Yi Du

Single nanoparticle tracking (SPT) is a unique and powerful tool to investigate the interaction between nanoparticles and cells, which is of great importance for nanotechnology applications in biom... Description

PARP1 inhibitors (PARPi) are currently used in the clinic for the treatment of ovarian and breast cancers, yet their therapeutic efficacy against hepatocellular carcinoma (HCC) has been disappointing. To ensure therapeutic efficacy of PARPi against HCC, a disease often diagnosed at intermediate to advanced stages with no effective treatment options, it is critical to identify not only biomarkers to predict PARPi resistance but also rational treatments to overcome this. Here, we report that a heterodimer of EGFR and MET interacts with and phosphorylates Y907 of PARP1 in the nucleus, which contributes to PARPi resistance. Inhibition of both EGFR and MET sensitized HCC cells to PARPi, and both EGFR and MET are known to be overexpressed in HCC. This report provides an explanation for the poor efficacy of PARPi against HCC and suggests combinatorial treatment consisting of EGFR, MET, and PARP inhibitors may be an effective therapeutic strategy in HCC. Significance: Regulation of PARP by the c-MET and EGFR heterodimer suggests a potentially effective combination therapy to sensitize HCC to PARPi.

EGFL6, a member of the EGF-like superfamily, plays an important role during embryonic development and has been implicated in promotion of tumor angiogenesis without affecting wound healing. There is very little known about the function of EGFL6 in cancer cells. Here, we investigated whether EGFL6 plays a direct role in cancer cells in addition to the promotion of tumor angiogenesis. Our study showed that EGFL6 promoted epithelial–mesenchymal transition (EMT) and stemness of breast cancer cells and increased cell migration and invasion in cell culture studies. We also found that EGFL6 reduced apoptotic signaling in cancer cells and promoted tumor growth in vivo. Importantly, expression of EGFL6 in cancer cells and tumor endothelial cells not only increased tumor angiogenesis but also promoted migration of cancer cells. Such dual engagement of cancer and stromal cells suggests crosstalk mediated by EGFL6 in the tumor microenvironment. Blockade of EGFL6 using our novel anti-EGFL6 monoclonal antibody significantly reduced cancer cell migration, tumor angiogenesis, and tumor growth in mouse xenograft tumor models. Silencing EGFL6 mRNA by shRNA transfection of cancer cells also significantly reduced cancer cell migration, tumor angiogenesis, and tumor growth in mouse xenograft tumor models. Taken together, the results of this study indicate that targeting EGFL6 is a unique strategy for inhibiting both cancer cell metastasis and tumor angiogenesis.

Inhibitors against poly (ADP-ribose) polymerase (PARP) are promising targeted agents currently used to treat BRCA-mutant ovarian cancer and are in clinical trials for other cancer types, including BRCA-mutant breast cancer. To enhance the clinical response to PARP inhibitors (PARPis), understanding the mechanisms underlying PARPi sensitivity is urgently needed. Here, we show enhancer of zeste homolog 2 (EZH2), an enzyme that catalyzes H3 lysine trimethylation and associates with oncogenic function, contributes to PARPi sensitivity in breast cancer cells. Mechanistically, upon oxidative stress or alkylating DNA damage, PARP1 interacts with and attaches poly-ADP-ribose (PAR) chains to EZH2. PARylation of EZH2 by PARP1 then induces PRC2 complex dissociation and EZH2 downregulation, which in turn reduces EZH2-mediated H3 trimethylation. In contrast, inhibition of PARP by PARPi attenuates alkylating DNA damage-induced EZH2 downregulation, thereby promoting EZH2-mediated gene silencing and cancer stem cell property compared with PARPi-untreated cells. Moreover, the addition of an EZH2 inhibitor sensitizes the BRCA-mutant breast cells to PARPi. Thus, these results may provide a rationale for combining PARP and EZH2 inhibition as a therapeutic strategy for BRCA-mutated breast and ovarian cancers.

Purpose: To explore whether a cross-talk exists between PARP inhibition and PD-L1/PD-1 immune checkpoint axis, and determine whether blockade of PD-L1/PD-1 potentiates PARP inhibitor (PARPi) in tumor suppression. Experimental Design: Breast cancer cell lines, xenograft tumors, and syngeneic tumors treated with PARPi were assessed for PD-L1 expression by immunoblotting, IHC, and FACS analyses. The phospho-kinase antibody array screen was used to explore the underlying mechanism of PARPi-induced PD-L1 upregulation. The therapeutic efficacy of PARPi alone, PD-L1 blockade alone, or their combination was tested in a syngeneic tumor model. The tumor-infiltrating lymphocytes and tumor cells isolated from syngeneic tumors were analyzed by CyTOF and FACS to evaluate the activity of antitumor immunity in the tumor microenvironment. Results: PARPi upregulated PD-L1 expression in breast cancer cell lines and animal models. Mechanistically, PARPi inactivated GSK3β, which in turn enhanced PARPi-mediated PD-L1 upregulation. PARPi attenuated anticancer immunity via upregulation of PD-L1, and blockade of PD-L1 resensitized PARPi-treated cancer cells to T-cell killing. The combination of PARPi and anti-PD-L1 therapy compared with each agent alone significantly increased the therapeutic efficacy in vivo. Conclusions: Our study demonstrates a cross-talk between PARPi and tumor-associated immunosuppression and provides evidence to support the combination of PARPi and PD-L1 or PD-1 immune checkpoint blockade as a potential therapeutic approach to treat breast cancer. Clin Cancer Res; 23(14); 3711–20. ©2017 AACR.

