Antisense Oligonucleotides In Combination Research Articles

Splice-Switching Antisense Oligonucleotides Targeting Extra- and Intracellular Domains of Epidermal Growth Factor Receptor in Cancer Cells.

Cancer is one of the leading causes of death globally. Epidermal growth factor receptor is one of the proteins involved in cancer cell proliferation, differentiation, and invasion. Antisense oligonucleotides are chemical nucleic acids that bind to target messenger ribonucleic acid and modulate its expression. Herein, we demonstrate the efficacy of splice-modulating antisense oligonucleotides to target specific exons in the extracellular (exon 3) and intracellular (exon 18, 21) domains of epidermal growth factor receptor. These antisense oligonucleotides were synthesized as 25mer 2'-O methyl phosphorothioate-modified ribonucleic acids that bind to complementary specific regions in respective exons. We found that PNAT524, PNAT525, PNAT576, and PNAT578 effectively skipped exon 3, exon 18, and exon 21 in glioblastoma, liver cancer, and breast cancer cell lines. PNAT578 treatment also skipped partial exon 19, complete exon 20, and partial exon 21 in addition to complete exon 21 skipping. We also found that a cocktail of PNAT576 and PNAT578 antisense oligonucleotides performed better than their individual counterparts. The migration potential of glioblastoma cancer cells was reduced to a greater extent after treatment with these antisense oligonucleotides. We firmly believe that using these splice-modulating antisense oligonucleotides in combination with existing EGFR-targeted therapies could improve therapeutic outcomes.

Abstract 701: Evaluation of an AKT-1 antisense oligonucleotide in combination with Lenvatinib and Everolimus in Renca-luciferase syngeneic orthotopic murine tumor model

Abstract Background: The combination of 18mg Lenvatinib and 5mg Everolimus per day is used in the clinic for advanced renal cancer patients. However, due to the severe side effects of Lenvatinib, the dose is often reduced to 12mg. Archexin, a fully phosphorothioated 20-mer antisense oligonucleotide, inhibits AKT-1 mRNA translation and inhibits tumor growth. Combination of Archexin with reduced-dosed Lenvatinib and Everolimus may reduce adverse reactions while enhancing therapeutic efficacy. Methods: First, Lenvatinib and Everolimus monotherapies were evaluated for antitumor efficacy in an orthotopic Renca-luciferase syngeneic model. 45 mice were randomly divided into 9 groups (5 in each group), vehicle control, Lenvatinib (5, 10, 20, and 30 mg/kg) and Everolimus (0.2, 0.5, 1, 2, and 4 mg/kg) via daily oral administration for 20 days. Next, we investigated the anti-tumor effect of the two- and three-drug combination. 35 mice were randomly divided into 7 groups (5 in each group), including vehicle control, Lenvatinib/Everolimus combinations (5+0.2, 10+0.2 and 10+0.5 mg/kg) and Archexin/Lenvatinib/Everolimus combinations (60+5+0.2, 60+10+0.2 and 60+10+0.5 mg/kg) via tail vein injection (vehicle/Archexin, Q3D*6 times) or oral administration (Lenvatinib and Everolimus, QD*18 days). Body weight was monitored daily. Tumor burden was measured by bioluminescence through whole-body fluorescence images, performed twice a week. Results: The results showed that Everolimus inhibited tumor growth in a dose-dependent manner. Partial response was observed in mice treated with varying doses of Lenvatinib(TGIs: 57.94%,76.65% and 60.22%), and no significant dose-effect correlation was found. The dose of Lenvatinib and Everolimus that partially inhibited the orthotopic tumor growth had also been identified and selected for subsequent study investigating drug combinations. The drugs combination study showed that three drug combinations (Archexin/Lenvatinib/Everolimus) had superior efficacy compared to the Lenvatinib and Everolimus combination. The fluorescence signal intensities (Lg10) of the three-drug combination were significantly lower than that of the two-drug combination group with P value <0.05. No severe adverse effects were observed in the three drug combinations group. Conclusion: Three drugs combination of Archexin, Lenvatinib and Everolimus, demonstrated superior anti-tumor efficacy compared to the two-drug combination currently used in the clinic. This finding suggests the three-drug combination warrant investigation in the clinical trial in the patients with advanced renal cancer. Citation Format: Fengyang Xie, Jia Wei, Lan Deng, Chao Wang, Ben Zhao, Robert J. Lee, Yuxin Angela Men. Evaluation of an AKT-1 antisense oligonucleotide in combination with Lenvatinib and Everolimus in Renca-luciferase syngeneic orthotopic murine tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 701.

