EXO1 protects BRCA1-deficient cells against toxic DNA lesions

Inactivating mutations in the BRCA1 and BRCA2 genes impair DNA double-strand break (DSB) repair by homologous recombination (HR), leading to chromosomal instability and cancer. Importantly, BRCA1/2 deficiency also causes therapeutically targetable vulnerabilities. Here, we identify the dependency on the end resection factor EXO1 as a key vulnerability of BRCA1-deficient cells. EXO1 deficiency generates poly(ADP-ribose)-decorated DNA lesions during S phase that associate with unresolved DSBs and genomic instability in BRCA1-deficient but not in wild-type or BRCA2-deficient cells. Our data indicate that BRCA1/EXO1 double-deficient cells accumulate DSBs due to impaired repair by single-strand annealing (SSA) on top of their HR defect. In contrast, BRCA2-deficient cells retain SSA activity in the absence of EXO1 and hence tolerate EXO1 loss. Consistent with a dependency on EXO1-mediated SSA, we find that BRCA1-mutated tumors show elevated EXO1 expression and increased SSA-associated genomic scars compared with BRCA1-proficient tumors. Overall, our findings uncover EXO1 as a promising therapeutic target for BRCA1-deficient tumors.

FIRRM/C1orf112 is synthetic lethal with PICH and mediates RAD51 dynamics

Joint DNA molecules are natural byproducts of DNA replication and repair. Persistent joint molecules give rise to ultrafine DNA bridges (UFBs) in mitosis, compromising sister chromatid separation. The DNA translocase PICH (ERCC6L) has a central role in UFB resolution. A genome-wide loss-of-function screen is performed to identify the genetic context of PICH dependency. In addition to genes involved in DNA condensation, centromere stability, and DNA-damage repair, we identify FIGNL1-interacting regulator of recombination and mitosis (FIRRM), formerly known as C1orf112. We find that FIRRM interacts with and stabilizes the AAA⁺ ATPase FIGNL1. Inactivation of either FIRRM or FIGNL1 results in UFB formation, prolonged accumulation of RAD51 at nuclear foci, and impaired replication fork dynamics and consequently impairs genome maintenance. Combined, our data suggest that inactivation of FIRRM and FIGNL1 dysregulates RAD51 dynamics at replication forks, resulting in persistent DNA lesions and a dependency on PICH to preserve cell viability.

Evaluation of Ac-Lys0(IRDye800CW)Tyr3-octreotate as a novel tracer for SSTR2-targeted molecular fluorescence guided surgery in meningioma

Purpose

Meningioma recurrence rates can be reduced by optimizing surgical resection with the use of intraoperative molecular fluorescence guided surgery (MFGS). We evaluated the potential of the fluorescent tracer 800CW-TATE for MFGS using in vitro and in vivo models. It targets somatostatin receptor subtype 2 (SSTR₂), which is overexpressed in all meningiomas.

Methods

Binding affinity of 800CW-TATE was evaluated using [¹⁷⁷Lu] Lu-DOTA-Tyr³-octreotate displacement assays. Tumor uptake was determined by injecting 800CW-TATE in (SSTR₂-positive) NCI-H69 or (SSTR₂-negative) CH-157MN xenograft bearing mice and FMT2500 imaging. SSTR₂-specific binding was measured by comparing tumor uptake in NCI-H69 and CH-157MN xenografts, blocking experiments and non-targeted IRDye800CW-carboxylate binding. Tracer distribution was analyzed ex vivo, and the tumor-to-background ratio (TBR) was calculated. SSTR₂ expression was determined by immunohistochemistry (IHC). Lastly, 800CW-TATE was incubated on frozen and fresh meningioma specimens and analyzed by microscopy.

Results

800CW-TATE binding affinity assays showed an IC₅₀ value of 72 nM. NCI-H69 xenografted mice showed a TBR of 21.1. 800CW-TATE detection was reduced after co-administration of non-fluorescent DOTA-Tyr³-octreotate or administration of IRDye800CW. CH-157MN had no tumor specific tracer staining due to absence of SSTR₂ expression, thereby serving as a negative control. The tracer bound specifically to SSTR₂-positive meningioma tissues representing all WHO grades.

