The dynamic microenvironment associated with metastatic bone disease: Current concepts

Patients with bone metastases may experience debilitating pain, neurological conditions, increased risk of pathological fractures, and death. A deeper understanding of the bone microenvironment, the molecular biology of cancer types prone to metastasis, and how bone physiology promotes cancer growth, may help to uncover targeted treatment options. The purpose of this paper is to outline the current concepts relevant to topics including bone remodeling, angiogenesis, and immunomodulation as it relates to metastatic bone disease.

Abstract 2516: Loss of cadherin 11 in pancreatic cancer induces altered immune cell infiltration

Pancreatic ductal adenocarcinoma (PDAC) is one of the top five deadliest forms of cancer with very few treatment options. The 5-year survival rate for PDAC is 10% following diagnosis. Preclinical murine models have been developed that leverage key driver mutations and have significantly contributed to our understanding of PDAC. One such genetically engineered mouse model (GEMM) that has emerged as an important tool is the KPC mouse (LSL-KrasG12D/+;LSL-Trp53R172H/+; p48-Cre) that spontaneously develops pancreatic tumors at ~14-16 weeks of age. Cadherin-11 (Cdh11), a cell-to-cell adhesion molecule has been suggested to play a role in development of the desmoplastic stroma in PDAC, that leads to difficulties in drug accessibility and has been hypothesized to contribute to chemotherapeutic resistance and correlate with poor prognosis. However, the mechanisms by which Cdh11 deficiency in the stromal microenvironment of PDAC-bearing KPC mice influences tumor infiltrating immune cells, has yet to be fully understood. Single-cell RNA sequencing (scRNAseq) of the immune (CD45+) compartment of tumor bearing Cdh11 proficient (KPC/Cdh11+/+), tumor bearing Cdh11 deficient (KPC/Cdh11+/-), non-tumor bearing Cdh11 deficient (Cdh11+/-) and wildtype (Cdh11+/+) mice was performed. We observed a sharp decrease in the presence of myeloid/monocyte lineage cells (CD14+) in KPC/Cdh11+/- tumors and also an increase in T, B and plasma cells, compared to KPC/Cdh11+/+ tumors. Genes upregulated in infiltrating T- and NK cells specific to a Cdh11 deficient background include Cd8a, Nkg7, Maf. Additionally, genes found to be upregulated in B cell clusters in Cdh11 deficient mice include those related to B cell differentiation/activation such as Lgals1, Id2, Itgb1, Rgs1. The increase in B and T cell infiltration was specific to the Cdh11 deficient background, since both pancreata from KPC/Cdh11+/+and Cdh11+/- mice had elevated levels of infiltration. Immunohistochemical validation of these findings has confirmed these changes in tumor infiltrating immune cells. Additionally of note, an increase in antibody-producing plasma cells was observed specifically in a Cdh11 deficient background. Igkc, an immunoglobulin found to be enriched in plasma cells was highly expressed in this group of immune cells. We also observed that KPC/Cdh11+/-had significantly more Igkc expressing cells than KPC/Cdh11+/+. Future work is needed to clearly define the role of Cdh11 in modulating B, T and plasma cell behavior and subsequent contributions to PDAC outcome. This study received funding by LDRD 19-SI-003. This work was conducted under the auspices of the USDOE by LLNL (DE-AC52-07NA27344), LLNL-ABS-820889. This work was supported by AACR-AstraZeneca Fellowship in Immunooncology Research, grant 17-40-12-PERA; The Ruesch Center for the Cure of Gastrointestinal Cancers grant award; NIH R01 CA170653; and NIH Cancer Center Support Grant P30 CA051008.

Citation Format: Kelly A. Martin, Aimy Sebastian, Nicholas Hum, Ivana Peran, Stephen Byers, Elizabeth Wheeler, Matthew Coleman, Gabriela Loots. Loss of cadherin 11 in pancreatic cancer induces altered immune cell infiltration [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 2516.

