Novel murine glioblastoma models that reflect the immunotherapy resistance profile of a human disease

BACKGROUND

The lack of murine glioblastoma models that mimic the immunobiology of human disease has impeded basic and translational immunology research. We, therefore, developed murine glioblastoma stem cell lines derived from Nestin-CreERT2QkL/L; Trp53L/L; PtenL/L (QPP) mice driven by clinically relevant genetic mutations common in human glioblastoma. This study aims to determine the immune sensitivities of these QPP lines in immunocompetent hosts and their underlying mechanisms.

METHODS

The differential responsiveness of QPP lines was assessed in the brain and flank in untreated, anti-PD-1, or anti-CTLA-4 treated mice. The impact of genomic landscape on the responsiveness of each tumor was measured through whole exome sequencing. The immune microenvironments of sensitive (QPP7) versus resistant (QPP8) lines were compared in the brain using flow cytometry. Drivers of flank sensitivity versus brain resistance were also measured for QPP8.

RESULTS

QPP lines are syngeneic to C57BL/6J mice and demonstrate varied sensitivities to T cell immune checkpoint blockade ranging from curative responses to complete resistance. Infiltrating tumor immune analysis of QPP8 reveals improved T cell fitness and augmented effector-to-suppressor ratios when implanted subcutaneously (sensitive), which are absent on implantation in the brain (resistant). Upregulation of PD-L1 across the myeloid stroma acts to establish this state of immune privilege in the brain. In contrast, QPP7 responds to checkpoint immunotherapy even in the brain likely resulting from its elevated neoantigen burden.

CONCLUSIONS

These syngeneic QPP models of glioblastoma demonstrate clinically relevant profiles of immunotherapeutic sensitivity and potential utility for both mechanistic discovery and evaluation of immune therapies.

Gender Differences in a Mouse Model of Hepatocellular Carcinoma Revealed Using Multi-Modal Imaging

The worldwide incidence of hepatocellular carcinoma (HCC) continues to rise, in part due to poor diet, limited exercise, and alcohol abuse. Numerous studies have suggested that the loss or mutation of PTEN plays a critical role in HCC tumorigenesis through the activation of the PI3K/Akt signaling axis. The homozygous knockout of PTEN in the livers of mice results in the accumulation of fat (steatosis), inflammation, fibrosis, and eventually progression to HCC. This phenotype bears a striking similarity to non-alcoholic steatohepatitis (NASH) which is thought to occupy an intermediate stage between non-alcoholic fatty liver disease (NAFLD), fibrosis, and HCC. The molecular and physiological phenotypes that manifest during the transition to HCC suggest that molecular imaging could provide a non-invasive screening platform to identify the hallmarks of HCC initiation prior to the presentation of clinical disease. We have carried out longitudinal imaging studies on the liver-specific PTEN knockout mouse model using CT, MRI, and multi-tracer PET to interrogate liver size, steatosis, inflammation, and apoptosis. In male PTEN knockout mice, significant steatosis was observed as early as 3 months using both magnetic resonance spectroscopy (MRS) and computed tomography (CT). Enhanced uptake of the apoptosis tracer 18F-TBD was also observed in the livers of male PTEN homozygous knockout mice between 3 and 4 months of age relative to heterozygous knockout controls. Liver uptake of the inflammation tracer [18F]4FN remained relatively low and constant over 7 months in male PTEN homozygous knockout mice, suggesting the suppression of high-energy ROS/RNS with PTEN deletion relative to heterozygous males where the [18F]4FN liver uptake was elevated at early and late time points. All male PTEN homozygous mice developed HCC lesions by month 10. In contrast to the male cohort, only 20% (2 out of 10) of female PTEN homozygous knockout mice developed HCC lesions by month 10. Steatosis was significantly less pronounced in the female PTEN homozygous knockout mice relative to males and could not accurately predict the eventual occurrence of HCC. As with the males, the [18F]4FN uptake in female PTEN homozygous knockout mice was low and constant throughout the time course. The liver uptake of 18F-TBD at 3 and 4.5 months was higher in the two female PTEN knockout mice that would eventually develop HCC and was the most predictive imaging biomarker for HCC in the female cohort. These studies demonstrate the diagnostic and prognostic role of multi-modal imaging in HCC mouse models and provide compelling evidence that disease progression in the PTEN knockout model is highly dependent on gender.