Conclusion

800CW-TATE demonstrated sufficient binding affinity, specific SSTR₂-mediated tumor uptake, a favorable biodistribution, and high TBR. These features make this tracer very promising for use in MFGS and could potentially aid in safer and a more complete meningioma resection, especially in high-grade meningiomas or those at complex anatomical localizations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11060-021-03739-1.

Cyclin E expression is associated with high levels of replication stress in triple-negative breast cancer

Replication stress entails the improper progression of DNA replication. In cancer cells, including breast cancer cells, an important cause of replication stress is oncogene activation. Importantly, tumors with high levels of replication stress may have different clinical behavior, and high levels of replication stress appear to be a vulnerability of cancer cells, which may be therapeutically targeted by novel molecularly targeted agents. Unfortunately, data on replication stress is largely based on experimental models. Further investigation of replication stress in clinical samples is required to optimally implement novel therapeutics. To uncover the relation between oncogene expression, replication stress, and clinical features of breast cancer subgroups, we immunohistochemically analyzed the expression of a panel of oncogenes (Cyclin E, c-Myc, and Cdc25A,) and markers of replication stress (phospho-Ser33-RPA32 and γ-H2AX) in breast tumor tissues prior to treatment (n = 384). Triple-negative breast cancers (TNBCs) exhibited the highest levels of phospho-Ser33-RPA32 (P < 0.001 for all tests) and γ-H2AX (P < 0.05 for all tests). Moreover, expression levels of Cyclin E (P < 0.001 for all tests) and c-Myc (P < 0.001 for all tests) were highest in TNBCs. Expression of Cyclin E positively correlated with phospho-RPA32 (Spearman correlation r = 0.37, P < 0.001) and γ-H2AX (Spearman correlation r = 0.63, P < 0.001). Combined, these data indicate that, among breast cancers, replication stress is predominantly observed in TNBCs, and is associated with expression levels of Cyclin E. These results indicate that Cyclin E overexpression may be used as a biomarker for patient selection in the clinical evaluation of drugs that target the DNA replication stress response.

Modeling of Cisplatin-Induced Signaling Dynamics in Triple-Negative Breast Cancer Cells Reveals Mediators of Sensitivity

Triple-negative breast cancers (TNBCs) display great diversity in cisplatin sensitivity that cannot be explained solely by cancer-associated DNA repair defects. Differential activation of the DNA damage response (DDR) to cisplatin has been proposed to underlie the observed differential sensitivity, but it has not been investigated systematically. Systems-level analysis-using quantitative time-resolved signaling data and phenotypic responses, in combination with mathematical modeling-identifies that the activation status of cell-cycle checkpoints determines cisplatin sensitivity in TNBC cell lines. Specifically, inactivation of the cell-cycle checkpoint regulator MK2 or G3BP2 sensitizes cisplatin-resistant TNBC cell lines to cisplatin. Dynamic signaling data of five cell cycle-related signals predicts cisplatin sensitivity of TNBC cell lines. We provide a time-resolved map of cisplatin-induced signaling that uncovers determinants of chemo-sensitivity, underscores the impact of cell-cycle checkpoints on cisplatin sensitivity, and offers starting points to optimize treatment efficacy.

Quantitative proteomics analysis identifies MUC1 as an effect sensor of EGFR inhibition

Tumor responses to cancer therapeutics are generally monitored every 2-3 months based on changes in tumor size. Dynamic biomarkers that reflect effective engagement of targeted therapeutics to the targeted pathway, so-called "effect sensors", would fulfill a need for non-invasive, drug-specific indicators of early treatment effect. Using a proteomics approach to identify effect sensors, we demonstrated MUC1 upregulation in response to epidermal growth factor receptor (EGFR)-targeting treatments in breast and lung cancer models. To achieve this, using semi-quantitative mass spectrometry, we found MUC1 to be significantly and durably upregulated in response to erlotinib, an EGFR-targeting treatment. MUC1 upregulation was regulated transcriptionally, involving PI3K-signaling and STAT3. We validated these results in erlotinib-sensitive human breast and non-small lung cancer cell lines. Importantly, erlotinib treatment of mice bearing SUM149 xenografts resulted in increased MUC1 shedding into plasma. Analysis of MUC1 using serial blood sampling may therefore be a new, relatively non-invasive tool to monitor early and drug-specific effects of EGFR-targeting therapeutics.