Personalized Development of Antisense Oligonucleotides for Exon Skipping Restores Type XVII Collagen Expression in Junctional Epidermolysis Bullosa.

Intermediate junctional epidermolysis bullosa caused by mutations in the COL17A1 gene is characterized by the frequent development of blisters and erosions on the skin and mucous membranes. The rarity of the disease and the heterogeneity of the underlying mutations renders therapy developments challenging. However, the high number of short in-frame exons facilitates the use of antisense oligonucleotides (AON) to restore collagen 17 (C17) expression by inducing exon skipping. In a personalized approach, we designed and tested three AONs in combination with a cationic liposomal carrier for their ability to induce skipping of COL17A1 exon 7 in 2D culture and in 3D skin equivalents. We show that AON-induced exon skipping excludes the targeted exon from pre-mRNA processing, which restores the reading frame, leading to the expression of a slightly truncated protein. Furthermore, the expression and correct deposition of C17 at the dermal–epidermal junction indicates its functionality. Thus, we assume AON-mediated exon skipping to be a promising tool for the treatment of junctional epidermolysis bullosa, particularly applicable in a personalized manner for rare genotypes.

Targeting the 5′ untranslated region of SMN2 as a therapeutic strategy for spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by mutations in the survival motor neuron 1 (SMN1) gene. All patients have at least one copy of a paralog, SMN2, but a C-to-T transition in this gene results in exon 7 skipping in a majority of transcripts. Approved treatment for SMA involves promoting exon 7 inclusion in the SMN2 transcript or increasing the amount of full-length SMN by gene replacement with a viral vector. Increasing the pool of SMN2 transcripts and increasing their translational efficiency can be used to enhance splice correction. We sought to determine whether the 5′ untranslated region (5′ UTR) of SMN2 contains a repressive feature that can be targeted to increase SMN levels. We found that antisense oligonucleotides (ASOs) complementary to the 5′ end of SMN2 increase SMN mRNA and protein levels and that this effect is due to inhibition of SMN2 mRNA decay. Moreover, use of the 5′ UTR ASO in combination with a splice-switching oligonucleotide (SSO) increases SMN levels above those attained with the SSO alone. Our results add to the current understanding of SMN regulation and point toward a new therapeutic target for SMA.

Response to radiotherapy in pancreatic ductal adenocarcinoma is enhanced by inhibition of myeloid-derived suppressor cells using STAT3 anti-sense oligonucleotide.

Pancreatic ductal adenocarcinoma (PDAC) has a heterogeneous tumor microenvironment (TME) comprised of myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages, neutrophils, regulatory T cells, and myofibroblasts. The precise mechanisms that regulate the composition of the TME and how they contribute to radiotherapy (RT) response remain poorly understood. In this study, we analyze changes in immune cell populations and circulating chemokines in patient samples and animal models of pancreatic cancer to characterize the immune response to radiotherapy. Further, we identify STAT3 as a key mediator of immunosuppression post-RT. We found granulocytic MDSCs (G-MDSCs) and neutrophils to be increased in response to RT in murine and human PDAC samples. We also found that RT-induced STAT3 phosphorylation correlated with increased MDSC infiltration and proliferation. Targeting STAT3 using an anti-sense oligonucleotide in combination with RT circumvented RT-induced MDSC infiltration, enhanced the proportion of effector T cells, and improved response to RT. In addition, STAT3 inhibition contributed to the remodeling of the PDAC extracellular matrix when combined with RT, resulting in decreased collagen deposition and fibrotic tissue formation. Collectively, our data provide evidence that targeting STAT3 in combination with RT can mitigate the pro-tumorigenic effects of RT and improve tumor response.

