Transposon DNA sequences facilitate the tissue-specific gene transfer of circulating tumor DNA between human cells

The exchange of genes between cells is known to play an important physiological and pathological role in many organisms. We show that circulating tumor DNA (ctDNA) facilitates cell-specific gene transfer between human cancer cells and explain part of the mechanisms behind this phenomenon. As ctDNA migrates into the nucleus, genetic information is transferred. Cell targeting and ctDNA integration require ERVL, SINE or LINE DNA sequences. Chemically manufactured AluSp and MER11C sequences replicated multiple myeloma (MM) ctDNA cell targeting and integration. Additionally, we found that ctDNA may alter the treatment response of MM and pancreatic cancer models. This study shows that retrotransposon DNA sequences promote cancer gene transfer. However, because cell-free DNA has been detected in physiological and other pathological conditions, our findings have a broader impact than just cancer. Furthermore, the discovery that transposon DNA sequences mediate tissue-specific targeting will open up a new avenue for the delivery of genes and therapies.

DNA-PK is activated by SIRT2 deacetylation to promote DNA double-strand break repair by non-homologous end joining

DNA-dependent protein kinase (DNA-PK) plays a critical role in non-homologous end joining (NHEJ), the predominant pathway that repairs DNA double-strand breaks (DSB) in response to ionizing radiation (IR) to govern genome integrity. The interaction of the catalytic subunit of DNA-PK (DNA-PKcs) with the Ku70/Ku80 heterodimer on DSBs leads to DNA-PK activation; however, it is not known if upstream signaling events govern this activation. Here, we reveal a regulatory step governing DNA-PK activation by SIRT2 deacetylation, which facilitates DNA-PKcs localization to DSBs and interaction with Ku, thereby promoting DSB repair by NHEJ. SIRT2 deacetylase activity governs cellular resistance to DSB-inducing agents and promotes NHEJ. SIRT2 furthermore interacts with and deacetylates DNA-PKcs in response to IR. SIRT2 deacetylase activity facilitates DNA-PKcs interaction with Ku and localization to DSBs and promotes DNA-PK activation and phosphorylation of downstream NHEJ substrates. Moreover, targeting SIRT2 with AGK2, a SIRT2-specific inhibitor, augments the efficacy of IR in cancer cells and tumors. Our findings define a regulatory step for DNA-PK activation by SIRT2-mediated deacetylation, elucidating a critical upstream signaling event initiating the repair of DSBs by NHEJ. Furthermore, our data suggest that SIRT2 inhibition may be a promising rationale-driven therapeutic strategy for increasing the effectiveness of radiation therapy.

Abstract 713: BBI-608 modulates DNA repair pathways, induces apoptosis and impacts response to 5-Fluorouracil and ionizing radiation in pancreatic cancer cells

Background: BBI-608 has been shown to modulate multiple oncogenic cellular pathways which are often constitutively active in pancreatic ductal adenocarcinoma (PDAC). Among these are key mediators of DNA repair and cellular survival pathways. We hypothesized that BBI-608 would sensitize PDAC cells to chemoradiotherapy.

Methods: The combined effects of BBI-608 and chemoradiotherapy (5-FU + IR) were evaluated in human (MIA PaCa-2) and murine (PANC-02) PDAC cell lines using a Br-dU cell proliferation assay. To elucidate the mechanism of action, effects on the expression of DNA damage and repair (pATM, γ-H2AX, p53; pATR, and Rad51) molecules were examined by Western blot. Apoptosis was assessed via Annexin V staining and flow cytometric analysis to evaluate mechanism of cell death following treatment of MIA PaCa-2 and PANC-02 cell lines. The in vivo activity of BBI-608, 5-FU + IR, alone and in combination, were evaluated in C57BL/6 mice bearing subcutaneous PANC-02 tumors.

Results: The combination of BBI-608 and chemoradiotherapy significantly decreased (p<0.001) cell proliferation and induced Annexin V positive cells in both MIA PaCa-2 and PANC-02 cell lines. BBI-608 and chemoradiotherapy also decreased the activation of pATR, MDM2, and Rad51 and increased pATM, γ-H2AX and p53. Administration of BBI-608 potentiated the effects of chemoradiotherapy in vivo in mice bearing subcutaneous PANC-02 tumors as measured by tumor volume.