Directed Evolution of PD-L1-Targeted Affibodies by mRNA Display

Therapeutic monoclonal antibodies directed against PD-L1 (e.g., atezolizumab) disrupt PD-L1:PD-1 signaling and reactivate exhausted cytotoxic T-cells in the tumor compartment. Although anti-PD-L1 antibodies are successful as immune checkpoint inhibitor (ICI) therapeutics, there is still a pressing need to develop high-affinity, low-molecular-weight ligands for molecular imaging and diagnostic applications. Affibodies are small polypeptides (∼60 amino acids) that provide a stable molecular scaffold from which to evolve high-affinity ligands. Despite its proven utility in the development of imaging probes, this scaffold has never been optimized for use in mRNA display, a powerful in vitro selection platform incorporating high library diversity, unnatural amino acids, and chemical modification. In this manuscript, we describe the selection of a PD-L1-binding affibody by mRNA display. Following randomization of the 13 amino acids that define the binding interface of the well-described Her2 affibody, the resulting library was selected against recombinant human PD-L1 (hPD-L1). After four rounds, the enriched library was split and selected against either hPD-L1 or the mouse ortholog (mPD-L1). The dual target selection resulted in the identification of a human/mouse cross-reactive PD-L1 affibody (M1) with low nanomolar affinity for both targets. The M1 affibody bound with similar affinity to mPD-L1 and hPD-L1 expressed on the cell surface and inhibited signaling through the PD-L1:PD-1 axis at low micromolar concentrations in a cell-based functional assay. In vivo optical imaging with M1-Cy5 in an immune-competent mouse model of lymphoma revealed significant tumor uptake relative to a Cy5-conjugated Her2 affibody.

Mistiming Death: Modeling the Time-Domain Variability of Tumor Apoptosis and Implications for Molecular Imaging of Cell Death

PURPOSE

Apoptosis, in the context of cancer, is a form of programmed cell death induced by chemotherapy, radiotherapy, and immunotherapy. As this is a central pathway in treatment response, considerable effort has been expended on the development of molecular imaging agents to non-invasively measure tumor apoptosis prior to quantitative changes in tumor dimensions. Despite these efforts, clinical trials directed at imaging apoptosis by PET, SPECT, and MRI have failed to robustly predict response to treatment with high sensitivity and specificity. Although these shortcomings may be linked to probe design, we propose that the combination of variability in the timing of maximal in vivo tumor apoptosis and sub-optimal sampling times fundamentally limits the predictive power of PET/SPECT apoptosis imaging.

PROCEDURES

Herein, we surveyed the literature describing the time course of therapy-induced tumor apoptosis in vivo and used these data to construct a mathematical model describing the onset, duration, amplitude, and variability of the apoptotic response. Uncertainty in the underlying time of initiation of tumor apoptosis was simulated by Gaussian, uniform, and Landau distributions centered at the median time-to-maximum apoptotic rate derived from the literature. We then computationally sampled these models for various durations to simulate PET/SPECT imaging agents with variable effective half-lives.

RESULTS

Models with a narrow Gaussian distribution of initiation times for tumor apoptosis predicted high contrast ratios and strong predictive values for all effective tracer half-lives. However, when uncertainty in apoptosis initiation times were simulated with uniform and Landau distributions, high contrast ratios and predictive values were only obtained with extremely long imaging windows (days). The imaging contrast ratios predicted in these models were consistent with those seen in pre-clinical apoptosis PET/SPECT imaging studies and suggest that uncertainty in the timing of tumor cell death plays a significant role in the maximal contrast obtainable. Moreover, when uncertainty in both apoptosis initiation and imaging start times were simulated, the predicted contrast ratios were dramatically reduced for all tracer half-lives.