Abstract B09: Selective depletion of YAP1 with next-generation (constrained ethyl-cEt) antisense oligonucleotides results in tumor regression in mouse models of HCC with YAP1 activation

Abstract The Hippo pathway plays important roles in tissue homeostasis. When dysregulated in adult tissues, however, it contributes to the development of a variety of cancers including hepatocellular carcinoma (HCC). YAP1 is the final regulator of the Hippo pathway and is associated with poor prognosis of HCC patients, and more recently has been suggested to be involved in tumor immune evasion. Here, we employed next-generation constrained ethyl (cEt) antisense oligonucleotides (ASOs) to selectively target YAP1 in the genetically engineered mouse (GEM) model of HCC (Salvador KO mice) as well as in a spontaneous carcinogen-induced model of HCC (diethylnitrosamine, DEN-induced HCC). In YAP1-activated Salvador KO mice with established HCC tumors, systemic treatment with YAP1 ASO at 25 mg/kg resulted in a marked reduction in YAP1 protein level in tumor (>90%) and regression of existing tumors, in contrast to the tumors in vehicle or control ASO-treated animals that significantly increased in size. In the DEN-induced HCC model, YAP1 was strongly activated in tumors as demonstrated by nuclear localization of YAP1 protein and the gene signature we previously identified (SOH). YAP1 ASOs produced either complete tumor stasis when DEN tumors were grown in immune-deficient mice, or complete regressions when tumors were grown in immune-competent animals. In accordance with this, YAP1 ASO treatment resulted in significant infiltration of T cells and myeloid lineage cells in the tumors in immune-competent mice. Importantly, when tumor-bearing animals were taken off the treatment after tumor regression was observed with YAP1 ASO, the antitumor response was sustained for more than 1 year, with 4 out of 16 animals remaining tumor-free in YAP1 ASO group. Furthermore, YAP1 ASO in combination with anti-PD1 antibody led to enhanced antitumor activity in the same tumor model. Collectively, these results suggest a potential therapeutic use of YAP1 ASO in the treatment of HCC with YAP1 activation as a single agent or in combination with immuno-oncology drugs. Broad screens have identified the human YAP1 ASO clinical development compound YAP1RX. Citation Format: Youngsoo Kim, Joanna Schmidt, Minji Jo, Jing Yi, Xiaolin Luo, Rachel Fleming, Sun Young Yim, Ju-Seog Lee, Brett P. Mornia, Randy L. Johnson, Gordon Mills, A. Robert MacLeod. Selective depletion of YAP1 with next-generation (constrained ethyl-cEt) antisense oligonucleotides results in tumor regression in mouse models of HCC with YAP1 activation [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr B09.

Recognition memory reconsolidation requires hippocampal Zif268

Object recognition memory (ORM) serves to distinguish familiar items from novel ones. Reconsolidation is the process by which active memories are updated. The hippocampus is engaged in ORM reconsolidation through a mechanism involving induction of long-term potentiation (LTP). The transcription factor Zif268 is essential for hippocampal LTP maintenance and has been frequently associated with memory processes. However, its possible involvement in ORM reconsolidation has not been determined conclusively. Using Zif268 antisense oligonucleotides in combination with behavioural, biochemical and electrophysiological tools in rats, we found that hippocampal Zif268 is necessary to update ORM through reconsolidation but not to retrieve it or keep it stored. Our results also suggest that knocking down hippocampal Zif268 during ORM reconsolidation deletes the active recognition memory trace.

Long‐term survival of a child with refractory anaplastic large cell lymphoma following therapy with an antisense oligonucleotide, topotecan, and vinblastine

Anaplastic large cell lymphoma includes a subset of highly aggressive tumours and has a relapse rate of 30% at 2 years. Relapsed patients often have poor clinical outcome. The use of antisense oligonucleotides to down-regulate Bcl-2 protein can reverse chemotherapy resistance. The authors describe an 11-year-old boy with recurrent anaplastic large cell lymphoma who had received double high-dose chemotherapy followed by autologous haematopoietic stem-cell transplantation, had refractory disease and then had achieved long-term remission with the use of an antisense oligonucleotides in combination with vinblastine and topotecan.

Combination of FXI Antisense Oligonucleotide and Plavix® Treatment Results in Enhanced Antithrombotic Activity without Increased Risk of Bleeding in Mouse Models of Thrombosis.

