Profiling of collagen and extracellular matrix deposition from cell culture using in vitro ExtraCellular matrix mass spectrometry imaging (ivECM-MSI)

While numerous approaches have been reported towards understanding single cell regulation, there is limited understanding of single cell production of extracellular matrix phenotypes. Collagens are major proteins of the extracellular microenvironment extensively used in basic cell culture, tissue engineering, and biomedical applications. However, identifying compositional regulation of collagen remains challenging. Here, we report the development of In vitro ExtraCellular Matrix Mass Spectrometry Imaging (ivECM-MSI) as a tool to rapidly and simultaneously define collagen subtypes from coatings and basic cell culture applications. The tool uses the mass spectrometry imaging platform with reference libraries to produce visual and numerical data types. The method is highly integrated with basic in vitro strategies as it may be used with conventional cell chambers on minimal numbers of cells and with minimal changes to biological experiments. Applications tested include semi-quantitation of collagen composition in culture coatings, time course collagen deposition, deposition altered by gene knockout, and changes induced by drug treatment. This approach provides new access to proteomic information on how cell types respond to and change the extracellular microenvironment and provides a holistic understanding of both the cell and extracellular response.

Acceleration and transport of relativistic electrons in the jets of the microquasar SS 433

SS 433 is a microquasar, a stellar binary system that launches collimated relativistic jets. We observed SS 433 in gamma rays using the High Energy Stereoscopic System (H.E.S.S.) and found an energy-dependent shift in the apparent position of the gamma-ray emission from the parsec-scale jets. These observations trace the energetic electron population and indicate that inverse Compton scattering is the emission mechanism of the gamma rays. Our modeling of the energy-dependent gamma-ray morphology constrains the location of particle acceleration and requires an abrupt deceleration of the jet flow. We infer the presence of shocks on either side of the binary system, at distances of 25 to 30 parsecs, and that self-collimation of the precessing jets forms the shocks, which then efficiently accelerate electrons.

HostSeq: a Canadian whole genome sequencing and clinical data resource

HostSeq was launched in April 2020 as a national initiative to integrate whole genome sequencing data from 10,000 Canadians infected with SARS-CoV-2 with clinical information related to their disease experience. The mandate of HostSeq is to support the Canadian and international research communities in their efforts to understand the risk factors for disease and associated health outcomes and support the development of interventions such as vaccines and therapeutics. HostSeq is a collaboration among 13 independent epidemiological studies of SARS-CoV-2 across five provinces in Canada. Aggregated data collected by HostSeq are made available to the public through two data portals: a phenotype portal showing summaries of major variables and their distributions, and a variant search portal enabling queries in a genomic region. Individual-level data is available to the global research community for health research through a Data Access Agreement and Data Access Compliance Office approval. Here we provide an overview of the collective project design along with summary level information for HostSeq. We highlight several statistical considerations for researchers using the HostSeq platform regarding data aggregation, sampling mechanism, covariate adjustment, and X chromosome analysis. In addition to serving as a rich data source, the diversity of study designs, sample sizes, and research objectives among the participating studies provides unique opportunities for the research community.

Abstract 5847: The splanchnic mesenchyme is the main tissue origin of fibroblasts in the pancreas during homeostasis and tumorigenesis