Abstract P043: Extracellular matrix modulates T cell clearance of malignant cells in vitro

Introduction: Emerging evidence suggests that tumor extracellular matrix (ECM) may play a role in tumor-immune interactions. Breast tumors with high immune infiltrates have a distinct ECM profile, and T cell exclusion has been linked to specific ECM signatures. Despite this evidence suggesting a link between immune infiltrates and tumor matrix, it remains unclear whether ECM can directly affect the ultimate step in tumor clearance by the immune system, T cell mediated cytotoxicity.

Methods: We compared clearance of 4T1 mammary gland carcinoma cells (MCC) seeded on ECM arrays by T cells isolated from spleens of MHC mismatched strain of mice. Briefly, 4T1 were seeded at 10k/ml for 1 hour, cultured for 24 hours then cocultured with T cells for 2 hours before fixing and staining. For RNA sequencing, ECM proteins (Collagen 1 -Col1, Collagen 4- Col4, Fibronectin -Fn or Vitronectin- Vtn) were coated onto plates at 250ug/ml, then 4t1 were added for 24 hours, then T cells were added for 24 hours followed by RNA isolation and sequencing.

Results: We compared number of cells per spot with and without T cells across all ECM combinations and found that co-culture with T cells reduced the average number of MCCs, but this difference did not reach statistical significance. Only in the following conditions did MCC number significantly decrease: Col1 alone, Col6 alone, Fn alone, Vtn alone and Col6+ Eln (Fig 2B). In Col4 containing conditions, MCC cell number increased in the presence of T cells. Intensity of CD274 (PD-L1) and the MHC class 1 protein H2-Kd varied with substrate (p<10−19, p<10−22 respectively) with significantly higher expression of PD-L1 in Col1 and Vtn conditions vs. Col4 or Laminin, and higher H2-Kd in Vtn conditions. These findings demonstrate a defect in T cell mediated MCC clearance in some ECM conditions that is distinct from the PD-L1 checkpoint. Comparing transcriptomes across, we observed that all MCC+ T cell conditions separated from MCC alone conditions (Fig. 3B), largely due to expression of known T cell related genes (such as Ptprc, Trbc2, Sell, Itk, and Il7r). Differentially regulated gene counts between MCC+ T cells and MCC alone conditions were lowest in the Col4 condition (Fig. 3BC-E), and significance and number of genes from T cell associated ontologies were lowest in the Col4 conditions (Fig. 3E). We observed that MCC on Col4 upregulated cytokines including Ccl2, Cxcl3, Cxcl10, and Tgfβ2, compared to both Fn and Vtn conditions, suggesting that this condition could suppress immune activation through altered cytokine expression.

This work was funded by LDRD 19-SI-003 under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-8235222

Citation Format: Claire Robertson, Aimy Sebastian, Aubree Hinckley, Naiomy Rios-Arce, William Hynes, Wei He, Nicholas Hum, Elizabeth Wheeler, Gabriela Loots, Matthew Coleman, Monica Moya. Extracellular matrix modulates T cell clearance of malignant cells in vitro [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P043.

Abstract 2741: Loss of Cadherin-11 in PDAC induces altered immune cell infiltration and remodels stromal landscape