Abstract 4173Factor XI (FXI) is a serine protease produced in the liver that contributes to thrombin generation via the intrinsic coagulation pathway. Also, it is a key component of an amplification pathway that is thought to sustain thrombin production at a wound site to maintain fibrin clot integrity. Loss of function mutations in the human FXI gene results in FXI deficiency, a disorder which is associated with only mild bleeding. In addition, high levels of FXI are a risk factor for thrombosis. We have previously presented the antithrombotic efficacy and safety of antisense oligonucleotide (ASO) mediated FXI depletion in various animal models of thrombosis. We have demonstrated that in combination with Lovenox®, FXI ASO treatment increases antithrombotic activity but does not increase bleeding risk. The purpose of the current study was to evaluate the relative risk/benefit of ASO mediated Factor XI depletion in combination with the platelet antagonist Plavix®. The “risk” component was bleeding tendency as measured by blood volume loss following tail nick, and the “benefit” component was antithrombotic effect in arterial and venous mouse models of thrombosis. Our study investigated a 20 mg/kg dose of FXI ASO in combination with a dose response of Plavix® and indicates that antisense mediated FXI depletion provides enhanced antithrombotic protection when given in combination with Plavix®. The combination of FXI ASO and Plavix® did not result in increased bleeding tendency. In contrast, treatment with a small molecule inhibitor of factor Xa in combination with Plavix® significantly increased bleeding. The approach used in this study is being used to define the ability of FXI ASO to combine with standard of care agents for the treatment of thrombosis. Disclosures:Gao:Isis Pharmaceuticals, Inc.: Employment. Crosby:Isis Pharmaceuticals, Inc.: Employment. MacLeod:Isis Pharmaceuticals: Employment. Bhattacharjee:Isis Pharmaceuticals, Inc.: Employment. Lowenberg:Isis Pharmaceuticals, Inc.: Consultancy. Levi:Isis Pharmaceuticals, Inc.: Consultancy. Monia:Isis Pharmaceuticals, Inc.: Employment.

Down-regulation of Mcl-1 with antisense technology alters the effect of various cytotoxic agents used in treatment of squamous cell carcinoma of the head and neck

Antisense oligonucleotides have recently been identified as new anticancer agents. Since human head and neck cancer cells highly express the antiapoptotic protein myeloid cell leukemia-1 (Mcl-1), the aim of this study was to explore the efficacy of the Mcl-1 suppression in combination with various cytotoxic agents in the head and neck cancer cell line SCC9. After oligonucleotide transfection and/or treatment with cisplatin, 5-fluorouracil (5-FU), gemcitabine, paclitaxel or cetuximab, proliferation assays were performed to determine cell viability. The expression patterns of Mcl-1, Bax and Bak were assessed by Western blot analysis and the apoptotic cells were determined by immunohistochemistry using the M30 antibody. A combined Mcl-1 antisense oligonucleotide treatment with paclitaxel, cetuximab and gemcitabine led to a significant reduction in the viable cells. However, the combination with cisplatin and 5-FU showed only moderate synergistic cytotoxic effects. According to the cytotoxic data, distinct apoptosis rates were observed after the combined treatment with the different substances. Western blot analysis also showed a significant suppression of the Mcl-1 synthesis. Our data show that the Mcl-1 antisense oligonucleotide in combination with certain cytotoxic agents has the potential to significantly decrease cell viability in vitro.

Antitumor Mechanisms of Systemically Administered Epidermal Growth Factor Receptor Antisense Oligonucleotides in Combination with Docetaxel in Squamous Cell Carcinoma of the Head and Neck

Squamous cell carcinoma of the head and neck (SCCHN) is one of the most common malignancies worldwide, with low 5-year survival rates. Current strategies that block epidermal growth factor receptor (EGFR) have limited effects when administered as single agents. Targeting EGFR via intratumoral administration of phosphorothioate-modified antisense oligonucleotides has antitumor efficacy in xenograft models of SCCHN. Because intratumoral delivery of therapeutic agents has limited clinical application, the present study was undertaken to examine the therapeutic mechanisms of systemically delivered phosphorothioate-modified EGFR antisense oligonucleotides alone, or in combination with docetaxel, in a SCCHN xenograft model. EGFR antisense oligonucleotides were administered at 5 mg/kg i.p. daily in athymic mice bearing 1483 human SCCHN xenografts alone or in combination with docetaxel at 2.5 mg/kg i.p. once a week for 4 weeks. Administration of EGFR antisense oligonucleotides in combination with docetaxel improved antitumor efficacy and resulted in lower expression levels of EGFR, fewer proliferating cells, and more apoptotic cells in the tumors compared with controls. Systemic administration of phosphorothioated EGFR antisense oligonucleotides for 30 days increased the retention of docetaxel in the tumor by approximately 4-fold compared with tumors treated with docetaxel alone or docetaxel and EGFR sense oligonucleotides (P < 0.05). Combination of EGFR antisense oligonucleotides with low doses of docetaxel has antitumor efficacy, and it may be an effective treatment strategy for SCCHN.