Conclusion: These data identify a role for BBI-608 as a modulator of DNA damage and apoptosis. These effects enhanced the efficacy of chemoradiotherapy in cell lines and in vivo models of PDAC and provide rationale for continued investigation in the pre-clinical and clinical setting.

Note: This abstract was not presented at the meeting.

Citation Format: Batoul Farran, Ganji P. Nagaraju, Sneha G. Shipra, Shipra R. Bethi, Gregory B. Lesinski, Bassel El-Rayes. BBI-608 modulates DNA repair pathways, induces apoptosis and impacts response to 5-Fluorouracil and ionizing radiation in pancreatic cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 713.

Abstract 4074: Heat shock protein 90 inhibitors alter pancreatic stellate cell cytokine production and enhances the efficacy of immune checkpoint blockade in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has a prominent fibrotic stroma, which is a result of interactions between tumor, immune and pancreatic stellate cells (PSC). Prior work from our laboratory has defined a role for stroma-derived cytokines such as IL-6 as a significant barrier restraining immunity against PDAC. Our group is pursuing novel approaches to target pathways in the tumor microenvironment (TME), in an effort to improve access of effector immune cells to PDAC and response to immunotherapy. Heat shock protein-90 (Hsp90), is a chaperone protein and a versatile target in pancreatic cancer. Hsp90 regulates a diverse array of cellular processes of relevance to both the tumor and the immune system. However, to date the role of Hsp90 in PSC has not been explored in detail. We hypothesize that targeting Hsp90 can modulate the TME, through its ability to target inflammatory signaling and cytokine production by PSC and enhance the efficacy of immunotherapy. Treatment of immortalized and primary patient PSC with the Hsp90 inhibitor XL888 led to decreased IL-6 at the transcript and protein level in vitro. XL888 directly limited PSC growth, and reduced expression of alpha-SMA, Jak/STAT and MAPK signaling intermediates as determined via immunoblot. Combined therapy with XL888 and anti-PD-1 was efficacious in C57BL/6 mice bearing syngeneic subcutaneous (Panc02) or orthotopic (KPC-Luc) tumors, as compared to treatment with either agent alone. The treatment was well-tolerated, with no difference in body weight observed in either model. Laboratory studies are assessing immune and stromal biomarkers to define the impact on PSC, cytokines and T-cell biomarkers in the TME. Finally, we have completed the dose escalation phase of a Phase Ib/II clinical trial of XL888 (Hsp90i) and pembrolizumab (anti-PD-1) at our institution. Expansion cohorts of patients with metastatic pancreatic cancer (n=16) or colorectal cancer (n=16) are now accruing, with paired biopsy and peripheral blood samples to address the impact of Hsp90 inhibition on anti-PD-1 mediated T cell proliferation, cytokine production, and PSC-derived cytokine signatures.

Citation Format: Mohammad Zaidi, Yuchen Zhang, Michael B. Ware, Matthew R. Farren, Hannah Komar, Brian Olson, Ganji P. Nagaraju, Mehmet Akce, Olatunji Alese, Shishir Maithel, Juan Sarmiento, Walid Shaib, Christina Wu, Bassel El-Rayes, Gregory B. Lesinski. Heat shock protein 90 inhibitors alter pancreatic stellate cell cytokine production and enhances the efficacy of immune checkpoint blockade in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4074.

Altering the cytokine profile in the pancreatic cancer microenvironment with heat shock protein-90 inhibitors to enhance immunotherapy