CONCLUSIONS

These studies illustrate the effect of uncertainty of apoptosis initiation on the predictive power of PET/SPECT apoptosis imaging agents and suggest that long integration times are required to surmount uncertainty in the time domain of this biological process.

Directed evolution of cyclic peptides for inhibition of autophagy

In recent decades it has become increasingly clear that induction of autophagy plays an important role in the development of treatment resistance and dormancy in many cancer types. Unfortunately, chloroquine (CQ) and hydroxychloroquine (HCQ), two autophagy inhibitors in clinical trials, suffer from poor pharmacokinetics and high toxicity at therapeutic dosages. This has prompted intense interest in the development of targeted autophagy inhibitors to re-sensitize disease to treatment with minimal impact on normal tissue. We utilized Scanning Unnatural Protease Resistant (SUPR) mRNA display to develop macrocyclic peptides targeting the autophagy protein LC3. The resulting peptides bound LC3A and LC3B—two essential components of the autophagosome maturation machinery—with mid-nanomolar affinities and disrupted protein–protein interactions (PPIs) between LC3 and its binding partners in vitro. The most promising LC3-binding SUPR peptide accessed the cytosol at low micromolar concentrations as measured by chloroalkane penetration assay (CAPA) and inhibited starvation-mediated GFP-LC3 puncta formation in a concentration-dependent manner. LC3-binding SUPR peptides re-sensitized platinum-resistant ovarian cancer cells to cisplatin treatment and triggered accumulation of the adapter protein p62 suggesting decreased autophagic flux through successful disruption of LC3 PPIs in cell culture. In mouse models of metastatic ovarian cancer, treatment with LC3-binding SUPR peptides and carboplatin resulted in almost complete inhibition of tumor growth after four weeks of treatment. These results indicate that SUPR peptide mRNA display can be used to develop cell-penetrating macrocyclic peptides that target and disrupt the autophagic machinery in vitro and in vivo.

SUPR peptide mRNA display was used to evolve a cell-permeable, macrocyclic peptide for autophagy inhibition.

Mammalian Expression and In Situ Biotinylation of Extracellular Protein Targets for Directed Evolution

Directed evolution is a powerful tool for the selection of functional ligands from molecular libraries. Extracellular domains (ECDs) of cell surface receptors are common selection targets for therapeutic and imaging agent development. Unfortunately, these proteins are often post-translationally modified and are therefore unsuitable for expression in bacterial systems. Directional immobilization of these targets is further hampered by the absence of biorthogonal groups for site-specific chemical conjugation. We have developed a nonadherent mammalian expression system for rapid, high-yield expression of biotinylated ECDs. ECDs from EGFR, HER2, and HER3 were site-specifically biotinylated in situ and recovered from the cell culture supernatant with yields of up to 10 mg/L at >90% purity. Biotinylated ECDs also contained a protease cleavage site for rapid and selective release of the ECD after immobilization on avidin/streptavidin resins and library binding. A model mRNA display selection round was carried out against the HER2 ECD with the HER2 affibody expressed as an mRNA-protein fusion. HER2 affibody-mRNA fusions were selectively released by thrombin and quantitative PCR revealed substantial improvements in the enrichment of functional affibody-mRNA fusions relative to direct PCR amplification of the resin-bound target. This methodology allows rapid purification of high-quality targets for directed evolution and selective elution of functional sequences at the conclusion of each selection round.