In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. CAFs are also a major cell type in the desmoplastic stroma in PDAC and may account for half of the entire tumor tissue. Multiple subtypes of CAFs have been suggested, but the tissue origin(s) of CAF subtypes are unknown and genetic tools to robustly target them in vivo are lacking. Here we aimed to examine three potential tissue sources of CAFs: the pancreatic epithelium (through epithelium-to-mesenchyme transition), the bone marrow (through circulation), and the pancreatic mesenchyme or tissue resident fibroblasts (TRFs) in the normal pancreas (through proliferation). We utilized a genetically engineered mouse model of PDAC, where Kras and p53 mutations were engineered in the pancreatic epithelium using an Flp-Frt system. To determine whether the pancreatic epithelium gives rise to CAFs, we permanently labeled the pancreatic epithelium with a GFP reporter and traced their cell descendants by GFP expression. Despite robust GFP labeling of the epithelium, GFP expression was rarely identified in CAFs. To determine whether the bone marrow gives rise to CAFs, we transplanted donor bone marrow carrying a ubiquitously expressed GFP reporter to GFP-negative recipient mice. We found that minimal proportion of pancreatic CAFs were tagged with GFP. Lastly, to determine whether pancreatic TRFs give rise to CAFs, we used an inducible CreER-LoxP system to allow for permanent Tomato labeling in TRF progenitors, the splanchnic mesenchyme, during mid-gestation. Lineage tracing in PDAC showed that the vast majority of CAFs were labeled with Tomato expression, suggesting their splanchnic origin. Furthermore, certain splanchnic gene expression signatures persisted in subsets of CAFs in both the PDAC mouse model and human patient samples. Deletion of one of the splanchnic genes, Gata6, in CAFs resulted in increased tumor burden in the pancreas, suggesting a tumor-restraining role of Gata6 in CAFs. In summary, we found that the pancreatic epithelium and bone marrow contributes to a minimal proportion of CAFs in PDAC. Meanwhile, pancreatic TRFs are derived from the splanchnic mesenchyme during fetal development and they expand to contribute to the vast majority of CAFs in PDAC. Moreover, the persistence of splanchnic signature defines subtypes of CAFs, with a potential tumor-suppressing function. This study provides genetic approaches to robustly target CAFs in vivo, and novel insights into CAF origin, heterogeneity and function in PDAC.

Citation Format: Lu Han, Yongxia Wu, Kun Fang, Sean Sweeney, Ulyss Roesner, Melodie Parrish, Khushbu Patel, Tom Walter, Julia Piermattei, Anthony Trimboli, Julia Lefler, Cynthia Timmers, Xue-Zhong Yu, Victor Jin, Michael Zimmermann, Angela Mathison, Raul Urrutia, Michael Ostrowski, Gustavo Leone. The splanchnic mesenchyme is the main tissue origin of fibroblasts in the pancreas during homeostasis and tumorigenesis [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 5847.

Abstract 1344: myCAFs and iCAFs have similar lineage

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense stroma primarily composed of cancer associated fibroblasts (CAFs). These fibroblasts are a diverse population of cells; some groups of fibroblasts have been shown to play tumor supporting roles while others have been shown to be tumor suppressing. Two prolific and well-characterized CAF subtypes—myofibroblasts (myCAFs) and inflammatory CAFs (iCAFs)—could potentially have different regulatory effects on tumor growth. Understanding the tissue origin of these two groups of CAFs could assist in understanding the complex and heterogeneous roles they might play in PDAC development. Previous studies in our group showed that the splanchnic mesenchyme, a layer of mesenchyme adjacent to the fetal pancreatic epithelium, gives rise to the majority of the total CAF population. Here, I aim to test the hypothesis that both iCAFs and myCAFs originate from the splanchnic mesenchyme. myCAFs have been previously observed to be proximal to tumor cells and express αSMA at a higher level, while iCAFs have been observed to be distal to tumor cells and express αSMA at a lower level. Here, we used a genetically engineered mouse PDAC model carrying KrasG12D/+;p53Frt/+;Pdx1FlpO/+;Isl1cre/+;R26Tomato/+ alleles. In this model, epithelial specific FlpO expression leads to Kras activation and p53 deletion, causing tumorigenesis. Simultaneously, splanchnic specific Cre expression leads to permanent tomato expression in the splanchnic descendants. The pancreata of these mice were harvested, fixed, and mounted onto slides. Co-immunostaining with αSMA and tomato was then done. The stained slides were scanned, and the Inform software was used to segment and phenotype the cells. More than 95% of αSMA high cells were tomato positive, and more than 95% of αSMA low cells were also tomato positive. We thus conclude that both myCAFs and iCAFs originate from the splanchnic mesenchyme. Consistent with previous in vitro studies, this lineage tracing study suggests that different CAF subtypes are likely due to patterning influenced by different factors within the tumor microenvironment.

Citation Format: Thomas S. Walter, Lu Han, Michael Ostrowski. myCAFs and iCAFs have similar lineage [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 1344.

Search for Dark Matter Annihilation Signals in the H.E.S.S. Inner Galaxy Survey

The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented γ-ray survey of the Galactic Center (GC) region, i.e., the Inner Galaxy Survey, at very high energies (≳100  GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant γ-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section ⟨σv⟩. Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach ⟨σv⟩ values of 3.7×10^{-26}  cm^{3} s^{-1} for 1.5 TeV DM mass in the W^{+}W^{-} annihilation channel, and 1.2×10^{-26}  cm^{3} s^{-1} for 0.7 TeV DM mass in the τ^{+}τ^{-} annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based γ-ray observations thus probe ⟨σv⟩ values expected from thermal-relic annihilating TeV DM particles.