One feature of pancreatic ductal adenocarcinoma (PDAC) is the fibrotic stroma, which is a result of interactions between tumor cells, immune suppressive cells and pancreatic stellate cells (PSC). Stroma-derived cytokines including IL-6 represent a significant barrier restraining immunity against PDAC. Targeting pathways in the tumor microenvironment (TME) that regulate cytokine secretion can be an innovative means to improve access of effector immune cells to PDAC. We hypothesize that targeting Hsp90 can modulate the TME, through its ability to target inflammatory signaling and cytokine production by PSC and enhance the efficacy of immunotherapy. The Hsp90 inhibitor XL888 led to a concentration-dependent inhibition of IL-6 and MCP-1 production by PSC in vitro. Concurrently, PSC displayed growth inhibition as determined by MTT assay, and reduced alpha-SMA expression, a marker of cell activation. Inhibition of Jak/STAT and MAPK signaling was confirmed via immunoblot. These data compliment our published results indicating that Hsp90 inhibitors modulate survival pathways and PDAC growth in vitro and in vivo. This has led to an investigator-initiated Phase Ib/II clinical trial of XL888 (Hsp90i) and pembrolizumab (anti-PD-1) now accruing at our institution. Extensive laboratory correlative studies are ongoing to examine the impact of Hsp90 inhibition on anti-PD-1 mediated T cell proliferation, cytokine production, and impact on PSC-derived cytokine signatures. This work is being performed in paired biopsy samples (pre- and on-treatment), and peripheral blood from expansion cohorts of patients with metastatic pancreatic cancer (n=16) or colorectal cancer (n=16).

Broad targeting of angiogenesis for cancer prevention and therapy

Deregulation of angiogenesis – the growth of new blood vessels from an existing vasculature – is a main driving force in many severe human diseases including cancer. As such, tumor angiogenesis is important for delivering oxygen and nutrients to growing tumors, and therefore considered an essential pathologic feature of cancer, while also playing a key role in enabling other aspects of tumor pathology such as metabolic deregulation and tumor dissemination/metastasis. Recently, inhibition of tumor angiogenesis has become a clinical anti-cancer strategy in line with chemotherapy, radiotherapy and surgery, which underscore the critical importance of the angiogenic switch during early tumor development. Unfortunately the clinically approved anti-angiogenic drugs in use today are only effective in a subset of the patients, and many who initially respond develop resistance over time. Also, some of the anti-angiogenic drugs are toxic and it would be of great importance to identify alternative compounds, which could overcome these drawbacks and limitations of the currently available therapy. Finding “the most important target” may, however, prove a very challenging approach as the tumor environment is highly diverse, consisting of many different cell types, all of which may contribute to tumor angiogenesis. Furthermore, the tumor cells themselves are genetically unstable, leading to a progressive increase in the number of different angiogenic factors produced as the cancer progresses to advanced stages. As an alternative approach to targeted therapy, options to broadly interfere with angiogenic signals by a mixture of non-toxic natural compound with pleiotropic actions were viewed by this team as an opportunity to develop a complementary anti-angiogenesis treatment option. As a part of the “Halifax Project” within the “Getting to know cancer” framework, we have here, based on a thorough review of the literature, identified 10 important aspects of tumor angiogenesis and the pathological tumor vasculature which would be well suited as targets for anti-angiogenic therapy: (1) endothelial cell migration/tip cell formation, (2) structural abnormalities of tumor vessels, (3) hypoxia, (4) lymphangiogenesis, (5) elevated interstitial fluid pressure, (6) poor perfusion, (7) disrupted circadian rhythms, (8) tumor promoting inflammation, (9) tumor promoting fibroblasts and (10) tumor cell metabolism/acidosis. Following this analysis, we scrutinized the available literature on broadly acting anti-angiogenic natural products, with a focus on finding qualitative information on phytochemicals which could inhibit these targets and came up with 10 prototypical phytochemical compounds: (1) oleanolic acid, (2) tripterine, (3) silibinin, (4) curcumin, (5) epigallocatechin-gallate, (6) kaempferol, (7) melatonin, (8) enterolactone, (9) withaferin A and (10) resveratrol. We suggest that these plant-derived compounds could be combined to constitute a broader acting and more effective inhibitory cocktail at doses that would not be likely to cause excessive toxicity. All the targets and phytochemical approaches were further cross-validated against their effects on other essential tumorigenic pathways (based on the “hallmarks” of cancer) in order to discover possible synergies or potentially harmful interactions, and were found to generally also have positive involvement in/effects on these other aspects of tumor biology. The aim is that this discussion could lead to the selection of combinations of such anti-angiogenic compounds which could be used in potent anti-tumor cocktails, for enhanced therapeutic efficacy, reduced toxicity and circumvention of single-agent anti-angiogenic resistance, as well as for possible use in primary or secondary cancer prevention strategies.

Organotin-Induced Hyperglycemia in the Crab, Oziotelphusa senex senex Fabricius

Injection of three different organotin compounds such as tripalmitin, fentin and fenbutatin produced a significant increase in the hemolymph sugar level of intact crabs at Oziotelphusa senex senex apparently by stimulating release of the hyperglycemic hormone (HGH).