Abstract 2417: Predictive and therapeutic impact of DNA damage response activation in locally advanced cervical cancer patients

Recent advances in improving outcome of locally advanced cervical cancer (LACC) were made by addition of cisplatin to radiotherapy. However, total 5-year survival rates are still ∼66%, underscoring the need for new therapy strategies.

Current therapeutic strategies in cervical cancer consist of cisplatin and radiotherapy, which exert their anti-cancer effects by inducing high levels of DNA lesions including DNA double strand breaks (DSBs), with the aim to induce cell death in tumor cells.

However, tumor cells can respond to these therapy-induced DNA lesions by activation of the DNA damage response (DDR). The DDR is a complex signalling network, consisting of multiple kinases and transcriptional programs that function in parallel to arrest ongoing cell cycle progression, which allows time for DNA repair. Effective DNA repair may thus counteracts therapy-induced cancer cell death.

Cervical cancers already have a partial dysfunction of the DDR due to frequent, human papilloma virus (HPV) infection. As a result, HPV-infected cervical tumors are thought to rely heavily on remaining DDR activity for their survival. We therefore hypothesize that the residual DDR activity may provide an ‘Achilles heel’ which could be exploited therapeutically using specific DDR inhibitors, to increase tumor cell sensitivity to cisplatin and ionizing radiation.

Firstly, we examined the expression and activation status of the key DDR components ATM, Chk2, ATR, Chk1, DNA-PK and MK2 in 375 cervical cancer patients using immunohistochemistry. We found that these DDR components were all abundantly expressed in cervical cancer tissues, underscoring the availability of these components for targeting by DDR inhibitors.

Subsequently, we tested chemo- or radiosensitization of specific chemical inhibitors against ATM (KU-55933), ATR (NU-6027), DNA-PK (KU-0060648), Chk1/2 (AZD7762) and MK2 (MK2-inhibitor III) using HPV-positive cervical cancer cell lines HeLa and SiHa. MTT-assay analyses showed that ATR, Chk1/2 and DNA-PK inhibition, sensitized cervical cancer cells to cisplatin. In contrast, clonogenic survival assays revealed that inhibition of ATM, DNA-PK and Chk1/2 caused radiosensitization. In order to uncover how DDR inactivation is most effective in a combined chemo-radiotherapy setting, we therefore optimised an in vitro ‘combination therapy survival assay’ reflecting the different DNA lesions given in clinical LACC therapy. We showed that targeting of ATM, ATR and Chk1/2 caused effective chemo-radiosensitization of cervical cancer cells.

Our data show that DDR components are abundantly expressed in cervical cancer. Furthermore, we show that targeting of individual DDR kinases has differential effects on chemo- or radiotherapy sensitivity. Finally, we show that ATM, ATR and Chk1/2 inhibition are promising strategies to further improve the efficacy of platinum-based chemoradiation.

Citation Format: Hylke W. Wieringa, Marieke Everts, G.Bea A. Wisman, Ate G.J. van der Zee, Elisabeth G.E. de Vries, Marcel A.T.M. van Vugt. Predictive and therapeutic impact of DNA damage response activation in locally advanced cervical cancer patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2417. doi:10.1158/1538-7445.AM2014-2417

Abstract 3641: The predictive and prognostic roles of DNA damage response genes in epithelial ovarian cancer