Hirudo medicinalis: A Platform for Investigating Genes in Neural Repair

We have used the nervous system of the medicinal leech as a preparation to study the molecular basis of neural repair. The leech central nervous system, unlike mammalian CNS, can regenerate to restore function, and contains identified nerve cells of known function and connectivity. We have constructed subtractive cDNA probes from whole and regenerating ganglia of the ventral nerve cord and have used these to screen a serotonergic Retzius neuron library. This identifies genes that are regulated as a result of axotomy, and are expressed by the Retzius cell. This approach identifies many genes, both novel and known. Many of the known genes identified have homologues in vertebrates, including man. For example, genes encoding thioredoxin (TRX), Rough Endoplasmic Reticulum Protein 1 (RER-1) and ATP synthase are upregulated at 24 h postinjury in leech nerve cord. To investigate the functional role of regulated genes in neuron regrowth we are using microinjection of antisense oligonucleotides in combination with horseradish peroxidase to knock down expression of a chosen gene and to assess regeneration in single neurons in 3-D ganglion culture. As an example of this approach we describe experiments to microinject antisense oligonucleotide to a leech isoform of the structural protein, Protein 4.1. Our approach thus identifies genes regulated at different times after injury that may underpin the intrinsic ability of leech neurons to survive damage, to initiate regrowth programs and to remake functional connections. It enables us to determine the time course of gene expression in the regenerating nerve cord, and to study the effects of gene knockdown in identified neurons regenerating in defined conditions in culture.

Inhibition of survivin expression suppresses the growth of aggressive non-Hodgkin's lymphoma.

Survivin is a member of the inhibitor of apoptosis protein (IAP) family and functions both as an apoptosis inhibitor and a regulator of cell division. Survivin overexpression is common in many human tumors and correlates with survival in large cell non-Hodgkin's lymphoma. To evaluate this molecule as a potential therapeutic target in large-cell lymphoma, we evaluated the effect of survivin inhibition both in vitro and in vivo. Using an antisense oligonucleotide (ASO) approach, cell growth was significantly inhibited in the DoHH2, RL and HT lymphoma cell lines. In a lymphoma xenograft model, the development of tumors as well as the growth of established tumors was inhibited in the survivin ASO-treated mice compared to controls. To assess the efficacy of the survivin ASO in combination with other biological agents, we combined the survivin ASO with an anti-CD20 monoclonal antibody, rituximab. The effect of survivin ASO and rituximab in combination was additive in vitro. In vivo, however, suppression of tumor growth with the combination was not significantly superior to controls. We conclude that inhibition of survivin expression is an attractive therapeutic strategy in aggressive non-Hodgkin's lymphomas, and that combining survivin ASO with rituximab may enhance the efficacy of this approach.

Cooperative inhibitory effects of antisense oligonucleotide of cell adhesion molecules and cimetidine on cancer cell adhesion.

