Tumorigenesis driven by the BRAFV600E oncoprotein requires secondary mutations that overcome its feedback inhibition of migration and invasion

BRAFV600E mutation occurs in 46% of melanomas and drives high levels of ERK activity and ERK-dependent proliferation. However, BRAFV600E is insufficient to drive melanoma in GEMM models, and 82% of human benign nevi harbor BRAFV600E mutations. We show here that BRAFV600E inhibits mesenchymal migration by causing feedback inhibition of RAC1 activity. ERK pathway inhibition induces RAC1 activation and restores migration and invasion. In cells with BRAFV600E, mutant RAC1, overexpression of PREX1, PREX2, or PTEN inactivation restore RAC1 activity and cell motility. Together, these lesions occur in 48% of BRAFV600E melanomas. Thus, although BRAFV600E activation of ERK deregulates cell proliferation, it prevents full malignant transformation by causing feedback inhibition of cell migration. Secondary mutations are, therefore, required for tumorigenesis. One mechanism underlying tumor evolution may be the selection of lesions that rescue the deleterious effects of oncogenic drivers.

Abstract 2034: Discovery of novel therapeutic targets using 3D chromatin conformation and patient-specific gene regulatory networks

Regulatory networks containing enhancer to gene edges define cellular state and their rewiring is a hallmark of cancer. While efforts, such as ENCODE, have revealed these networks for reference tissues and cell-lines by integrating multi-omics data, the same methods cannot be applied for large patient cohorts due to the constraints on generating ChIP-seq and three-dimensional data from limited material in patient biopsies. Moreover, many cancer types lack effective targeted therapeutic options and in cancers where first-line targeted therapies are available, treatment resistance is a huge challenge, owing to both genetic and epigenetic alterations. Recent technological advances have enabled the use of ATAC-seq and RNA-seq on patient biopsies in a high-throughput manner. To tackle these problems, we trained a supervised machine learning model using genomic 3D signatures of physical enhancer-gene connections that can predict accurate connections using data from ATAC-seq and RNA-seq assays only. Using these data, we achieved an AUROC (area under receiver operating characteristic curve) of 0.91 for the identification of true regulatory element-gene connections and, importantly, can distinguish between active regulatory elements with connections to target genes and poised elements with no connections to target genes. Our predicted regulatory elements are validated by multi-omics data, including histone modification marks from ENCODE, with an average specificity of 0.92. Our model, applied on chromatin accessibility and transcriptomic data from 400 cancer patients across 22 cancer types revealed novel cancer-type and subtype-specific enhancer-gene connections for known cancer genes with experimental support for accurate prediction of subtype-specific enhancer target genes using CRISPRi in MCF7, T47D and MDA-MB-231 cell lines which represent hormone-receptor (HR) positive and HR- subtypes of breast cancer. We leverage these predictions to construct patient-specific gene regulatory networks, identify the key transcription factors (TFs) in these networks, clusters of patients with similar networks across cancer sites of origin and subsequently identify therapeutic vulnerabilities either by direct targeting of TFs or proteins that they co-operate with. We identify commonly used therapeutic agents for specific cancer types such as ESR1-targeting agents in ER+ breast cancer, KRAS and EGFR inhibitors in Lung and Colon cancers in addition to multiple novel therapeutic targets. We validated four novel candidates identified for neuroendocrine, liver and renal cancers, which have a dismal prognosis with current therapeutic options.

Here we present a computational approach that combines multi-omics machine learning and network analysis then leverages these datasets to identify novel drug targets based on tumor lineage.

Citation Format: Andre Neil Forbes, Duo Xu, Sandra Cohen, Ann Palladino, Priya Pancholi, Ekta Khurana. Discovery of novel therapeutic targets using 3D chromatin conformation and patient-specific gene regulatory networks [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 2034.

Whole-genome sequencing of clinical Clostridioides difficile isolates reveals molecular epidemiology and discrepancies with conventional laboratory diagnostic testing

BACKGROUND

The high clinical burden of Clostridioides difficile infections merits rapid and sensitive identification of affected individuals. However, effective diagnosis remains challenging. Current best practice guidelines recommend molecular and/or direct toxin detection-based screening for symptomatic individuals, but previous work has called into question the concordance and performance of extant clinical assays.

AIM

To better correlate the genomic and phenotypic properties of clinical C. difficile isolates with laboratory testing outcomes in both C. difficile-infected patients and asymptomatic carriers.

METHODS

Whole-genome sequencing of clinical C. difficile isolates collected from an inpatient population at a single healthcare institution was performed, enabling examination of their molecular epidemiology and toxigenic gene content. Genomic findings were compared with clinical testing outcomes, identifying multiple diagnostic discrepancies.

FINDINGS

Toxigenic culture, considered a 'reference standard', provided perfect sensitivity and specificity in predicting toxigenic gene content, whereas reduced performance was observed for Simplexa C. difficile Direct Assay (100% specificity, 88% sensitivity), Gene Xpert CD/Epi Assay (86% specificity, 83% sensitivity), and Quick Check Complete Tox A/B (100% specificity, 30% sensitivity). Genomic analysis additionally revealed variability in toxin gene sequences among C. difficile strains, phylogenomic equivalency between isolates from affected patients and carriers, and patient carriage with uncommon environmentally derived C. difficile lineages, as well as presenting opportunities for tracing pathogen transmission events.

CONCLUSION

These results highlight the variable performance of clinical stool-based testing approaches as well as the potential diagnostic utility of whole-genome sequencing as an alternative to conventional testing algorithms.

