Identification and targeting immune-activated transcriptional pathways for cancer stem cell immunotherapy in solid tumors
The cross-talk between immune system and cancer stem cells in the tumor microenvironment, and the mechanisms on how they interact to influence tumor development and progression is still not fully understood. Using tumor samples from ovarian and breast cancer patients, researchers from the University of Michigan identified cluster of differentiation (CD33)-expressing myeloid derived suppressor cells (MDSC) that inhibited T cell activation and, enhanced CSC gene expression, sphere formation and metastasis. In ovarian cancer, the MDSCs increased the expression of miRNA101 which subsequently decreased the expression of CtBP, a known co-repressor of stem cell core genes. The miRNA101-mediated decrease of CtBP consequently resulted in increased cancer cell “stemness” and, metastatic and tumorigenic potential. In breast cancer, MDSCs correlate with increased CSC numbers and gene signature. The MDSCs promote and maintain breast cancer cell stemness via IL-6 mediated activation/ phosphorylation of STAT3 and NOS- dependent activation of Notch signaling, both of which are known to promote the transcription of genes involved in tumor formation, cell proliferation and metastasis. Although CD33 has been a therapeutic target for hematological malignancies, these studies suggest that it may also be targeted for immunotherapy of solid tumors. In a colorectal cancer, IL-22 increased tumor sphere formation, and increased the expression of core cancer stem cell genes (NANOG, SOX2 and OCT3/4) and a human cancer stem cell marker (aldehyde dehydrogenase 1 (ALDH1). IL-22 promotes cancer stemness by STAT3 activation which directly targets and induces the expression of disruptor of telomeric 1 like (DOT1L), a histone 3 lysine 79 (H3K79) methyltransferase. IL-22 induces DOT1L expression in colon cancer cells and selectively increases H3K79 dimethylation (H3K79me2) at the promoter of core stem cell genes (SOX2, NANOF, OCT3/4). Thus, IL-22 signaling activates STAT3 which induces the expression of cancer stem cell genes by promoting a transcriptionally chromatin environment via DOT1L- mediated H3K79 methylation at gene promoters. Blocking DOT1L activity by using a chemical inhibitor and/or shRNA knockdown decreased IL-22 dependent colon cancer stemness and tumorigenic potential. Increased levels of DOT1lL and H3K79me2 correlate with poor survival among colon cancer patients. In addition, increased levels of tumor associated CD33+ MDSCs, DOT1L and H3K79me2 were found to be independent predictors of poor survival among (breast, ovary and colon) cancer patients. Therefore, CD33+ MDSC, miRNA101, IL-22 and DOT1L may be used as CSC biomarkers and solid tumor prognostic markers. More importantly, these proteins can be targeted for immunotherapy to reduce the tumorigenic and metastatic potential of CSC in solid tumors.
Role of immune response in tumor formation and development
Epithelial cancers arising in tissues that include breast, ovary and colon account for a significant cancer burden and constitute approximately 35.6% of all cancers. Cells within a tumor population exhibit heterogeneity in terms of mutations, proliferative and differentiative capacities. This is partly attributed to inherent differences in tumor regenerating capacity of CSCs that exhibit “stem-like” properties with the ability to self-renew, generate tumor cells and continually sustain tumor growth. Cancer stem cells are isolated using several cell surface markers and the presence of a high proportion of cancer cells expressing CSC markers predicts poor patient outcome and appears to be a risk factor for relapse. The interaction between tumor cells and their microenvironment also has a strong influence on the tumorigenic process. The tumor microenvironment is the main area where tumor cells and the host immune system interact and has been the subject of intensive investigation primarily due to its role in tumor immune invasion, tumor dissemination and metastasis. The physiologic immune response is triggered by pro-inflammatory signals released by cells infected by a pathogen which then recruit and activate Th cells, immature dendritic cells and macrophages. Upon activation, Th cells secrete chemical messengers called cytokines which then causes Th cells to multiply and exchange signaling messengers between themselves and other cells of the immune system to destroy the invading pathogen. When pro-inflammatory cytokines reach a determinate concentration, MDSCs are recruited to the site of inflammation, turn off the immune response and promote tissue remodeling and repair. MDSC are a heterogeneous population of immature myeloid cells that are also increased during carcinogenesis. In humans, MDSCs are identified by by their phenotype of Lin-HLA-DR-CD33+ or CD11b+CD14-CD33+. MDSCs play an important part in suppression of host immune responses through several mechanisms such as production of arginase 1, release of reactive oxygen species (ROS) and reactive nitrogen intermediates (RNI) and secretion of immune-suppressive cytokines. The persistent production of ROS and RNI of MDSC can induce gene mutations that promote cancer initiation and tumor formation. Newly transformed cancer cells then recruit additional MDSCs that further suppress the immune response and assist the tumor cells in escaping from immune recognition. This allows the tumor cells to invade the surrounding tissue, seed and metastasize to distal sites.
- CD33+ MDSC, miRNA101, CtBP, IL22, DOT1L as biomarkers for cancer stem cells in solid tumors
- CD33+ MDSC, miRNA101, CtBP, IL22, DOT1L as prognostic markers for breast, ovarian and colon cancer
- CD33+ MDSC, miRNA101, CtBP, IL22, DOT1L as molecular targets for solid tumor therapy
- New biomarkers for cancer stem cell
- New prognostic markers for tumorigenesis and metastasis
- New molecular targets for inhibiting cancer stem cell proliferation
- New molecular targets for cancer immunotherapy