Tumor Microenvironment in Cancer Progression

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

We have established that during primary tumor growth there is a formation of a niche environment in distant tissue sites during metastatic initiation. This pre-metastatic tissue has an influx of bone marrow-derived cells including populations of myeloid hematopoietic cells, which provide factors such as matrix metalloproteases to remodel extracellular matrix and pro-growth and survival signals such as VEGF and arginase to support the colonizing disseminated tumor cells. These sites are created as a systemic response to tumor progression and may be organ specific damage response programs in specific microenvironments. Using syngeneic cells lines that have a high spontaneous metastatic rate, we have identified unique changes within the bone marrow microenvironment that lead to mobilization of bone marrow-derived hematopoietic stem and progenitor cells that are recruited to the pre-metastatic niche in multiple tumor models including E0771 breast carcinoma, F4 osteosarcoma, 76-9 and M3-9M pediatric rhabdomyosarcomas and B16 melanoma. Previously we have shown that CD11b myeloid cells expressed VEGFR1 in the pre-metastatic tissue. We have now discovered these cells are hematopoietic progenitor cells that become an immune suppressive myeloid population that alter the local immune environment favoring immune evasion similar to sanctuary sites in stem cell niches (Giles et al Cancer Research 2016). We have also identified the central role of immune suppression in creation of pre-metastatic and early metastatic niche and the means of reprogramming this immune suppression to limit metastasis (Kaczanowska et al Cell 2021). These cells are immune suppressive myeloid cells derived from mobilized bone marrow-derived hematopoietic stem and progenitor cells we demonstrated play an integral role in regulating tumor specific T cells and T cell responses (Giles et al Cancer Research 2016; Kaczanowska et al Cell 2021). We have also been able to manipulate metastatic progression by altering these unique bone marrow-derived cell enriched areas. We have new data demonstrating that the pre-metastatic niche has similar features to physiological stem cell niches in order to promote distant tumor cell survival. We have found that the localized tumor prior to established metastasis is activating the hematopoietic stem cell niche within the bone marrow and inducing proliferation of hematopoietic stem cells and mobilization of these cells into the circulation. We have found that there are changes that occur in the bone marrow microenvironment in response to tumor secreted factors that induce the myeloid skewing and expansion of hematopoietic progenitor cells that we have seen during tumor progression (Giles et al Cancer Research 2016). Targeting the skewing to prevent the expansion in hematopoietic progenitor cells and myeloid cells may be a way to reset this maladaptive response to a growing tumor and prevent metastatic progression. We have on-going investigations examining the small molecular inhibitor PLX3397 that targets CSF1R found on myeloid cells, cKit and FLT3-ITD which we have determined that when the drug is given in the adjuvant setting can limit metastatic progression in tumor bearing hosts. We have initiated and completed the Phase I dose escalation of PLX3397 in pediatric and adolescent patients with recurrent or refractory tumors (Boal et al Clinical Cancer Research). We have also developed a new cell therapy approach platform to reprogram these recruited immune suppressive myeloid cells by introducing genetically engineered myeloid cells (GEMys) that express IL12. These IL12 GEMys can reverse the immune suppression program in the pre-metastatic niche and lead to inhibition of metastatic progression and significantly prolong overall survival in highly metastatic murine models (Kaczanowska et al Cell 2021). IL12 GEMys when given following fludarabine and cyclophosphamide tumor bearing hosts lead to long term cures in these metastatic pre-clinical models (Kaczanowska et al Cell 2021). In addition to investigations into the recruited hematopoietic progenitor bone marrow derived cell populations that become immune suppressive cells in pre-metastatic sites, we continue to investigate the essential changes in stromal cells including pericytes, vascular cells and fibroblasts as well as the extracellular matrix in the pre-metastatic and metastatic niche. We have established several lineage tracing models to better track and characterize these stromal cell populations as well as genetically manipulate key genes within specific cell populations. Using these models, we can interrogate the function of specific proteins to these cells and their role in the metastatic process. A specific transcription factor KLF4 we have discovered is critical to mediating this stromal cell plasticity. These stromal cells that become activated create a distinct extracellular matrix that support disseminated tumor cell survival. We are currently investigating the role of tumor conditioned media and tumor derived exosomes in making local changes in the stromal cell compartment and matrix that provides the scaffolding for bone marrow-derived cells and are essential component of the pre-metastatic niche (Murgai et al Nat Med 2017). We have identified two critical cellular pathways in pre-metastatic niche formation related to inflammation and stem cell biology including myeloid cells and stromal cell populations. Understanding the activation of these stem cell niche/wound repair pathways and inflammation- related pathways in the metastatic process are an active area of investigation. In addition to our existing stromal models, we have developed a new lineage tracing model to track mesenchymal cells that support nerves. These models are robust and show a new phenotype of mesenchymal nerve support cells that are found in bone and other sites and we have preliminary data to suggest a function in the pre-metastatic niche in bone during bone metastasis. Our current investigations reveal important components of the dysregulated microenvironments that occur during metastatic progression. Our novel cell therapy approach can provide a platform locally rebalance these altered microenvironments and a potential new therapeutic approach to limit metastatic progression in pediatric and adult patients at high risk for cancer progression. We are developing multiple approaches to translate this new cell therapy platform into the clinic setting. We are also actively exploring which cargo are most effective to rebalance dysregulated microenvironments that occur during metastasis. As many cancers have a dense extracellular matrix and we determined that extracellular matrix remodeling is occurring in an enhanced fashion from stromal cell expansion. We are investigating modulation of extracellular matrix through cell therapy delivery of extracellular matrix remodeling proteins. More dense matrix is associated with malignant tissue. We aim to explore the impact of matrix remodeling on metastatic progression. We have developed robust cell engineering strategies, culture conditions and reproducible assays for cell therapy development. We continue to develop functional studies that help demonstrate human genetically engineered myeloid cell therapy (GEMys) can effectively deliver the cargo and that the cargo has the anticipated response in vitro and in preclinical in vivo studies. We are preforming extensive IND enabling studies. We are also developing correlative markers to explore response and *TRUNCATED*