CHD7 expression predicts survival outcomes in patients with resected pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with poor outcomes with current therapies. Gemcitabine is the primary adjuvant drug used clinically, but its effectiveness is limited. In this study, our objective was to use a rationale-driven approach to identify novel biomarkers for outcome in patients with early-stage resected PDAC treated with adjuvant gemcitabine. Using a synthetic lethal screen in human PDAC cells, we identified 93 genes, including 55 genes linked to DNA damage responses (DDR), that demonstrated gemcitabine sensitization when silenced, including CHD7, which functions in chromatin remodeling. CHD7 depletion sensitized PDAC cells to gemcitabine and delayed their growth in tumor xenografts. Moreover, CHD7 silencing impaired ATR-dependent phosphorylation of CHK1 and increased DNA damage induced by gemcitabine. CHD7 was dysregulated, ranking above the 90th percentile in differential expression in a panel of PDAC clinical specimens, highlighting its potential as a biomarker. Immunohistochemical analysis of specimens from 59 patients with resected PDAC receiving adjuvant gemcitabine revealed that low CHD7 expression was associated with increased recurrence-free survival (RFS) and overall survival (OS), in univariate and multivariate analyses. Notably, CHD7 expression was not associated with RFS or OS for patients not receiving gemcitabine. Thus, low CHD7 expression was correlated selectively with gemcitabine sensitivity in this patient population. These results supported our rationale-driven strategy to exploit dysregulated DDR pathways in PDAC to identify genetic determinants of gemcitabine sensitivity, identifying CHD7 as a novel biomarker candidate to evaluate further for individualizing PDAC treatment.

Abstract 342: Silencing of IGF1R induces mesenchymal-to-epithelial transition and inhibits the metastatic properties of triple negative breast cancer cells

Next to skin cancer, breast cancer is the second most common cancer diagnosed among American women and affects nearly 1.3 million women worldwide each year. Aggressive, metastatic disease is directly responsible for the majority of breast cancer-related deaths. Breast tumors lacking expression of three receptors, estrogen receptor (ER), progesterone receptor (PR), and HER2, are commonly referred to as triple negative breast cancers (TNBCs) and make up 15-20% of all diagnosed breast cancers cases. Disparities exist in terms of survival following diagnosis of TNBC, and a devastating reality is that this diagnosis is highly correlated with incurable, metastatic disease. Despite tremendous advantages in treatments for hormone-sensitive breast tumors, a significant number of women with TNBC experience disease progression due to the unavailability of targeted therapies. Insulin-like growth factor-1 receptor (IGF1R) plays a role in breast cancer proliferation, adhesion, invasion, and migration. Overexpression of IGF1R has been noted in 50% of primary breast tumors and in nearly 65% of TNBCs. Consequently, high IGF1R expression in breast cancers correlates well with, high tumor grade, shorter disease-free survival, and poor prognosis. We report the in vitro effects of IGF1R inhibition on the metastatic properties of mesenchymal TNBC cells lines using two methods: (1) shRNA lentiviral system and (2) picropodophyllin (PPP), an IGF1R tyrosine kinase inhibitor. Stably transfected mesenchymal TNBC cells showed down-regulation of IGF1R protein levels, which resulted in mesenchymal-epithelial-transition (MET), as confirmed by up-regulation of epithelial marker, E-cadherin, and down-regulation of mesenchymal marker, vimentin. Importantly, this MET was accompanied by reduced colony formation, cell motility, and invasion. Cell survival assays and fluorescence-activated cell sorting (FACS) analysis revealed that PPP also effectively decreased cell viability and induced cell death, respectively, in TNBC cells. Furthermore, PPP dramatically inhibited cell invasion and migration. Our findings indicate that inhibitors of IGF1R exhibit promising anti-cancer activity in TNBC cells of mesenchymal origin by triggering MET, inducing cell death, and reducing invasive and metastatic properties. Given the very poor outcomes for patients with metastatic TNBCs, we believe the use of IGF1R inhibitors warrant further investigation as prospective anti-cancer options for treating a subset of mesenchymal TN breast carcinomas.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 342. doi:1538-7445.AM2012-342