Inactivation of Fbxw7 Impairs dsRNA Sensing and Confers Resistance to PD-1 Blockade

The molecular mechanisms leading to resistance to PD-1 blockade are largely unknown. Here, we characterize tumor biopsies from a patient with melanoma who displayed heterogeneous responses to anti-PD-1 therapy. We observe that a resistant tumor exhibited a loss-of-function mutation in the tumor suppressor gene FBXW7, whereas a sensitive tumor from the same patient did not. Consistent with a functional role in immunotherapy response, inactivation of Fbxw7 in murine tumor cell lines caused resistance to anti-PD-1 in immunocompetent animals. Loss of Fbxw7 was associated with altered immune microenvironment, decreased tumor-intrinsic expression of the double-stranded RNA (dsRNA) sensors MDA5 and RIG1, and diminished induction of type I IFN and MHC-I expression. In contrast, restoration of dsRNA sensing in Fbxw7-deficient cells was sufficient to sensitize them to anti-PD-1. Our results thus establish a new role for the commonly inactivated tumor suppressor FBXW7 in viral sensing and sensitivity to immunotherapy. SIGNIFICANCE: Our findings establish a role of the commonly inactivated tumor suppressor FBXW7 as a genomic driver of response to anti-PD-1 therapy. Fbxw7 loss promotes resistance to anti-PD-1 through the downregulation of viral sensing pathways, suggesting that therapeutic reactivation of these pathways could improve clinical responses to checkpoint inhibitors in genomically defined cancer patient populations.This article is highlighted in the In This Issue feature, p. 1241.

STIM1-mediated calcium influx controls antifungal immunity and the metabolic function of non-pathogenic Th17 cells

Immunity to fungal infections is mediated by cells of the innate and adaptive immune system including Th17 cells. Ca²⁺ influx in immune cells is regulated by stromal interaction molecule 1 (STIM1) and its activation of the Ca²⁺ channel ORAI1. We here identify patients with a novel mutation in STIM1 (p.L374P) that abolished Ca²⁺ influx and resulted in increased susceptibility to fungal and other infections. In mice, deletion of STIM1 in all immune cells enhanced susceptibility to mucosal C. albicans infection, whereas T cell‐specific deletion of STIM1 impaired immunity to systemic C. albicans infection. STIM1 deletion impaired the production of Th17 cytokines essential for antifungal immunity and compromised the expression of genes in several metabolic pathways including Foxo and HIF1α signaling that regulate glycolysis and oxidative phosphorylation (OXPHOS). Our study further revealed distinct roles of STIM1 in regulating transcription and metabolic programs in non‐pathogenic Th17 cells compared to pathogenic, proinflammatory Th17 cells, a finding that may potentially be exploited for the treatment of Th17 cell‐mediated inflammatory diseases.

Abstract A48: Inactivation of Fbxw7 impairs dsRNA sensing and confers resistance to PD-1 blockade

Immunotherapies such as anti-PD-1 antibodies can induce durable responses in a subset of cancer patients, but intrinsic or acquired resistance occurs in most cases. Understanding the molecular mechanisms that drive resistance and response to immunotherapies could therefore lead to alternative treatment strategies exhibiting greater efficacy and precision. To identify new tumor cell-intrinsic mechanisms of resistance to PD-1 blockade, we evaluated metastatic melanoma patients who exhibited complete regression of all but one metastatic site following anti-PD-1 therapy. In one patient, we observed a loss-of-function mutation in the tumor suppressor gene F-Box and WD repeat domain containing 7 (FBXW7)—specifically in the resistant tumor. Using an immunocompetent, anti-PD-1 sensitive melanoma mouse model, we demonstrated that Fbxw7 loss of function in tumor cells causes resistance to PD-1 blockade. We showed that the genetic deletion of Fbxw7 in tumor cells alters the tumor immune microenvironment—including decreased effector cells and increased suppressive cells—in addition to diminished responses to viral sensing and interferon signaling pathways in vivo. Mechanistically, we found that Fbxw7 is necessary for the expression of the dsRNA sensors Mda5 and Rig-I. As a consequence, Fbxw7 is required for dsRNA-induced type I interferon production and interferon signaling in tumor cells. Conversely, restoration of the dsRNA signaling pathway in Fbxw7-deficient cells is sufficient to increase MHC-I expression and to suppress growth of Fbxw7-deficient tumors, thereby promoting antitumor immunity. Our findings establish a hitherto unrecognized role of the tumor suppressor gene FBXW7 in tumor immunity and sensitivity to immunotherapy. Collectively, these findings establish a novel tumor-intrinsic pathway of resistance and suggest that therapeutic reactivation of viral sensing pathways could improve clinical responses to checkpoint inhibitors in genomically defined populations.

Citation Format: Cécile Gstalder, David Liu, Diana Miao, Alexander Devine, Bart Lutterbach, Priya Pancholi, Megha Shettigar, Elizabeth Buchbinder, Scott Carter, Michael Manos, Vanesa Rojas-Rudilla, Ryan Brennick, Evisa Gjini, Ana Lako, Scott Rodig, Charles Yoon, Gordon Freeman, F. Stephen Hodi, Eliezer M. Van Allen, Rizwan Haq. Inactivation of Fbxw7 impairs dsRNA sensing and confers resistance to PD-1 blockade [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A48.

