The CXCR1 Axis: A Putative Therapeutic Cancer Stem Cell-Like Marker in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has one of the lowest survival rates of all cancers in the United States. Not only is PDAC found at the late stages, but patients also present with or develop chemotherapy resistance at an elevated frequency. Left with limited options for treatment, researchers are investigating new options for these patients. One major area of interest is the sub-population of cells in the tumor called cancer stem cells (CSCs). These cells are known for having high resistance to chemotherapy, along with propagating and re-building the tumor after most non-CSCs have been therapeutically targeted. Previous studies have determined CXCR4, ALDH1, CD24, CD44, and CD133 as markers for CSC-like PDAC cells. In the present study, we investigate the closely related CXCR1 as another possible marker and therapeutic target for PDAC CSCs. CXCR1 is known for its role in inflammation and wound healing. The CXCR1 axis includes the ligands CXCL6 and IL-8, both of which promote the progression of cancer. Previously, Ginesteir et al. has shown targeting the CXCR1 axis in triple negative breast cancer reduced CSC-like phenotypes in vitro and in vivo. Investigations of CXCR1 in PDAC demonstrate IL-8 induces increased tumorsphere formation in vitro (Chen et al.), leading us to investigating CXCR1 in PDAC CSCs. We hypothesize that PDAC cells with high CXCR1 activity also exhibit increased CSC-like characteristics and targeting CXCR1 will reduce those characteristics. To investigate the role of CXCR1 in CSC-like phenotype of PDAC, we used the PDAC cell line CD18, along with its gemcitabine resistant (GemR) counterpart. We used the CXCR1/2 antagonist Navarixin at high enough concentrations to inhibit CXCR1. Using the previously found gemcitabine and navarixin IC50 concentrations for each parent cell line, we treated cells for 72 hours. Post-treatment, we analyzed the expression of several known CSC markers, CXCR1, and IL-8 through qRT-PCR and ELISA. We expected to see higher expression and activity of CXCR1 in cells with higher known CSC marker expression. We also anticipated that gemcitabine treatment would induce higher expression of CSC markers, whereas navarixin would exhibit lower expression. From our results, we see the beginning trends of gemcitabine treated cells having increased expression of the CSC markers and navarixin decreasing or not changing the expression levels. These results differ for IL-8, which undergoes an increase in expression when treated with both gemcitabine and navarixin, which may warrant further exploration into the role of ligands in CSC-like phenotypes. One possible explanation for this difference would be the regulation of IL-8 expression based on CXCR1 activity, as IL-8 interacts with CXCR1.https://digitalcommons.unmc.edu/surp2021/1040/thumbnail.jp

Targeting the CXCR1/2 Axis in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is notoriously challenging to diagnose and treat. This tumor has an aggressive phenotype and benign clinical features until severe disease dissemination, which makes it too late to eradicate. Although it is only the 10th most common cancer in the United States, it is the fourth leading cause of cancer-related deaths. The treatment options are complicated further due to tumor heterogeneity, meaning not all tumor cells are in the same state phenotypically or epigenetically. They also express cytokines, chemokines, and receptors differently. Here we explore the usage of CXCR1 and CXCR2 and their ligands in PDAC tumor progression and chemoresistance. These two axes are G-protein-coupled receptors with many downstream effectors. Historically known for their role in neutrophil activation and recruitment, the literature discerns that many tumors also utilize them for angiogenesis, survival, proliferation, and migration. In this dissertation research, we investigated these receptors and their ligands in three studies. First, we evaluated their role in PDAC growth and metastasis through in vivo modeling with CXCR1/2 antagonist treatment. We demonstrate that CXCR1/2 antagonism decreases proliferation and increases apoptosis; higher necrosis associated with II higher fibrosis. We then demonstrated that CXCR2 and its ligands CXCL1, 5, and 8 have increased expression in the gemcitabine-resistant derived cell lines. Only parental cell lines have increased CXCR2 axis expression in the presence of gemcitabine, which is concentration- and dose-dependent. The CXCR1/2 antagonists decrease cell proliferation alone and in combination with gemcitabine in the parental- and gemcitabine-resistant cell lines. In vivo studies of the CD18/HPAF gemcitabine-resistant cell line support that combination treatment is superior for these tumors. Our final study evaluated CXCR1 as potential cancer stem cell marker and therapeutic target. The results exhibit a strong association between cancer stem cell markers and CXCR1, with combination treatment decreasing the percentage of cancer stem cell marker-expressing cells. Together, CXCR1 and CXCR2 prove to be therapeutic targets in PDAC, allowing us to target several tumor phenotypes. These results lay strong groundwork for the continued exploration of these receptors as a therapeutic option to eliminate PDAC

CXCR1: A Cancer Stem Cell Marker and Therapeutic Target in Solid Tumors

Therapy resistance is a significant concern while treating malignant disease. Accumulating evidence suggests that a subset of cancer cells potentiates tumor survival, therapy resistance, and relapse. Several different pathways regulate these purported cancer stem cells (CSCs). Evidence shows that the inflammatory tumor microenvironment plays a crucial role in maintaining the cancer stem cell pool. Typically, in the case of the tumor microenvironment, inflammatory pathways can be utilized by the tumor to aid in tumor progression; one such pathway is the CXCR1/2 pathway. The CXCR1 and CXCR2 receptors are intricately related, with CXCR1 binding two ligands that also bind CXCR2. They have the same downstream pathways but potentially separate roles in the tumor microenvironment. CXCR1 is becoming more well known for its role as a cancer stem cell identifier and therapeutic target. This review elucidates the role of the CXCR1 axis as a CSC marker in several solid tumors and discusses the utility of CXCR1 as a therapeutic target