The Bone Microenvironment in Prostate Cancer Metastasis.

The propensity of prostate cancer cells to seed the skeleton and then progress into clinically relevant metastatic tumors is widely recognized and a major cause of morbidity and mortality for patients. The natural history of prostate adenocarcinoma most frequently begins with a tumor diagnosed at a localized stage, which is successfully treated by surgical and/or radiation therapy modalities. A relevant percentage of patients are clinically cured but approximately 20-30% will develop biochemical signs of recurrence, which respond to the inhibition of androgen receptor (AR) signaling by hormone-deprivation and receptor antagonists, before the inevitable transition into castration-resistant prostate cancer (CRPC). This stage simultaneously presents with or is rapidly followed by secondary tumors, which involve the skeleton in more than 90% of cases (mCRPC). While generalization in clinical practice is always unwise, it is indisputable that bone-metastatic prostate cancer is virtually incurable. Decades of research have revealed that the tissue microenvironment provided by the bone marrow is as important as the cell-autonomous features of tumor cells in fostering the right conditions that lead to establishment and progression of metastatic tumors in the skeleton.

5-azacytidine induces transcriptome changes in Escherichia coli via DNA methylation-dependent and DNA methylation-independent mechanisms.

BACKGROUND: Escherichia coli K-12 strains contain DNA cytosine methyltransferase (Dcm), which generates 5-methylcytosine at 5'CCWGG3' sites. Although the role of 5-methylcytosine in eukaryotic gene expression is relatively well described, the role of 5-methylcytosine in bacterial gene expression is largely unknown. RESULTS: To identify genes that are controlled by 5-methylcytosine in E. coli, we compared the transcriptomes of cells grown in the absence and presence of the DNA methylation inhibitor 5-azacytidine. We observed expression changes for 63 genes. The majority of the gene expression changes occurred at early stationary phase and were up-regulations. To identify gene expression changes due to a loss of DNA methylation, we compared the expression of selected genes in a wild-type and dcm knockout strain via reverse transcription quantitative PCR. CONCLUSIONS: Our data indicate that 5-azacytidine can influence gene expression by at least two distinct mechanisms: DNA methylation loss and a mechanism that is independent of DNA methylation loss. In addition, we have identified new targets of 5-methylcytosine-mediated regulation of gene expression. In summary, our data indicate that 5-azacytidine impacts the composition of the bacterial transcriptome, and the primary effect is increased gene expression at early stationary phase.

Regulation of Tumor and Metastasis Initiation by Chemokine Receptors.

Tumor-initiating cells (TICs) are a rare sub-population of cells within the bulk of a tumor that are major contributors to tumor initiation, metastasis, and chemoresistance. TICs have a stem-cell-like phenotype that is dictated by the expression of master regulator transcription factors, including OCT4, NANOG, and SOX2. These transcription factors are expressed via activation of multiple signaling pathways that drive cancer initiation and progression. Importantly, these same signaling pathways can be activated by select chemokine receptors. Chemokine receptors are increasingly being revealed as major drivers of the TIC phenotype, as their signaling can lead to activation of stemness-controlling transcription factors. Additionally, the cell surface expression of chemokine receptors provides a unique therapeutic target to disrupt signaling pathways that control the expression of master regulator transcription factors and the TIC phenotype. This review summarizes the master regulator transcription factors known to dictate the TIC phenotype, along with the complex signaling pathways that can mediate their expression and the chemokine receptors that are most upstream of this phenotype.

IL-1ß expression driven by androgen receptor absence or inactivation promotes prostate cancer bone metastasis.

We report the inverse association between the expression of androgen receptor (AR) and interleukin-1beta (IL-1ß) in a cohort of patients with metastatic castration resistant prostate cancer (mCRPC). We also discovered that AR represses the IL-1ß gene by binding an androgen response element (ARE) half-site located within the promoter, which explains the IL-1ß expression in AR-negative (ARNEG) cancer cells. Consistently, androgen-depletion or AR-pathway inhibitors (ARIs) de-repressed IL-1ß in ARPOS cancer cells, both in vitro and in vivo. The AR transcriptional repression is sustained by histone de-acetylation at the H3K27 mark in the IL-1ß promoter. Notably, patients' data suggest that DNA methylation prevents IL-1ß expression, even if the AR-signaling axis is inactive. Our previous studies show that secreted IL-1ß supports metastatic progression in mice by altering the transcriptome of tumor-associated bone stroma. Thus, in prostate cancer patients harboring ARNEG tumor cells or treated with ADT/ARIs, and with the IL-1ß gene unmethylated, IL-1ß could condition the metastatic microenvironment to sustain disease progression.

Subsets of cancer cells expressing CX3CR1 are endowed with metastasis-initiating properties and resistance to chemotherapy.

Metastasis-initiating cells (MICs) display stem cell-like features, cause metastatic recurrences and defy chemotherapy, which leads to patients' demise. Here we show that prostate and breast cancer patients harbor contingents of tumor cells with high expression of CX3CR1, OCT4a (POU5F1), and NANOG. Impairing CX3CR1 expression or signaling hampered the formation of tumor spheroids by cell lines from which we isolated small subsets co-expressing CX3CR1 and stemness-related markers, similarly to patients' tumors. These rare CX3CR1High cells show transcriptomic profiles enriched in pathways that regulate pluripotency and endowed with metastasis-initiating behavior in murine models. Cancer cells lacking these features (CX3CR1Low) were capable of re-acquiring CX3CR1-associated features over time, implying that MICs can continuously emerge from non-stem cancer cells. CX3CR1 expression also conferred resistance to docetaxel, and prolonged treatment with docetaxel selected CX3CR1High phenotypes with de-enriched transcriptomic profiles for apoptotic pathways. These findings nominate CX3CR1 as a novel marker of stem-like tumor cells and provide conceptual ground for future development of approaches targeting CX3CR1 signaling and (re)expression as therapeutic means to prevent or contain metastasis initiation.

Impeding Circulating Tumor Cell Reseeding Decelerates Metastatic Progression and Potentiates Chemotherapy.

Circulating tumor cells (CTCs) are commonly detected in the systemic blood of patients with cancer with metastatic tumors. However, the mechanisms controlling the viability of cancer cells in blood and length of time spent in circulation, as well as their potential for generating additional tumors are still undefined. Here, it is demonstrated that CX3CR1, a chemokine receptor, drives reseeding of breast CTCs to multiple organs. Antagonizing this receptor dramatically impairs the progression of breast cancer cells in a relevant model of human metastatic disease, by affecting both tumor growth and numerical expansion. Notably, therapeutic targeting of CX3CR1 prolongs CTC permanence in the blood, both promoting their spontaneous demise by apoptosis and counteracting metastatic reseeding. These effects lead to containment of metastatic progression and extended survival. Finally, targeting CX3CR1 improves blood exposure of CTCs to doxorubicin and in combination with docetaxel shows synergistic effects in containing overall tumor burden. IMPLICATIONS: The current findings shed light on CTCs reseeding dynamics and support the development of CX3CR1 antagonism as a viable strategy to counteract metastatic progression.