Background: Despite platinum-based chemotherapy, 5-year survival of advanced stage ovarian cancer patients is only 15-30%. Exposure to platinum-based chemotherapeutics induces double strand DNA breaks (DSBs) and subsequently leads to activation of the DNA damage response (DDR). Therefore inhibition of components of the DDR may lead to better response to therapy. Aim of this study was to investigate in a large series of ovarian cancer patients the predictive and prognostic role of the activation status of four DDR-proteins- ATM, a key controller in the DDR, and three ATM substrates, including Chk2, 53BP1 and γ-H2AX, of which the latter is a direct readout for DNA damage. Methods: Expression of phospho-ATM, Chk2, phospho-Chk2, 53BP1, phospho-53BP1 and γ-H2AX was immunohistochemically assessed in 309 patients with chemo-naive ovarian cancer. Expression levels were related to clinicopathological characteristics and survival. Response to platinum-based chemotherapy was analyzed by defining two populations with either an optimal therapy response or a very poor therapy response. Both groups consisted of patients with advanced stage ovarian cancer, &gt;2 cm residual disease after primary surgery and were all treated with platinum-based chemotherapy. The responder group had a well-defined PFS of more than 18 months while the non-responder group had a PFS of less than 6 months. Results: In the two well-defined groups with the largest contrast regarding response to treatment, positive γ-H2AX expression (OR=0.193; p=0.036) and positive Chk2 expression (OR=0.149; p=0.011) were related to a good response to platinum-based chemotherapy. In advanced stage patients, phospho-53BP1 expression was independently related to a worse disease-specific survival (HR=1.905; p= 0.044). Conclusion: High DDR protein expression in advanced stage ovarian cancers suggests a high degree of genomic instability, while the negative prognostic impact of phospho-53BP1 may be due to enhanced repair capacity of chemotherapy-induced DSBs on the long term.

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 3641. doi:1538-7445.AM2012-3641

Characterization of infectivity of knob-modified adenoviral vectors in glioma

Malignant glioma continues to be a major target for gene therapy and virotherapy due to its aggressive growth and the current lack of effective treatment. However, these approaches have been hampered by inefficient infection of glioma cells by viral vectors,particularly vectors derived from serotype 5 adenoviruses (Ad5). This results from limited cell surface expression of the primary adenovirus receptor, coxsackie-adenovirus-receptor (CAR), on tumor cells. To circumvent this problem, Ad fiber pseudotyping,the genetic replacement of either the entire fiber or fiber knob domain with its structural counterpart from another human Ad serotype that recognizes a cellular receptor other than CAR, has been shown to enhance Ad infectivity in a variety of tumor types,including human glioma. Here, we have extended the paradigm of genetic pseudotyping to include fiber domains from non-human or"xenotype" Ads for infectivity enhancement of human glioma cell populations. In this study, we evaluated the gene transfer efficiency of a panel of Ad vectors which express one of five different "xenotype"fiber knob domains, including those derived from murine,ovine, porcine and canine species, in both human glioma cell lines as well as primary glioma tumor cells from patients. Adenovirus vectors displaying either canine Ad or porcine Ad fiber elements had the highest gene transfer to both glioma cell lines and primary tumor cells. The correlation between the viral infectivity of modified adenovirus vectors and expression of human CAR and CD46(an adenovirus type B receptor) on the surfaces of tumor cells was also analyzed. Taken together, human adenovirus vectors modified with "xenotype" fiber elements could be excellent candidates to target human glioma.

Mesenchymal stem cells as a vehicle for targeted delivery of CRAds to lung metastases of breast carcinoma

PURPOSE

Alternative and complementary therapeutic strategies need to be developed for metastatic breast cancer. Virotherapy is a novel therapeutic approach for the treatment of cancer in which the replicating virus itself is the anticancer agent. However, the success of virotherapy has been limited due to inefficient virus delivery to the tumor site. The present study addresses the utility of human mesenchymal stem cells (hMSCs) as intermediate carriers for conditionally replicating adenoviruses (CRAds) to target metastatic breast cancer in vivo.

EXPERIMENTAL DESIGN

HMSC were transduced with CRAds. We used a SCID mouse xenograft model to examine the effects of systemically injected CRAd loaded hMSC or CRAd alone on the growth of MDA-MB-231 derived pulmonary metastases (experimental metastases model) in vivo and on overall survival.

RESULTS

Intravenous injection of CRAd loaded hMSCs into mice with established MDA-MB-231 pulmonary metastatic disease homed to the tumor site and led to extended mouse survival compared to mice treated with CRAd alone.

CONCLUSION

Injected hMSCs transduced with CRAds suppressed the growth of pulmonary metastases, presumably through viral amplification in the hMSCs. Thus, hMSCs may be an effective platform for the targeted delivery of CRAds to distant cancer sites such as metastatic breast cancer.