Measurement of bempedoic acid and its keto metabolite in human plasma and urine using solid phase extraction and electrospray LC-MS/MS

Bempedoic acid, a new therapeutic for treatment of hypercholesterolemia, inhibits hepatic ATP-citrate lyase in the cholesterol synthesis pathway after its conjugation with coenzyme A. Sensitive and selective methods were required to study the pharmacokinetic behavior of bempedoic acid and its active 8-keto metabolite in clinical studies. A mixed mode anion exchange extraction on 96-well plates was developed to favor high, selective recoveries of these dicarboxylic acids from urine or plasma. Adsorptive losses in urine led to inaccurate measurements unless samples were acidified and diluted with isopropanol prior to any specimen transfers. Tandem mass spectrometry with negative ion electrospray ionization permitted lower limits of measurement of 20 and 10 ng/mL for the drug and metabolite in either matrix. The methods were validated to current regulatory standards and have been the basis for pharmacokinetic measurements in 26 clinical studies involving over 15,000 samples.

mRNA Display Discovery of a Novel Programmed Death Ligand 1 (PD-L1) Binding Peptide (a Peptide Ligand for PD-L1)

Programmed death ligand 1 (PD-L1) is a critical immune checkpoint ligand whose overexpression on tumor cells provides a mechanism of escape from immune surveillance. The interaction between PD-L1 and PD-1 on T cell lymphocytes suppresses both T cell activation and effector function and is engaged by cancers to dampen antitumor immunity. Here, we used mRNA display to engineer an 18-residue linear peptide that binds to human PD-L1. This peptide, which we term SPAM (signal peptide-based affinity maturated ligand), is nonhomologous to known PD-L1 binding peptides and mAbs, with dissociation constants (K_D) of 119 and 67 nM for unglycosylated and glycosylated human PD-L1, respectively. The SPAM peptide is highly selective for human PD-L1 and shows no significant binding to either mouse PD-L1 or human PD-L2. Competition binding assays indicate that the SPAM peptide binding site overlaps with the binding site of PD-1 as well as therapeutic anti-PD-L1 antibodies. Taken together, these results suggest that the SPAM peptide specifically binds to human PD-L1 and could potentially serve as a PD-L1 affinity agent and PD-L1/PD-1 pathway modulator.

Purification of poly-dA oligonucleotides and mRNA-protein fusions with dT25-OAS resin

Solid-phase resins functionalized with poly-deoxythymidine (dT) oligos facilitate purification of poly-adenylated molecules from solution through high affinity, high selectivity base-pairing interactions. These resins are commonly used to purify messenger RNA (mRNA) from complex biological mixtures as well as mRNA-protein fusion molecules for mRNA Display selections. Historically, dT-conjugated cellulose was the primary resin for poly-dA purification, but its scarcity has prompted the development of alternative resins, most notably dT-functionalized magnetic beads. In order to develop a cost-effective alternative to commercially available poly-dT resins for large-scale purifications of mRNA-protein fusions, we investigated the purification properties of dT25-conjugated Oligo Affinity Support resin (dT25-OAS) alongside poly-dT14 magnetic beads and dT25-cellulose. dT25-OAS was found to have the highest dA21 oligo binding capacity at 4 pmol/µg, followed by dT14-magnetic beads (1.1 pmol/µg) and dT25-cellulose (0.7 pmol/µg). To determine the resin specificity in the context of a complex biological mixture, we translated mRNA-protein fusions consisting of a radiolabeled Her2 affibody fused to its encoding mRNA. Commercial dT25-cellulose showed the highest mRNA-affibody purification specificity, followed by dT25-OAS and dT14-magnetic beads. Overall, dT25-OAS showed exceptionally high binding capacity and low background binding, making it an attractive alternative for large-scale mRNA purification and mRNA Display library enrichment.

