficient cells, supporting a role for SLs in HDR impairment. Together, our data suggest that SLs increase genome instability and cell death by a unique mechanism of inducing DNA damage and inhibiting DNA repair.

SUBMITTER: Croglio MP

PROVIDER: S-EPMC4924693 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Analogs of the novel phytohormone, strigolactone, trigger apoptosis and synergize with PARP inhibitors by inducing DNA damage and inhibiting DNA repair.

Croglio Michael P MP Haake Jefferson M JM Ryan Colin P CP Wang Victor S VS Lapier Jennifer J Schlarbaum Jamie P JP Dayani Yaron Y Artuso Emma E Prandi Cristina C Koltai Hinanit H Agama Keli K Pommier Yves Y Chen Yu Y Tricoli Lucas L LaRocque Jeannine R JR Albanese Christopher C Yarden Ronit I RI

Oncotarget 20160301 12

Strigolactones are a novel class of plant hormones produced in roots that regulate shoot and root development. We previously reported that strigolactone analogs (SLs) induce G2/M cell cycle arrest and apoptosis in a variety of human cancer cells and inhibit tumor growth of human breast cancer xenografts in mice. SLs had no significant influences on non-transformed cells. Here we report for the first time that SLs induce DNA damage in the form of DNA double-strand breaks (DSBs) and activate the D ...[more]

PMID: 26910887

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Project description:PurposeTriple-negative breast cancer (TNBC) is the most challenging and aggressive subtype of breast cancer with limited treatment options because of tumor heterogeneity, lack of druggable targets and therapy resistance. TNBCs are characterized by overexpression of growth factor receptors such as epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor (VEGFR), and platelet derived growth factor receptor (PDGFR) making them promising therapeutic targets. Regorafenib is an FDA approved oral multi-kinase inhibitor that blocks the activity of multiple protein kinases including those involved in the regulation of tumor angiogenesis [VEGFR1-3, TIE2], tumor microenvironment [PDGFR-β, FGFR] and oncogenesis (KIT, RET, RAF-1, BRAF). In the current study, we examined the radiosensitizing effects of Regorafenib on TNBC cell lines and explored the mechanism by which Regorafenib enhances radiosensitivity.MethodsMDA-MB-231 and SUM159PT (human TNBC cell lines) and MCF 10a (human mammary epithelial cell line) were treated with Regorafenib, ionizing radiation or a combination of both. Following treatment with Regorafenib and radiation we conducted clonogenic assay to determine radiosensitivity, immunoblot analysis to assess the effect on key signaling targets, tube formation to evaluate effect on angiogenesis and comet assay as well as western blot for γH2AX to assess DNA damage response (DDR).ResultsRegorafenib reduced cell proliferation and enhanced radiosensitivity of MDA-MB-231 and SUM159PT cell lines but had no effect on the MCF 10a cells. Clonogenic survival assays showed that the surviving fraction at 2 Gy for both MDA-MB-231 and SUM159PT was reduced from 66.4 ± 8.9 and 88.2 ± 1.7 in controls to 38.1 ± 4.9 and 75.1 ± 1.1 following a 24 hr pretreatment with 10 μM and 5 μM Regorafenib, respectively. A marked reduction in the expression of VEGFR, PDGFR, EGFR and the downstream target, ERK, was observed with Regorafenib treatment alone or in combination with radiation. We also observed a significant inhibition of VEGF-A production in the TNBC cell lines following treatment with Regorafenib. Further, the addition of conditioned medium from Regorafenib-treated tumor cells onto human umbilical vein endothelial cells (HUVEC) suppressed tube formation, indicating an inhibition of tumor angiogenesis. Regorafenib also decreased migration of TNBC cells and suppressed radiation-induced DNA damage repair in a time-dependent manner.ConclusionsOur findings demonstrate that Regorafenib enhanced radiosensitivity of breast cancer cells by inhibiting the expression of multiple receptor tyrosine kinases, VEGF-mediated angiogenesis and DNA damage response in TNBC. Therefore, combining Regorafenib with radiation and antiangiogenic agents will be beneficial and effective in controlling TNBC.

Dataset Information

Analogs of the novel phytohormone, strigolactone, trigger apoptosis and synergize with PARP inhibitors by inducing DNA damage and inhibiting DNA repair.

Publications

Analogs of the novel phytohormone, strigolactone, trigger apoptosis and synergize with PARP inhibitors by inducing DNA damage and inhibiting DNA repair.

Similar Datasets

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