Directing adenovirus across the blood–brain barrier via melanotransferrin (P97) transcytosis pathway in an in vitro model

Adenovirus serotype 5 (Ad5) is widely used in the development of gene therapy protocols. However, current gene therapy strategies involving brain are mostly based on intra-cranial injection. A major obstacle for systemically administered vectors to infect brain tissue is the blood-brain barrier (BBB). One strategy to cross the BBB is transcytosis, a transcellular transport process that shuttles a molecule from one side of the cell to the other side. Recently, melanotransferrin (MTf)/P97 was found to be able to cross the BBB and accumulate in brain. We thus hypothesize that re-directing Ad5 vectors to the MTf transcytosis pathway may facilitate Ad5 vectors to cross the BBB. To test this hypothesis, we constructed a bi-specific adaptor protein containing the extracellular domain of the coxsackie-adenovirus receptor (CAR) and the full-length melanotransferrin (sCAR-MTf), and investigated its ability to re-direct Ad5 vectors to the MTf transcytosis pathway. We found this adaptor protein could re-direct Ad5 to the MTf transcytosis pathway in an in vitro BBB model, and the transcytosed Ad5 viral particles retained their native infectivity. The sCAR-MTf-mediated Ad5 transcytosis was temperature- and dose dependent. In addition, we examined the directionality of sCAR-MTf-mediated Ad5 transcytosis, and found the efficiency of apical-to-basal transcytosis was much higher than that of basal-to-apical direction, supporting a role of this strategy in transporting Ad5 vectors towards the brain. Taken together, our study demonstrated that re-directing Ad5 to the MTf transcytosis pathway could facilitate gene delivery across the BBB.

A human adenoviral vector with a chimeric fiber from canine adenovirus type 1 results in novel expanded tropism for cancer gene therapy

The development of novel therapeutic strategies is imperative for the treatment of advanced cancers like ovarian cancer and glioma, which are resistant to most traditional treatment modalities. In this regard, adenoviral (Ad) cancer gene therapy is a promising approach. However, the gene delivery efficiency of human serotype 5 recombinant adenoviruses (Ad5) in cancer gene therapy clinical trials to date has been limited, mainly due to the paucity of the primary Ad5 receptor, the coxsackie and adenovirus receptor (CAR), on human cancer cells. To circumvent CAR deficiency, Ad5 vectors have been retargeted by creating chimeric fibers possessing the knob domains of alternate human Ad serotypes. Recently, more radical modifications based on 'xenotype' knob switching with non-human adenovirus have been exploited. Herein, we present the characterization of a novel vector derived from a recombinant Ad5 vector containing the canine adenovirus serotype 1 (CAV-1) knob (Ad5Luc1-CK1), the tropism of which has not been previously described. We compared the function of this vector with our other chimeric viruses displaying the CAV-2 knob (Ad5Luc1-CK2) and Ad3 knob (Ad5/3Luc1). Our data demonstrate that the CAV-1 knob can alter Ad5 tropism through the use of a CAR-independent entry pathway distinct from that of both Ad5Luc1-CK2 and Ad5/3-Luc1. In fact, the gene transfer efficiency of this novel vector in ovarian cancer cell lines, and more importantly in patient ovarian cancer primary tissue slice samples, was superior relative to all other vectors applied in this study. Thus, CAV-1 knob xenotype gene transfer represents a viable means to achieve enhanced transduction of low-CAR tumors.

Transductional targeting of adenovirus vectors for gene therapy

Cancer gene therapy approaches will derive considerable benefit from adenovirus (Ad) vectors capable of self-directed localization to neoplastic disease or immunomodulatory targets in vivo. The ablation of native Ad tropism coupled with active targeting modalities has demonstrated that innate gene delivery efficiency may be retained while circumventing Ad dependence on its primary cellular receptor, the coxsackie and Ad receptor. Herein, we describe advances in Ad targeting that are predicated on a fundamental understanding of vector/cell interplay. Further, we propose strategies by which existing paradigms, such as nanotechnology, may be combined with Ad vectors to form advanced delivery vehicles with multiple functions.