Caspase-3 Substrates for Noninvasive Pharmacodynamic Imaging of Apoptosis by PET/CT

Quantitative imaging of apoptosis in vivo could enable real-time monitoring of acute cell death pathologies such as traumatic brain injury, as well as the efficacy and safety of cancer therapy. Here, we describe the development and validation of F-18-labeled caspase-3 substrates for PET/CT imaging of apoptosis. Preliminary studies identified the O-benzylthreonine-containing substrate 2MP-TbD-AFC as a highly caspase 3-selective and cell-permeable fluorescent reporter. This lead compound was converted into the radiotracer [¹⁸F]-TBD, which was obtained at 10% decay-corrected yields with molar activities up to 149 GBq/μmol on an automated radiosynthesis platform. [¹⁸F]-TBD accumulated in ovarian cancer cells in a caspase- and cisplatin-dependent fashion. PET imaging of a Jo2-induced hepatotoxicity model showed a significant increase in [¹⁸F]-TBD signal in the livers of Jo2-treated mice compared to controls, driven through a reduction in hepatobiliary clearance. A chemical control tracer that could not be cleaved by caspase 3 showed no change in liver accumulation after induction of hepatocyte apoptosis. Our data demonstrate that [¹⁸F]-TBD provides an immediate pharmacodynamic readout of liver apoptosis in mice by dynamic PET/CT and suggest that [¹⁸F]-TBD could be used to interrogate apoptosis in other disease states.

Measurement of lidocaine and 2,6-dimethylaniline in minipig plasma, skin, and dermal tapes using UHPLC with electrospray MS/MS

Sensitive LC-MS/MS methods were developed to measure lidocaine and its metabolite 2,6-dimethylaniline (2,6-DMA) with application to transdermal studies. The methods for lidocaine in minipig plasma, tissue biopsies, and dermal tapes utilized mixed mode/SCX solid phase extraction, with lower quantitation limits of 25 pg/mL in plasma, 15 ng/g tissue, and 5 ng/tape. 2,6-DMA was measured in plasma and skin tissue homogenates by ultrafiltration and (for tissue) by further derivatization with 4-methoxybenzoyl chloride to form the corresponding benzamide derivative, which extended the lower limit of quantitation to 200 pg/mL. The methods allowed local measurement of lidocaine in stratum corneum, punch biopsies, and plasma and of 2,6-DMA in plasma and biopsies obtained from minipigs dosed with experimental transdermal formulations. Quantitation limits were approximately 7-fold lower than previously reported for lidocaine and 3-fold lower for 2,6-DMA.

Automated, Resin-Based Method to Enhance the Specific Activity of Fluorine-18 Clicked PET Radiotracers

Radiolabeling of substrates with 2-[¹⁸F]fluoroethylazide exploits the rapid kinetics, chemical selectivity, and mild conditions of the copper-catalyzed azide-alkyne cycloaddition reaction. While this methodology has proven to result in near-quantitative labeling of alkyne-tagged precursors, the relatively small size of the fluoroethylazide group makes separation of the ¹⁸F-labeled radiotracer and the unreacted precursor challenging, particularly with precursors >500 Da (e.g., peptides). We have developed an inexpensive azide-functionalized resin to rapidly remove unreacted alkyne precursor following the fluoroethylazide labeling reaction and integrated it into a fully automated radiosynthesis platform. We have carried out 2-[¹⁸F]fluoroethylazide labeling of four different alkynes ranging from <300 Da to >1700 Da and found that >98% of the unreacted alkyne was removed in less than 20 min at room temperature to afford the final radiotracers at >99% radiochemical purity with specific activities up to >200 GBq/μmol. We have applied this technique to label a novel cyclic peptide previously evolved to bind the Her2 receptor with high affinity, and demonstrated tumor-specific uptake and low nonspecific background by PET/CT. This resin-based methodology is automated, rapid, mild, and general allowing peptide-based fluorine-18 radiotracers to be obtained with clinically relevant specific activities without chromatographic separation and with only a minimal increase in total synthesis time.