Abstract 3645: The splanchnic mesenchyme is the main tissue origin of fibroblasts in the pancreas during homeostasis and tumorigenesis

In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. CAFs are also a major cell type in the desmoplastic stroma in PDAC and may account for half of the entire tumor tissue. Multiple subtypes of CAFs have been suggested, but the tissue origin(s) of CAF subtypes are unknown and genetic tools to robustly target them in vivo are lacking. Here we aimed to examine three potential tissue sources of CAFs: the pancreatic epithelium (through epithelium-to-mesenchyme transition), the bone marrow (through circulation), and the pancreatic tissue resident fibroblasts (TRFs) in the normal pancreas (through proliferation). We utilized a genetically engineered mouse model of PDAC, where Kras and p53 mutations were engineered in the pancreatic epithelium using an Flp-Frt system. To determine whether the pancreatic epithelium gives rise to CAFs, we permanently labeled the pancreatic epithelium with a GFP reporter and traced their cell descendants by GFP expression. Despite robust GFP labeling of the epithelium, GFP expression was rarely identified in CAFs, suggesting little contribution of epithelium to the CAF pool. To determine whether the bone marrow gives rise to CAFs, we transplanted donor bone marrow carrying a ubiquitously expressed GFP reporter allele to GFP-negative recipient mice. We found that only a small portion of pancreatic CAFs were tagged with GFP. Lastly, to determine whether pancreatic TRFs give rise to CAFs, we used an inducible CreER-LoxP system to allow for permanent Tomato labeling in TRFs progenitors, the splanchnic mesenchyme, during mid-gestation. Lineage tracing in PDAC showed that the vast majority of CAFs were labeled with Tomato expression, suggesting their splanchnic origin. Furthermore, certain splanchnic gene expression signatures were persistent in subsets of CAFs in both the PDAC mouse model and human patient samples. In summary, we found that bone marrow contributes to a small portion of CAFs in PDAC, and the pancreatic epithelium contributes even less. Meanwhile, pancreatic TRFs are derived from the splanchnic mesenchyme during fetal development and they expand to contribute to the vast majority of CAFs in PDAC. Moreover, the persistence of splanchnic signature defines subtypes of CAFs. This study provides approaches to robustly target CAFs in vivo, and novel insights into CAF origin and heterogeneity in PDAC.

Citation Format: Lu Han, Yongxia Wu, Melodie Parrish, Khushbu Patel, Tony Trimboli, Julia Lefler, Xuezhong Yu, Michael Zimmermann, Angela Mathison, Raul Urrutia, Michael Ostrowski, Gustavo Leone. The splanchnic mesenchyme is the main tissue origin of fibroblasts in the pancreas during homeostasis and tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3645.

The Arterial Anastomosis Between Deep Inferior Epigastric Artery and Small Polar Renal Artery in Kidney Transplantation: A Case Report

The presence of multiple renal arteries is the most common form of vascular anomalies found in donor kidneys. In rare cases, small renal polar arteries may be found. They can be anastomosed with deep inferior epigastric arteries, resulting in vascular augmentation of transplanted kidneys and contributing to better graft function. Renal perfusion may be increased via 2 types of vascular reconstruction known as "turbocharging" and "supercharging". Turbocharging uses vascular sources within the same organ area, whereas supercharging uses distant vascular sources. Using additional vessels can either complicate the surgery or, contradictorily, ease the way of procedure. This case study presents a kidney transplant during which arterial anastomosis between deep inferior epigastric artery and small polar renal artery was performed.