Abstract 1698: Loss of MHC-I expression is associated with altered immune microenvironment and decreased response to PD-1 checkpoint inhibition

Cancer immunotherapies, such as PD-1 inhibitors, achieve durable responses in a subset of cancer patients, however, a significant proportion of patients fail to respond to treatment. Defects in antigen presentation, such as the loss of MHC-I expression, are a major mechanism of resistance to PD-1 inhibitors. Developing new therapeutic strategies that overcome the lack of antigen presentation will improve cancer treatment and patient survival. To develop a pre-clinical model to evaluate therapies that could overcome resistance, we have generated a unique PD-1 blockade sensitive, syngeneic immunocompetent melanoma mouse model. We generated defects in antigen presentation using the CRISPR/Cas9 system, creating B2m-deficient melanoma cell lines. We demonstrated that B2m is necessary for IFN-gamma induced MHC-I surface expression. Unlike control tumors, we found that B2m-deficient tumors were resistant to PD-1 blockade, leading to decreased mouse overall survival. Using multi-parameter flow cytometry, we showed an increase in NK cell, regulatory T cell and dendritic cell infiltration in B2m-deficient tumors compared to controls, while the other immune cell population were unchanged. Since NK cell activity is negatively regulated by MHC-I, our findings suggest that additional factors are required to further invigorate infiltrating NK cells and to trigger a NK cell-mediated anti-tumor response. We are currently evaluating new approaches targeting NK cells and regulatory T cells on B2m-deficient tumors. This pre-clinical model could enable the development of a therapeutic strategy serving to improve the treatment of tumors lacking antigen presentation.

Citation Format: Cecile Gstalder, Priya Pancholi, Dorota Sadowicz, Rizwan Haq. Loss of MHC-I expression is associated with altered immune microenvironment and decreased response to PD-1 checkpoint inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1698.

Abstract 5805: Palbociclib synergistically enhances the anticancer activity of cisplatin in P53 mutant model of upper gastrointestinal cancers

Background: Upper Gastrointestinal Cancers (UGCs) respond poorly to conventional chemotherapy due to overactive intrinsic mechanisms that mediate cellular proliferation and drug resistance. Dysregulated cell division due to increased activity of cyclin-dependent kinases 4/6 (CDK4/6) is one such mechanism that drives progression of UGCs, making them an important therapeutic target. Palbociclib is a second generation cdk4/6 specific inhibitor approved for treatment of ER+ breast cancers. Since Cisplatin (CDDP) is a first line therapeutic agent frequently used for treatment of UGCs we hypothesized that Palbociclib would complement the DNA-damaging activity of CDDP. To test this hypothesis, we investigated the potential therapeutic benefit of Palbociclib alone and in combination with CDDP in P53 mutant model of UGCs. Methods: In this study, we evaluated the effect of Palbociclib treatment alone and/or in combination with CDDP on FLO-1 (P53 mutant) UGC cell viability, survival, and cell cycle progression, respectviely. The MTT cell viability assay and Compusyn mediated median effect plot analysis (MEPA)(Chou and Talaly) were used to determine synergistic drug combinations of Palbociclib and CDDP in FLO-1 UGC cells. Results: The cell viability data and MEPA indicated that Palbociclib and CDDP show significant synergistic anticancer activity in FLO-1 UGC cells at a ratio of 1:2 and 1:3, respectively. The clonogenic cell survival assay data showed that in comparison to treatment with Palbociclib (0.5µM) or CDDP (1.0 and 1.5µM) alone, the combination treatments (Palbociclib:CDDP) at a ratio of 1:2 and 1:3 exhibited significantly elevated (p<0.05) inhibition of cellular survival in FLO-1 UGC cell lines. In addition, the Combination Index (CI) values of 0.66 and 0.71 for the aforementioned combination ratios suggests a strong synergism between the two drugs. Furthermore, the cell cycle data exhibited a marked increase (p<0.05) in the percentage of FLO-1 cells in the sub-G1-phase (cell death) after treatment with Palbocicb and CDDP combinations for 72 hrs., respectively . Conclusions: Our in vitro data indicate that Palbociclib, as a single agent, is an effective therapeutic strategy for inhibiting UGC cells. Additionally, Palbociclib in combination with CDDP synergistically enhances the anti-tumor activity of CDDP against P53 mutant UGC cells[MM1] . The observed synergism can potentially translate into reduced individual drug dosages and toxicity for Palbociclib and/or CDDP when used in combination.

Citation Format: Dhvanir Kansara, Amruta Samant, Priya Pancholi, Tanvi Visal, Shraddha Patel, Vikas Sehdev. Palbociclib synergistically enhances the anticancer activity of cisplatin in P53 mutant model of upper gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5805.

Abstract 4180: RS-41, a multi-targeted kinase inhibitor, induces cell cycle arrest and apoptosis in p53 mutant and wild type models of upper gastrointestinal cancers

Introduction: Upper Gastrointestinal Cancers (UGCs) are a leading cause of cancer-related mortality and account for approximately 1.1 million deaths worldwide. UGCs respond poorly to conventional chemotherapy due to constitutive over activity of multiple oncogenic signaling mechanisms, including the epidermal growth factor receptor (EGFR), ERBB2/HER-2, Aurora kinases, and JAK-STAT pathways. In addition, presence of mutant P53 further imparts resistance to conventional chemotherapeutic agents. Therefore, novel small molecule inhibitors that target multiple kinases associated with oncogenic

progression could pave the way for improved chemotherapy and better therapeutic outcomes. In this study, we characterized the anticancer activity of RS-41, an investigational 4-phenylbenzamidopyrrolo[2,3-d]-pyrimidin-4-amine multi-kinase inhibitor, in P53 mutant and wild type models of UGC.

Methods: Target kinase inhibition and selectivity screening assays were performed to determine potency and selectivity of kinase inhibition for RS-41. In addition, MTT-cell viability assay, clonogenic cell survival assay, cell cycle analyses, and western blot analyses were done to evaluated the effect of RS-41 treatment on cell viability, survival, cell cycle progression, and expression of apoptotic markers in P53 mutant (FLO-1) and P53 wild type (AGS) UGC cells, respectively.