Employment of liver tissue slice analysis to assay hepatotoxicity linked to replicative and nonreplicative adenoviral agents

Whereas virotherapy has emerged as a novel and promising approach for neoplastic diseases, appropriate model systems have hampered preclinical evaluation of candidate conditionally replicative adenovirus agents (CRAds) with respect to liver toxicity. This is due to the inability of human viral agents to cross species. We have recently shown the human liver tissue slice model to be a facile means to validate adenoviral replication. On this basis, we sought to determine whether our ex vivo liver tissue slice model could be used to assess CRAd-mediated liver toxicity. We analyzed and compared the toxicity of a conditionally replicative adenovirus (AdDelta24) to that of a replication incompetent adenovirus (Adnull [E1-]) in mouse and human liver tissue slices. To accomplish this, we examined the hepatic apoptosis expression profile by DNA microarray analyses, and compared these results to extracellular release of aminotransferase enzymes, along with direct evidence of apoptosis by caspase-3 immunhistochemical staining and TUNEL assays. Human and mouse liver tissue slices demonstrated a marked increase in extracellular release of aminotransferase enzymes on infection with AdDelta24 compared to Adnull. AdDelta24-mediated liver toxicity was further demonstrated by apoptosis induction, as detected by caspase-3 immunohistochemical staining, TUNEL assay and microarray analysis. In conclusion, concordance of CRAd-mediated apoptosis in both the human and the mouse liver tissue slice models was demonstrated, despite the limited replication ability of CRAds in mouse liver slices. The results of this study, defining the CRAd-mediated apoptosis gene expression profiles in human and mouse liver, may lay a foundation for preclinical liver toxicity analysis of CRAd agents.

Selective induction of tumor-associated antigens in murine pulmonary vasculature using double-targeted adenoviral vectors

Targeted therapies directed to tumor-associated antigens are being investigated for the treatment of cancer. However, there are few suitable animal models for testing the ability to target these tumor markers. Therefore, we have exploited mice transgenic for the human coxsackie and adenovirus receptor (hCAR) to establish a new model for transient expression of human tumor-associated antigens in the pulmonary vasculature. Systemic administration of Ad in hCAR mice resulted in an increase in transgene expression in the lungs compared to wild-type mice, as determined using a luciferase reporter gene. To reduce transgene expression in the liver, the predominant organ of ectopic Ad localization and transgene expression following systemic administration, we utilized the endothelial-specific flt-1 promoter, which resulted in a further increased lung-to-liver ratio of luciferase expression. Administration of an adenoviral vector encoding the tumor-associated antigen carcinoembryonic antigen (CEA) under transcriptional control of the flt-1 promoter resulted in selective expression of this antigen in the pulmonary vasculature of hCAR mice. Feasibility of targeting to expressed CEA was subsequently demonstrated using adenoviral vectors preincubated with a bifunctional adapter molecule recognizing this tumor-associated antigen, thus demonstrating utility of this transient transgenic animal model.

Mesothelin-mediated targeting of adenoviral vectors for ovarian cancer gene therapy

Adenoviruses (Ads) are efficient gene transfer vehicles, but Ad-mediated gene therapy for ovarian cancer remains limited in vivo by inefficient and nonspecific gene transfer. Mesothelin (MSLN), a cell surface glycoprotein, is overexpressed in ovarian cancer but not in normal tissues except mesothelial cells. Therefore, MSLN is an attractive candidate for transcriptional and transductional targeting in the context of ovarian cancer gene therapy. We evaluated the expression of MSLN mRNA and MSLN surface protein in ovarian cancer cells. Ads containing the MSLN promoter driving reporter gene expression were created and tested in ovarian cancer cell lines and purified ovarian cancer cells isolated from patients. To evaluate transductional targeting, we used an Ad vector containing an Fc-binding domain within the fiber protein, which served as a docking domain for binding with anti-MSLN immunoglobulins. Both RT-PCR and flow cytometry revealed high MSLN gene and protein expression in ovarian cancer cells. The MSLN promoter was activated in ovarian cancer cells, but showed significantly reduced activity in normal control cells. Transductional targeting of Ads via anti-MSLN antibody increased transgene expression in ovarian cancer cells. This report describes the use of MSLN for transcriptional as well as transductional targeting strategies for ovarian cancer gene therapy.