Outcomes of kidney transplantation during the SARS-CoV-2 pandemic at one centre in Poland

The SARS-CoV-2 pandemic has significantly affected the number of transplanted organs worldwide. The rules and restrictions related to transplantation activities in Poland are included in the updated guidelines of the Polish Organizational and Coordination Centre for Transplantation. Our clinic faces the same problems as the rest of the hospitals in the country. Not only are the number of recipients falling, but there are also numerous restrictions concerning, among other things, qualification of donors and recipients and even preparation of centers for long-term care in the event of infection of organ recipients with the SARS-CoV-2 virus. Statistics showed, after an initial fall in the number of kidneys transplanted, a temporary normalization during the summer months, only to record a fall again with an increase in new cases of COVID-19. A total of 29 kidneys were transplanted at our center between March and December 2020. Kidney transplantation is not only linked to the operation itself, but also to the follow-up care of the recipients. Reduced immunity among recipients due to immunosuppressive treatment as well as comorbidities among recipients contribute to this group being at increased risk of symptomatic SARS-CoV-2 infection. The number of cases of SARS-CoV-2 infection among kidney transplant recipients at our center was 7, of which we recorded 2 deaths due to COVID-19 in the period after kidney transplant. Postoperative complications probably related to previous SARS-CoV-2 infection occurred in 1 patient.

Time-resolved hadronic particle acceleration in the recurrent nova RS Ophiuchi

Recurrent novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to the accretion of fresh material from a binary companion. The shock generated when ejected material slams into the companion star's wind can accelerate particles. We report very-high-energy (VHE, [Formula: see text]) gamma rays from the recurrent nova RS Ophiuchi, up to a month after its 2021 outburst, observed using the High Energy Stereoscopic System. The VHE emission has a similar temporal profile to lower-energy GeV emission, indicating a common origin, with a two-day delay in peak flux. These observations constrain models of time-dependent particle energization, favoring a hadronic emission scenario over the leptonic alternative. Shocks in dense winds provide favorable environments for efficient acceleration of cosmic-rays to very high energies.

Abstract PR-013: The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts

In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. CAFs are also a major cell type in the desmoplastic stroma in PDAC and may account for half of the entire tumor tissue. Multiple subtypes of CAFs have been suggested, but the tissue origin(s) of CAF subtypes are unknown and genetic tools to robustly target them in vivo are lacking. Here we aimed to examine three potential tissue sources of CAFs: the pancreatic epithelium (through epithelium-to-mesenchyme transition), the bone marrow (through circulation), and the pancreatic mesenchyme or tissue resident fibroblasts (TRFs) in the normal pancreas (through proliferation). We utilized a genetically engineered mouse model of PDAC, where Kras and p53 mutations were engineered in the pancreatic epithelium using an Flp-Frt system. To determine whether the pancreatic epithelium gives rise to CAFs, we permanently labeled the pancreatic epithelium with a GFP reporter and traced their cell descendants by GFP expression. Despite robust GFP labeling of the epithelium, GFP expression was rarely identified in CAFs, suggesting little contribution of epithelium to the CAF pool. To determine whether the bone marrow gives rise to CAFs, we transplanted donor bone marrow carrying a ubiquitously expressed GFP reporter allele to GFP-negative recipient mice. We found that only a small proportion of pancreatic CAFs were tagged with GFP, suggesting their bone marrow origin. Lastly, to determine whether pancreatic TRFs give rise to CAFs, we used an inducible CreER-LoxP system to allow for permanent Tomato labeling in TRFs progenitors, the splanchnic mesenchyme, during mid-gestation. Lineage tracing in PDAC showed that the vast majority of CAFs were labeled with Tomato expression, suggesting their splanchnic origin. Furthermore, certain splanchnic gene expression signatures were persistent in subsets of CAFs in both the PDAC mouse model and human patient samples. In summary, we found that bone marrow contributes to a small proportion of CAFs in PDAC, and the pancreatic epithelium contributes even less. Meanwhile, pancreatic TRFs are derived from the splanchnic mesenchyme during fetal development and they expand to contribute to the vast majority of CAFs in PDAC. Moreover, the persistence of splanchnic signature defines subtypes of CAFs. This study provides approaches to robustly target CAFs in vivo and novel insights into CAF heterogeneity in PDAC.

Citation Format: Lu Han, Yongxia Wu, Melodie Parrish, Khushbu Patel, Xuezhong Yu, Michael Ostrowski, Gustavo Leone. The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PR-013.