Personalized or precision medicine is an emerging treatment approach tailored to individuals or certain groups of patients based on their unique characteristics. These types of therapies guided by biomarkers tend to be more effective than traditional approaches, especially in cancer. The inhibitor against poly (ADP-ribose) polymerase (PARP), olaparib (Lynparza, AstraZeneca), which was approved by the US Food and Drug Administration (FDA) in 2014, demonstrated efficacy specifically for ovarian cancer patients harboring mutations in BRCA genes, which encode proteins in DNA double-strand break repairs. However, the response to PARP inhibitors has been less encouraging in other cancer types that also carry defects in the BRCA genes. Thus, furthering our understanding of the underlying mechanism of PARP inhibitors and resistance is critical to improve their efficacy. In this review, we summarize the results of preclinical studies and the clinical application of PARP inhibitors, and discuss the future direction of PARP inhibitors as a potential marker-guided personalized medicine for cancer treatment.

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal disease characterized by a prominent desmoplastic stroma that may constrain tumor progression but also limit the access of therapeutic drugs. In this study, we explored a tumor-targeting strategy that enlists an engineered anti-angiogenic protein consisting of endostatin and cytosine deaminase linked to uracil phosphoribosyltransferase (EndoCD). This protein selectively binds to tumor vessels to compromise tumor angiogenesis and converts the non-toxic 5-fluorocytosine (5-FC) to the cytotoxic 5-fluorouracil to produce a chemotherapeutic bystander effect at the pancreatic tumor site. We found that resveratrol increased the protein stability of EndoCD through suppression of chymotrypsin-like proteinase activity and synergistically enhances EndoCD-mediated 5-FC-induced cell killing. In various PDAC mouse models, the EndoCD/5-FC/resveratrol regimen decreased intratumoral vascular density and stroma formation and enhances apoptosis in tumors cells as well as in surrounding endothelial, pancreatic stellate, and immune cells, leading to reduced tumor growth and extended survival. Thus, the EndoCD/5-FC/resveratrol combination may be an effective treatment option for PDAC.

C-Met binds to and phosphorylates PARP1 in cancer cells, thereby reducing PARP1 binding to a PARP inhibitor; c-Met and PARP inhibitor combination therapy shows improved efficacy in preclinical models of breast and lung cancer. Poly (ADP-ribose) polymerase (PARP) inhibitors have emerged as promising therapeutics for many diseases, including cancer, in clinical trials1. One PARP inhibitor, olaparib (Lynparza, AstraZeneca), was recently approved by the FDA to treat ovarian cancer with mutations in BRCA genes. BRCA1 and BRCA2 have essential roles in repairing DNA double-strand breaks, and a deficiency of BRCA proteins sensitizes cancer cells to PARP inhibition2,3. Here we show that the receptor tyrosine kinase c-Met associates with and phosphorylates PARP1 at Tyr907 (PARP1 pTyr907 or pY907). PARP1 pY907 increases PARP1 enzymatic activity and reduces binding to a PARP inhibitor, thereby rendering cancer cells resistant to PARP inhibition. The combination of c-Met and PARP1 inhibitors synergized to suppress the growth of breast cancer cells in vitro and xenograft tumor models, and we observed similar synergistic effects in a lung cancer xenograft tumor model. These results suggest that the abundance of PARP1 pY907 may predict tumor resistance to PARP inhibitors, and that treatment with a combination of c-Met and PARP inhibitors may benefit patients whose tumors show high c-Met expression and who do not respond to PARP inhibition alone.

Triple-negative breast cancer (TNBC), which is closely related to basal-like breast cancer, is a highly aggressive subtype of breast cancer that initially responds to chemotherapy but eventually develops resistance. This presents a major clinical challenge as there are currently no effective targeted therapies available due to its lack of HER2 and estrogen receptor expression. Here, we show that cyclin E and the enhancer of zeste 2 (EZH2) are closely co-expressed in TNBC patients, and cyclin E/CDK2 phosphorylates EZH2 at T416 (pT416-EZH2) in vivo. Phosphorylation of EZH2 at T416 enhances the ability of EZH2 to promote TNBC cell migration/invasion, tumorsphere formation, and in vivo tumor growth. In addition, high pT416-EZH2 correlates with poorer survival in TNBC patients. These findings suggest that pT416 has the potential to serve as a therapeutic biomarker for the aggressive forms of breast cancer and provide a rationale for the use of CDK2 inhibitors to treat TNBC.