Comparison of E-selectin expression at mRNA and protein levels in murine models of inflammation

BACKGROUND

Drug targeting to activated endothelial cells via E-selectin is currently being explored as a new approach to treat chronic inflammatory disorders. This approach uses E-selectin directed antibodies as carrier molecules to selectively deliver anti-inflammatory drugs into activated endothelial cells, thereby theoretically decreasing drug-associated side-effects. Therapeutic effects of developed drug targeting constructs will have to be tested in animal models of inflammation, in which E-selectin is expressed during the course of the disease. In this study several murine models of inflammation were investigated regarding expression of E-selectin.

METHODS

E-selectin expression was determined both at the mRNA level using RT-PCR and at the protein level by immunohistochemistry using two monoclonal antibodies (10E9.6 and MES-1). The models studied included delayed type hypersensitivity induced skin inflammation, dextran sodium sulphate induced colitis, kidney ischemia/reperfusion injury, atherosclerosis in ApoE knockout mice, and collagen induced arthritis.

RESULTS

In all animal models E-selectin mRNA expression was detected, although to a different extent. In contrast, only the delayed type hypersensitivity model and, to a minor extent, the collagen induced arthritis model showed E-selectin protein expression.

CONCLUSION

These results stress the need to determine E-selectin protein expression and not only mRNA expression, when choosing an animal model for testing E-selectin directed drug targeting preparations. In addition, in the arthritis model, E-selectin protein detection was dependent on the particular anti-E-selectin antibody used. This finding may not only have implications for the development and/or choice of homing devices to be used in E-selectin directed drug targeting preparations, but also for inflammation research in general.

A naturally occurring 6-9-kilodalton interleukin-1 (IL-1) inhibitor prevents IL-1-mediated islet cytotoxicity but not IL-1-mediated suppression of insulin secretion

Earlier studies have shown direct effects of interleukin-1 (IL-1) on isolated pancreatic islets. Coculture of isolated rat pancreatic islets with human rIL-1 beta for 6 days resulted in dose-dependent cytotoxicity (up to 100%) and suppression of insulin secretion (up to 88.5%). The cytotoxic effects of rIL-1 beta beta were blocked by the simultaneous presence of a naturally occurring 6-9-kilodalton (kDa) inhibitor of IL-1-induced T-cell proliferation. However, the ability of rIL-1 beta to suppress insulin secretion was not blocked by the 6-9-kDa inhibitor of IL-1 activity. This IL-1 inhibitor is produced by mononuclear cells and is resistant to pH 2, sensitive to heating at 56 degrees C for 30 min, has a pI of 4.5-5.6, and appears to be different from other recognized IL-1 inhibitors in both composition and mechanism of action. Unlike this IL-1 inhibitor, a monoclonal antibody specific for rIL-1 beta was able to neutralize both the islet cytotoxic and insulin modulatory effects of rIL-1 beta. These results demonstrate the use of an IL-1 inhibitor to prevent at least one mechanism of islet destruction, and suggest separate pathways for IL-1 mediated islet cytotoxicity and suppression of insulin secretion.

Influence of thyroid state on mechanical restitution of rat myocardium

The purpose of this study was to determine whether thyroid state affects the beat-to-beat regulation of contractile strength in cardiac muscle. Transmembrane action potential and isometric force were simultaneously recorded in right ventricular papillary muscles from euthyroid, hypothyroid, and hyperthyroid rats. Large thyroid state-dependent alterations in the contractile response of the muscles were not accompanied by any significant difference in the action potential. During steady-state stimulation, single test stimuli were interpolated at varying intervals. Action potential duration and peak force of the test responses were plotted against the test stimulus interval to produce electrical and mechanical restitution curves. In all muscles studied, electrical and mechanical restitution followed different time courses; over a wide range of test intervals, action potential duration and peak force of the test responses changed in opposite directions. Thyroid state profoundly affected the recovery of contractile strength, while only minor differences were found among the electrical restitution curves of the three groups of preparations. Mechanical recovery was much faster in hyperthyroid and slower in hypothyroid than in euthyroid muscles. We conclude that electrical and mechanical restitutions occur through separate processes and that the thyroid state affects only the mechanisms responsible for the contractile recovery of rat myocardium. The modifications induced by thyroid dysfunction on contractile recovery might be accounted for by an effect of thyroid state on a time-dependent recycling of calcium by the sarcoplasmic reticulum.