To explore the cooperative effects of antisense oligonucleotide (ASON) of cell adhesion molecules and cimetidine on the expression of E-selectin and ICAM-1 in endothelial cells and their adhesion to tumor cells. After treatment of endothelial cells with ASON and/or cimetidine and induction with TNF-alpha, the protein and mRNA changes of E-selectin and ICAM-1 in endothelial cells were examined by flow cytometry and RT-PCR, respectively. The adhesion rates of endothelial cells to tumor cells were measured by cell adhesion experiment. In comparison with TNF-alpha inducing group, lipo-ASON and lipo-ASON/cimetidine could significantly decrease the protein and mRNA levels of E-selectin and ICAM-1 in endothelial cells, and lipo-ASON/cimetidine had most significant inhibitory effect on E-selectin expression (from 36.37+/-1.56% to 14.23+/-1.07%, P<0.001). Meanwhile, cimetidine alone could inhibit the expression of E-selectin(36.37+/-1.56% vs 27.2+/-1.31%, P<0.001), but not ICAM-1 (69.34+/-2.50% vs 68.07+/-2.10%,P>0.05) and the two kinds of mRNA, either. Compared with TNF-alpha inducing group, the rate of adhesion was markedly decreased in lipo-E-selectin ASON and lipo-E-selectin ASON/cimetidine treated groups(P<0.05), and lipo-E-selectin ASON/cimetidine worked better than lipo-E-selectin ASON alone except for HepG2/ECV304 group (P<0.05). However, the decrease of adhesion was not significant in lipo-ICAM-1 ASON and lipo-ICAM-1 ASON/cimetidine treated groups except for HepG2/ECV304 group (P>0.05). These data demonstrate that ASON in combination with cimetidine in vitro can significantly reduce the adhesion between endothelial cells and hepatic or colorectal cancer cells, which is stronger than ASON or cimetidine alone. This study provides some useful proofs for gene therapy of antiadhesion.

Bcl-x(L) antisense oligonucleotides radiosensitise colon cancer cells.

Advanced colon cancer is a malignancy with poor response to various treatment modalities including ionising radiation (IR) and chemotherapy. Both IR and chemotherapeutic agents have been shown to act by inducing apoptosis, a type of cell death antagonised by the Bcl-xL gene product. Since approximately 60% of human colon cancers express Bcl-xL, it was the aim of this study to explore the potential of Bcl-xL antisense oligonucleotides as a novel radiosensitisation strategy. Caco-2 colon cancer cells were treated with Bcl-xL antisense oligonucleotides in combination with IR or cisplatin, and Bcl-xL protein expression, apoptosis, cell viability and clonogenic survival were examined. Bcl-xL antisense oligonucleotide specifically reduced the Bcl-xL protein level by almost 50% in Caco-2 cells. The decreased threshold for the induction of apoptosis resulted in a 300% increase of apoptosis after IR or cisplatin treatment and led to a 60% reduction of cell proliferation beyond response rates achieved with IR. These data suggest that Bcl-xL is an important factor contributing to the treatment resistance of human colon cancer. Specific reduction of Bcl-xL protein levels by antisense oligonucleotides qualifies as a promising therapeutic strategy for colon cancer that may help overcome resistance and improve clinical outcome in this malignancy.

Bcl-xL Antisense Oligonucleotides Chemosensitize Human Glioblastoma Cells

Background: Resistance to chemotherapy in glioblastoma has been linked to the expression of antiapoptotic Bcl-2 family members including Bcl-xL. Methods: Bcl-xL expression was specifically reduced in M059K glioblastoma cells with antisense oligonucleotides (ISIS 16009, ISIS 16967) as assessed by Western blotting. Induction of apoptosis by treatment with antisense oligonucleotides in combination with paclitaxel in cell culture was monitored by WST-1 assays and flow cytometric analysis. Results: Antisense oligonucleotide-mediated reduction of Bcl-xL levels led to enhanced cytotoxicity in M059K cells when compared to the use of a mismatch control oligonucleotide (p < 0.001). A decreased threshold for the induction of apoptosis led to significantly enhanced cytotoxic responses to paclitaxel treatment in WST-1 assays (p < 0.001) and flow cytometric analyses. Conclusion: Combination treatment using Bcl-xL antisense oligonucleotides and paclitaxel may qualify as a promising strategy to ultimately improve the clinical outcome of glioblastoma.

Differential regulation of the response to DNA damage in Ewing's sarcoma cells by ETS1 and EWS/FLI-1.