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal forms of cancer with very few treatment options. Less than 10 percent of patients diagnosed with PDAC survive 5 years post diagnosis. Mutations in CDKN2A, SMAD4, KRAS and P53 have been well linked to the development of PDAC. Preclinical murine models have been developed that leverage key driver mutations and have significantly contributed to our understanding of PDAC. One such genetically engineered mouse model (GEMM) that has emerged as an important tool in PDAC investigations is the KPC mouse (LSL-KrasG12D/+LSL-Trp53R172H/+Pdx-1-Cre) that spontaneously develops pancreatic tumors at ~14-16 weeks of age. Cadherin-11 (Cdh11), a cell-to-cell adhesion molecule, is highly expressed in desmoplastic stroma, a characteristic of PDAC, that leads to difficulties in drug accessibility and has been hypothesized to contribute to chemotherapeutic resistance. However, the mechanisms by which Cdh11 deficiency in the stromal microenvironment of PDAC-bearing mice (KPC) influences therapeutic outcomes, has yet to be fully understood. Single-cell RNA sequencing (scRNAseq) of both the non-immune (CD45-) and immune (CD45+) cellular compartments of tumor bearing (KPC/Cdh11+/+), tumor bearing Cdh11 deficient (KPC/Cdh11+/-), non-tumor bearing Cdh11 deficient (Cdh11-/+) and wildtype (KP) were performed. We observed changes in the abundance and types of infiltrating immune cells (T-cells, B-cells, myeloid lineage cells) of KPC/Cdh11+/- tumors when compared to tumors harvested from KPC/Cdh11+/+ mice. KPC/Cdh11+/+ pancreata had significantly more myeloid cells while KPC/Cdh11+/- tumors favored an increase in the numbers of infiltrating B- and T- cells. Genes upregulated in infiltrating T-cells specific to KPC/Cdh11+/+ mice include Spp1, Ifi30, Apoe, Ifitm3, Fn1. The increase in B and T cell infiltration was specific to the Cdh11-/+ deficient background, since both pancreata from KPC/Cdh11+/- and Cdh11-/+ mice had elevated levels of infiltration, compared to the KPC group. We also observed a decrease in the number of antigen-presenting cancer associated fibroblasts (apCAFs) in Cdh11-/+ and KPC/Cdh11+/- pancreata, denoted by the lack of CD74+ fibroblasts. Further validation of these findings will help to define the role of Cdh11-/+ in modulating B and T-cell behavior in addition to providing insight into Cdh11-/+ as a therapeutic target for PDAC through altering the tumor microenvironment.

Citation Format: Kelly A. Martin, Aimy Sebastian, Nicholas Hum, Ivana Peran, Stephen Byers, Elizabeth K. Wheeler, Matthew A. Coleman, Gabriela Loots. Loss of Cadherin-11 in PDAC induces altered immune cell infiltration and remodels stromal landscape [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2741.

Sclerostin depletion may induce inflammation in the bone marrow

The interactions between long-term hematopoietic stem cells (LT-HSCs) and cells in the bone microenvironment result in changes in stem cell behavior that are incompletely understood. Our goal is to define the molecular mechanisms that guide the behavior of LT-HSCs after exposure to an irregular bone marrow (BM) niche. Sclerostin (Sost) is a secreted Wnt antagonist that is important for bone homeostasis. We hypothesized that that loss of Sost would influence LT-HSC differentiation and migration. To test this, we performed hematopoietic progenitor transplantation assays to track donor-derived hematopoiesis in wild-type (WT) and Sost-knockout (KO) recipients. We observed increased frequencies of donor-derived myelopoiesis as well as decreased lymphopoiesis in WT to KO chimeras possibly due to an inflammatory microenvironment. We are currently investigating LT-HSC inflammatory response genes, such as C/EBP-beta and PU.1, as well as BM serum inflammatory cytokine levels. As the SostKO mice age, we observe extramedullary hematopoiesis (EMH) in the spleen compared to age matched controls. We hypothesize that changes in the BM microenvironment as well as cytokine levels in the spleen induce LT-HSC migration to the spleen. We are characterizing the EMH LT-HSC splenic niche by investigating LT-HSC localization as well as examining cytokines, such as CXCL12, known to induce LT-HSC migration to the spleen. Taken together, our data indicates that depletion of Sost in the bone regulates LT-HSC differentiation and migration. Our results could have significant impact on the tracking of hematopoietic function in human patients treated with SOST-depleting antibodies for bone diseases such as osteoporosis.