Results: The kinase selectivity screening assay characterized RS-41 for its selectivity against a panel of 90 human kinases. The kinase screening analyses showed that RS-41 selectively inhibits AURKA (IC50-0.96±0.03µM), JAK2 (IC50-1.21±0.17µM), and EGFR (IC50-5.92±0.75µM) kinases, respectively. The cell viability data indicate that treatment with RS-41 mediates significant (P≤0.05) inhibition of FLO-1 and AGS UGC cell viability. The clonogenic cell survival data showed that treatment with RS-41 for 24 hrs. suppresses subsequent formation of colonies in both FLO-1 and AGS UGC cells. The cell cycle data

exhibited a marked increase (P≤0.05) in the percentage of FLO-1 and AGS cells in the sub-G1-phase (cell death) after treatment with RS-41 for 24 and 72 hrs., respectively. The western blotting data further confirmed induction of apoptosis in FLO-1 and AGS cells as evidenced by an increase in expression of various markers of apoptosis (P73/P53, cleaved PARP, and/or cleaved caspase 3) following treatment with RS-41 for 24 and 72 hrs.

Conclusions: Our in vitro data indicate that inhibition of various oncogenic kinases with RS-41 is an effective therapeutic strategy for inducing apoptosis in both P53 mutant and wild type UGC cells. Our study suggests that RS-41 is a promising multi-kinase inhibitor with a potential to further enhance chemotherapeutic options for treatment of UGC.

Citation Format: Tanvi Visal, Shraddha Patel, Priya Pancholi, Samhita Bapat, Amruta Samant, Dhvanir Kansara, Sonali Kurup, Vikas Sehdev. RS-41, a multi-targeted kinase inhibitor, induces cell cycle arrest and apoptosis in p53 mutant and wild type models of upper gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4180. doi:10.1158/1538-7445.AM2017-4180

Abstract 2172: ON 123300, an orally administered novel CDK4/6 + ARK5 inhibitor, exhibits potent antitumor activity in vivo: comparative studies with Palbociclib

Background: The overexpression of cyclin-dependent kinases 4/6 (CDK4/6) is known to cause cell cycle dysregulation in certain cancer types, making these cell cycle kinases attractive targets for pharmacological inhibition. The effectiveness of first-generation non-selective cyclin-dependent kinases, such as roscovitine and flavopiridol, was hampered by toxicities, leading to the development of second-generation compounds like IBRANCE®/Palbociclib that specifically inhibit CDK4 and 6. ON 123300 is a third-generation potent CDK4/6 inhibitor that also inhibits ARK5 with low nanomolar potency and has the potential to improve upon second-generation compounds. Previous studies have demonstrated the inhibitory effect of single-agent ON 123300 in various pre-clinical cancer models of MM and leukemia. In this study, we investigated the comparative therapeutic potential of ON 123300 as an oral anticancer agent and a second-generation inhibitor, Palbociclib, in xenografted Rb+ve mouse models.

Methods: MDA-MB-435S xenografted mice were treated once a day for 21 days with ON 123300 (125mg/kg) or Palbociclib (125mg/kg). Tumor volumes were measured and peripheral blood was gathered to evaluate the effects on hematological parameters. Separately, Western blot analyses were performed to determine the effect of CDK4/6 inhibition on p-Rb following intra-tumoral treatment with ON 123300 (2.5µM) or Palbociclib (2.5µM).

Results: ON 123300 and Palbociclib reduced tumor growth with an equivalent magnitude during the 21-day treatment period, suggesting that the two compounds were equally effective in this model. Both compounds decreased RBC and platelet counts, however Palbociclib had a

more prominent and statistically significant (P≤0.05) inhibitory effect on neutrophil counts when compared to ON 123300 (30.70 ± 3.55 vs. 45.10 ± 2.04). Western blot analysis of tumor tissues demonstrated equivalent effects on p-Rb for both compounds.

Conclusions: Xenograft data indicates that a third-generation CDK4/6 inhibitor, ON 123300, is as effective as Palbociclib in an Rb+ve xenograft model. Moreover, this study also suggests that ON 123300 may have the added advantage of reduced neutropenia compared to Palbociclib. Prior preclinical data suggest that ON 123300 may be efficacious in Rb-ve tumors, where second-generation compounds have diminished single-agent

activity, and our ongoing studies are aimed at further characterizing the in vivo activity of ON 123300 in this setting.

Citation Format: Shraddha Patel, Priya Pancholi, Tanvi Visal, Amruta Samant, Dhvanir Kansara, V J. Rajadhyaksha, Benjamin S. Hoffman, Manoj Maniar, Vikas Sehdev. ON 123300, an orally administered novel CDK4/6 + ARK5 inhibitor, exhibits potent antitumor activity in vivo: comparative studies with Palbociclib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2172. doi:10.1158/1538-7445.AM2017-2172

Omega-3 Fatty Acid Grafted PAMAM-Paclitaxel Conjugate Exhibits Enhanced Anticancer Activity in Upper Gastrointestinal Cancer Cells

Upper Gastrointestinal Cancers (UGCs) are a leading cause of cancer-related deaths worldwide. Paclitaxel (PTX) is frequently used for the treatment of UGCs; however, low bioavailability, reduced solubility, and dose-dependent toxicity impede its therapeutic use. PAMAMG_4.0 -NH₂ -DHA is synthesized by linking amine-terminated fourth-generation poly(amidoamine) (PAMAMG_4.0 -NH₂ ) dendrimers with omega-3 fatty acid docosahexaenoic acid (DHA). Next, PAMAMG_4.0 -NH₂ -DHA-PTX (DHATX) and PAMAMG_4.0 -NH₂ -PTX (PAX) conjugates are synthesized by subsequent covalent binding of PTX with PAMAMG_4.0 -NH₂ -DHA and PAMAMG_4.0 -NH₂ , respectively. ¹ H-NMR and MALDI-TOF analyses are performed to confirm conjugation of DHA to PAMAMG_4.0 -NH₂ and PTX to PAMAMG_4.0 -NH₂ -DHA. The cell viability, clonogenic cell survival, and flow cytometry analyses are used to determine the anticancer activity of PTX, PAX, and DHATX in UGC cell lines. The in vitro data indicate that treatment with DHATX is significantly more potent than PTX or PAX at inhibiting cellular proliferation, suppressing long-term survival, and inducing cell death in UGC cells.