Abstract PO-114: STAT3 in cancer-associated fibroblasts promotes an immunosuppressive tumor microenvironment

One of the defining characteristics of pancreatic ductal adenocarcinoma (PDAC) is the formation of a dense stroma comprised of cancer associated fibroblasts (CAFs) and immune cell populations. This stroma is immunosuppressive and can act as a physical barrier against common therapeutic treatments. Attempts to therapeutically target the PDAC stroma have yielded contradictory results, suggesting both tumor promoting and tumor limiting roles for CAFs. These studies emphasize the need to understand important transsignaling pathways between CAFs, tumor cells, and the immune microenvironment. IL-6 is a pleiotropic cytokine involved in several physiological functions and its increased expression is strongly associated with poor survival rates in PDAC patients. STAT3 is a major downstream target of IL-6, and its aberrant activation has been implicated in PDAC tumor progression and immune evasion. IL-6 expression and the IL-6/STAT3 signaling axis in PDAC has been characterized in epithelial tumor cells, however its stromal-specific function on PDAC has yet to be elucidated. We hypothesized that the STAT3 signaling axis in pancreatic CAFs contributes to the immunosuppressive and fibrotic phenotype seen with disease progression. Employing CreLoxP technology, the fibroblast specific protein-1 (Fsp-Cre) transgene was used to conditionally delete STAT3 in fibroblasts in the PdxFlp; KrasG12D; p53frt/frt (KPF) PDAC mouse model developed by our lab. Deletion of STAT3 in fibroblasts significantly increased the survival in a cohort of KPF mice compared to those with intact STAT3. In preliminary investigations, we found an increase in CD8+ T cell infiltration but a decrease in regulatory T cells in the STAT3-deleted cohort. We also observed a decrease in immunosuppressive M2 macrophage populations and an increase in M1 macrophages in the STAT3-deleted cohort. These preliminary results demonstrate a previously unexplored role of IL-6/STAT3 signaling in fibroblasts during PDAC progression.

Citation Format: Julia E. Lefler, Michael Ostrowski, Catherine MarElia-Bennett. STAT3 in cancer-associated fibroblasts promotes an immunosuppressive tumor microenvironment [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-114.

Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow

Gamma-ray bursts (GRBs), which are bright flashes of gamma rays from extragalactic sources followed by fading afterglow emission, are associated with stellar core collapse events. We report the detection of very-high-energy (VHE) gamma rays from the afterglow of GRB 190829A, between 4 and 56 hours after the trigger, using the High Energy Stereoscopic System (H.E.S.S.). The low luminosity and redshift of GRB 190829A reduce both internal and external absorption, allowing determination of its intrinsic energy spectrum. Between energies of 0.18 and 3.3 tera-electron volts, this spectrum is described by a power law with photon index of 2.07 ± 0.09, similar to the x-ray spectrum. The x-ray and VHE gamma-ray light curves also show similar decay profiles. These similar characteristics in the x-ray and gamma-ray bands challenge GRB afterglow emission scenarios.

Abstract PR001: The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts

In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. CAFs are also a major cell type in the desmoplastic stroma in PDAC and may account for half of the entire tumor tissue. Multiple subtypes of CAFs have been suggested, but the tissue origin(s) of CAF subtypes are unknown and genetic tools to robustly target them in vivo are lacking. Here we aimed to examine three potential tissue sources of CAFs: the pancreatic epithelium (through epithelium-to-mesenchyme transition), the bone marrow (through circulation), and the pancreatic mesenchyme or tissue resident fibroblasts (TRFs) in the normal pancreas (through proliferation). We utilized a genetically engineered mouse model of PDAC, where Kras and p53 mutations were engineered in the pancreatic epithelium using an Flp-Frt system. To determine whether the pancreatic epithelium gives rise to CAFs, we permanently labeled the pancreatic epithelium with a GFP reporter and traced their cell descendants by GFP expression. Despite robust GFP labeling of the epithelium, GFP expression was rarely identified in CAFs, suggesting little contribution of epithelium to the CAF pool. To determine whether the bone marrow gives rise to CAFs, we transplanted donor bone marrow carrying a ubiquitously expressed GFP reporter allele to GFP-negative recipient mice. We found that only a small proportion of pancreatic CAFs were tagged with GFP, suggesting their bone marrow origin. Lastly, to determine whether pancreatic TRFs give rise to CAFs, we used an inducible CreER-LoxP system to allow for permanent Tomato labeling in TRFs progenitors, the splanchnic mesenchyme, during mid-gestation. Lineage tracing in PDAC showed that the vast majority of CAFs were labeled with Tomato expression, suggesting their splanchnic origin. Furthermore, certain splanchnic gene expression signatures were persistent in subsets of CAFs in both the PDAC mouse model and human patient samples. In summary, we found that bone marrow contributes to a small proportion of CAFs in PDAC, and the pancreatic epithelium contributes even less. Meanwhile, pancreatic TRFs are derived from the splanchnic mesenchyme during fetal development and they expand to contribute to the vast majority of CAFs in PDAC. Moreover, the persistence of splanchnic signature defines subtypes of CAFs. This study provides approaches to robustly target CAFs in vivo and novel insights into CAF heterogeneity in PDAC.