Natural killer cell development and maturation is regulated by Sostdc1

Natural killer (NK) cells are specialized lymphocytes with innate ability to eliminate virally infected and cancerous cells. NK cells stochastically express Ly49 activating and inhibitory surface receptors, through mechanisms that are not fully understood. Ly49 expression during NK cell development is regulated by a combination of external and internal factors, such as major histocompatibility complex class I (MHC-I) ligands and cytokines. Global deletion of sclerostin domain containing-1 (Sostdc1), a secreted protein, leads to altered bone homeostasis via dysregulation of Wnt and BMP signaling, which in turn, could result in altered immune cell development in the bone marrow (BM). Using Sostdc1-knockout (KO) mice, we have discovered a novel role for Sostdc1 in NK cell development. Flow cytometric analysis of the Ly49 repertoire in immature (CD27+CD11b-; iNK), transitional (CD27+CD11b+, tNK) and most mature (CD27-CD11b+, mNK) Sostdc1-KO NK cells demonstrated expression differences in Ly49G2, I, H, and D receptors. We also observed a progressive increase in tNK cell numbers and frequencies as the KOs aged from 12 weeks to 30 weeks, indicating a slowing or partial block in NK cell maturation with aging. Reciprocal BM chimera experiments showed that Sostdc1 regulates NK cells through cellintrinsic and cell-extrinsic manners. Consistent with this, Sostdc1 is expressed in the bone periosteum and we discovered Sostdc1 expression in CD45+ NK1.1-CD11b+ BM cells and iNK cells. Taken together, these data support a role for Sostdc1 in the regulation of NK cell differentiation and identify potential NK cell niches. Current studies are investigating whether Sostdc1-KO NK cells respond to stimulation and lyse MHC-I deficient target cells.

Sclerostin expression in distinct osteolineage cell types differentially regulates hematopoietic stem cell and B lymphocyte development

Investigation of the reciprocal effects of hematopoietic cell types and osteolineage cells on each other’s cell fates have clinical applications to improve bone fracture healing, prevent age-related bone loss and immune deficiencies. A significant knowledge gap exists as to the contribution of different osteolineage cells to the differentiation, proliferation, and long term survival of B cells in the BM. In global sclerostin knockout (SostKO) mice, we previously uncovered a cell-extrinsic requirement for sclerostin on B lymphocyte development. It is widely accepted that sclerostin is transcribed primarily in osteocytes (OCYs), but whether is it expressed and/or active in other bone progenitors has been controversial. In order to identify the Sost-expressing osteolineage cell type that is responsible for B cell support, we analyzed hematopoietic differentiation in mice lacking Sost in mesenchymal stem cells (MSCs) [Prx1-Cre], osteoblasts (OBs) [Col1a-Cre] and OCYs [Dmp1-Cre] through the use of conditional Sost-KO (cKO) mice. Loss of Sost expression in MSCs resulted in reduced BM cellularity, whereas this was unaffected by Sost-deficiency in OB and OCYs. Furthermore, MSC-specific depletion of Sost caused an accumulation of early B cell progenitors. In contrast, loss of Sost in OBs and OCYs resulted in a reduction of mature “recirculating” B cells in the BM. Remarkably, the percentage of long-term CD150+ CD48− HSCs was significantly reduced in MSC-cKO mice, but was not affected in OB- and OCY-cKOs. The data described herein suggest that Sost deficiency in MSCs, OBs, and OCYs differentially regulates hematopoietic stem cell retention, survival, maintenance and B cell differentiation in the bone microenvironment.

Nanolipoprotein delivery enhances immunostimulatory properties of innate immune agonists and provides protection against lethal influenza challenge (P4218)

Therapies targeting the innate immune system have the potential to provide transient, non-specific protection from a variety of infectious organisms. As such, we have employed a nanolipoprotein (NLP) platform to enhance the efficacy of synthetic innate immune agonists. NLPs are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins. We demonstrate that the synthetic Toll-like receptor (TLR) ligands monophosphoryl lipid A (MPLA) and CpG oligodeoxynucleotides (CpG ODNs) can be readily incorporated into NLPs. Further, conjugation of both MPLA and CpG ODNs to NLPs significantly enhances their immunostimulatory profiles in vivo compared to administration of agonists alone. Specifically, conjugation to NLPs promotes agonist trafficking to secondary lymphoid organs, enhances and prolongs stimulation of innate immune cells, significantly increases cytokine production, and enhances upregulation of myriad immunoregulatory genes in vivo. Importantly, enhancement of cytokine production by agonists conjugated to NLPs was also observed in primary human dendritic cells. Strikingly, BALB/c mice pretreated with NLP-CpG constructs prior to a lethal influenza challenge were protected from weight-loss induced death, whereas pretreatment with CpG alone had no effect on survival. Taken together, these data suggest that NLP:agonist conjugates potentially represent a novel therapeutic measure against emerging pathogens.