Extended-Spectrum β-lactam Resistance in the Enteric Flora of Patients at a Tertiary Care Medical Centre

The dissemination of Enterobacteriaceae expressing resistance to extended-spectrum cephalosporins, which are therapeutically used in both human and veterinary medicine, is of critical concern. The normal commensal flora of food animals may serve as an important reservoir for the zoonotic food-borne transmission of Enterobacteriaceae harbouring β-lactam resistance. We hypothesized that the predominant AmpC and ESBL genes reported in US livestock and fresh retail meat products, bla_CMY-2 and bla_CTX-M , would also be predominant in human enteric flora. We recovered enteric flora from a convenience sample of patients included in a large tertiary medical centre's Clostridium difficile surveillance programme to screen for and estimate the frequency of carriage of AmpC and ESBL resistance genes. In- and outpatient diarrhoeic submissions (n = 692) received for C. difficile testing at the medical centre's clinical diagnostic laboratory from July to December, 2013, were included. Aliquoted to a transport swab, each submission was inoculated to MacConkey broth with cefotaxime, incubated at 37°C and then inoculated to MacConkey agars supplemented with cefoxitin and cefepime to select for the AmpC and ESBL phenotypes, with bla_CMY and bla_CTX-M genotypes confirmed by PCR and sequencing. From the 692 diarrhoeic submissions, our selective culture yielded 184 isolates (26.6%) with reduced susceptibility to cefotaxime. Of these, 46 (6.7%) samples harboured commensal isolates carrying the AmpC bla_CMY . Another 21 (3.0%) samples produced isolates harbouring the ESBL bla_CTX-M : 19 carrying CTX-M-15 and 2 with CTX-M-27. Our results indicate that β-lactam resistance genes likely acquired through zoonotic food-borne transmission are present in the enteric flora of this hospital-associated population at lower levels than reported in livestock and fresh food products.

Abstract 4776: Dichloro [4,40-bis(4,4,4-trifluorobutyl)-2,20-bipyridine] platinum, a novel Cisplatin analog, exhibits enhanced anticancer activity in preclinical models of upper gastrointestinal cancers

Background: Upper Gastrointestinal Cancers (UGCs) respond poorly to conventional chemotherapy due to variable P53 status and overactive mechanisms that mediate drug resistance. Platinum based compounds like Cisplatin (CDDP) are frequently used for treatment of UGCs. However, clinical use of CDDP is limited due to development of drug resistance and dose limiting side-effects resulting in nausea, vomiting, neutropenia, thrombocytopenia and renal toxicity. In this study we investigated the anticancer potency of a novel CDDP derivative (dichloro [4,40-bis(4,4,4-trifluorobutyl)-2,20-bipyridine] platinum) (DCTF-CDDP) and compared it to CDDP in P53 wild type and mutant models of UGCs. Methods: For this study, we evaluated the effect of CDDP or its derivative (DCTF-CDDP) on AGS (P53 wild type) and FLO-1 (P53 mutant) UGC cell viability, survival, and expression of apoptotic markers. Results: The cell viability data indicated that DCTF-CDDP treatment was comparatively more effective than CDDP at inhibiting AGS (CDDP IC50: 6.3 ± 0.2 μM; DCTF IC50: 1.7 ± 0.5μM) and FLO-1 (CDDP IC50: 2.5 ± 0.68 μM; DCTF IC50: 0.5 ± 0.6μM) UGC cancer cell viability. The clonogenic cell survival assay data also showed that DCTF-CDDP was significantly (p<0.05) more potent at suppressing UGC cell survival when compared to CDDP. Similarly, the western blot data also showed that treatment with increasing concentrations (1, 2.5, and 5 μM) of CDDP and DCTF-CDDP for 24h induced higher levels of P53/P73 and cleaved PARP with DCTF-CDDP treatment in UGC cells. Conclusions: Our in vitro data indicate that DCTF-CDDP is significantly more potent at inhibiting cell viability and inducing apoptosis in P53 wild type and mutant UGC cells. Our study suggests that DCTF-CDDP could be an effective CDDP derivative that can be used to achieve better therapeutic outcome at lower doses and toxic side effects.

Citation Format: Samhita Bapat, Tanmay Dichwalkar, Priya Pancholi, Byron L. Bennett, Vikas Sehdev. Dichloro [4,40-bis(4,4,4-trifluorobutyl)-2,20-bipyridine] platinum, a novel Cisplatin analog, exhibits enhanced anticancer activity in preclinical models of upper gastrointestinal cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4776.