Citation Format: Lu Han, Yongxia Xu, Sean Sweeney, Ulyss Roesner, Melodie Parrish, Khushbu Patel, Xuezhong Yu, Michael Ostrowski, Gustavo Leone. The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr PR001.

Abstract PO-032: Targeting the KRAS dimerization interface enhances T-cell mediated anti-tumor response in vivo

RAS is the most frequently mutated human oncogene and about 20% of all human cancers harbor mutations in one of three RAS oncogenes (K, N and H-RAS) with pancreatic cancers harboring RAS mutations in >90% of tumors. Therapeutically targeting RAS has been highly challenging and other than allele specific KRAS (G12C) inhibitors, no direct RAS inhibitor has been approved for clinical trial. However, KRAS (G12C) mutations are less abundant in some cancers like pancreatic cancer, thus there remains an unmet need for inhibitors that target the more common RAS mutants. This demand devising novel strategies to identify new approaches to inhibit RAS. Previously, we developed the H/KRAS-specific monobody called NS1 that allosterically inhibit RAS-mediated signaling by targeting the α4-α5 dimerization interface. When used as a genetically encoded intracellular reagent, NS1 inhibited the growth of H/KRAS-mutant human tumor lines both in vitro and in xenograft tumor models. However, these tumor models lack a functional immune system. Here, we evaluated the potency of targeting KRAS dimerization interface with NS1 in an immune-competent murine model of pancreatic cancer. Although human and murine KRAS differ by a single amino acid [Asp (D) to Glu (E)] at position 132 in the NS1 binding region of the allosteric lobe, NS1 bound similarly to human and murine KRAS both in vitro and in vivo. Furthermore, NS1 expression inhibited ERK-MAPK activation, proliferation and anchorage-independent growth of engineered KPC cells derived from pancreatic tumor in the KPC genetic mouse model. Finally, when these engineered KPC cells were injected orthotopically in immune-competent C57/B6 mice, we observed a dramatic decrease in tumor growth kinetics and tumor burden in NS1 expressing cohorts. Similarly, NS1 expression resulted in decreased ERK-MAPK activation and increased apoptosis. NS1 expressing tumors were characterized by increased infiltration of helper CD4+ T cells and macrophage. Thus, inhibition of mutant KRAS by NS1 results in an enhanced anti-tumor immune response in a syngeneic model for pancreatic cancer. These results establish that targeting α4-α5 dimerization interface of RAS can be a viable therapeutic option for targeting KRAS-mutant pancreatic cancer.

Citation Format: Imran Khan, Julia Lefler, Catherine Marelia, Mariyam Zuberi, Eric Denbaum, Akiko Koide, Cynthia Timmers, Michael Ostrowski, Shohei Koide, John O’Bryan. Targeting the KRAS dimerization interface enhances T-cell mediated anti-tumor response in vivo [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-032.