In vitro and in vivo characterization of nanolipoproteins (NLPs) conjugated with innate immune agonists: implications for host-based therapeutics (53.12)

Modulation of the innate immune system has the potential to provide transient, non-specific protection from a variety of infectious organisms. Activation of innate immunity is rapid and short-lived, therefore methods aimed at enhancing and prolonging the response will increase the effectiveness of innate immune targeting as a therapeutic measure. In order to enhance the stimulatory properties of innate immune agonists, we have employed a nanolipoprotein (NLP) platform. NLPs are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins, analogous to reconstituted HDLs. NLPs have been successfully used in numerous biotechnology applications, including drug delivery and diagnostic imaging. Here, we show that two synthetic TLR ligands: monophosphoryl lipid A (MPLA) and CpG oligodeoxynucleotides (CpG ODNs) can be readily incorporated into NLPs. In addition, the delivery of agonist-conjugated NLPs significantly enhances immunostimulatory effects relative to agonists alone, at low doses, both in vitro and in vivo. Our data demonstrate that conjugation to NLPs promotes agonist trafficking to secondary lymphoid organs, increases cytokine production, and induces upregulation of immunoregulatory genes in peripheral organs. These data suggest that treatment with NLP:agonist conjugates may provide transient protection against lethal pathogen challenge, and experiments to determine their effectiveness at countering infection are ongoing.

Innate immune agonists conjugated to nanolipoproteins elicit robust inflammatory responses in mouse macrophages: implications for host-based therapeutics. (52.10)

Modulation of the innate immune system has the potential to provide transient, non-specific protection from a variety of infectious organisms. We hypothesize that combinatorial formulations of synthetic innate immune agonists may significantly enhance protection over single-agonist formulations. To readily incorporate multiple, chemically diverse agonists onto a single particulate platform for co-localized delivery, nanolipoprotein particles (NLPs) will be used. NLPs are discoidal, nanometer-sized particles comprised of self-assembled phospholipid membranes and apolipoproteins, analogous to reconstituted HDLs. NLPs assembled with human apolipoproteins have been used for numerous biotechnology applications, including membrane protein solubilization, drug delivery, and diagnostic imaging. NLPs can be functionalized to incorporate myriad agonists, including CpG-containing oligonucleotides, monophosphoryl Lipid A, muramyl dipeptide, flagellin, and an LL-37 analog. Development of NLPs incorporating CpGs and MPLA will be described, as well as preliminary results from in vitro analyses, including quantitative inflammatory cytokine secretion, cellular cytotoxicity, and cellular localization. Our data indicate that agonist:NLP constructs are internalized by macrophages, are immunostimulatory, and induce low levels of cellular cytotoxicity.

ECRbase: database of evolutionary conserved regions, promoters, and transcription factor binding sites in vertebrate genomes

Evolutionary conservation of DNA sequences provides a tool for the identification of functional elements in genomes. We have created a database of evolutionary conserved regions (ECRs) in vertebrate genomes, entitled ECRbase, which is constructed from a collection of whole-genome alignments produced by the ECR Browser. ECRbase features a database of syntenic blocks that recapitulate the evolution of rearrangements in vertebrates and a comprehensive collection of promoters in all vertebrate genomes generated using multiple sources of gene annotation. The database also contains a collection of annotated transcription factor binding sites (TFBSs) in evolutionary conserved and promoter elements. ECRbase currently includes human, rhesus macaque, dog, opossum, rat, mouse, chicken, frog, zebrafish and fugu genomes. It is freely accessible at http://ecrbase.dcode.org.