Abstract 2200: Omega-3 fatty acid conjugated paclitaxel dendrimers exhibit enhanced anticancer activity in various preclinical models of gastrointestinal cancers

Background: Paclitaxel (PTX) is frequently used for the treatment of advanced gastrointestinal (GI) cancers. However, development of drug resistance, dose-dependent toxicity, and lack of oral bioavailability are some of the major limiting factors that impede the therapeutic use of PTX for treatment of GI cancers. Drug conjugates of dendrimers, such as poly (amidoamine) (PAMAM), have been reported to effectively overcome bioavailability and dose-dependent toxicity related limitations. Therefore, in this study we synthesized and investigated the anticancer potential of omega-3 fatty acid [docosahexanoic acid (DHA)]-poly (amido)amine (PAMAM)-paclitaxel conjugates in various in vitro models of gastrointestinal cancers. Methods: DHA was conjugated to amine-terminated PAMAMG4 dendrimers using coupling agents HOBt and HBTU. PAMAMG4-DHA was then conjugated to PTX using PTX-NHS-ester. The conjugates were purified by size exclusion chromatography and characterized using 1H-NMR, MALDI-TOF-MS and high-resolution ESI-MS. The percentage payload of PTX conjugated to PAMAMG4-DHA and in vitro stability of PAMAMG4-DHA-PTX were evaluated using HPLC. Cell viability, clonogenic cell survival, and western blot analyses were done to evaluate the cell viability, survival, and induction of apoptotic proteins (P53 and P21), respectively. The in vitro cytotoxicity and induction of apoptosis was investigated in AGS, FLO-1, and MIA PaCa-2 GI cancer cell lines after treatment with PTX or PAMAMG4-DHA-PTX. Results: The 1H-NMR, MALDI-TOF and high-resolution ESI mass spectra confirmed the conjugation of DHA to PAMAM and PTX to PAMAM-DHA. The in vitro stability data showed that PAMAM-DHA-PTX conjugate was stable in human plasma for 24 hours. The cell viability data indicated that treatment with PAMAMG4-DHA-PTX is significantly more potent than PTX at inhibiting proliferation of esophageal (FLO-1: PTX IC50: 3.8±0.68 nM, PAMAMG4-DHA-PTX IC50: 1.1±0.17 nM), gastric (AGS: PTX IC50: 5.1±0.58 nM, PAMAMG4-DHA-PTX IC50: 1.4±0.23 nM), and pancreatic (MIA PaCa: PTX IC50: 5.1±0.75 nM, PAMAMG4-DHA-PTX IC50: 1.8±0.35 nM) cancer cell lines. The clonogenic cell survival data shows a similar activity where treatment with PAMAMG4-DHA-PTX exhibited enhanced inhibition of long term survival of FLO-1, AGS, and MIA PaCa cells when compared to PTX. The protein expression data further showed that compared to PTX treatment with PAMAMG4-DHA-PTX induced higher expression of P53 and P21 pro-apoptotic protein in AGS gastric cancer cell line. Conclusions: Overall our findings indicate that paclitaxel was successfully conjugated with PAMAMG4-DHA resulting in the synthesis of a novel PAMAMG4-DHA-PTX conjugate that exhibits enhanced anticancer activity than PTX alone in various in vitro models of GI cancers.

Citation Format: Tanmay Dichwalkar, Samhita Bapat, Priya Pancholi, V. K. Yellepeddi, Vikas Sehdev. Omega-3 fatty acid conjugated paclitaxel dendrimers exhibit enhanced anticancer activity in various preclinical models of gastrointestinal cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2200.

Abstract 4687: Rigosertib synergistically enhances the anticancer activity of Cisplatin in various preclinical models of upper gastrointestinal cancers

Background: Upper Gastrointestinal Cancers (UGCs) respond poorly to conventional chemotherapy due to overactive intrinsic mechanisms that mediate drug resistance.] Rigosertib is an investigational anticancer agent, that inhibits cellular signaling by acting as a Ras mimetic to effect the activation of multiple pathways associated with oncogenic transformation and drug resistance. Previous studies have demonstrated the inhibitory effect of rigosertib with conventional platinum based anticancer agents in various pre-clinical cancer models. We hypothesized that the novel mechanism of action of rigosertib would complement the DNA-damaging activity of Cisplatin (CDDP), the standard of care in UGC. To test this hypothesis, we investigated the potential therapeutic benefit of rigosertib alone and in combination with CDDP in P53 wild type and mutant models of UGCs. Methods: For this study, we evaluated the effect of rigosertib treatment alone and/or in combination with CDDP on AGS (P53 wild type) and FLO-1 (P53 mutant) UGC cell viability, survival, and expression of apoptotic markers. The MTT cell viability assay and Compusyn mediated median effect plot analysis (MEPA)(Chou and Talaly) were used to determine synergistic drug combinations of rigosertib and CDDP in AGS and FLO-1 UGC cells, respectively. Results: The cell viability data and MEPA indicated that rigosertib and CDDP show optimal synergistic anticancer activity in both AGS and FLO-1 UGC cells at a ratio of 1:10, respectively. The clonogenic cell survival assay data showed that in comparison to treatment with Rigosertib (AGS: 100nM; FLO-1: 50nM) or CDDP (AGS: 1000nM; FLO-1: 500nM) alone, the combination treatment at a ratio of 1:10 significantly increased (p<0.05) inhibition of cellular survival in AGS and FLO-1 UGC cell lines. The Combination Index of 0.5 suggests a strong synergism between the two drugs. Similarly, the western blot data after treatment with Rigosertib (100nM) and/or CDDP (1000nM) for 24h induced higher levels of P53/P73, P21, and cleaved PARP with Rigosertib (100nM) and CDDP (1000nM) combination treatment in UGC cells. Conclusions: Our in vitro data indicate that rigosertib, as a single agent, is an effective therapeutic strategy for inducing apoptosis in UGC cells Additionally, rigosertib in combination with CDDP synergistically enhances the anti-tumor activity of CDDP against UGC cells. The observed synergism can translate into lower drug toxicity as significant anticancer activity can be achieved with much lower doses of rigosertib and CDDP when used in combination.

