CDC7 kinase (DDK) inhibition disrupts DNA replication leading to mitotic catastrophe in Ewing sarcoma.

Ewing sarcoma is the second most common bone malignancy in children and adolescents. In recent years, a large body of evidence has emerged that suggests Ewing tumors harbor large amounts of replication stress (RS). CDC7, also known as DDK (DBF4-dependent kinase), is a serine/threonine kinase that is involved in a diverse array of cellular functions including the regulation of DNA replication initiation and activation of the RS response. Due to DDK's diverse roles during replication, coupled with the fact that there is an increased level of RS within Ewing tumors, we hypothesized that Ewing sarcoma cells would be particularly vulnerable to DDK inhibition. Here, we report that DDK inhibition resulted a significant reduction in cell viability and the induction of apoptosis, specifically in Ewing sarcoma cells. Treatment with DDK inhibitors dramatically reduced the rate of replication, prolonged S-phase, and led to a pronounced increase in phospho-CDC2 (Y15), indicating delay of mitotic entry. The induction of cell death corresponded to mitotic exit and G1 entry, suggesting improper mitotic progression. In accordance with this, we find that DDK inhibition caused premature mitotic entry resulting in mitotic abnormalities such as anaphase bridges, lagging chromosomes, and cells with >2 poles in Ewing sarcoma cells. This abnormal progression through mitosis resulted in mitotic catastrophe as evidenced by the formation of micronuclei and induction of DNA damage. Together, these findings suggest that DDK activity is required for the faithful and timely completion of DNA replication in Ewing cells and that DDK inhibition may present a viable therapeutic strategy for the treatment of Ewing sarcoma.

Clinicopathologic and molecular analysis of a BCOR-CCNB3 undifferentiated sarcoma of the kidney reveals significant epigenetic alterations.

Undifferentiated soft tissue sarcomas (UDSTSs) are a group of mesenchymal tumors that remain a diagnostic challenge because of their morphologic heterogeneity and unclear histologic origin (Peters et al., Mod Pathol28: 575 [2015]). In this case report, we present the first multiomics molecular signature for a BCOR-CCNB3 sarcoma (BCS) that includes mutation analysis, gene expression, DNA methylation, and micro RNA (miRNA) expression. We identify a paucity of additional mutations in this tumor and detail that there is significant dysregulation of gene expression of epigenetic remodeling agents including key members of the PRC, Sin3A/3b, NuRD, and NcoR/SMRT complexes and the DNA methyltransferases DNMT1, DNMT3a, and DNMT3b. This is accompanied by significant DNA methylation changes and dysregulation of multiple miRNAs with known links to tumorigenesis. This study significantly increases our understanding of the BCOR effects on fusion-positive undifferentiated sarcomas at both the genomic and epigenomic level and suggests that as better-tailored and more refined treatment algorithms continue to evolve, epigenetic modifying agents should be further evaluated for their efficacy against these tumors.

Establishing a role for environmental toxicant exposure induced epigenetic remodeling in malignant transformation.

Humans are exposed to a wide variety of environmental exposures throughout their lifespan. These include both naturally occurring toxins and chemical toxicants like pesticides, herbicides, and industrial chemicals, many of which have been implicated as possible contributors to human disease susceptibility [1-3]. We, and others, have hypothesized that environmental exposures may cause adaptive epigenetic changes in regenerative cell populations and developing organisms, leading to abnormal gene expression and increased disease susceptibility later in life [3]. Common epigenetic changes include changes in miRNA expression, covalent histone modifications, and methylation of DNA. Importantly, due to their heritable nature, abnormal epigenetic modifications which occur within stem cells may be particularly deleterious. Abnormal epigenetic changes in regenerative cell linages can be passed onto a large population of daughter cells and can persist for long periods of time. It is well established that an accumulation of epigenetic changes can lead to many human diseases including cancer [4-6]. Subsequently, it is imperative that we increase our understanding of how common environmental toxins and toxicants can induce epigenetic changes, particularly in stem cell populations. In this review, we will discuss how common environmental exposures in the United States and around the world may lead to epigenetic changes and discuss potential links to human disease, including cancer.