Ewing's sarcoma (EWS) cells contain levels of poly(ADP-ribose) polymerase (PARP) significantly higher than other eukaryotic cells. Previously, we cloned the PARP gene promoter region from EWS cells, showed that it contained multiple ETS-binding sites and demonstrated a positive regulation of PARP by ETS1. We now report that, contrary to ETS1, EWS/FLI-1, an aberrant ETS transcription factor present in most EWS cells, is a negative effector of PARP transcription. Because PARP levels have been associated with cellular resistance or sensitivity to genotoxic agents, we studied the effect of modifying PARP levels in EWS cells on their response to DNA damage by modulating the expression of ETS1 or EWS/FLI-1 using antisense methodology. Results show that stable down-regulation of ETS1 increases the resistance of EWS cells to various genotoxic agents, whereas down-regulation of EWS/FLI-1 has pro-apoptotic effects. Because down-regulation EWS/FLI-1 does not dramatically change PARP levels, these results suggest a direct effect for EWS/FLI-1 in the DNA damage response of EWS cells. Since expression of the aberrant fusion proteins by EWS cells is essential for maintaining their neoplastic phenotype, our results suggest that the use of antisense oligonucleotides in combination with chemotherapeutic agents or radiation may be doubly effective by causing both an increase in sensitivity to therapeutic agents and a simultaneous down-regulation, or reversion, of the neoplastic phenotype of EWS cells.

Modulation of multidrug resistance in human ovarian cancer cell lines by inhibition of P-glycoprotein 170 and PKC isoenzymes with antisense oligonucleotides.

Multidrug resistance in human ovarian carcinoma cell lines is caused by the expression of several related proteins, namely P-glycoprotein 170 (Pgp-170), glutathione S-transferase-pi GST-pi), and thymidylate synthase (TS). These proteins seem to be regulated by a common mechanism in which the expression of protein kinase C (PKC) is involved. Additionally, the function of Pgp-170 is dependent on PKC phosphorylation. However, in ovarian carcinoma cell lines the role of different PKC enzymes responsible for resistance is not quite clear. In the present study we circumvented resistance in taxol resistant human ovarian carcinoma cell lines with antisense oligonucleotides to PKC alpha and PKC beta mRNA and compared the effects with those obtained by Pgp-170 antisense oligonucleotides. We found a significant inhibition of cell number after treatment with Pgp-170 antisense oligonucleotides in combination with taxol. Additionally, resistance could be reversed by treatment with taxol and antisense oligomers to PKC alpha and PKC beta. This shows that regulatory correlations between these proteins exist and that inhibition of the mRNA of PKC alpha and PKC beta isoforms and Pgp-170 can reverse multidrug resistance.

Synergistic growth inhibition and induction of apoptosis by a novel mixed backbone antisense oligonucleotide targeting CRIPTO in combination with C225 anti-EGFR monoclonal antibody and 8-Cl-cAMP in human GEO colon cancer cells.

We have evaluated the antiproliferative effect of a novel mixed backbone antisense oligonucleotide generated against the 5'-coding region of the human CRIPTO mRNA in GEO human colon cancer cells. We have also evaluated the effects of this anti-CRIPTO antisense oligonucleotide in combination with a chimeric anti-human epidermal growth factor receptor (EGFR) monoclonal antibody (MAb C225) and with 8-Cl-cAMP, a cAMP analog that specifically inhibits type I protein kinase A (PKAI), since a functional EGFR-driven autocrine pathway is operative and PKAI is overexpessed in GEO colon cancer cells. Treatment with a single agent at low doses determined a 15-35% growth inhibition. A synergistic antiproliferative effect was observed when combinations of two agents were used with a co-operativity quotient ranging between 1.5 and 2.2. Furthermore, the combined treatment with all three drugs caused an almost complete suppression of the ability of GEO cells to form colonies in soft agar. We next evaluated whether any combination of 8-Cl-cAMP, the anti-CRIPTO antisense oligonucleotide and MAb C225 could induce programmed cell death in GEO cells. Treatment with each agent alone at all doses tested did not cause DNA fragmentation. The treatment with any combination of two agents was not able to induce apoptosis. In contrast, treatment with all three compounds determined an approximately three-fold increase in DNA fragmentation. In conclusion, the combination of selective antineoplastic agents directed against different but related key signal tranduction pathways efficiently inhibits cell growth and causes apoptosis in human colorectal cancer cells.

Antiangiogenic and antitumor effect of VEGF antisense oligonucleotide in combination with anti-EGFR C225 monoclonal antibody in human colon cancer

Antiangiogenic and antitumor effect of VEGF antisense oligonucleotide in combination with anti-EGFR C225 monoclonal antibody in human colon cancer