Citation Format: Priya Pancholi, Tanmay Dichwalkar, Samhita Bapat, V. J. Rajadhyaksha, Benjamin S. Hoffman, Manoj Maniar, Vikas Sehdev. Rigosertib synergistically enhances the anticancer activity of Cisplatin in various preclinical models of upper gastrointestinal cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4687.

DNA prime/canarypox boost-based immunotherapy of chronic hepatitis B virus infection in a chimpanzee

There are about 200 million chronic hepatitis B virus (HBV) carriers at high risk of development of cirrhosis and hepatocellular carcinoma. Termination of the carrier state may avert these risks. We have investigated immunotherapy for chronic HBV infection in a chimpanzee HBV carrier using recombinant DNA-based immunization followed by a recombinant canarypox booster. One week after the booster, HBV DNA declined greater than 400-fold and remained undetectable by the quantitative polymerase chain reaction (PCR) assay for 186 weeks. Plasma levels of hepatitis B surface antigen (HBsAg) declined for only a short time. The decline in HBV DNA correlated with a boost in gamma interferon production without a corresponding boost in cytotoxic T lymphocyte levels, and decline in the transcriptional template or covalently closed circular DNA level. Confirmation of these findings requires further studies in chimpanzees and/or in humans.

DNA prime-canarypox boost with polycistronic hepatitis C virus (HCV) genes generates potent immune responses to HCV structural and nonstructural proteins

DNA vaccination was employed to study immune responses to hepatitis C virus (HCV) proteins. As an immunizing strategy, we studied immune responses of BALB/c (H-2d) and C57BL/6 mice (H-2b) to HCV genes delivered intramuscularly as a polycistronic construct capsid/E1/E2/NS2/NS3 (pRC/C-NS3) encoding 5 structural and nonstructural proteins. We also evaluated canarypox virus containing the same HCV genes as a means for potentiating immune responses to naked DNA. Our results indicate that mice that received a polycistronic pRC/C-NS3 with canarypox booster had enhanced antibody and cellular responses to HCV proteins. Immunodominant CD8(+) T cell responses to several HCV structural and nonstructural proteins, characterized by cytotoxicity and interferon (IFN)-gamma production or IFN-gamma production without significant cytotoxicity, were observed in both strains of mice. The combination of naked DNA with a nonreplicating canarypox booster encoding HCV polycistronic pRC/C-NS3 genes appears to diversify and enhance T cell responses to HCV proteins.

Immunoserologic evidence of Human Granulocytic Ehrlichiosis in Danish patients with Lyme neuroborreliosis

Human Granulocytic Ehrlichiosis (HGE) is a recently described human illness in the US which manifests as fever, myalgia and headache combined with pancytopenia and elevated concentrations of hepatic transaminases. Genetic analyses indicate that the agent of HGE appears to be an Ehrlichia species that is closely related to E. equi and E. phagocytophila. Ixodes dammini and I. scapularis were identified as potential vectors of HGE. Ixodes ticks are also the vector of Borrelia burgdorferi, the agent of Lyme borreliosis. The presence of antibodies against Ehrlichia in 132 sera from Danish patients with definite Lyme neuroborreliosis were examined in order to provide immunoserologic evidence of this infection in Denmark. Patients with Lyme neuroborreliosis were chosen as a test cohort, as these patients had been infested by a tick sufficient for transmission of B. burgdorferi. All had cerebrospinal fluid lymphocytic pleocytosis. As controls, serum samples from 50 healthy Danish blood donors were included. Of the 132 patients with Lyme neuroborreliosis, 5 (3.8%) reacted with the E. equi antigen substrate at titres 1:128. None of the blood donors were found seropositive for E. equi. At least 2 of the patients found seropositive for HGE constituted probable cases of HGE with E. equi antibody titres of at least 80 combined with fever, headache and myalgias. However, in no cases were we able to detect the presence of the HGE agent in the serum by PCR. We conclude that human exposure to granulocytic Ehrlichiae species may also occur in Europe, although further studies will be necessary to document active infection with these potential pathogens.

Ixodes dammini as a potential vector of human granulocytic ehrlichiosis

Little is known about the epidemiology and mode of transmission of the agent of human granulocytic ehrlichiosis (HGE). Analyses of an engorged female Ixodes dammini tick removed from an HGE patient and 101 field-collected I. dammini and Dermacentor variabilis from three Wisconsin counties for Borrelia burgdorferi and Ehrlichia phagocytophila/Ehrlichia equi DNA revealed that the patient tick and 7 of 68 I. dammini ticks from Washburn County collected in 1982 and 1991 were positive for ehrlichial DNA; 10 ticks from the same collections were positive for B. burgdorferi. Two specimens (2.2%) were positive for both organisms. Serologic evidence for exposure to the agent of HGE or its relatives was detected in 3 of 25 Lyme disease patients from the upper Midwest. These data argue that I. dammini is a common vector for transmission of both Lyme disease and HGE.

Presentation of mycobacterial antigens by human dendritic cells: lack of transfer from infected macrophages

When exposed to a challenge of 10 Mycobacterium bovis BCG cells per antigen-presenting cell, most human monocytes engulf several organisms. In contrast, blood dendritic cells which are potent antigen-presenting cells for several antigens are not detectably phagocytic for mycobacteria. We investigated the possibility that infected macrophages might regurgitate antigens for presentation by populations of human blood dendritic cells. Macrophages were infected with M. bovis BCG, mixed with uninfected dendritic cells, and added to immune T cells, either bulk T cells or cloned populations from BCG vaccinees or patients recovering from tuberculosis. The macrophages were from donors who were mismatched to the T cells so that transfer of antigen to major histocompatibility complex-matched dendritic cells could be evaluated. As we describe, there was no evidence for the transfer of mycobacterial antigens from macrophages to dendritic cells in a form that was stimulatory for the T cells.