Abstract PO-051: The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts

In pancreatic ductal adenocarcinoma (PDAC), cancer associated fibroblasts (CAFs) play critical and complex roles in the tumor microenvironment. CAFs are also a major cell type in the desmoplastic stroma in PDAC and may account for half of the entire tumor tissue. Multiple subtypes of CAFs have been identified based on gene expressions, but the tissue origin(s) of CAF subtypes are unknown and genetic tools to robustly target them in vivo are lacking. Here we aimed to examine three potential tissue sources of CAFs: the pancreatic epithelium (through epithelium-to-mesenchyme transition), the bone marrow (through migration via the circulation), and the pancreatic mesenchyme or tissue resident fibroblasts (TRFs) in the normal pancreas (through proliferation). We utilized a genetically engineered mouse model of PDAC, where Kras and p53 mutations were engineered in the pancreatic epithelium using an Flp-Frt system. To determine whether the pancreatic epithelium gives rise to CAFs, we permanently labeled the pancreatic epithelium with a GFP reporter and traced their cell descendants by GFP expression. Despite robust GFP labeling of the epithelium, GFP expression was rarely identified in CAFs, suggesting little contribution of epithelium to the CAF pool. To determine whether the bone marrow gives rise to CAFs, we transplanted donor bone marrow carrying a ubiquitously expressed GFP reporter allele to GFP-negative recipient mice. We found that only a small proportion of pancreatic CAFs were tagged with GFP, suggesting a small proportion of CAFs have a bone marrow origin. Lastly, to determine whether the splanchnic mesenchyme during fetal development gives rise to CAFs, we used an inducible CreER-Loxp system to activate Tomato expression in the splanchnic mesenchyme during mid-gestation, and lineage traced their cell descendants. Tomato expression was identified in the majority of both pancreatic TRFs and CAFs, suggesting that they originate from the splanchnic mesenchyme. In summary, we found that TRFs are derived from the splanchnic mesenchyme during fetal development and they expand to contribute to the vast majority of CAFs in PDAC. The bone marrow contributes to a small proportion of CAFs, and the pancreatic epithelium contributes even less. This provides approaches to robustly target CAFs in vivo to further investigate their heterogeneity and function in PDAC.

Citation Format: Lu Han, Yongxia Wu, Sean Sweeney, Ulyss Roesner, Khushbu Patel, Melodie Parrish, Xuezhong Yu, Cynthia Timmers, Michael Ostrowski, Gustavo Leone. The splanchnic mesenchyme during fetal development is the major source of pancreatic cancer associated fibroblasts [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-051.

Transplantation of a Kidney With Duplicated Ureter Harvested From a Donor With Vascular Anomaly in the Form of Double Inferior Vena Cava: A Case Report

During the organ procurement procedure, a surgeon encounters anatomic anomalies not very often but also not uncommonly. These changes may put the success of the transplant into question. Despite the thorough diagnosis of the potential donor, these anomalies are often diagnosed during organ donation. In our paper we present a case of kidney transplantation with duplicated ureter. The organ was collected from a donor with duplicated inferior vena cava. After transplantation, the kidney functioned immediately. Taking into consideration the well-being of the recipient, organs with anatomic abnormalities should be carefully considered for transplantation. This is especially important when there is a constant shortage of organs for transplantation.

BSCI-11. STROMAL PLATELET DERIVED GROWTH FACTOR RECEPTOR-β (PDGFRβ) PROMOTES BREAST CANCER BRAIN METASTASIS

Stromal platelet-derived growth factor receptor-beta (PDGFRβ) has emerged as an actionable mediator of breast tumor-stromal communication. As a receptor tyrosine kinase, PDGFRβ is activated by its ligand, PDGFB, which is released by neighboring tumor epithelium and endothelium. However, how PDGF signaling mediates breast cancer (BC) initiation, progression, and metastasis remains unclear. To evaluate PDGFRβ in this disease, we developed a mouse model of stromal-specific PDGFRβ activation using the Fsp-cre transgene previously published by our group. Mesenchymal-specific activation of PDGFRβ promotes preferential experimental brain metastasis of PDGFB-expressing mammary tumor cells when injected intravenously and accelerates intracranial tumor growth of these cells. Mammary tumor cells expressing low levels of PDGFB do not exhibit a similar increase in brain metastases in PDGFRβ mutant mice. To our knowledge, this is the first example where genetic manipulation of the stroma leads to an increased incidence of BCBM. Our pre-clinical data suggests that primary breast tumors that express high PDGFB could preferentially metastasize to the brain. To test this in patients, we analyzed PDGFB protein expression in a tissue microarray comprised of HER2-positive and triple negative BC primary tumors. While high PDGFB did not correlate with site-independent metastatic recurrence, it was prognostic of brain metastasis, mirroring our mouse data. Our findings suggest that high primary tumor PDGFB expression defines a subset of BC patients predisposed to brain metastases. These patients may benefit from therapeutic intervention of PDGFRβ signaling. To test this pre-clinically, we treated mice harboring intracranial tumors with the PDGFR-specific inhibitor, crenolanib. Excitingly, crenolanib treatment significantly inhibited the brain tumor burden in these mice. Combined, our findings (1) advocate that primary tumor expression of PDGFB is a novel prognostic biomarker for the development of BCBM and (2) support clinical trial evaluation of PDGFR inhibitors for the prevention and treatment of BCBM.