Induction of autophagy by ARHI (DIRAS3) alters fundamental metabolic pathways in ovarian cancer models

BACKGROUND

Autophagy is a bulk catabolic process that modulates tumorigenesis, therapeutic resistance, and dormancy. The tumor suppressor ARHI (DIRAS3) is a potent inducer of autophagy and its expression results in necroptotic cell death in vitro and tumor dormancy in vivo. ARHI is down-regulated or lost in over 60 % of primary ovarian tumors yet is dramatically up-regulated in metastatic disease. The metabolic changes that occur during ARHI induction and their role in modulating death and dormancy are unknown.

METHODS

We employed Nuclear Magnetic Resonance (NMR)-based metabolomic strategies to characterize changes in key metabolic pathways in both cell culture and xenograft models of ARHI expression and autophagy. These pathways were further interrogated by cell-based immunofluorescence imaging, tracer uptake studies, targeted metabolic inhibition, and in vivo PET/CT imaging.

RESULTS

Induction of ARHI in cell culture models resulted in an autophagy-dependent increase in lactate production along with increased glucose uptake and enhanced sensitivity to glycolytic inhibitors. Increased uptake of glutamine was also dependent on autophagy and dramatically sensitized cultured ARHI-expressing ovarian cancer cell lines to glutaminase inhibition. Induction of ARHI resulted in a reduction in mitochondrial respiration, decreased mitochondrial membrane potential, and decreased Tom20 staining suggesting an ARHI-dependent loss of mitochondrial function. ARHI induction in mouse xenograft models resulted in an increase in free amino acids, a transient increase in [¹⁸F]-FDG uptake, and significantly altered choline metabolism.

CONCLUSIONS

ARHI expression has previously been shown to trigger autophagy-associated necroptosis in cell culture. In this study, we have demonstrated that ARHI expression results in decreased cellular ATP/ADP, increased oxidative stress, and decreased mitochondrial function. While this bioenergetic shock is consistent with programmed necrosis, our data indicates that the accompanying up-regulation of glycolysis and glutaminolysis is autophagy-dependent and serves to support cell viability rather than facilitate necroptotic cell death. While the mechanistic basis for metabolic up-regulation following ARHI induction is unknown, our preliminary data suggest that decreased mitochondrial function and increased metabolic demand may play a role. These alterations in fundamental metabolic pathways during autophagy-associated necroptosis may provide the basis for new therapeutic strategies for the treatment of dormant ovarian tumors.

Abstract 604: A multi-layered, hydrogel system for automated 3D high throughput drug screening of cancer-stromal cell co-cultures

Pre-clinical drug screens, involving culturing well-annotated cancer cell lines on two-dimensional (2D) tissue culture plastic, poorly recapitulate in vivo tumor characteristics and yield candidate drugs which fail clinical trials. We created a multi-layer, hyaluronic acid (HA)-based hydrogel system that incorporates three layers: an acellular cushion layer; an encapsulated cancer cell layer for growth in three dimensions (3D); and a collagen-containing layer that supports the growth of stromal cells on top of the hydrogel (2.5D). Utilizing high-throughput robotic delivery coupled with automated advanced imaging, this formulation provides a highly reproducible system for spheroid culture of prostate (C4-2B) or endometrial (Ishikawa) cancer cell lines in mono- or co-culture with matched stromal cells (HS27a or ESS-1, respectively). Both culture systems provided high cancer cell viability over one week of culture. Cells were treated with drugs from a panel of chemotherapeutic compounds. Cells cultured in our 3D multi-layer HA-based system responded to cytotoxic drugs distinctly from cells grown in 2D and 3D-aliginate, and better predicted the efficacy of chemotherapeutics in clinical trials. We have also successfully incorporated cells derived from patient derived xenograft (PDX) models in our 3D culture system. Wider adoption of 3D automated screening has the potential to speed drug discovery and increase success of drugs in clinical trials.

Citation Format: Pamela E. Constantinou, Brian J. Engel, Lindsey K. Sablatura, Nathaniel J. Doty, Daniel D. Carson, Mary C. Farach-Carson, Daniel A. Harrington, Thomas I. Zarembinski. A multi-layered, hydrogel system for automated 3D high throughput drug screening of cancer-stromal cell co-cultures. [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 604.