Sequestration from immune CD4+ T cells of mycobacteria growing in human macrophages

CD4+ helper T cells mediate resistance to tuberculosis, presumably by enhancing the antimicrobial activity of macrophages within which the Mycobacterium tuberculosis organism grows. A first step in resistance should be the presentation of mycobacterial antigens by macrophages to CD4+ T cells. However, when the antigenic stimulus is limited to organisms growing in human monocytes, the organisms become sequestered from immune CD4+ T cells. This block in presentation is selective for growing mycobacteria and not for other stimuli. Sequestration would allow replicating organisms to persist in infected individuals and may contribute to virulence.

Dendritic cells efficiently immunoselect mycobacterial-reactive T cells in human blood, including clonable antigen-reactive precursors

Given the persistence of tuberculosis throughout the world, the delineation of mechanisms that lead to protective immunity to Mycobacterium tuberculosis is important. We have evaluated the presenting function of human dendritic cells for mycobacterial antigens, since these antigen-presenting cells (APC) are particularly effective in initiating antigen-specific T-cell responses. Dendritic cells from blood prove to be active APC for mycobacteria-specific proliferative responses by CD4+ T cells from bacillus Calmette-Guérin (BCG)-vaccinated individuals. In the first 24-48 hr of the response, dendritic cells that have been pulsed with mycobacterial antigens, including live BCG, effectively bind T cells forming discrete cell clusters. The clusters represent about 1% of the applied T cells. Clusters are highly enriched in mycobacterial reactivity while the non-clusters are depleted. Clustered T cells can be used as a starting point to expand antigen-specific cell lines. Mitogen and allogeneic feeder cells were used as APC to expand the mycobacterial-reactive lines, because the antigen-specific T cells had been preselected by virtue of their binding to antigen-pulsed dendritic cells. We discuss the advantages of obtaining antigen-reactive T cells by using dendritic cells as immunoadsorbents. These lines should help delineate the range of mycobacterial antigens and T-cell responses that participate in host responses to mycobacteria.

An approach to isolating T cell lines that react to antigens presented on the surface of dendritic cells

We describe an approach that might be useful for identifying antigens on surfaces of antigen presenting cells. It is known that dendritic cells carry antigens in situ and are efficient at clustering antigen-specific T cells. Using the human mixed lymphocyte reaction (MLR) system, we have shown that alloreactive CD4+ T cells can be selected by their capacity to cluster with dendritic cells in the first 2 days of the MLR. Small numbers of clustered cells, 1-10/culture well, could then be expanded as antigen-specific lines in presence of either antigen or mitogen, sodium periodate. Few antigen-specific lines could be isolated from the nonclustered fraction. When T cell lines derived from the dendritic T cell clusters were maintained without antigen, i.e. using second party (syngeneic antigen-presenting cells (APC] or irrelevant antigen bearing APC, i.e. third-party (HLA-mismatched) stimulator cells plus mitogen, the T cells retained their specificity for the original stimulating alloantigen over the time course tested, several weeks to months. These findings show that by using dendritic cells as immunoadsorbents one can prepare antigen-specific cell lines and maintain the specificity of the lines without the need for adding exogeneous antigen during either immunoselection or cloning. We discuss the possible use of dendritic cells as a means for raising T cell lines and clones that recognize antigens being carried by APC and which might be pertinent to protective immunity and autoimmunity.

Immunobiological studies with mycobacterial ribonucleic acid-protein complex: Part I--Immune responses and protective role against experimental tuberculosis

Ribonucleic acid (RNA) isolated from M. tuberculosis H37Ra was found to be native in nature as determined by hyperchromicity studies using ribonuclease. Mycobacterial RNA-protein (Myc. RNA-P) when injected as RNA-P-FIA complexes induced weak humoral immune responses and strong cell-mediated immune (CMI) responses which were directed against Myc. RNA. Protection comparable to BCG was induced in mice immunized with RNA-FIA complexes against LD50 dose of M. tuberculosis as monitored by increased survival rates, decreased lung density, root specific lung weight (RSLW) and by decreased viable counts of M. tuberculosis in lung, liver and spleen of immunized mice. Enzymatic degradation studies revealed Myc. RNA component to specifically mediate protection while the protein component was found ineffective.

Immunobiological studies with mycobacterial ribonucleic acid-protein complex: Part II--Mechanism of protective immunity against experimental tuberculosis

Passive transfer of protective antituberculous immunity against LD50 dose of M. tuberculosis H37Rv was found to be mainly mediated by immune T-cells harvested from spleens of donor mice immunized with Myc. RNA-P-FIA complexes as monitored by indices of percent survival, root specific lung weight, lung density and by bacterial enumeration from different organs. Treatment of immune T-cells with anti-Thy 1.2. monoclonal antibodies plus complement prior to passive transfer, completely abrogated its protective effect thereby confirming their protective nature. Passive transfer of immune sera as well as immune T + B cells did not induce any enhancement in protective immunity.

Immunogenicity of ribonucleic acid-protein fraction of Mycobacterium tuberculosis encapsulated in liposomes

Immunologically potent RNA-protein extracted from Mycobacterium tuberculosis strain H37Ra, when entrapped in phosphatidylcholine multilamellar liposomes and injected into mice, induced both cellular and humoral immune responses. Significant protection against infection with M. tuberculosis H37Rv was also induced in the immunised mice, as monitored by (i) higher survival rates, (ii) decreased viable counts of M. tuberculosis H37Rv in lungs, livers and spleens, (iii) lower lung density, and (iv) lower root specific lung weight, in comparison with a control group of unimmunized mice.