MUC1 stimulates EGFR expression and function in endometrial cancer

The current standard of care for endometrial cancer patients involves hysterectomy with adjuvant radiation and chemotherapy, with no effective treatment for advanced and metastatic disease. MUC1 is a large, heavily glycosylated transmembrane protein that lubricates and protects cell surfaces and increases cellular signaling through the epidermal growth factor receptor (EGFR). We show for the first time that MUC1 stimulates EGFR expression and function in endometrial cancer. siRNA knockdown and CRISPR/Cas knockout of MUC1 reduced EGFR gene expression, mRNA, protein levels and signaling. MUC1 bound strongly to two regions of the EGFR promoter: -627/-511 and -172/-64. MUC1 knockout also reduced EGFR-dependent proliferation in two dimensional culture, as well as growth and survival in three dimensional spheroid cultures. MUC1 knockout cells were more sensitive to the EGFR inhibitor, lapatinib. Finally, MUC1 and EGFR co-expression was associated with increased cellular proliferation in human endometrial tumors. These data demonstrate the importance of MUC1-driven EGFR expression and signaling and suggest dual-targeted therapies may provide improved response for endometrial tumors.

Multilayered, Hyaluronic Acid-Based Hydrogel Formulations Suitable for Automated 3D High Throughput Drug Screening of Cancer-Stromal Cell Cocultures

Validation of a high-throughput compatible 3D hyaluronic acid hydrogel coculture of cancer cells with stromal cells. The multilayered hyaluronic acid hydrogels improve drug screening predictability as evaluated with a panel of clinically relevant chemotherapeutics in both prostate and endometrial cancer cell lines compared to 2D culture.

Abstract 4267: MUC1 increases epidermal growth factor receptor levels and signaling in endometrial cancer cell lines

Endometrial cancer is the most common gynecological cancer, affecting over 600,000 women in the United States. Furthermore, increased incidence of endometrial cancer is observed among obese and premenopausal women. Currently, the standard of care is hysterectomy with the addition of radiation and chemotherapy for late stage cancers. Novel therapies are required to avoid surgical complications associated with obese patients and to preserve the fertility of young patients. MUC1 is a large, heavily glycosylated transmembrane protein that functions to lubricate mucosal surfaces, protect cells from external insult and modulates the embryo implantation process. Recent evidence suggests that the C-terminus of MUC1 is involved in intracellular signaling through interaction with several cancer-associated proteins. One of these proteins is the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase that influences cellular proliferation, migration and apoptosis. Elevated MUC1 levels are associated with increased levels and signaling of EGFR in breast cancer; however, this phenomenon has not been described in the context of endometrial cancer and the mechanisms involved are not well understood in any context. To this end, human endometrial cancer cell lines were subjected to siRNA knockdown of MUC1 followed by qRT-PCR, western blotting, EGFR promoter-driven luciferase assays, proliferation and migration assays. These assays demonstrate a correlation of MUC1 levels with EGFR mRNA levels, protein levels, signaling, gene expression and cellular proliferation and migration. These results demonstrate that MUC1 control of EGFR levels and signaling also occurs in endometrial cancer-derived cell lines. Future experiments will elucidate the mechanisms by which MUC1 promotes EGFR gene expression and signaling in endometrial cancer. These insights may provide novel MUC1-based targets for endometrial cancer therapies which when used in conjunction with current non-surgical treatments may provide a therapeutic strategy that avoids surgical complications and preserves fertility. (Work supported by NIH grants RO1 HD 29963 and NCI 2P5098258-06 as well as Rice University funds to DDC).

Citation Format: Brian J. Engel, Daniel D. Carson. MUC1 increases epidermal growth factor receptor levels and signaling in endometrial cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4267. doi:10.1158/1538-7445.AM2013-4267

Progress toward a biomimetic leaf: 4,000 h of hydrogen production by coating-stabilized nongrowing photosynthetic Rhodopseudomonas palustris

Intact cells are the most stable form of nature's photosynthetic machinery. Coating-immobilized microbes have the potential to revolutionize the design of photoabsorbers for conversion of sunlight into fuels. Multi-layer adhesive polymer coatings could spatially combine photoreactive bacteria and algae (complementary biological irradiance spectra) creating high surface area, thin, flexible structures optimized for light trapping, and production of hydrogen (H(2)) from water, lignin, pollutants, or waste organics. We report a model coating system which produced 2.08 +/- 0.01 mmol H(2) m(-2) h(-1) for 4,000 h with nongrowing Rhodopseudomonas palustris, a purple nonsulfur photosynthetic bacterium. This adhesive, flexible, nanoporous Rps. palustris latex coating produced 8.24 +/- 0.03 mol H(2) m(-2) in an argon atmosphere when supplied with acetate and light. A simple low-pressure hydrogen production and trapping system was tested using a 100 cm(2) coating. Rps. palustris CGA009 was combined in a bilayer coating with a carotenoid-less mutant of Rps. palustris (CrtI(-)) deficient in peripheral light harvesting (LH2) function. Cryogenic field emission gun scanning electron microscopy (cryo-FEG-SEM) and high-pressure freezing were used to visualize the microstructure of hydrated coatings. A light interaction and reactivity model was evaluated to predict optimal coating thickness for light absorption using the Kubelka-Munk theory (KMT) of reflectance and absorptance. A two-flux model predicted light saturation thickness with good agreement to observed H(2) evolution rate. A combined materials and modeling approach could be used for guiding cellular engineering of light trapping and reactivity to enhance overall photosynthetic efficiency per meter square of sunlight incident on photocatalysts.

Hydrogen Production by Photoreactive Nanoporous Latex Coatings of Nongrowing Rhodopseudomonas palustris CGA009

Nonuniform light distribution is a fundamental limitation to biological hydrogen production by phototrophic bacteria. Numerous light distribution designs and culture conditions have been developed to reduce self-shading and nonuniform reactivity within bioreactors. In this study, highly concentrated (2.0 x 108 CFU/muL formulation) nongrowing Rhodopseudomonas palustris CGA009 were immobilized in thin, nanoporous, latex coatings. The coatings were used to study hydrogen production in an argon atmosphere as a function of coating composition, thickness, and light intensity. These coatings can be generated aerobically or anaerobically and are more reactive than an equivalent number of suspended or settled cells. Rhodopseudomonas palustris latex coatings remained active after hydrated storage for greater than 3 months in the dark and over 1 year when stored at -80 degrees C. The initial hydrogen production rate of the microphotobioreactors containing 6.25 cm2, 58.4 mum thick Rps. palustris latex coatings illuminated by 34.1 PAR mumol photons m-2 s-1 was 6.3 mmol H2 m-2 h-1 and had a final yield of 0.55 mol H2 m-2 in 120 h. A dispersible latex blend has been developed for direct comparison of the specific activity of settled, suspended, and immobilized Rps. palustris.

Dissociation reactions of gaseous ferro-, ferri-, and apo-cytochrome c ions

Electrochemical reduction of the iron bound in the heme group of cytochrome c is shown to occur in the nano-electrospray capillary if the protein is sprayed from neutral water using a steel wire as the electrical contact. Quadrupole ion trap collisional activation is used to study the dissociation reactions of cytochrome c as a function of the oxidation state of the iron. Oxidized (Fe(III)) cytochrome c dissociates via sequence-specific amide bond cleavage, while the reduced (Fe(II)) form of the protein dissociates almost exclusively by loss of protonated heme. Apo-cytochrome c, from which the heme has been removed either via gas-phase dissociation of the reduced holo-protein or via solution chemistry, dissociates via amide bond cleavage in similar fashion to the oxidized holo-protein.